Wideband antenna

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DESCRIPTION

Broadband antenna.

Technical field

The present invention relates to an antenna used in radio communication, which includes a wireless Local Area Network (LAN: Local Area Netwok). More particularly, it relates to a broadband antenna comprising a conical radiation electrode and a ground conductor.

More particularly, the present invention relates to a broadband antenna in which its inherent quality of broadband characteristics is sufficiently maintained and further reduction in size is achieved.

Especially, it refers to a broadband antenna in which profile and width reduction is achieved.

Background technique

With the speed improvement and price reduction of wireless LAN systems, the demand for wireless LAN systems has recently increased significantly. Especially these days, the introduction of personal area network (PAN: Personal Area Netwok) has been widely considered to build a small-scale wireless network among a plurality of pieces of common electronic equipment around the house for information communication. For example, different radio communication systems have been defined that use different frequency bands, such as the 2.4 GHz band and the 5 GHz band, for which licenses from the competent authorities are unnecessary.

In radio communication that includes wireless LAN, information is transmitted through antennas. For example, a monoconical antenna comprises a radiation electrode formed in an essentially conical concavity in a dielectric, and a ground electrode formed on the underside of the dielectric. Thus, a small antenna having broadband characteristics can be constituted by the wavelength shortening effect from the dielectric located between the radiation electrode and the ground electrode.

An antenna having broadband characteristics can be used in UWB (Ultra-WideBand: Ultra-WideBand) communication, in which, for example, data is distributed as an ultra-wide frequency band such as 3 GHz to 10 GHz. for transmission and reception. A small antenna contributes to the reduction in size and weight of the radio equipment.

For example, Japanese Unexamined Patent Publication No. Hei 8 (1996) -139515 describes a small dielectric vertically polarized antenna for wireless LAN. This dielectric vertically polarizing antenna is constituted as follows: a base of a cylindrical dielectric is conically hollowed out and a radiation electrode is formed therein, and a ground electrode is formed on the opposite side. The radiation electrode is drawn to the side of the ground electrode through a conductor in a through hole. (Reference is made to Figure 1 in the Unexamined Patent Publication).

Figure 5 of the Unexamined Patent Publication illustrates the antenna characteristics of the dielectric vertical polarization antenna. According to this figure, its operating band is approximately 100 MHz. (The center frequency is approximately 2.5 GHz; therefore, the relative bandwidth is approximately 4%). The mono cone antenna inherently has an operating band of less than one eighth; therefore, the above antenna cannot be said to sufficiently provide the expected broadband characteristics.

Miniaturization of an antenna means, for example, reducing its profile and width. For example, Japanese Unexamined Patent Publication No. Hei 9 (1997) -153727 presents a proposal regarding reducing the width of the monocone antenna. However, the proposal is such that a radiation conductor must simply be formed in the form of a semi-elliptical solid of revolution, and it is unknown whether it is applicable to the structure of an antenna whose side face is covered with dielectric is unknown.

Figure 31 schematically illustrates the general constitution of a monoconical antenna having a single conical radiation electrode. The monoconical antenna illustrated in the figure comprises a radiation conductor made essentially conical in shape, and a ground conductor formed with a gap arranged between it and the radiation conductor. Electrical signals are fed into the separation space.

Figure 32 illustrates an example of the VSWR (Voltage Standing Wave Ratio) characteristic of a monocone antenna. A VSWR of no more than 2 is obtained in a wide range from 4 GHz to 9 GHz, and this indicates that the antenna has a relatively large bandwidth.

One of the known methods of further widening the band of this monocone antenna is by loading resistance in the radiation conductor. Fig. 33 and Fig. 34 illustrate examples of monoconical antenna constitutions whose radiation conductor is formed from a low conductivity member containing a resistance component, rather than high conductivity metal. With this constitution the reflective power decreases

ES 2 297 565 T3 towards a feed portion, and this results in an expanded matching band. Especially since the lower limit frequency of the matching band is expanded (downward), the above constitutions are also used as means for reducing the antenna size. As illustrated in Figure 33, the radiation electrode can be formed of a material having a constant low conductivity. However, if the conductivity is distributed as illustrated in Figure 34 (lower conductivity on the upper base side), the effect is better produced.

Various methods are known to load resistance into the radiation conductor of a monocone antenna. Concrete examples include a method of adhering a low conductivity member, formed as a sheet, to a conical insulator, and a method of applying a low conductivity member prepared as a coating material. (Reference is made to “Optimizing a Cone Antenna for Pulsed Radiation: An Efficient Design Using Resistive Loading,” written by James G. Maloney et al. (IEEE Transactions on Antennas and Propagation, Vol. 41, No. 7, July 1993, pp. 940-947), for example).

However, if mass production is considered, the method of adhering a sheet is certainly of lower productivity, and it is not realistic. With the coating method it is difficult to make the coating thickness uniform to control conductivity, and this method is also unrealistic.

The NUSSEIBEH ET AL paper: "Transient Response of a Wide Angle Cone with Dielectric Charge", RADIO SCIENCE, AMERICAN GEOPHYSICAL UNION, WASHINGTON, DC., US, vol. 31, No. 5, September 1996 (1996-09), pages 1047-1052, describes an antenna according to the preamble of claim 1.

An object of the present invention is to provide an excellent monocone antenna comprising a conical radiation electrode and a ground conductor.

Another object of the present invention is to provide an excellent mono cone antenna in which its inherent quality of broadband characteristics is sufficiently maintained and further size reduction is achieved.

A further object of the present invention is to provide an excellent monocone antenna in which profile and width reduction is achieved.

The present invention has been made with the above problems in mind.

The present invention consists of a monoconical antenna comprising: a conical radiation electrode having an apex and a ground conductor arranged in the vicinity of the radiation electrode and extending the radiation electrode, in which said antenna is constituted in such a way that electrical signals are fed to between a vertex region of the radiation electrode and a region of the ground conductor.

