JP2010239496A - Planar antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small planar antenna capable of being surface-mounted to a circuit board, easy adjustment of resonance frequency and having excellent radiation characteristics and gains. <P>SOLUTION: The planar antenna includes a rectangular substrate having upper and lower surfaces and side surfaces linking the upper and lower surfaces, a rectangular radiation electrode formed on the upper surface of the substrate, a first ground electrode formed on the lower surface of the substrate, a band-like feed electrode formed on a side surface of the substrate and extending from the lower surface to the upper surface, and a pair of second ground electrodes formed on the same side surface as that of the feed electrode, facing each other with the feed electrode interposed therebetween, and extending from the first ground electrode with intervals between end portions thereof and the radiation electrode being equal to each other. An end portion of the radiation electrode faces an end portion of the feed electrode, and power is fed to the radiation electrode by capacitive coupling. The end portions of the second ground electrodes closer to the end portion of the radiation electrode are formed in the shape of a comb. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a planar antenna used in a communication system using linearly polarized radio waves such as WLAN (Wireless Local Area Network) and a communication system using circularly polarized radio waves such as GPS (Global Positioning System). is there.

  Research on flat antennas has been actively conducted to reflect the trend of electronic devices to become smaller, thinner and lighter. A microstrip antenna (MSA), which is a kind of planar antenna, has characteristics that a band is narrow and directivity is large. Also called a microstrip patch antenna or patch antenna, the radiation electrode of the antenna is etched into a metal pasted on an insulating substrate, or a conductor paste such as Ag or Cu is printed on a ceramic substrate and baked. Formed. The shape of the radiation electrode of the planar antenna is simple, such as a rectangle or a circle, and its size is determined by the wavelength at the resonance frequency, so it is often used at a frequency higher than the UHF band.

  FIG. 10 shows a perspective view of an example of a conventional planar antenna. The planar antenna 10 includes a rectangular radiation electrode 50 on one main surface of a flat substrate 70, a ground electrode 100 is formed on almost the entire other main surface, and the radiation electrode penetrates the substrate 70 from the other main surface side. A feed line 60 connected to 50 is formed. Each side of the radiation electrode 50 is formed so as to be approximately a half of the effective wavelength (including the wavelength shortening effect by the material constituting the substrate) at the feeding frequency. Since the voltage and current differ depending on the position of the connection point between the feed line 60 and the radiation electrode 50, matching the input impedance to 50Ω by taking the feed point F away from the center of the radiation electrode 50. I can do it. In the drawing, the position of the feeding point F is on the diagonal line of the radiation electrode 50, but may be provided at other positions such as on the center line.

  If the length of each side of the radiation electrode 50 is the same, the position of the feeding point F is on the diagonal line of the radiation electrode 50, and power is fed from the feeding point F at a position that forms an angle of 45 degrees with the two diagonal lines. Waves are excited. When the length of each side of the radiation electrode 50 is made different, the long side is made slightly longer than ½ of the effective wavelength, and the short side is made short, the radiation electrode 50 has a phase difference of 90 degrees and the amplitude is equal. Two resonance mode currents (arrows) are generated to excite circularly polarized electromagnetic waves.

  When the position of the feeding point F is on the center line of the radiation electrode 50, linearly polarized waves are excited if the diagonal lines of the radiation electrode 50 have the same length. If one diagonal length is made different from the other diagonal length, currents in two resonance modes having a phase difference of 90 degrees and equal amplitude are generated in the radiation electrode 50, and circularly polarized electromagnetic waves are generated. Can be excited. As a method of making the diagonal lengths of the radiation electrode 50 different, cuts are provided at two corners of the radiation electrode 50 facing each other, the radiation electrode 50 is formed into a rhombus, or a rectangle or an ellipse is formed inside the radiation electrode 50. The length of the current path is adjusted by a degenerative separation means such as providing a shape or cross-shaped slit.

  Although the advantage of this antenna is that it can cope with various polarized waves, the feeding to the radiating electrode 50 is a structure in which the feeding point F is provided in the plane, so that a pin feeding method is used, or the radiating electrode 50 is provided. There is a problem that surface mounting is difficult because it is necessary to take a structure such as forming a through hole in a supporting substrate and providing a feed line there. Further, there is a problem that the position of the feeding point is limited due to the impedance adjustment.

