The fast-wave oscillation type antenna with multi-layer grounding

Fast wave oscillating antenna with multi-layer ground plane

Background of the invention

The present invention relates to a fast-wave oscillation antenna with a multilayer ground plane, in particular to a micro-miniature fast-wave oscillation antenna with a multilayer ground plane that can be installed using surface adhesion technology and can use dielectric materials with a small relative permittivity. antenna.

With the widespread use of wireless communication mobile phones, hidden antennas have attracted more and more attention. Because of its small size, the hidden antenna can be installed by surface adhesion technology, so it can be integrated into the entire radio frequency electronic circuit board, which greatly improves its reliability and enhances the quality of the mobile phone.

Common hidden antennas use metal patch-shaped microstrip lines. 1 is a metal patch microstrip antenna (patch antenna), in which a dielectric substrate 11 is located on the ground plane 12, a metal patch 13 is located in the middle of the dielectric substrate 11, and the signal can be fed through the feeder 14 To proceed. This method is common in many active antenna designs.

Figure 2 is another metal patch microstrip antenna. Its structure is mostly similar to that of Figure 1. The difference from Figure 1 is that the feeder 15 is extended along the surface of the dielectric substrate 11, and the via hole of the ceramic substrate is used. ) Go down the edge. Adopting this feeding method can be made into a surface-mounted antenna.

FIG. 3 is yet another conventional metal patch microstrip antenna. Its structure is mostly similar to that of FIG. 1, but the difference from FIG. 1 is that a probe or coaxial line 16 is used to feed signals. This method is obviously not suitable for connecting with other microwave circuits by surface adhesion, because the coaxial cable requires the use of microwave connectors. Studies have shown that the resonance frequency of a microstrip antenna is approximately inversely proportional to<img file="TW401652B_D0001.tif" />(ε_<i>r</i>Is the relative dielectric constant). Due to the limitation of this condition, the microstrip antenna shown in FIGS. 1 to 3 usually needs to use a dielectric substrate with a dielectric constant higher than 20 to achieve the purpose of miniaturization. In addition, research has also shown that the ground plane of limited size has a great influence on the microstrip antenna. Therefore, the ground surface must be larger than the area of the metal patch for the microstrip line to work normally; if the ground area is too small, it will affect the performance of the antenna.

In addition, by using the resonance phenomenon of dielectric materials, and coupling the energy to the dielectric resonator with a microstrip line or a slotted line, it is also possible to design a hidden antenna used in general integrated circuits. But its size is roughly the same<img file="TW401652B_D0002.tif" />It is inversely proportional, so this type of antenna also usually requires the use of high-dielectric constant dielectric materials.

Observe the simplified model of the monopole antenna used in the mobile phone. As shown in Fig. 4(a), the length of the monopole antenna 42 on the mobile phone housing 41 is about one-fourth of the free space wavelength. Figure 4(b) shows a simplified model of another helical antenna of a mobile phone. The total length of this helical antenna 43 is also close to the free space wavelength λ₀Therefore, these two antennas are obviously not suitable for use as hidden micro-miniature mobile phone antennas.

In addition, these two antennas both use the chassis as the ground plane, and the area of the ground plane is usually quite large, which is about 2 in a general design.<img file="TW401652B_D0003.tif" />(λ₀Is the free-space wavelength). As this type of mobile phone gets smaller and smaller, the ground plane of the relative-to-earth antenna becomes smaller and smaller, so the performance of the antenna is affected.

In view of this, the present invention proposes a specially designed micro-miniature antenna, which uses a floating microstrip line in addition to the non-radiating wave mode (bound mode), and there is also a fast wave leakage mode that is dependent on the non-radiating wave mode, and The mode current and the transverse electric field (magnetic field) of the two are very similar in the range close to the microstrip line. Therefore, a fast-wave oscillation antenna with a multilayer ground plane can be designed based on the resonance of the fast-wave leakage mode.

This antenna includes a fast wave oscillating device and a multilayer grounding device. The fast wave oscillating device includes two parts. The first part is a rectangular parallelepiped medium; the second part is a microstrip on the surface of the rectangular parallelepiped medium. The way of climbing the line is adjusted according to the required radiation field type, and it is densely packed within a small medium surface. One end of the microstrip line is used to feed signals, and the other end is a circuit breaker.

The multilayer grounding device is located under the fast wave oscillation device, and its main part is a plurality of parallel layers located under the medium, and a plurality of via holes, and all of the grooves formed by the parallel layers The surface, all the inner surfaces of the via holes and all the outer surface parts of the multilayer grounding device are metal ground planes.