The monoconical antenna is characterized in that: the straight line connecting the apex of the conical radiation electrode and the center of the base of the conical radiation electrode is not perpendicular to the base of the conical radiation electrode.

To solve the problem of reduction of profile or width, the monoconical antenna according to the present invention is constituted so that the impedance matching is compensated by setting the vertex of the circular cone off-center.

Other objects, features, and advantages of the present invention will become apparent from the following embodiments of the present invention and from the more detailed description taken in connection with the accompanying drawings.

Brief description of the drawings

Figure 1 is a drawing illustrating the appearance and constitution of a mono cone antenna 1;

Fig. 2 is a drawing illustrating a calculation example (electromagnetic field simulation result) of the frequency characteristics of the monocone antenna based on the constitution of Fig. 1;

Fig. 3 is a drawing illustrating another calculation example (electromagnetic field simulation result) of the frequency characteristics of the monocone antenna based on the constitution of Fig. 1;

Fig. 4 is a drawing including diagrams and graphs illustrating the semi-cone angle as a function of frequency characteristics (right) and a graph represented by an expression for setting the semi-cone angle (left). The figure illustrates the relationship between them when the relative dielectric constant e_r dielectric 10 is 1.

Fig. 5 is another drawing including diagrams and graphs illustrating the semi-cone angle as a function of frequency characteristics (right) and a graph represented by the expression for setting the semi-cone angle (left). The figure illustrates the relationship between them when the relative dielectric constant e_r dielectric 10 is 3.

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Fig. 6 is a further drawing including diagrams and graphs illustrating the half-cone angle as a function of frequency characteristics (right) and a graph represented by the expression for setting the half-cone angle (left). Figure 1 illustrates the relationship between them when the relative dielectric constant e_r dielectric 10 is 5;

Fig. 7 is a further drawing including diagrams and graphs illustrating the half-cone angle as a function of frequency characteristics (right) and a graph represented by the expression for setting the half-cone angle (left). The figure illustrates the relationship between them when the relative dielectric constant e_r dielectric 10 is 8.

Figure 8 is a drawing illustrating the constitutions of monoconical antennas constituted so that the semi-cone angle α of the essentially conical concavity formed in an end face of a dielectric is in accordance with a predetermined rule corresponding to the relative dielectric constant e_r.

Figure 9 are drawings illustrating the antenna characteristics of a monocone antenna with the optimum half cone angle for the relative dielectric constant e_r 2 and 4, respectively.

Fig. 10 is a drawing illustrating an example of a monocone antenna whose profile is reduced compared to the constitution of the optimum half cone angle;

Figure 11 is a drawing illustrating the VSWR characteristics of a mono cone antenna having the constitution illustrated in Figure 10;

Fig. 12 is a drawing illustrating an example of a mono cone antenna whose width is reduced compared to the optimal half cone angle constitution;

Figure 13 is a drawing illustrating the VSWR characteristics of a mono cone antenna having the constitution illustrated in Figure 12;

Fig. 14 is a drawing illustrating an example of the constitution of a monocone antenna provided with a feed portion structure suitable for serial production;

Figure 15 is a drawing illustrating how a mono cone antenna having the constitution illustrated in Figure 14 is mounted on a circuit board;

Figure 16 is a drawing illustrating the cross-sectional structure of a mono cone antenna using low-profile build;

Figure 17 is the impedance characteristic diagram and VAWR characteristic diagram of the low profile mono cone antenna illustrated in Figure 16;

Fig. 18 is a drawing illustrating the cross-sectional structure of a low profile monocone antenna according to one embodiment of the invention, in which the apex of the conical radiation electrode is set off-center by 25% with respect to the radius.

Figure 19 is the impedance characteristic diagram and VSWR characteristic diagram of the low profile mono cone antenna illustrated in Figure 18;

Figure 20 is a drawing illustrating the constitution of another mono cone antenna;

Fig. 21 is a drawing illustrating a calculation example to demonstrate the electrical effect of the monocone antenna of Fig. 20;

Fig. 22 are drawings illustrating antenna constitutions in which two detached electrode portions are formed in the depth direction of the concavity formed in an insulator;

Figure 23 are drawings illustrating examples of the formation of the ground conductor on the other end face of the insulator. In these examples, the resistive load is applied to biconical antennas formed by arranging radiation electrodes on the antenna surfaces of essentially conical concavities formed symmetrically on both end faces;

Figure 24 is a drawing illustrating the cross-sectional structure of another antenna;

Fig. 25 is a drawing illustrating the constitution of a conical antenna in which two portions cut and peeled off in the depth direction of the essentially conical radiation electrode formed in an insulator are formed;

Figure 26 is a drawing illustrating examples of biconical antenna constitutions made using cone antennas that are formed by providing cut and peeled circumferential portions at radiation electrodes formed on the surfaces of the cone insulators;

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Figure 27 is a drawing illustrating the cross-sectional structure of a further cone antenna;

Figure 28 is a drawing illustrating the cross-sectional structure of a modification of the cone antenna illustrated in Figure 27;

Figure 29 is a drawing illustrating the constitution of a biconical antenna formed using a conical antenna that is formed by providing a low conductivity member filling the feed electrode formed on the surface of the conical concavities of an insulator;

Figure 30 is a drawing illustrating the cross-sectional structure of a modification of the cone antenna illustrated in Figure 29;

Fig. 31 is a drawing illustrating the constitution (conventional example) of a mono cone antenna having a single cone radiation electrode;

Figure 32 is a drawing illustrating an example (conventional example) of the VSWR (Voltage Standing Wave Ratio) characteristics of a monocone antenna;

Fig. 33 is a drawing illustrating the constitution (conventional example) of a monocone antenna in which a radiation conductor is constituted by a low conductivity member containing a resistance component instead of high conductivity metal;

Figure 34 is a drawing illustrating the constitution (conventional example) of a conical antenna in which a radiation conductor is constituted by a non-uniform, low conductivity member, containing a resistance component instead of high conductivity metal. .