With respect to such a problem, Patent Document 1 discloses a planar antenna that facilitates surface mountability and impedance matching. FIG. 11 is a perspective view thereof. The planar antenna 10 has a radiation electrode 50 formed on the upper surface of a flat substrate 70 made of a dielectric, and a microstrip-shaped feeding electrode (feeding line) 60 having one end open from the side surface to the upper surface of the substrate 70. The ground electrode 100 is formed on the bottom surface, and the open end of the power supply electrode and one side that is the edge of the radiation electrode are arranged close to each other via a gap.
Since this planar antenna can be fed using the side surface of the substrate, it is not necessary to use a feed line or feed pin that penetrates, and surface mounting on the circuit board becomes easy. Further, since the power supply electrode and the radiation electrode are capacitively coupled, there is an advantage that the adjustment of impedance is relatively easy.

  Further, Patent Document 2 describes a planar antenna in which other ground electrodes 100a and 100b are formed so as to be located on both sides of the feeding electrode 60 formed on the side surface, which is continuous with the ground electrode 100 on the bottom surface side ( FIG. 12). A capacitance is formed between the ground electrodes 100a and 100b and the radiation electrode 50, and the resonance frequency is lowered due to the increase in capacitance. On the other hand, if the radiation electrode is made small, the resonance frequency increases. Therefore, by adding capacitance by the ground electrodes 100a and 100b, the antenna can be made compact with respect to the antenna not provided with the ground electrodes 100a and 100b.

Japanese Patent Application Laid-Open No. 11-074721 JP 2000-183637 A

  In the antennas disclosed in the cited document 1 and the cited document 2, since the feeding electrode is formed on the main surface on which the radiation electrode is formed, the upper surface area of the antenna must be increased accordingly. As a result, the outer dimensions of the antenna are increased. In addition, if the feed electrode is formed long, the electric field from the feed electrode to the ground electrode of the circuit board mounted is likely to increase, and there is a problem that the antenna efficiency is lowered.

  In the antenna disclosed in Patent Document 2, the ground electrode and the radiation electrode are formed on different surfaces. In such a case, the dimension between the electrodes at the time of electrode formation in each antenna tends to vary, and accordingly, the resonance frequency varies in various ways, a desired frequency band cannot be secured, and it cannot be put on the market. However, there is no recognition in Patent Document 2. When the ground electrode and the radiation electrode are formed on the same surface, it is necessary to increase the top surface area of the antenna.

  Accordingly, an object of the present invention is to provide a small planar antenna that can be surface-mounted on a circuit board, can easily adjust the resonance frequency, has excellent radiation characteristics, and gain.

The present invention includes a rectangular substrate having an upper surface and a side surface connecting the upper and lower surfaces, a rectangular radiation electrode formed on one upper surface of the substrate, a first ground electrode formed on the lower surface of the substrate, A strip-shaped power supply electrode formed on the side surface of the substrate and extending from the lower surface side to the upper surface side, formed on the same side surface as the power supply electrode, facing the power supply electrode and extending from the first ground electrode; A pair of second ground electrodes having the same distance from the radiation electrode, the end of the radiation electrode being opposed to the end of the power supply electrode and feeding power by capacitive coupling, and the end of the second ground electrode on the side of the radiation electrode The flat antenna is characterized in that the portion is formed in a comb-teeth shape.
It is preferable that the radiation electrode has a belt-like extension extending from one side to the side surface, and is fed by capacitive coupling with the end facing the end of the feeding electrode.

  Furthermore, in the present invention, a plurality of strip-like extensions extending from one side to the side of the radiation electrode are provided, and one end of the extension is opposed to the end of the power supply electrode to supply power by capacitive coupling, and the other extension. The end of the part may be opposed to the second ground electrode.

  The radiation electrode is preferably rectangular in plan view, and may be cut out by forming a part of the periphery or the inside thereof for degeneration and separation. Further, the outer periphery may be formed in a comb-teeth shape so as to make the outer peripheral length look longer. In the planar antenna of the present invention, the feeding point is on the center line of the radiation electrode. In such a configuration, the current flows strongly to the edge of the radiation electrode parallel to the center line. Since the current path is lengthened by the slit and the resonance frequency is lowered, the planar antenna can be miniaturized. A plurality of slits may be provided on one side to form a comb shape, or may be provided on two opposite sides.