Because the microstrip lines in the fast wave oscillation device are densely distributed within a small dielectric surface, and the multilayer grounding device greatly increases the grounding area in a limited space, the size of the antenna can be greatly reduced. Moreover, this antenna can be directly mounted on a printed circuit board using surface mount technology. More specifically, the antenna of the present invention does not need to use a high-dielectric constant dielectric material, as long as the relative dielectric constant value is between 2 and 5, the general dielectric material can be used.

<p>11Dielectric substrate</p><p>12Grounding surface</p><p>13Metal Patch</p><p>14Feeder</p><p>15The feeder connected to the via hole</p><p>16Probe or coaxial line feed</p><p>41Mobile phone case</p><p>42Monopole antenna</p><p>43Spiral antenna</p><p>AFast wave oscillator</p><p>A0, A1, A2, A3Microstrip</p><p>BMultilayer grounding device</p><p>B1~B9Parallel layer</p><p>B10~B17,69Access hole</p><p>1, 2, 3, 4Groove</p><p>CHollow area</p><p>51Antenna input/output</p><p>55,57Antenna ground terminal</p><p>61Input/output terminal of external circuit board</p><p>65, 67The ground terminal of the external circuit board</p><p>70Metal grounding</p><p>81Metal wire</p><p>82Dielectric substrate</p><p>83Air Belt</p><p>84Ground surface</p><p>101The antenna of the present invention</p><p>103External circuit board</p><p>105The ground plane of the external circuit board</p>

The purpose, advantages and features of the present invention can be more clearly understood from the detailed description of the following preferred embodiments and with reference to the drawings, in which: Figure 1 is a conventional metal patch microstrip antenna; Figure 2 is another use path Hole-fed conventional metal patch microstrip antenna; Fig. 3 is another conventional metal patch microstrip antenna fed by probe or coaxial line; Fig. 4(a) shows a conventional mobile phone A simplified model of a monopole antenna; Figure 4(b) shows a simplified model of another conventional helical antenna for a mobile phone; Figure 5(a) shows a cross-sectional view of a suspended ideal microstrip line structure; Figure 5( b) is the propagation constant of the non-radiation mode and the fast-wave leakage mode of the suspended microstrip line; Figure 6(a) is the current distribution in the transverse direction of the non-radiation mode and the fast-wave leakage mode; Figure 6(b) Is the current distribution in the longitudinal direction of the non-radiation mode and the fast-wave leakage mode; Figure 7 shows the mode direction electric field shape of the leakage mode when the floating microstrip line is at different positions (heights); Figure 8 shows the floating ideal microstrip Strip line structure; Fig. 9(a) is an embodiment of a small fast-wave oscillation antenna with a multilayer ground plane; Fig. 9(b) is a partial enlarged view of Fig. 9(a); Fig. 9(c) is Fig. 9 (a) Schematic diagram; Figure 10 (a) shows a situation where the antenna of an embodiment of the present invention is mounted on an external circuit board; Figure 10 (b) shows the wiring of the part of the external circuit substrate corresponding to the antenna of the embodiment of the present invention; 11 is the equivalent circuit of the antenna according to the embodiment of the present invention; FIG. 12 is the one port Smith diagram of the embodiment of the present invention (one port Smith Chart) measurement results; Figure 13 is the measurement results of the one port scattering parameter of the embodiment of the present invention; Figure 14(a) is the microstrip line of the antenna of the embodiment of the present invention at a resonance frequency of 260MHz (That is, the current distribution diagram of one side of the A area in Fig. 9(a)); Fig. 14(b) is the microstrip line of the antenna of the embodiment of the present invention at a resonance frequency of 260MHz (that is, the microstrip line in Fig. 9(a) Area A) the current distribution diagram on the opposite side; FIG. 15 is the radiation field shape of the antenna of the embodiment of the present invention in the YZ plane when the resonant frequency is 260MHz.

Figure 5(a) is a cross-sectional view of a suspended ideal microstrip line structure, where the parameters are<i>x</i>₁=300 <i>mm</i>，<i>b</i>=421.6<i>mm</i>，<i>w</i>=1.6<i>mm</i>，<i>h</i>=0.762 <i>mm</i>;ε<i>r</i>₁=1.0, ε<i>r</i>₂=2.1 and ε<i>r</i>₃=1.0 Figure 5(b) shows the two modes of the suspended microstrip line corresponding to Figure 5(a) and assuming that all metal conductors have infinite conductivity, namely γ_<i>m</i>=β_<i>m</i>+<i>j</i>˙0 and γ_<i>l</i>=β_<i>l</i>+<i>j</i>˙α_<i>l</i>. Where γ_<i>m</i>With γ_<i>l</i>Are the propagation constants of the non-radiating wave mode and the leaking wave mode, β_<i>m</i>With β_<i>l</i>Are the phase constants of the non-radiating wave mode and the leaking wave mode, α_<i>l</i>Is the attenuation constant of the leakage mode.