With reference to the drawings, the present invention will be described in more detail in the following.

Figure 1 illustrates the appearance and constitution of the monocone antenna 1 according to a first example.

As illustrated in the figure, the monoconical antenna 1 comprises: an essentially conical concavity 11 formed in an end face of a dielectric cylinder 10; a conical radiation electrode 12 disposed on the surface of the concavity, the electrode extending upwardly from an apex (region) 14 to its base (on the upper side of Figure 1); and a ground conductor 13 which is arranged in the proximity and essentially parallel to the first end face of the dielectric 10. The monoconical antenna 1 is thus constituted such that electrical signals are fed between the proximal vertex region 14 of the radiation electrode 12 and the ground conductor region 13.

With respect to the angle α of the semi-cone (angle between the central axis and the lateral face of the cone) of the essentially conical concavity 11 formed in the first end face of the dielectric 10, the monoconical antenna 1 according to this example is constituted as follows : the angle α of the semi-cone is determined by a predetermined rule according to the relative dielectric constant e_r. The rule is, for example, as follows:

(1) If the monocone antenna 1 is covered with a dielectric with a relative dielectric constant e_r = 2, the monocone antenna 1 is constituted so that the angle of the semi-cone is approximately 45 degrees.

(2) If the monocone antenna 1 is covered with a dielectric with the relative dielectric constant e_r = 3, the monocone antenna 1 is constituted so that the semi-cone angle is approximately 37 degrees.

(3) If the monocone antenna 1 is covered with a dielectric with a relative dielectric constant e_r = 5, the mono cone antenna 1 is constituted so that the half cone angle is approximately 28 degrees.

(4) If the monocone antenna 1 is covered with a dielectric with the relative dielectric constant e_r = 8, the monocone antenna 1 is constituted so that the semi-cone angle is approximately 23 degrees.

The rule on which the previous constitution of monocone antenna 1 is based is Expression (1) that follows. Expression (1) describes the relationship between the semi-cone angle α of the concavity 11 formed in an end face of the dielectric 10 and the relative dielectric constant e_r.

α = 0.8 tng^-1(1.7 / e_r) + 13 (Angle unit: degree) (1)

The effective range of setting the semi-cone angle is between the value given by Expression (1) above plus several degrees and minus several degrees. Any value within this range does not pose a problem in practical use.

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With the aforementioned monocone antenna constitution, the bandwidth of an antenna is drastically improved.

Figure 2 and Figure 3 illustrate examples of calculations of the frequency characteristics of a monocone antenna according to this example (the results of electromagnetic field simulations). Figure 2 illustrates the frequency characteristics in the form of a Smith graph (center: 50 Ω) and VSWR characteristics diagram whose frequency characteristics are measured when the relative dielectric constant e_r is 3 and the semi-cone angle is 40 degrees. Figure 3 illustrates them as measured when the relative dielectric constant e_r is 8 and the semi-cone angle is 22 degrees.

In any constitution example, the antenna has a spiral characteristic in the vicinity of the center of the Smith graph, and obtains favorable frequency characteristics. An antenna is said to have favorable antenna characteristics in the frequency domain if VSWR is not greater than 2. In any constitution example, the relative bandwidth with VSWR <2 amounts to approximately 100%. It is evident that the bandwidth is drastically improved compared to feature examples presented in Japanese Unpublished Patent Publication No. Hei 8 (1996) -139515.

Regarding the method for the constitution of the monoconical antenna according to this example, the shape of the concavity 11 formed in an end face of the dielectric 10 is not limited to the circular cone. Even if it is in the shape of an elliptical cone or a pyramid, the effect of the present invention still occurs. If pyramidal concavity is used, the definition of semi-cone angle α is as follows: the mean of the minimum angle and the maximum angle between angles formed between the central axis and the lateral face.

There is also no special limitation on the outer shape of the dielectric cylinder 10. Basically, any shape, including circular cylinder and prism, is acceptable as long as the radiation electrode is covered by it. The radiation electrode can be formed by filling the conical recess 11 with it, rather than forming it on the surface of the recess 11.

The effective range of the relative dielectric constant e_r it is up to 10 or so.

Electromagnetic field simulations were performed and Expression (1) above was approximately deduced, on which a fixation of the angle α of the semi-cone of the circular cone formed on the first end face of the dielectric was based. From the results of various simulations the following was found: as illustrated in figure 4 to figure 7, the value of the semi-cone angle leading to the optimal adaptation of the circular cone formed on the first end face of a dielectric depends on the relative dielectric constant e_r of the covered dielectric. The approximate design significant curve is obtained by approximately formulating an approximate expression and adjusting its coefficients. With respect to Fig. 4 to Fig. 7, a further description will now be given.

Figure 4 includes diagrams and graphs illustrating the half-cone angle as a function of frequency characteristics (right) and a graph representing the half-cone angle based on the expression for fixation according to the present example (left). (The diagrams and graphs on the right illustrate three cases: case in which the semi-cone angle is 58 degrees; case in which the semi-cone angle is 40 degrees; and case in which the semi-cone angle is 24 degrees, from up). The figure illustrates the relationship between them when the relative dielectric constant e_r of dielectric 10 is 1. Frequency characteristics diagrams include Smith graph and VSWR characteristics diagram.

From the frequency characteristic diagrams to the right of the figure, the following is evident: when the semi-cone angle is approximately 58 degrees, the Smith graph has a spiral near the center, and the width of relative band with VSWR <2. That is, the following is evident: the semi-cone angle that leads to optimal adaptation is 58 degrees, and furthermore the value of the semi-cone angle is very close to the line represented by the expression to establish the semi-cone angle according to the example.

