Small-size antenna for portable radio communication device

This invention relates to antennas, and more particularly to a small-sized antenna, particularly suitable for use in a portable radio communication device having a transmitter in the form of a meander line.

Recently, portable radio communication devices have become miniaturized and lightweight, and therefore carried out intensive development of small antennas suitable for use in such devices. Such compact antenna should be convenient and simple to operate by the user and should have an omnidirectional radiation pattern in azimuth and a relatively high aperture in elevation. Furthermore, in conditions when the portable radio device is located near the user's body, the latter should minimally affect the basic characteristics of the antenna, m. E. The input impedance and gain value fluctuations.

One solution designed to meet the above requirements, described in US Patent 4700194 N by 13 October 1987. In accordance with this solution, when the antenna current flows in the grounding circuit and the terminal in the housing, the current flowing in the antenna change if the terminal housing located near the user's body, so that the input impedance and gain of the antenna can vary greatly. As a result, even without using a quarter-wave circuit rejection or balun, as in prior art antennas to a vertical half-wave dipole to a coaxial screen at the bottom, good electrical isolation may be provided between the antenna and circuit ground koaksil Hoc transmission line or electrical circuit.

FIG. 1 is a diagram illustrating the construction of a known quarter-wavelength microstrip antenna (CHMPA) which is described in the aforementioned U.S. Patent N 4700194. In accordance with FIG. 1 centered with respect to the dielectric antenna 61 includes a radiation element on one surface of the dielectric and the ground element on another surface. The first radiating element 62 (first feeder means) is electrically connected to the signal conductor of the transmission line. The second radiating element is structured on the ground element so that electrically connects a ground conductor of the transmission line and the ground element located at a position where the standing voltage wave induced on the ground element, takes a minimum value. In a conventional microstrip antenna ground plane does not act as a ground, if the size of the ground plane is small compared to a wavelength at the operating frequency. In this case, a sinusoidal variation of the distribution voltage or voltage standing wave induced in the grounding screen. As a result, a parasitic current is induced in the outer conductor of the coaxial transmission line. In the antenna of FIG. 1 to reduce the probability of generating such parasitic current to a minimum outer conductor of the transmission line connected to the ground element at a second feed point where the voltage standing wave induced on the ground element becomes minimum. With such a design the parasitic current on the transmission line can be reduced or eliminated without any quarter-wave rejection circuit, which is used in conventional designs of vertical antennas to form a half-wave coaxial dipole screen at the bottom. Accordingly, deviations in the characteristics of the antenna can be significantly reduced when the antenna is located in proximity to the body of the user or some circuitry.

FIG. 2 and 4 are diagrams showing variation of the gain in dB as a function of the length L of the known quarter-wave patch antenna, and FIG. 3 is a graph illustrating gain characteristics change depending on the width W of the well-known quarter-wavelength microstrip antenna.

A disadvantage of the known quarter-wavelength microstrip antenna is that the change in the performance characteristics of the antenna depends considerably on the thickness of the substrate of the printed circuit board (PPP). Greater thickness results in PPS higher gain, but increases the size and weight of the antenna, causing inconvenience to the user of the portable communication device, which becomes more cumbersome. In contrast, if the PPP has a small thickness, although such a device which is used as a portable, but the antenna gain can be reduced accordingly.

The object of the invention is to provide an antenna having a small size and weight and providing a high gain and efficient use in a portable communication device. It is desirable to minimize the change of the antenna characteristics when the antenna is located near the user's body.

In an embodiment of the present invention, small-size antenna for portable radio communication apparatus includes an emitter formed as a loaded monopole radiator and a ground. Emitter formed as a loaded monopole, comprising first and second conductors on a printed circuit board substrate, said first conductor having predetermined length and is oriented in the horizontal direction and the second conductor has a meander line shape and oriented in a vertical direction. Ground radiator includes a first grounded emitter and a second emitter is grounded on the bottom of printed circuit board substrate, wherein the first and second ground radiators are symmetrical relative to the second conductor.

The invention is explained in more detail in the following description, the accompanying drawings in which: FIG. 1 - a diagram illustrating the construction of a quarter-wavelength microstrip antenna known from the prior art; FIG. 2 - a graph illustrating a change in gain characteristics depending on the total length of the antenna of FIG. 1: FIG. 3 - a graph illustrating gain characteristics change depending on the width of the antenna of FIG. 1; FIG. 4 - a graph illustrating a change in gain characteristics depending on the non-metallized length Gz of the antenna of FIG. 1; FIG. 5 - a diagram illustrating the construction of an antenna in a monopole antenna according to one embodiment of the invention; FIG. 6 - a detailed diagram of the antenna of FIG. 5; FIG. 7 - a graph illustrating a current distribution of a loaded monopole and an equivalent monopole; FIG. 8 - a graph of antenna gain versus length of a dipole; FIG. 9 - a graph of antenna gain versus width of a dipole.

FIG. 5 schematically shows the antenna as a monopole made according to an embodiment of the present invention. The antenna is shown for use in conjunction with a pager 10 bidirectional, but the invention may also have another use.