  The comb electrode at the end of the second ground electrode is preferably configured to extend substantially parallel to one side of the opposing radiation electrode. Here, the term “substantially parallel” means that the line segment direction in which the comb-shaped electrode extends may be roughly aligned with the opposite sides of the radiation electrode as a whole, even if it is not strictly parallel, and is parallel enough to contribute to the solution of the problem. This includes the case where it can be said. Therefore, the outer periphery of the radiation electrode may have a comb-like shape even if it is strictly non-parallel due to variations in forming each electrode.

  The planar antenna of the present invention can change the resonance frequency by trimming the comb-tooth electrode at the end of the second ground electrode. The end portion of the comb electrode is connected to the band-like portion of the second ground electrode by the connecting electrode. The free end side of the comb-teeth electrode may be the feeding electrode side or the opposite side.

The substrate is a printed circuit board or a ceramic substrate, and the dielectric material constituting the substrate is an insulator, and is selected from materials that can effectively affect the electric field strength and the speed of electromagnetic waves traveling inside the substrate. Is done.
As the printed board, a Teflon (registered trademark) glass fiber board (PTFE board), a polyphenylene ether board (PPE board), or the like is generally used. Although these substrates have a low dielectric constant (εr = 1.1 to 5.0) and are not suitable for miniaturization, the dielectric loss tan δ is as small as 10 ⁻³ to 10 ⁻⁴ and the antenna has excellent gain. It becomes.

A planar antenna on a printed circuit board is suitable when the shape is relatively limited, such as in-vehicle use, but it may be difficult to mount it on a communication device such as a mobile phone or a small GPS terminal. In such a case, a ceramic substrate using dielectric ceramics having a high dielectric constant of _εr of 200 or less is preferable. If the relative dielectric constant is high, the length L of one side of the radiation electrode is shortened, and the planar antenna can be miniaturized. The choice of the dielectric constant depends on the external dimensions and characteristics of the planar antenna is required, if the epsilon _r exceeds 200, a reduction in loss and gain-bandwidth is increased.

In the present invention, it is preferable that the pair of second ground electrodes be arranged at equal intervals along the power supply electrode until reaching the tip portion thereof. By configuring the power supply electrode with a coplanar structure in this way, loss at the power supply electrode is reduced, and the antenna characteristics are improved. Further, the amount of power supplied to the radiation electrode can be increased by strengthening capacitive coupling with the second ground electrode by providing another extension portion on the radiation electrode.
In the present invention, it is preferable that power is fed by capacitive coupling with the end of the power supply electrode and the extended portion of the radiation electrode facing each other and having a gap. Further, the gap length in the capacitive coupling portion is configured to be sufficiently narrower than the width between the second ground electrode and the feeding electrode. According to such a configuration, the impedance can be easily adjusted by adjusting the gap length, and the reduction of the specific bandwidth can be prevented. In particular, when the dielectric constituting the substrate has a high relative dielectric constant, the effect is remarkably exhibited.

  According to the present invention, it is possible to provide a small planar antenna which can be surface-mounted on a circuit board, can easily adjust the resonance frequency, has excellent radiation characteristics and gain, and is small.

1 is a perspective view of a planar antenna according to an embodiment of the present invention. It is a front view of the planar antenna which concerns on one Example of this invention. It is a front view of the planar antenna which concerns on the other Example of this invention. It is a figure which shows the change of the resonant frequency by trimming of the planar antenna which concerns on one Example of this invention. It is a figure which shows the VSWR characteristic by the trimming of the planar antenna which concerns on one Example of this invention, and a bandwidth. It is a perspective view of the evaluation board which mounted the plane antenna concerning one example of the present invention. It is a figure for demonstrating the evaluation method of the planar antenna which concerns on one Example of this invention. It is a perspective view of the planar antenna which concerns on the other Example of this invention. It is a front view of the planar antenna which concerns on the other Example of this invention. It is a perspective view of the conventional planar antenna. It is a perspective view of the other conventional planar antenna. It is a perspective view of the other conventional planar antenna.

Embodiments of the present invention will be described below. Note that the materials and manufacturing methods used in the planar antenna described below do not limit the present invention and can be variously modified within the scope of the present invention.
FIG. 1 is a perspective view of a planar antenna according to an embodiment of the present invention. FIG. 1 (a) is a perspective view seen from the upper surface side where a radiation electrode is formed, and FIG. It is the perspective view seen from the lower surface side which is formed and becomes a mounting surface. FIG. 2 is a front view showing the surface on which the second ground electrode is formed, and FIG. 3 is a front view formed in another mode.