Figure 5 includes graphs illustrating the semi-cone angle as a function of frequency characteristics (right) and a graph representing the semi-cone angle based on the expression for fixation according to the present example (left). (The diagrams and graphs on the right illustrate three cases: case in which the semi-cone angle is 58 degrees; case in which the semi-cone angle is 40 degrees; and case in which the semi-cone angle is 24 degrees, from up). The figure illustrates the relationship between them when the relative dielectric constant e_r dielectric 10 is 3. The frequency characteristics diagrams comprise the Smith graph and the VSWR characteristics diagram.

From the frequency characteristic diagrams to the right of the figure, the following is evident: when the semi-cone angle is approximately 40 degrees, the Smith graph has a spiral near the center, and the bandwidth is maximized relative, with VSWR <2. That is, the following is evident: the semi-cone angle that leads to optimal adaptation is 40 degrees, and furthermore the value of the semi-cone angle is very close to the line represented by the expression to set the semi-cone angle according to this example .

Figure 6 includes diagrams and graphs illustrating the semi-cone angle as a function of frequency characteristics (right) and a graph representing the semi-cone angle based on the expression for fixation of

ES 2 297 565 T3 according to the present example (left). (The diagrams and graphs on the right illustrate three cases: case where the semi-cone angle is 40 degrees; case where the semi-cone angle is 26 degrees; and case where the semi-cone angle is 15 degrees, from above). The figure illustrates the relationship between them when the relative dielectric constant e_rdielectric 10 is 5. The frequency characteristics diagrams comprise the Smith graph and the VSWR characteristics diagram.

From the frequency characteristic diagrams on the right of the figure, the following is evident: When the semi-cone angle is approximately 26 degrees, the Smith graph has a spiral near the center, and the width of relative band with VSWR <2. That is, the following is evident: the semi-cone angle that leads to optimal adaptation is 26 degrees, and furthermore the value of the semi-cone angle is very close to the line represented by the expression to set the semi-cone angle according to the present example.

Figure 7 includes diagrams and graphs illustrating the half-cone angle as a function of frequency characteristics (right) and a graph representing the half-cone angle based on the expression for fixation according to the present example (left). (The diagrams and graphs on the right illustrate three cases: case where the semi-cone angle is 36 degrees; case where the semi-cone angle is 22 degrees; and case where the semi-cone angle is 10 degrees, from above ). The figure illustrates the relationship between them when the relative dielectric constant e_r of dielectric 10 is 8. Frequency characteristics diagrams comprise Smith graph and VSWR characteristics diagram.

From the frequency characteristics diagrams to the right of the figure, the following is evident: when the semi-cone angle is approximately 22 degrees, the Smith graph has a spiral near the center, and the width of relative band with VSWR <2. That is, the following is evident: the semi-cone angle that leads to optimal adaptation is 22 degrees, and furthermore the value of the semi-cone angle is very close to the line represented by the expression for fixing the semi-cone angle according to this example.

The monoconical antenna of a second example comprises an essentially conical concavity formed in an end face of a dielectric cylinder; a radiation electrode arranged on the surface of the concavity (or arranged so that the concavity is filled with it); and a ground conduit disposed in the vicinity of, and essentially parallel to, the other end face opposite the first end face of the dielectric. The monocone antenna is thus constituted such that electrical signals are fed to between the proximal vertex region of the radiation electrode and the region of the ground conduit. The monocone antenna can be constituted as a small antenna having relatively broadband characteristics due to the effect of shortening the wavelength from the dielectric located between the radiation electrode and the ground electrode.

A setting of the half cone angle of a mono cone antenna has been found to have great influence on the impedance matching band. Then, the following was deduced: the impedance matching band can be maximized by determining the semi-cone angle α (formed between the central axis and the lateral face of a cone) of a conical concavity formed in an end face of a dielectric by means of the following expression, which describes its relationship to the relative dielectric constant e_r:

α = 0.8 tang^-1(1.7 / e_r) + 13 (Angle unit: degree) (2)

That is, the optimal semi-cone angle of a circular cone depends on the relative dielectric constant of the dielectric. As illustrated in Figure 8, for example, the optimal semi-cone angle is 48 degrees when the relative dielectric constant e_r is 2, and 31 degrees when the relative dielectric constant e_r en 4. Figure 9 illustrates the antenna characteristics of a monocone antenna with an optimal half cone angle for the relative dielectric constant e_r 2 and 4, respectively. However, the figure represents the antenna characteristics by VSWR characteristics. From figure 9, the following is evident: favorable impedance matching is obtained in an ultra-wide band by designing the monocone antenna on the basis of expression (2) above, which describes the relationship between the relative dielectric constant and_r and the optimum angle α of the semicone of the concavity.

In the monocone antenna constituted on the basis of Expression (2) above, its side face is covered with a dielectric, whereby the miniaturization effect inevitably occurs. (This is caused by the fact that the wavelength of the electromagnetic field produced between the radiation electrode and the ground conductor is shortened). In packaging, therefore, a dielectric that meets miniaturization demands is appropriately selected, and a semicone angle of the circular cone is then determined.

With the constitution of the monoconical antenna on the basis of Expression (2) above, the reduction of the antenna size can be achieved by improving the relative dielectric constant e_r dielectric. However, in connection with this, the semi-cone angle α is also small (that is, the antenna becomes larger than its width). Therefore, the height of the antenna is not extremely reduced. In fact, it is frequently requested low profile.

Conversely, extremely slim or slim build may sometimes be desired. If a monocone antenna is constituted according to Expression (2) above, this is achieved by improving the relative dielectric constant e_r. In reality, however, dielectrics of various relative dielectric constants do not exist infinitely. Furthermore, the dielectrics available are naturally limited in terms of the possibility of work in training.

ES 2 297 565 T3 of electrodes and cut and heat resistors. Therefore, a desired leaner constitution is very likely to be difficult to execute.

The semi-cone angle of a circular cone whose profile or width is reduced deviates from an optimum value that leads to favorable impedance matching. To solve this, this example is constructed so that it is compensated by staggering the semi-cone angle.