Referring to FIG. 5, antenna system 20 includes an emitter 12 of a conductor, made in shape of the loaded monopole antenna, a ground radiator 13, taken along the meander line shape, and coaxial transmission line (coaxial cable) 27 for connecting the radiator 12 of the conductor and the ground radiator 13 to PPP 11 equipped with a radio frequency power amplifier. More specifically, the coaxial cable 27 comprises a signal conductor (not shown) with one end connected to the radiator 12, and a ground conductor connected to the grounded emitter 13. Thus the signal conductor of the coaxial cable 27 at its other end connected to the signal conductor of the portable radio (the drawing not shown) and the ground conductor of the coaxial cable is connected to a grounded part of the portable radio communication apparatus. The emitter 12 of the conductor and the ground radiator 13 arranged on one main surface of the PCB 21, which can be placed in the housing 28, an antenna in a hinged cover. The housing 28 in the form of a hinged lid is moved together with the antenna system 20 relative to the housing of pager 10. That is. The antenna system 20 is moved from position to position the Y axis Z, where the pager housing is centered about the axis X. In the operating position the antenna system 20 is in vertical position (oriented in the Z direction, as shown in FIG. 5).

FIG. 6 shows a detailed diagram of the antenna of FIG. 5, showing more specifically the PCB 21 of the antenna system 20. The emitter 12 of the conductor formed on the loaded monopole shape is composed of an oriented in the first example, in the horizontal direction of the first conductor 23 and oriented in a second, e.g., in the vertical direction of the second conductor 22 having a meander line shape. The upper end of conductor 22, oriented in the vertical direction, is loaded by a conductor 23, oriented in the horizontal direction. In this example the electrical length of the conductor 22 is 0.49 wavelength and the electrical length of the conductor 23 is 0.3 wavelength. This design is based on a consideration of the fact that the length of the antenna having the highest gain of the equivalent antenna in a vertical unsymmetrical vibrator is 0.625 wavelength. In addition, whole antenna system 20, which uses the load and a meander line shape and the above lengths to maximize the gain, is particularly suitable for use in conjunction with the housing 28 in the form of a rectangular or square flip cover.

Ground radiator 13 is placed at the bottom of the PCB 21 of the antenna system 20 parallel to the conductor 23, oriented in the horizontal direction. In the illustrated configuration, a ground radiator 13 is divided into two parts, symmetrical relative to the vertical part of the radiator 12, namely, the first and second radiators 24 and 25 symmetrical relative to the vertical conductor 22 and connected to the grounding of the coaxial transmission line 27 at the point 26 of the feeder earth. More specifically, the first ground radiator 24 is placed with the first side of the conductor 22 and the second ground radiator 25 is placed on the second side of the conductor 22, the first and second ground radiators 24 and 25 are connected to each other. To improve the efficiency of the earthing of the radiator 13, each of ground radiators 24 and 25 preferably has an electrical length equal to half the wavelength. The quality of the PCB 21 of the antenna system 20 according to a preferred embodiment of the invention, may correspond to FR-4 with a thickness, for example, 0.25 mm. PCB 21 can be placed in the housing 28 as a flip cover of polycarbonate. The capacitor 34 and inductance 35 are used for impedance matching.

The antenna according to the preferred embodiment of the invention operates as follows. The efficiency of the antenna is determined by the effectiveness of radiation, which can be determined using the following equation: where η - radiation efficiency, Rr - radiation resistance, Ohm, RL-loss resistance in ohms.

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In equation (1) with a decrease in the length of the emitter radiation resistance Rr decreases.

To increase the radiation efficiency to a value close to the antenna efficiency, it is necessary to increase the length of the radiator Rr and use a low loss conductor with a low resistance RL. Thus, possible embodiments of the present invention may be implemented using a meander line shape for the conductor to reduce the physical length of the antenna radiator, while increasing the radiation efficiency by increasing the length of the radiator as a function of wavelength. Finally, the antenna gain can be increased without increasing the physical length of the radiator.

The article Kharchenko "antenna wire in the form of a meander line." (Radio, N 8, 1979, p. 21) discloses that increasing frequency (reducing period) meander line antenna conductor, the antenna bandwidth is narrowed. Therefore, as shown in FIG. 6, in this embodiment of the present invention, a horizontally oriented conductor 23 loaded on the radiator 22, so that the electric equivalent length can be increased to a desired value without excessively narrowing the antenna bandwidth. The achieved effect is that the antenna works like an antenna with a radiator of increased length, thereby enhancing the antenna gain.

FIG. 7 is a graph illustrating the current distribution in a loaded monopole and an equivalent monopole, wherein portion 7a of the graph illustrates the loaded monopole and the current distribution in it, and portion 7b illustrates the current distribution is generated in the antenna by an equivalent monopole. It is desirable to obtain good current distribution in the vertically oriented antenna conductor. Thus, the antenna operates in the same manner as with increasing length at Δ lv, using the horizontal conductor (loaded radiator), as can be seen from the following expression (2): L v eqv = lv + Δ lv, where Δ lv - lengthening equivalent vertical conductor.