  The planar antenna 10 includes a substrate 70 made of a rectangular parallelepiped dielectric, a first ground electrode 100 formed on the lower surface of the substrate 70, and a radiation electrode 50 having a side length of approximately λ / 2 formed on the upper surface. The power supply electrode 60 is formed on the side surface. Among these, the first ground electrode is formed to extend to the side surface of the substrate 70, and constitutes second ground electrodes 110a and 110b opposed to each other with the feeding electrode 60 interposed therebetween. Further, a part of the radiation electrode 50 is formed in a band shape, and becomes an extended portion 55 that goes around the side surface and forms an open end. The feeding electrode 60 is formed through a gap 120 in the vicinity of the open end of the extension 55 of the radiation electrode 50 formed on one side of the substrate 70, and the other end wraps around the lower surface of the substrate 70. The first ground electrode and the gap are formed. The end portions 200 of the second ground electrodes 110a and 110b are formed in a comb-like shape, and are connected to the belt-like electrode by the connecting electrode 220 that connects the comb-like electrodes 210 (210a, 210b, 210c, and 210d).

  The number and formation interval of the comb electrodes 210 are appropriately set according to the capacitance value to be adjusted. Each comb-tooth electrode 210 is formed in a strip shape and parallel to the opposite side of the radiation electrode 50 on the upper surface, and from the open end side of the comb-tooth electrode 210 adjacent to the radiation electrode 50, the end portions 200 of the second ground electrodes 110 a and 110 b. Is trimmed while measuring the frequency characteristics of VSWR with a laser or the like to adjust the resonance frequency. The free end of the comb-tooth electrode 210 may be on the power supply electrode side or on the opposite side.

  A capacitance is formed between the radiation electrode 50 and the ground electrode by the second ground electrodes 110a and 110b formed on the side surface of the substrate 70, but the resonance frequency increases as the capacitance value decreases. Therefore, in consideration of variations in the formation of each electrode and variations in the dielectric characteristics of the dielectric material constituting the substrate 70, each electrode is formed to be lower than a desired resonance frequency, and the second is confirmed while confirming the resonance frequency. If the end portions 200 of the ground electrodes 110a and 110b are trimmed, a desired resonance frequency and frequency band are secured.

The dielectric material constituting the substrate can be appropriately selected according to the target frequency. However, in order to obtain a sufficient gain as antenna characteristics while being small in size, the relative dielectric constant ε _r Is about 5 to 200 dielectric material. If epsilon _r of about 10 as a ceramic material of alumina based ceramics, 40 or less value, if calcium titanate-based ceramics, magnesium titanate-based ceramics include barium titanate-based ceramics when 200 or less. In addition, it is selected in consideration of temperature characteristics and loss.

The radiation electrode 50 and its extension 55, the first and second ground electrodes 100, 110a, 110b, and the feeding electrode 60 have a thickness of several μm to 20 μm by printing and baking a good conductor such as silver paste on the substrate. It is formed as a conductor film. As the conductor, in addition to silver, a paste containing gold, copper, palladium, platinum, a silver palladium alloy, or a silver platinum alloy is used. A known manufacturing method such as a screen printing method can be employed for the formation, and other methods include plating and etching.
In FIG. 1, the radiation electrode 50 and the first ground electrode 100 are formed with an interval inward from the side surface of the substrate. This is for the purpose of preventing peeling of the electrode due to an external force, but each may be formed in the same size as the substrate, and in that case, the planar antenna can be further reduced in size.

If the radiation electrode 50 and the second ground electrodes 110a and 110b are too close to each other, the feedback current from the radiation electrode 50 is concentrated on the second ground electrodes 110a and 110b, so that the bandwidth for obtaining a desired VSWR value is reduced. Therefore, the distance and the opposing length are set in consideration of the relative permittivity of the dielectric constituting the substrate 70 and the like.
The shape of the second ground electrodes 110a and 110b is not limited to the illustrated I shape, and other shapes such as a T-shaped or L-shaped strip electrode having a wide side corresponding to the radiation electrode may be used. However, the width of the second ground electrodes 110a and 110b is set to ¼ or less of the length of one side of the opposing radiation electrode 50 so that the capacitance formed between the radiation electrode 50 does not become too large. Is preferred.
Further, on the side surface of the substrate 70 (including the side surface on which the second ground electrodes 110a and 110b are formed), a terminal electrode continuous with the first ground electrode 100 is provided so as to improve the mounting property to the circuit board and the fixing strength. It may be formed. In this case, the terminal electrode is formed in such a size and position that does not affect the antenna characteristics.