A more specific description will be given. If a low profile constitution is adopted, the semi-cone angle is made to vary stepwise so as to decrease as it passes from the base portion to the apex portion. However, the ratio of the height h of the concavity to the effective radius r of the base of the concavity is fixed according to the following expression, which describes its relationship with the relative dielectric constant e_r tang^-1(r / h)> 0.8 tang^-1(1.7 / e_r) + 13 (Angle unit: degree) (3)

If the lean constitution is adopted, the semi-cone angle is varied so that it increases as it goes from the base portion to the apex portion. However, the ratio of the height h of the concavity to the effective radius r of the base of the concavity is fixed according to the following expression, which describes its relationship with respect to the relative dielectric constant e_r.

tang^-1(r / h) <0.8 tang ¹ (1.7 / e_r) + 13 (Angle unit: degree) (4)

In any case of low-profile build and slim build, two half-cone angle steps are basically sufficient. Needless to add that the number of steps may be increased to three or more, or a portion may be present in which the semi-cone angle is continuously varied. However, the semi-cone angle of the apex portion of a radiation electrode must be less than 90 degrees. Furthermore, it is preferable that the variation of the semi-cone angle is smooth in the vicinity of the apex part of a radiation electrode. It follows that an effort has to be made to maintain an equiangular circular cone in the vicinity of the vertex portion, ie the feed portion according to Rumsey's Equiangular Theory. (Rumsey's Equiangular Theory refers to the document "Frequency Independent Antenna", written by V. Rumsey (Academic Press, 1966). Care must be taken not to depart from the previous principle. Otherwise, the ultra-wideband characteristics inherent in the mono antenna may be lost.

Figure 10 illustrates an example of a mono cone antenna whose profile is reduced compared to the constitution of the optimum angle of the semi cone. In the example illustrated in the figure, the profile is less than the constitution of the optimum semi-cone angle. In this example we select a dielectric with a relative dielectric constant e_r of 4; the height h of the circular cone is set at 6 mm; and the radius r of the base of the circular cone is set at 12.6 mm. Thus, as a natural consequence, the relationship set forth in Expression (3) above is maintained.

As illustrated in the figure, furthermore, two-step constitution is adopted. With this constitution, the semi-cone angle is staggered at a midpoint, and the value a_or of the semicone angle on the side of the base is set at 70 degrees, the value α being set at 45 degrees₁ of the semi-cone angle. Thus, the value of the semi-cone angle on the vertex side becomes smaller than on the base side.

Figure 11 illustrates the result of a simulation performed with respect to the VSWR characteristics of the monocone antenna having the constitution illustrated in Figure 10. As illustrated in the figure, favorable impedance matching is generally obtained, and is lost in largely a state in which impedance matching and thereby avoiding losing bandwidth characteristics. If the combination of semi-cone angle values ​​is more finely tuned, more favorable characteristics would be obtained.

Figure 12 illustrates an example of a mono cone antenna whose width is reduced compared to the optimal constitution of the half cone angle according to this example. In the example illustrated in the figure, the width is less than the optimal half cone angle constitution. In this example, a dielectric with relative dielectric constant e is selected_r of 2; the height h of the circular cone is set at 17.4 mm; and the radius r of the base of the circular cone is set to 9 mm. In this way, as a natural consequence, the relationship set forth in expression (4) above is maintained.

As illustrated in the figure, furthermore, the two-step constitution is adopted. With this constitution, the semi-cone angle is stepped at a midpoint, and the value a_or of the semi-cone angle on the side of the base is set at 11 degrees, the value α being set at 41 degrees₁ of the semi-cone angle on the vertex side. Thus, the value of the semi-cone angle on the vertex side becomes smaller than on the base side.

Figure 13 illustrates the result of a simulation performed with respect to the VSWR characteristics of a monocone antenna having the constitution illustrated in Figure 12. As illustrated in the figure, favorable impedance matching is generally obtained.

Figure 14 illustrates an example of the constitution of a mono cone antenna provided with a feed portion structure suitable for serial production.

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In the example illustrated in the figure, a track-like feed electrode is arranged at the base of a dielectric, and the feed electrode and a radiation electrode are electrically connected to each other through a hole made in the bottom of the dielectric. dielectric. As illustrated in the figure, this feed electrode is formed so that its first end reaches the side face of the dielectric.

A ground conductor is also formed at the base of the dielectric. As illustrated in the figure, the ground conductor is formed so that it deflects and surrounds the feed electrode. Furthermore, the ground conductor is also formed so that it extends to the side face of the dielectric.

The feed electrode and ground conductor illustrated in Figure 14 can be easily formed on the surface of a dielectric by plating, for example. Therefore, the use of such a monocone antenna as illustrated in the figure makes it possible to follow a technique for so-called surface mounting when the antenna is mounted on a circuit board in series production, and thus simplifies the making.

As illustrated in Figure 15, the monocone antenna body can be electrically attached and connected to a circuit board only by soldering the electrodes from the dielectric side face to the circuit board electrodes from the surface side.

The ground conductor need not necessarily be formed on the basis of a dielectric, and, alternatively, a ground conductor may be formed on the circuit board on which the antenna body is to be mounted. In this case, for example, adhesive can be used to fix the antenna body.

The monoconical antennas according to this example, illustrated in figure 10 and figure 12, are constituted in such a way that: when an antenna is reduced in profile or width on the basis of the optimal values ​​of the semi-cone angle obtained by the expressions ( 3) and (4) above, the deviation of its semi-cone angle from its optimal values ​​is compensated. This compensation is done by staggering the half cone angle, and this results in favorable impedance matching.