For loaded antenna as a monopole antenna, unless the current value at the end point "A" (see. FIG. 7) of the vertical conductor 22 becomes zero, the value is determined by reactive impedance of the horizontal conductor 23 of the antenna a loaded monopole. Only when the input reactive impedance of the loaded radiator at point A is equal to the input reactive impedance at point B of the equivalent monopole, then oriented in the vertical direction of the antenna conductor can be increased by Δ l.

In this situation, the input reactive impedances XA and XB of the loaded radiator at positions A and B are as shown below in (3) and (4): wherein the 1H - the length of the "shoulder" of the horizontal conductor of the loaded monopole (t. e., about half the total horizontal length of the entire conductor 23), a ZOH - own impedance of the horizontal conductor of the loaded monopole; wherein ZOV- own impedance of the vertical conductor of the loaded monopole.

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Furthermore, if the two input reactive impedance XA and XB are equal to each other, Δlv can be obtained from expression (5) as follows: As a result, equal to the sum eqv lv lv lv and Δ. Ie. Lv eqv = lv - Δ lv. In other words, it can be seen that the physical length of the antenna in the form of the unloaded vibrator is increased by Δ lv. Moreover, the housing of the terminal of the user device, coated with a metal film or the grounding fixed therein PPP may serve as a grounding for the entire antenna as a monopole. Consequently, if the user takes his terminal in hand, the radiation efficiency can be reduced despite the fact that it serves as a grounding ground radiator (cm. "Mobile Antenna Systems Handbook", K. Fujimoto, JR James, Artech House, Boston- London, 1994, pp. 217-243).

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The first and second ground radiators 24 and 25 are in the preferred embodiment so as to minimize the effect of the user's body on the radiation of the antenna as a monopole antenna, when the user terminal is located in close proximity to the human body. Since the antenna current is separated from the ground bidirectional pager 10, the reduction of the radiation efficiency can be minimized in a position where the user holds the device in his hand. Also, when the user actually utilizes the terminal device, the first and second ground radiators 24 and 25 are placed on the PCB 21 of the antenna installed on the upper surface 10 of the pager bidirectional farthest from the user's body in the operating position of the pager.

Radiation from the first and second ground radiators 24 and 25 depends on signal voltage law of variation. The alternating voltage signal may generate parasitic current flowing along the surface (ground) of the coaxial transmission line 27, thereby changing the antenna characteristics such as a radiation pattern, input impedance and gain. To eliminate the change of characteristics such first and second radiators 24 and 25 are opposite one another and centered with respect to the Z axis of the antenna on the PCB 21 and the electrical length of each of them is equal to L = (2n - 1) λ / 4, where n - a positive constant. E. The electrical length of each of the second ground radiators 24 and 25 is set equal to an odd multiple of a quarter wavelength. If the electrical length of each of the second ground radiators 24 and 25 is identical, the parasitic current flowing from the grounded surface 26 to its emitter grounded may be minimized. Consequently, there will be a very slight deterioration in antenna characteristics and radiation efficiency under the influence of a nearby body of the user, even if the grounding of 10 bi-directional pager is in the immediate vicinity.

FIG. 2-4 it follows that the gain characteristic of a quarter-wavelength microstrip antenna is a function of the lengths L and Gz and the width W of the antenna and that its gain characteristic is lower in comparison with the characteristic of the antenna gain of a dipole. FIG. 8 shows a plot of antenna gain versus length of a dipole, which can be compared with the graph shown in FIG. 2-4.

Compare antenna according to an embodiment of the present invention with the known aerial. If the parameters of the antenna according to the present invention (L = 47,3 mm; εγ = 4,5 mm; f = 916 MHz), adapted to the known antenna, it is possible to carry out the above comparison. Comparison of antenna gain according to the present invention and the known antenna is as follows.

If the construction illustrated FIG. 1, assume that b = λs / 4, L = 47,3 mm, εγ = 4,5 mm; f = 916 MHz, and d = 1.2 mm, then the parameters λs., b, Gr are defined as follows: b = λs / 4 = 38.6 mm, (7) Gz = L - b = 8,7 mm.

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Considering FIG. 2 and 4, for the case where L = 47.3 mm, and Gz = 8,7 mm, amplification, as shown in these figures, is approximately equal to - 12.5 dBd (-10.35 dBi). The antenna used in the present embodiment has an electrical length of 0.625 λ. For this case, the gain is approximately 3dBd (5,15 dBi), as seen from FIG. 8. Thus, in the known antenna gain may be deteriorated by about 15 dB. (Note that the graphs shown in FIGS. 8 and 9 relate to an antenna as a dipole antenna. However, the antenna gain in the form of a monopole antenna is essentially the same as that for an equivalent dipole antenna. Thus, it can be assumed that Figure . 8 and 9 represent gain of a monopole antenna vibrator according to the present invention).