The current distributions of these two modes in the horizontal and vertical directions are shown in Fig. 6(a) and Fig. 6(b). The modal currents are very similar in the vertical and horizontal directions of the microstrip line. In other words, if one of the modes is excited, the other will also be excited.

Except for the similarity of the mode currents, the transverse electric/magnetic fields of the two are also very similar in the range close to the microstrip line. Figure 7 shows the mode direction electric field shape of the leakage mode of the suspended microstrip line at different positions, where the parameters are (1)<i>x</i>_<i>b</i>1=299 <i>mm</i>，<i>x</i>_<i>t</i>1=303 <i>mm</i>，(2)<i>x</i>_<i>b</i>2=408 <i>mm</i>，<i>x</i>_<i>t</i>2=412 <i>mm</i>，(3)<i>x</i>_<i>b</i>3=677 <i>mm</i>，<i>x</i>_<i>t</i>3=681 <i>mm</i>; <i>y</i>₁=208.3<i>mm</i>，<i>y</i>₂=213.3<i>mm</i>It can be seen from Figure 7 that the leakage mode has a non-zero attenuation constant.

Detailed analysis shows that the two modes are coupled with each other, that is, the integral of the waveguide cross-sectional area<img file="TW401652B_D0004.tif" />or<img file="TW401652B_D0005.tif" />Not zero,<img file="TW401652B_D0006.tif" />Are the electric field strength of the cross section of the non-radiating wave mode and the leaking wave mode,<img file="TW401652B_D0007.tif" />They are the magnetic field strength of the cross section of the non-radiating wave mode and the leaking wave mode. In other words, if the conventional non-radiation wave mode is excited, this non-radiation wave mode will convert part of the energy into a leaky wave mode during propagation, and this leaky wave mode will send energy to the atmosphere during the propagation process. Conversely, a leaky wave mode in propagation will also convert part of the energy into a non-radiating wave mode.

As shown in FIG. 8, a suspended ideal microstrip line structure is formed by a metal wire 81, a dielectric substrate 82, an air belt 83 and a ground plane 84. The upper part of the metal wire 81 is also filled with air.

The antenna of the present invention is designed based on the above working principle and the suspended ideal microstrip line structure. It is composed of two major parts: one is a fast wave oscillation device, and the other is a grounding device formed by a multilayer ground plane and via holes.

Figure 9 (a) shows a preferred embodiment of the antenna of the present invention, in which part A represents a fast wave oscillation device, and part B represents a multilayer grounding device. In addition, in order to show the circuit of the fast wave oscillation device more clearly, the medium in the fast wave oscillation device circuit is removed in Part A. In addition, for the convenience of the following description, the X, Y, and Z axis directions of the three-dimensional space are set as the length, width, and height directions of the antenna, respectively. Fig. 9(b) is a partial enlarged view of Fig. 9(a).

The air belt 83 formed between the dielectric substrate and the ground in FIG. 8 corresponds to the hollow area C in FIG. 9(b), which can be formed by trenching or casting.

In Figure 9(b), the fast wave oscillator A is composed of a spiral metal microstrip line formed by a rectangular parallelepiped medium and microstrips A1, A2, A3, etc., surrounding the surface of the rectangular parallelepiped medium. The tail end of this spiral metal microstrip line forms an open circuit necessary for resonance. The other end A0 of the microstrip line connected to the microstrip A1 is used as the signal input/output end of the antenna. This type of fast wave oscillation device can be made by using printed circuit board technology or using casting and etching technology.

In Figure 9(b), the multilayer grounding device B is located under the rectangular parallelepiped medium of the fast wave oscillation device. The main part of the device is a plurality of parallel layers B1~B9 formed under the medium. Below these plane layers, in order to increase the surface area of the ground plane and consider the mechanical strength of the antenna, a plurality of via holes B10~B17 are made, and all the inner surfaces of the grooves 1~4 formed by the parallel layers, all via holes The inner surfaces of B10~B17 and all the outer surfaces of this multilayer grounding device B are metal ground planes, thereby forming a multilayer grounding device B. The production can be done by using the perforation technology of the printed circuit board, or using the technology of casting and gold plating.

In FIG. 9(b), the end point A0 of the microstrip line extends along the dielectric surface to the input/output terminal 51, and forms a coplanar waveguide input/output mode with the ground terminals 55 and 57 of the multilayer grounding device B.