Reducing the profile of an antenna poses a problem. The semi-cone angle of the cone deviates from the optimum value leading to favorable impedance matching. To solve this, the apex of the circular cone of the monocone antenna is set off-center and the impedance matching is thereby compensated. This is a modification according to the present invention, whereby the straight line connecting the apex of the essentially conical radiation electrode and the center of the base of the conical radiation electrode is not perpendicular to the base of the conical radiation electrode.

An example will be taken. Figure 16 illustrates the cross-sectional structure of a mono cone antenna using low profile build. In the example illustrated in the figure, the semi-cone angle of the circular cone is 64.5 degrees, which differs from 31 degrees, the optimal value with e_r = 4. As the dielectric to be filled in the area between the radiation electrode and the earth conductor, a material with a relative dielectric constant e is used_r of 4. Figure 17 includes the impedance characteristics diagram and VSWR characteristics diagram of the low profile mono cone antenna illustrated in figure 16. As evident from the figure, the impedance differs greatly from 50 ohm, and VSWR characteristics are impaired, especially in high frequency domain.

Meanwhile, Fig. 18 illustrates the cross-sectional structure of a low profile mono cone antenna according to the present invention, in which the apex of the conical radiation electrode is offset from the center by 25% relative to the radius. In this case, as illustrated in the figure, the straight line connecting the apex of the essentially conical radiation electrode and the center of the base of the conical radiation electrode is not perpendicular to the base of the conical radiation electrode.

Figure 19 includes the impedance characteristics diagram and VSWR characteristic diagram of the low profile mono cone antenna illustrated in figure 18. As is evident from the figure, the impedance characteristics are close to 50 ohms, and the characteristics VSWR's are improved as well. Especially, it is important that the lower limit frequency of the matching band is lowered.

As mentioned above, it is evident that if the impedance cannot be matched in a monocone antenna due to reduced profile or the like, fixing the apex of the off-center cone is effective as a means of improving its characteristics.

One such low profile structure, as illustrated in Figure 18, is also applicable when the relative dielectric constant e_r = 1, that is, it is applicable to a monocone antenna in which there is no dielectric material.

With regard to the method for constituting the monoconical antenna according to this embodiment, the configuration of the concavity formed in an end face of the dielectric is not limited to the circular cone. Even if it is made in the form of an elliptical cone or a pyramid, the effect of the present invention still occurs.

If pyramidal concavity is used, the definition of its semi-cone angle α is as follows: the mean of the minimum angle and the maximum angle between the angles formed between the central axis and the lateral face.

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There is also no special limitation on the outer shape of the dielectric cylinder. Basically any shape, including circular cylinder and prism, is acceptable as long as the radiation electrode is covered by it. The radiation electrode can be formed by filling the conical concavity 11 with it, rather than forming it on the surface of the concavity.

Figure 20 illustrates the constitution of the monocone antenna according to a third example. The monoconical antenna comprises: an insulator, an essentially conical concavity arranged in an end face of the insulator; a radiation electrode formed on the inner surface of the concavity; a detached portion obtained by circumferentially detaching part of the radiation electrode; a low conductivity member that fills the concavity to the level where the detached portion is buried; and a ground conductor in proximity and essentially parallel to the other end face of the insulator.

First, the essentially conical recess is arranged in the first end face of the insulator. The radiation electrode is formed on the inner face of the concavity by plating or the like. Next, part of the radiation electrode is circumferentially detached by cutting or the like. The low conductivity member is then filled to the level at which the detached portion is buried. For the low conductivity member, a conductor containing rubber or elastomer is appropriate. A desired conductivity is obtained relatively easily by adjusting the content of the conductor. Furthermore, the ground conductor is arranged in the vicinity and essentially parallel to the other end face of the insulator. Excused is to add that an electrode can be formed as a ground conductor directly on the other end face of the insulator.

As in conventional monocone antennas, the electrical signals are fed into the gap between the radiation electrode and the ground conductor. If electrical signals are fed from the side of the rear face of the ground conductor, the same constitution can be adopted as in conventional antennas. That is, a hole is made in the ground conductor, and the apex region of the radiation electrode extends to the rear face side.

The antenna illustrated in Figure 20 basically functions as a mono cone antenna. Incidentally, no conductor is present at the top base of the concavity; however, this is not a cause to impede the proper operation of the mono antenna. Furthermore, since the low conductivity member exists between the two divided radiation electrodes, the electrical effect equivalent to the resistive load occurs. (Figure 20 is represented so that the concavity is formed on the upper side of the insulator. However, the concepts of upper and lower do not exist due to the structure of the conical antenna. In this specification, the end face provided with the Concavity is designated as top base for convenience of description. However, this does not limit the scope of the present example. (It is the same with what follows)).

Figure 21 illustrates a calculation example to demonstrate the electrical effect of the mono cone antenna according to this example. To the left of the figure is the VSWR characteristic diagram obtained when the detached portion of the electrode is not formed, and to the right is that obtained when the detached portion is formed. (The other conditions are completely identical). The conditions for the calculation will be briefly described below. As is evident from the figure, the formation of the detached part of the electrode leads to the following advantages: the band in which VSWR is not greater than 2 is expanded to the low frequency band; adaptation is appropriately improved; and the band broadening of the cone antenna is achieved.

(1) Radiation electrode portion: It is assumed that a metal with a conductivity of 1x10 is used⁷ Ye.

Top Base Diameter: 12.6mm, Height: 12.6mm.

(2) Low conductivity member: It is assumed that a material with a conductivity of 2 S / m is used.

(3) Insulator: Assume a dielectric with a relative dielectric constant of 4 is used.

In the example of the cone antenna constitution illustrated in FIG. 20, a circumferential detached portion is formed in the radiation electrode formed on the inner surface of the insulator concavity. The member of the circumferential peeled portions is not limited to one. A more specific description will be given. As mentioned above, the presence of the low conductivity member between the radiation electrodes divided by the detached portion produces the electrical effect equivalent to the resistive load. For this purpose, two or more circumferential peeled portions may be provided, as required.

