JP2014110561A - Planar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact planar antenna of easy design, capable of handling a multiband.SOLUTION: The planar antenna includes a tabular antenna and a linear antenna. The antennas are configured to have mutually different center frequencies of a frequency band to be detected. The tabular antenna is formed in a disc shape. The total length of the linear antenna along the linear shape is configured to be a one-fourth wavelength of a detection radio wave at the center frequency of the frequency band detected by the linear antenna. The circumference of the tabular antenna is configured to be a half wavelength of the detection radio wave at the center frequency of the frequency band detected by the tabular antenna.

Description

  The present invention relates to a planar antenna.

  In recent years, wireless communication terminals are rapidly becoming multiband. Taking smartphones as an example, it is already standard to support 800 MHz band cellular systems, 2 GHz band cellular systems, WLAN (2.4 GHz band), and GPS. In the future, it is expected that correspondence to 700 MHz band and 900 MHz band short-range wireless communication, millimeter wave communication, IMT-Advanced, and the like will further advance. However, since the mounting space of the device is limited, the importance of a multiband antenna that can be shared in a plurality of wireless systems is increasing. In particular, a small and flat antenna that can be built in the housing of the apparatus and can be manufactured at low cost has attracted attention.

  Patent Document 1 below describes a “multi-resonant antenna” having discrete resonance points corresponding to a plurality of frequency bands as a multi-band planar antenna. Patent Document 2 listed below describes a “wideband antenna” in which impedance matching is continuously achieved over a wide frequency range.

JP 2010-278586 A JP 2006-33069 A

  The multi-resonant antenna as described in Patent Document 1 is realized by connecting a plurality of antenna elements having dimensions corresponding to respective resonance frequencies. Since the plurality of antenna elements interfere with each other electromagnetically, it is not easy to design, for example, to match three or more resonance frequencies to a desired frequency band. Therefore, the design of the multi-resonant antenna has a problem that skill is required.

  The wideband antenna as described in Patent Document 2 is relatively simple in design because the lower limit and the upper limit of the antenna band only need to be set so as to include all frequency bands to be supported. However, since the dimensions of the wideband antenna are determined in relation to the wavelength of the radio wave corresponding to the lower limit frequency of the antenna band (generally, about 1/4 to 1/2 of the wavelength), there is a problem that the antenna tends to be large. is there.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a planar antenna that is easy to design and can accommodate a small multiband.

  The planar antenna according to the present invention includes a flat antenna and a linear antenna, and these antennas are configured such that the center frequencies of the frequency bands to be detected are different from each other.

  Since the planar antenna of the present invention is compatible with multiband using a plurality of antennas having different center frequencies in the frequency bands detected from each other, it is easy to design while being small.

  Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

3 is a top view of the planar antenna according to Embodiment 1. FIG. It is a top view of the disk antenna which is an example of the conventional broadband antenna. It is a top view of the dipole antenna which is an example of the conventional narrow band antenna. It is a top view of the antenna which deform | transformed the dipole antenna shown in FIG. 3 is a design layout drawing of the planar antenna according to the first embodiment. It is a figure which shows the simulation result of the reflection characteristic of the planar antenna shown in FIG. 5, and the measurement result using the sample made as an experiment. FIG. 3 is a perspective view schematically showing a manufacturing example of the planar antenna according to the first embodiment. It is a schematic diagram of the radio | wireless communication terminal unit incorporating the planar antenna which concerns on Embodiment 1. FIG. It is a functional block diagram which shows one example of the radio | wireless communication terminal which can apply the planar antenna which concerns on Embodiment 1. FIG. 6 is a top view of a planar antenna according to Embodiment 2. FIG. It is a figure which shows typically the structural example which integrated the planar antenna which concerns on Embodiment 2 with the radio | wireless communication terminal module. 6 is a top view of a planar antenna according to Embodiment 3. FIG. 10 is a design layout drawing of the planar antenna according to the third embodiment. It is a figure which shows the simulation result of the reflection characteristic of the planar antenna shown in FIG. 13, and the measurement result of the sample made as an experiment.

<Embodiment 1>
FIG. 1 is a top view of a planar antenna according to Embodiment 1 of the present invention. 1 includes a feeding point 1, a first disk-shaped conductor 2a, a second disk-shaped conductor 2b, a first U-shaped linear conductor 3a, a second U-shaped linear conductor 3b, A first feed line 4a and a second feed line 4b are provided. The first disk-shaped conductor 2a and the second disk-shaped conductor 2b are configured as flat antennas. The first U-shaped linear conductor 3a and the second U-shaped linear conductor 3b are configured as a linear antenna.

  On both sides of the feed point 1, a first disc-like conductor 2a and a second disc-like conductor 2b are connected via a first feed line 4a and a second feed line 4b, respectively. The first U-shaped linear conductor 3a is arranged so as to branch from the first feeding line 4a, and the second U-shaped linear conductor 3b is arranged so as to branch from the second feeding line 4b.

  The first U-shaped linear conductor 3a includes a first straight line portion 3a-1, a second straight line portion 3a-2, and a third straight line portion 3a-3. The first straight line portion 3a-1 and the second straight line portion 3a-2 are joined at a substantially right angle, and the second straight line portion 3a-2 and the third straight line portion 3a-3 are joined at a substantially right angle. The U-shaped linear conductor 3a is formed in a U-shape. The second U-shaped linear conductor 3b has a first straight line portion 3b-1, a second straight line portion 3b-2, and a third straight line portion 3b-3. The first straight line portion 3b-1 and the second straight line portion 3b-2 are joined at a substantially right angle, and the second straight line portion 3b-2 and the third straight line portion 3b-3 are joined at a substantially right angle. The U-shaped linear conductor 3b is formed in a U-shape.