FIG. 10(a) schematically shows a situation where the antenna 101 of the present invention is mounted on an external circuit board 103. 10(b), the connection method of the antenna and the external circuit of the present invention is: the corresponding position of the external circuit substrate 103 also forms the input/output terminals 61, 65, 67 of the coplanar waveguide, where 61 is the signal input/output Terminals 65 and 67 are ground terminals. Using surface mount technology, 51, 55, and 57 are connected to 61, 65, and 67, respectively; and, also using surface mount technology, the multilayer grounding device has a side surface with a ground terminal and a signal input/output terminal through the corresponding position of the external circuit board Many of the via holes 69 and the surrounding metal 70 are connected to the ground surface 105 of the outer circuit board 103.

Fig. 9(c) is a schematic diagram of Fig. 9(a). Referring to Fig. 9(c), a set of design parameters of the antenna of the present invention are: the width and spacing of the microstrip are 0.39×10^-3λ₀With 0.17×10^-3λ₀(which is<i>w</i>=0.39×10^-3λ₀，<i>s</i>=0.17×10^-3λ₀), the height of the rectangular parallelepiped medium 10 is 0.039λ₀(in,<i>d</i>=0.032λ₀,<i>g</i>=6.9×10^-3λ₀), its length and width are respectively about 4.3×10^-3λ₀With 1.47×10^-3λ₀(which is<i>e</i>=4.3×10^-3λ₀,<i>f</i>=1.47×10^-3λ₀), ε_<i>r</i>=3.25, the number of turns of the spiral microstrip line N=57.

Based on the above parameters, the volume of the antenna of the present invention can be calculated to be about 0.25×10^-6<img file="TW401652B_D0008.tif" />, The average side length is about 0.63×10^-2λ₀. Achieve the purpose of miniaturization of antenna integrated circuit.

In addition, the length of the spiral microstrip line is approximately: 5.8×10^-3λ₀×57×2+0.17×10^-3λ₀×57=0.667λ₀

The total area of the spiral microstrip line is approximately: 0.667λ₀×3.9×10^-4λ₀=260×10^-6λ²₀

When the microstrip line resonates, the current intensity is roughly distributed on the microstrip line according to the shape of the cosine function with a phase angle between 0 and π/2 (this part will be described in detail later), and the cosine function is<img file="TW401652B_D0009.tif" />The area enclosed by the period is<img file="TW401652B_D0010.tif" />, So the average effective area of the spiral microstrip line is:<maths><img file="TW401652B_D0011.tif" /></maths>Equivalent to the charge evenly distributed in the effective area of 166×10^-6λ²₀Above the microstrip line.

The grounding area of the multilayer grounding device is estimated to be about 90.6×10^-6<img file="TW401652B_D0012.tif" />. When resonating, in Figure 9(b), there is a positive Q charge (Q is the amount of charge) flowing into the input terminal 51, and then enters the spiral microstrip line through A0, and then fills the metal surface of the microstrip line; at the same time, a part of the negative Q charge flows in The grounding terminals 55, 57 are then filled with all the metal surfaces of the multilayer grounding device. Another part of the negative Q charge flows into the ground terminals 65 and 67 of the external circuit board and the ground plane connected to them. Therefore, during resonance, the spiral microstrip line and the multilayer grounding device and the vicinity of the input ground terminal can maintain the charge balance. It can be seen that in the antenna of the present invention, the ground plane does not need to be as large as the ground plane of the existing mobile phone, but it is still sufficient for use.

Moreover, there is no need to use high dielectric constant dielectric materials, and the relative dielectric constant value is quite low such as ε_<i>r</i>A medium material between 2 and 5 is fine.

The important role of the fast wave leakage mode in the antenna of the present invention can be learned by the following calculations and inferences.

According to the conventional microwave circuit theory, if the broken end of the transmission line of a single-mode element does not have any fringing field effect, but is purely broken, then only<img file="TW401652B_D0013.tif" />(λ_<i>g</i>It is an odd multiple of the frequency corresponding to the single-mode propagation wavelength) to form a resonant circuit. And, corresponding to the first resonance frequency, the resonance equation is:<maths><img file="TW401652B_D0014.tif" /></maths>in,<i>l</i>Is the length of the microstrip line,<img file="TW401652B_D0015.tif" />Is the normalized phase constant,<img file="TW401652B_D0016.tif" />,and<i>k</i>₀Is the free space wave number.