Figure 22 illustrates conical antenna constitutions in which two detached electrode portions are formed in the depth direction of the concavity formed in the insulator. In this case, the low conductivity member of the concavity may be provided with a multilayer structure as illustrated on the right hand side of the figure. The multilayer structure is such that low conductivity members of different conductivities fill in level to the level at which each detached electrode portion is buried. At this time, the low conductivity members are distributed so that the conductivity is lower on the upper base side. Thus, the effect of lowering the reflective power to the feed portion is enhanced, and this results in an expanded matching band.

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The example is not limited to single cone antenna, and it is effective as a resistive loading method for two cone antenna. Figure 23 illustrates examples where the ground conductor is formed on the other end face of the insulator. In these examples, the resistive load is applied to biconical antennas formed by arranging radiation electrodes on the inner surfaces of essentially conical concavities formed symmetrically on both end faces.

Each of the biconical antennas illustrated in the figures comprises: an isolator; a first essentially conical concavity formed in an end face of the insulator; a first radiation electrode formed on the inner surface of the first concavity; a first detached portion obtained by circumferentially detaching part of the first radiation electrode; a first low conductivity member that fills the concavity to the level at which at least the first detached portion is buried; a second essentially conical concavity formed in the other end face of the insulator; a second radiation electrode formed on the inner surface of the second concavity; a second detached portion obtained by circumferentially detaching part of the second radiation electrode; and a second low conductivity member that fills the concavity to the level at which at least the second detached portion is buried.

In the examples illustrated in FIG. 23, electrical signals are fed into the gap between the two radiation electrodes. For this purpose, various methods can be used. For example, parallel lines can be extended from the insulator side face and connected to the vertex regions of the radiation electrodes. (This method is not shown in the figure).

As described in connection with Figure 22, the presence of the low conductivity member between the radiation electrodes divided by the detached portion produces the electrical effect equivalent to resistive charge. If the resistive load is applied to a biconical antenna, this constitution can be similarly adopted. That is, for the aforementioned purpose, two or more circumferentially peeled portions may be provided at each of the upper and lower radiation electrodes, as required. (Reference is made to the center of figure 23).

As illustrated on the right hand side of Figure 23, the low conductivity members in the concavities can be provided with a multilayer structure. The multilayer structure is such that low conductivity members of different conductivities respectively fill to the level at which each detached electrode portion is buried. At this time, the low conductivity members are distributed so that the conductivity is lower on the base side. Thus, the effect of lowering the reflective power to the feed portion is enhanced, and this results in an expanded matching band.

Figure 24 illustrates the cross-sectional structure of a mono cone antenna which is a modification of the third example. The monocone antenna illustrated in the figure comprises: an essentially conically formed isolator; a radiation electrode formed on the surface of the essentially conical insulator; a circumferential groove portion circumferentially dividing part of the radiation electrode along with the insulator located below it; a low conductivity member filling the circumferential groove portion, and a ground conductor disposed in the vicinity of the near apex region of the radiation electrode.

In the example illustrated in Figure 24, the radiation electrode is the first one formed on the surface of the insulator made of conical shape. The radiation electrode can be formed by plating or the like. Next, part of the radiation electrode is circumferentially peeled off and cut together with the insulator below it by cutting or the like. The cut cut and peeled portion thus obtained is filled with the low conductivity member. For the low conductivity member, a conductor containing rubber or elastomer is appropriate. A desired conductivity is obtained with relative ease by adjusting the content of the conductor. Furthermore, the second conductor is arranged in the vicinity of the vertex region of the radiation electrode.

With the monocone antenna constitution illustrated in Figure 24, the presence of the low conductivity member between the two radiation electrodes produces the electrical effect equivalent to resistive load. (This is the same as above).

Excused is to add that a bracket to fix the arrangement of the ground conductor and the insulator is required separately, although it is not shown in figure 24.

In the example of the conical antenna constitution illustrated in Figure 24, the radiation electrode formed on the surface of the insulator is provided with only a circumferentially cut and peeled portion. The example does not limit the member of the cut and peeled circumferential portions to one. A more specific description will be given. As mentioned above, the presence of the low conductivity member between the radiation electrodes divided by the detached portion produces the electrical effect equivalent to resistive charge. For this purpose, two or more cut and detached circumferential portions may be provided, as required.

Fig. 25 illustrates the constitution of a conical antenna in which two detached and shortened portions are formed in the depth direction of the essentially conical radiation electrode formed on the insulator. In this case, low conductivity members of different conductivities can fill the individual cut and peeled portions. At this time, the low conductivity members are distributed such that the conductivity is lower on the base side of the insulator. Thus the effect of lowering the reflective power towards the feed portion is enhanced, and this results in an expanded matching band.

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The example illustrated in Fig. 24 is not limited to single cone antenna and is effective as a resistive loading method for two cone antenna. Figure 26 illustrates examples of biconical antenna constitutions using cone antennas that are formed by providing cut and peeled circumferential portions at radiation electrodes formed on the surfaces of cone insulators.

The biconical antenna illustrated on the left of Figure 26 comprises a first insulator made essentially conical; a first radiation electrode formed on the surface of the essentially conical insulator; a first circumferential groove portion circumferentially dividing part of the first radiation electrode along with the insulator located below it; a first low conductivity member filling the first circumferential groove portion; a second insulator made essentially of conical shape, the vertex of which is opposite that of the first insulator and whose base is symmetrical with respect to that of the first insulator; a second radiation electrode formed on the surface of the essentially conical insulator; a second circumferential groove portion circumferentially dividing part of the second radiation electrode along with the insulator located below; and a second low conductivity member filling the second circumferential groove portion.