  The planar antenna 10 according to the present embodiment is configured such that only the radiation electrode 50 is formed on the upper surface of the substrate 70. Therefore, since the substrate 70 can be made smaller than the conventional planar antenna in which the feeding electrode is formed on the upper surface, the planar antenna 10 itself can also be reduced in size.

Since the basic structure of the planar antenna of this embodiment is the same as that shown in FIG. This planar antenna is a GPS antenna having a frequency band of 1575.42 ± 1.023 MHz. In this example, a Ti—Ba—Sm ceramic material was used as the dielectric material of the substrate. This ceramic material has a relative dielectric constant ε _r of 79 and a tan δ (at 4.8 GHz) of 4 × 10 ⁻⁴ .
Oxides such as TiO ₂ , BaCO ₃ , and Sm ₂ O _{3 that} are raw materials having a predetermined composition are weighed and mixed in a ball mill so as to be uniform by a wet process. Thereafter, the granulated powder obtained through calcination and pulverization is formed into a plate shape by pressure molding, fired at 1350 ° C., and the obtained plate-like body is formed into a predetermined shape (12) by a dicer (cutting machine). 0.070 mm × 12.0 mm × 3.0 mm) to produce a substrate 70 used for a planar antenna.

On the obtained substrate 70, the radiation electrode 50, the first ground electrode 100, the second ground electrodes 110a and 110b, and the feeding electrode 60 were printed and formed by screen printing using a silver paste, and baked to produce a planar antenna.
The radiation electrode 50 is formed in a square shape (excluding the extension), and the length of one side is 11.8 mm. This length is set in consideration of a dimension that is approximately ½ of the effective wavelength at a feeding frequency of 1575.42 MHz. The extension has a width of 0.65 mm, and the length from the upper surface to the end is 0.5 mm. The power supply electrode 60 has the same width as the extension, the opposing width is 0.65 mm, the length from the bottom is 2.0 mm, and the gap G is 0.5 mm. Second ground electrodes 110a and 110b were formed on both sides of the power supply electrode 60 with a spacing W of 1.525 mm. The length H from the bottom surface of the second ground electrodes 110a and 110b is both 2.0 mm. The first ground electrode 100 is also formed in a square shape, and the length of one side is 11.8 mm.

  The second ground electrodes 110a and 110b have a distance of 0.1 mm between the end and the top surface, and three comb electrodes having a width of 0.2 mm and a length of 1.5 mm are formed at intervals of 0.1 mm. ing. Measure the VSWR peak frequency, peak value, and bandwidth with a VSWR of 3.0 or less with the network analyzer when the comb-tooth electrodes of the second ground electrodes 110a and 110b are laser-trimmed together from the upper surface side. did. The results are shown in FIGS. “None” in the figure is an initial state in which trimming is not performed, and the first stage is trimming the comb-tooth electrode 210a of the second ground electrodes 110a and 110b, and the comb-tooth electrode 210b is connected to one side of the radiation electrode 50. It is in a state of being parallel. The second and subsequent stages are similarly trimmed with the comb electrodes 210b and 210c in the same manner. As the trimming was performed, the resonance frequency moved to the high frequency side, and the peak value of VSWR decreased and the bandwidth widened. Although the present embodiment shows the VSWR characteristics when each comb-tooth electrode is trimmed and removed, the VSWR characteristics also change as a part of the comb-tooth electrode facing one side of the radiation electrode 50 is trimmed. The resonance frequency can be easily set to a desired frequency.

  A planar antenna 10 having a resonance frequency adjusted to 1575.42 MHz is used as a sample, and is soldered and mounted on a printed board 200 having a thickness of 35 mm and a thickness of 0.6 mm, and the antenna is placed in an anechoic chamber (an anechoic chamber). Characteristics were evaluated. FIG. 6 shows a perspective view of an evaluation board on which a planar antenna is mounted. The ground conductor pattern GND is formed in all regions other than the line pattern connected to the power supply electrode 60 of the substrate 70. A reactance element (chip component) 250 constituting a matching circuit is mounted on the line pattern, and a coaxial connector (not shown) is formed at the end so that the coaxial line 300 is connected.