FIG. 11 shows the equivalent circuit of the antenna of the present invention, which is composed of an open circuit 31, a suspended microstrip line 32, a grounding system 33, and a power supply 34. Applying the above microwave circuit theory, if Figure 11 represents the resonance circuit corresponding to the first resonance frequency, the length of the microstrip line 32 should be<img file="TW401652B_D0017.tif" />。

The inventors calculated the first resonance frequency to be 260 MHz by using the above-mentioned antenna design parameters and the full-wave electromagnetic field theory of three-dimensional space. On the other hand, the antenna made by the above design parameters is used as the single port S₁₁The measurement of parameters (ie scattering parameters) can get the Smith chart and the corresponding S₁₁The input reflection coefficient diagrams are shown in Figure 12 and Figure 13 respectively.

In Figure 12, the vector analyzer scans from 240 MHz to 300 MHz. At low frequencies, it can be known that the measurement curve in the Smith chart starts from its rightmost end near the open end point, rotates clockwise from near the open end point to the left close to the short-circuit point, and then stops at the corresponding 300 MHz It is located at the upper right point of Smith Chart. After detailed analysis, it can be known that the frequency closest to the short-circuit end is the operating frequency 259 MHz at a phase angle of 180, and this frequency is the first resonance frequency. The difference from the theoretical calculation value is only 1 MHz.

The first resonance frequency can be confirmed more clearly from FIG. 13. Refer to Figure 13, S at resonance₁₁The value of is the smallest at 259 MHz, about -2.8dB, and its phase angle is 180. The quarter wavelength shown in Figure 11 (<img file="TW401652B_D0018.tif" />) When the resonator is in resonance, the reflection coefficient of its input must be a negative number, that is, the phase angle must be 180. Since this fast-wave leakage mode exhibits loss, S₁₁The absolute value of will be less than 1, that is, less than 0 dB.

Therefore, corresponding to the first resonance frequency, the length of the microstrip line used in the present invention<i>l</i>I.e. 0.667 λ₀Substituting in (1), we know<img file="TW401652B_D0019.tif" />Is 0.375. The phase velocity of the leakage mode relative to this value is:<maths><img file="TW401652B_D0020.tif" /></maths>Among them, c is the speed of light, and formula (2) indicates that the phase speed of the leakage mode is 2.66 times the speed of light, so it must be a fast wave.

Furthermore, the full-wave electromagnetic field theory of three-dimensional space can be used to calculate the current distribution on one side and the opposite side of the microstrip line at the resonant frequency of 260MHz (ie, area A in Figure 9(a)), respectively, as shown in Figure 14. (a) and Figure 14(b). Figure 14(a) and Figure 14(b) show that at the resonance frequency of 260 MHz, the current of the microstrip line is the largest at the input end, and then its current intensity gradually decreases, but the direction remains the same, always towards the open end (That is, the end of the antenna resonator), the current intensity becomes zero to the end of the open circuit. In other words, the magnitude of the mode current changes on the microstrip line like a cosine function between 0 and (π/2) phase angle. From this analysis, it can be seen that this resonance method must be a leakage wave to achieve.

Based on the above measurement data and theoretical calculation results, it can be concluded that the novel antenna of the present invention mainly relies on fast wave leakage mode conduction.

Then use the conventional full-wave integral equation to obtain the radiation field shape of the antenna of the embodiment of the present invention on a plane parallel to the YZ plane at a resonance frequency of 260MHz, as shown in Figure 15, where the angle θ is expressed on the plane The angle between the line from a certain point to the origin and the Z axis. Referring to Figure 15, this radiation field is very similar to that of a monopole antenna on an infinite horizontal conductor ground plane.

The above is a specific embodiment of the present invention, however, the present invention is not limited to this embodiment. For example, looking at the antenna structure of Figure 9(a), in fact, air is filled between the microstrip line of the fast wave oscillator and the outer surface of the multilayer grounding device, which is similar to the air belt 83 in Figure 8, so this hollow area C It is not necessary. Correspondingly, there is another antenna that does not have a hollow area C. In this case, the medium in the fast wave oscillation device A and the multilayer grounding device B are directly connected together.

The shape of the microstrip line is not limited to the spiral shape, and different shapes of the microstrip line can be used in the fast wave oscillation device according to the required radiation field type. For example, it is a plurality of parallel and closed ring-shaped metal microstrip lines, and the design method is similar to the above-mentioned specific embodiment.

Furthermore, the antenna of the present invention can also be directly input/output using a feeder. In this case, the input/output position of the corresponding antenna on the external circuit board also forms a direct input/output terminal. Then, one end of the microstrip line of the fast wave oscillation device for input/output signals is connected to the corresponding input/output end of the external circuit substrate by surface adhesion.

Therefore, various changes and implementations can be made without exceeding the spirit of the present invention and the scope of the following patent applications.