As illustrated in FIG. 26, the formation of the ground conductor on the other end face of each insulator in the vicinity of the near apex region of the radiation electrode is omitted. The conical insulators are arranged so that their respective vertices are opposite each other and their respective bases are symmetrical with each other, and the radiation electrode is formed on the surface of each conical insulator. Part of each radiation electrode is circumferentially cut and peeled off together with the insulator located below, and these cut and peeled portions are filled with the low conductivity member. It is useless to add that a support is required to fix the arrangement of the two cone antennas, although this is not shown in the figure.

In the example illustrated in Figure 26, electrical signals are fed into the gap between both radiation electrodes. For this purpose, several methods can be used. For example, parallel lines can be extended from the insulator side face and connected to the vertex regions of both radiation electrodes. (This method is not shown in the figure).

As mentioned above, the presence of the low conductivity member between the radiation electrodes divided by the cut and peeled portion produces the electrical effect equivalent to resistive charge. If the resistive load according to the example illustrated in Fig. 24 is applied to a biconical antenna, this constitution can be similarly adopted. For this purpose, as described in connection with Figure 25, two or more cut and peeled circumferential portions may be provided at each of the upper and lower radiation electrodes, as required. (Reference is made to the right side of Figure 26).

As illustrated on the right hand side of Figure 26, low conductivity members of different conductivities can fill the two detached cut portions formed in the depth direction of the essentially conical radiation electrode formed on each of the upper and lower insulators. At this time, the low conductivity members are distributed so that the conductivity is lower on the upper base side. Thus, the effect of lowering the reflective power to the feed portion is enhanced, and this results in an expanded matching band.

Figure 27 illustrates the cross-sectional structure of a monocone antenna which is another modification of the third example. The monocone antenna illustrated in the figure comprises an isolator; an essentially conical concavity arranged in an end face of the insulator; a feed electrode on the surface of the proximal vertex region of the concavity, a low conductivity member filling the cavity, a ground conductor arranged proximally and essentially parallel to the other end face of the insulator or formed directly on the other face end of the insulator.

In the example illustrated in the figure, the conical concavity is first formed on the surface of the insulator, and then the feed electrode is formed on the inner surface of the concavity in the vicinity of its apex. The feed electrode can be formed by plating or the like. The concavity is then filled with the low conductivity member. For the low conductivity member, a conductor containing rubber or elastomer is appropriate. A desired conductivity is obtained relatively easily by adjusting the content of the conductor. Then, the conductor is arranged near and essentially parallel to the other end face of the insulator. Alternatively, the ground conductor can be formed directly on the other end face of the insulator.

With the constitution of the monocone antenna illustrated in Fig. 27, the low conductivity member functions as a radiation conductor, and furthermore the electrical effect equivalent to resistive load is obtained. As illustrated in the figure, the area of ​​the electrode is significantly reduced and the cost can be correspondingly reduced. Unlike the examples mentioned above, the electrode stripping process is omitted and the cost can be correspondingly reduced.

The electrical signals are fed into the gap between the supply electrode and the ground conductor. If the electrical signals are fed from the back face side of the ground conductor, such a constitution can be adopted in which a hole is made in the ground conductor and the region of the apex of the concavity extends to the side of the back face.

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Figure 28 illustrates a modification of the monocone antenna illustrated in Figure 27. As illustrated in Figure 28, the low conductivity member filling the concavity may be provided with a multilayer structure in which members of different conductivities fill respectively up to individual predetermined levels. At this time, the low conductivity members are distributed so that the conductivity is lower on the upper base side. Thus, the effect of lowering the reflective power to the feed portion is enhanced, and this results in an expanded matching band.

The example illustrated in Fig. 27 is not limited to the single cone antenna and is effective as a resistive loading method for the two cone antenna. Figure 29 illustrates the cross-sectional structure of a biconical antenna formed using cone antennas that are formed by filling with a low conductivity member the feed electrodes formed on the surfaces of the conical recesses in an insulator.

In the biconical antenna illustrated in Figure 29, the formation of the ground conductor on both end faces of the insulator is omitted. The biconical antenna comprises: a first conical concavity and a second conical concavity formed symmetrically on both faces; a first feed electrode formed on the surface of the near apex region of the first concavity; a first low conductivity member that fills the first concavity; a second feed electrode formed on the surface of the near apex region of the second concavity; and a second low conductivity member that fills the second concavity.

With the biconical antenna constitution illustrated in Figure 29, the low conductivity members function as radiation conductors, and furthermore the electrical effect equivalent to resistive load is obtained. As illustrated in the figure, the area of ​​the electrodes is significantly reduced and the cost can be reduced accordingly. Unlike the above-mentioned embodiments, the electrode stripping process is omitted, whereby the cost is correspondingly reduced.

In the example illustrated in FIG. 29, electrical signals are fed into the gap between the first and second supply electrodes. For this purpose, various methods can be used. For example, parallel lines can be extended from the side face of the insulator and connected to the apex regions of both radiation electrodes. (This method is not shown in the figure).

Figure 30 illustrates a modification of the biconical antenna illustrated in Figure 29. As illustrated in Figure 30, the low conductivity member that flattens each concavity may be provided with a multilayer structure in which members of different conductivities respectively fill up to individual predetermined levels. At this time, the low conductivity members are distributed in such a way that the conductivity is lower on the upper base side. Thus, the effect of lowering the reflective power to the feeding part is enhanced, and this results in an expanded matching band.

In the examples mentioned above with reference to the figures, the radiation electrode of the cone antenna is made in a cone shape. The examples are not limited to this, and even if the shape of the radiation electrode is conical elliptical or pyramidal, the effect still occurs. There is also no special limitation on the shape of the isolating cylinder, and basically any shape, including circular cylinder and prism, can be adopted, easy to handle. In addition, the insulator is not limited to dielectric material, and even a magnetic material has no influence on the essential effect of the examples.

Industrial applicability

In accordance with the present invention, an excellent monocone antenna can be provided in which profile and width reduction is achieved regardless of dielectric selection.

The antenna thus obtained is useful, for example, as a small, low-profile antenna or a small slim antenna for ultra-wideband communication system.