  FIG. 7 is a diagram for explaining an antenna characteristic evaluation method. An antenna for measurement (a right-handed circularly polarized log / spiral antenna) 300 is arranged in a dark room 500 in which an electromagnetic wave absorber is laid on the inner wall without any gaps, and an antenna that rotates on a turntable arranged 3 m away In this configuration, radio waves are transmitted to the sample 200 and received by the planar antenna 10, and gain, radiation directivity, and VSWR are obtained based on the obtained received power. The measurement antenna 300 and the antenna sample 200 are each connected to a port of a network analyzer disposed outside the room by a coaxial cable. The power supply to the measurement antenna 300 was performed by a network analyzer. The total average gain including the YZ plane, the XY plane, and the ZX plane was −5.40 dBic. Adjustment of the resonance frequency by trimming is easy, and there is little variation among individual planar antennas, and excellent gain characteristics can be obtained.

  As another embodiment, the same procedure is applied to a sample in which the interval W between the feeding electrode 60 and the second ground electrodes 110a and 110b is changed to 0.5 mm to 2.675 mm and other dimensions are the same as those of the planar antenna. And measured and evaluated. When the interval W exceeded 1.525 mm, no significant difference was observed between the VSWR and the characteristics, but the gain decreased slowly. Further, when the interval W was narrowed, the gain was remarkably lowered, and when W was 0.5 mm, the gain was lowered to such an extent that it could not be put to practical use.

  Next, a gap G between the feeding electrode 60 and the extended portion 55 of the radiation electrode 50 was changed to 0.1 to 0.5 mm, and a sample having the same dimensions and shape as those of the planar antenna was prepared in the same procedure. Measurement was evaluated. As the gap G was narrowed, there was no significant difference between the VSWR and the characteristics, but the gain was improved moderately.

  Next, the length H of the second radiation electrodes 100a and 110b was changed, and a sample having the same dimensions and shape as those of the planar antenna was prepared in the same procedure, and measured and evaluated. The shorter the length H, the wider the VSWR, but when the length H was less than 1.5 mm (1/2 of the substrate thickness), the gain decreased to the extent that it could not be put to practical use.

Next, as shown in the perspective view of FIG. 8, three extending portions 55, 56a, and 56b are formed on the radiation electrode, and the two extending portions 56a and 56b are connected to the second ground electrode 110a through a gap of 0.5 mm. , 110b, and other dimensions and shapes were the same as those of the planar antenna, and the same procedure was used for measurement and evaluation. As a result, the gain was improved as compared with the case where the extensions 56a and 56b were not formed.
Further, as shown in the front view of FIG. 9, if the extension portions 56a and 56b and the second ground electrodes 110a and 110b and the facing portion are formed to be inclined, the capacity increases and the adjustment margin by trimming can also be increased. .

  According to the present invention, it is possible to provide a small planar antenna which can be surface-mounted on a circuit board, can easily adjust the resonance frequency, has excellent radiation characteristics and gain, and is small.

DESCRIPTION OF SYMBOLS 10 Planar antenna 50 Radiation electrodes 55, 56a, 56b Radiation electrode extension 60 Feed electrode 70 Substrate 100 First ground electrodes 110a, 110b Second ground electrode 200 Printed circuit board (evaluation board)

Claims (3)

  A rectangular substrate having a side surface connecting the upper and lower surfaces and the upper and lower surfaces, a rectangular radiation electrode formed on one upper surface of the substrate, a first ground electrode formed on the lower surface of the substrate, and a side surface of the substrate Formed on the same side surface as the power supply electrode, opposed to the power supply electrode and extending from the first ground electrode, and an end portion of the power supply electrode and the radiation electrode A pair of second ground electrodes having the same interval are provided, power is fed by capacitive coupling with the end of the radiation electrode facing the end of the power supply electrode, and the end of the second ground electrode on the side of the radiation electrode is comb-toothed A planar antenna characterized by being formed in a shape.   The planar antenna according to claim 1, wherein the comb electrode at the end of the second ground electrode extends substantially parallel to one side of the opposing radiation electrode.   The planar antenna according to claim 2, wherein the resonance frequency is changed by trimming the comb electrode at the end of the second ground electrode.

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