  The length of the first U-shaped linear conductor 3a and the length of the second U-shaped linear conductor 3b are respectively determined at the center frequency F1 of the frequency band detected by these linear antennas (and transmitted, and so on). It is configured to be a quarter of the radio wave wavelength. The length of the first U-shaped linear conductor 3a is the sum of the length of the first straight portion 3a-1, the length of the second straight portion 3a-2, and the length of the third straight portion 3a-3. The length of the second U-shaped linear conductor 3b is the sum of the length of the first straight portion 3b-1, the length of the second straight portion 3b-2, and the length of the third straight portion 3b-3. That is, these linear conductors are designed as dipole antennas.

  The circumference of the first disk-shaped conductor 2a and the circumference of the second disk-shaped conductor 2b are each configured to be one half of the radio wave wavelength at the center frequency F2 of the frequency band detected by these flat antennas. Has been. However, since radio waves can be detected by a path other than the path along the circumference of the disk, in reality, these flat antennas can detect radio waves in a frequency band in which the center frequency F3 is larger than F2. it can.

  The center frequencies F1, F2, and F3 of each frequency band described above have a relationship of F1 <F2 <F3. Therefore, the planar antenna according to the first embodiment functions as a multiband antenna that can detect these three frequency bands.

  Since the radio wave wavelength varies depending on the material and dimensions of the substrate on which the antenna is manufactured, the above-described conductor dimensions are not simply determined based on the radio wave wavelength in vacuum. Further, since the influence of the conductor existing around each radiating element, the extension of the length of the feed line, particularly the influence of the bent shape of the U-shaped linear conductor must be taken into consideration, the present invention is actually When designing an antenna according to the above, it is necessary to evaluate and evaluate by simulation or trial manufacture. Further, in FIG. 1, the first disk-shaped conductor 2a and the second disk-shaped conductor 2b have a perfect circle shape, but may have an elliptical shape or a semicircular shape.

  In the following, in order to compare with the planar antenna according to the first embodiment, the configuration of the conventional flat antenna and the conventional linear antenna and the detection characteristics of these conventional antennas will be described with reference to FIGS. .

  FIG. 2 is a top view of a disk antenna which is an example of a conventional broadband antenna. The broadband antenna shown in FIG. 2 includes a feeding point 1, a first disk-shaped conductor 2a, a second disk-shaped conductor 2b, a first feeding line 4a, and a second feeding line 4b.

  The first disk-shaped conductor 2a and the second disk-shaped conductor 2b operate as flat antennas that detect radio waves in a wide frequency band with the frequency at which the circumference of these disks becomes a half wavelength as the lower limit frequency. To do. Since it is a wide band, the frequency bands of a plurality of wireless systems can be covered together, but there is a problem that the size becomes large. For example, when the lower limit value of the operating frequency is set to 1 GHz, when these flat antennas are formed on a general printed board, the dimension in the major axis direction of the disc antenna is about 85 mm. Therefore, when considering incorporating in a portable radio | wireless communication terminal device, it is not realistic to apply a disc antenna with respect to a frequency band lower than 1 GHz.

  FIG. 3 is a top view of a dipole antenna which is an example of a conventional narrowband antenna. The dipole antenna shown in FIG. 3 includes a feeding point 1, a first linear conductor 0a, and a second linear conductor 0b. The first linear conductor 0a and the second linear conductor 0b operate as linear antennas that detect radio waves having a frequency at which the length of the linear conductors becomes a quarter wavelength.

  FIG. 4 is a top view of an antenna obtained by modifying the dipole antenna shown in FIG. The dipole antenna shown in FIG. 4 includes a feeding point 1, a first U-shaped linear conductor 3a, and a second U-shaped linear conductor 3b. The first U-shaped linear conductor 3a and the second U-shaped linear conductor 3b operate as antennas that detect radio waves having a frequency at which the length of these linear conductors becomes a quarter wavelength.

  By bending the dipole antenna as shown in FIG. 4, the antenna dimensions can be reduced at the same operating frequency. However, since the dipole antenna shown in FIGS. 3 and 4 has a narrow band, it is difficult to cover the frequency bands of a plurality of radio systems together.

  In order to solve the problems of the conventional antenna described above, a planar antenna according to the present invention has been devised. The planar antenna shown in FIG. 1 uses, for example, a first U-shaped linear conductor 3a and a second U-shaped linear conductor 3b as a radiating element for a wireless system having a frequency band of 1 GHz or less, A plurality of wireless systems having a frequency band of 1 GHz or more are designed so that the first disk-shaped conductor 2a and the second disk-shaped conductor 2b are used as radiating elements.

  The antenna size can be reduced by processing a long frequency band of 1 GHz or less using a bent linear conductor. By covering a plurality of frequency bands of 1 GHz or more with a disk-shaped conductor that covers a wide band, an antenna that is robust against frequency fluctuations can be configured. This will be supplemented below.

  When adjusting the dimensions of the first U-shaped linear conductor 3a and the second U-shaped linear conductor 3b and adjusting the resonance frequency of the linear antenna to a frequency band of 1 GHz or less in the antenna design process. The operating frequency of the flat antenna by the first disc-shaped conductor 2a and the second disc-shaped conductor 2b that covers a plurality of frequency bands of 1 GHz or more is affected by the influence, but the operating frequency of the flat antenna is Since it is a wide band, the influence on the return loss is small. Therefore, the entire antenna can be made robust against frequency fluctuations.

  5 and 6 show specific design examples of the planar antenna according to the first embodiment. In this design example, BC0 (825-875 MHz), BC6 (1920-2130 MHz), and GPS band (1575 MHz) of cdma2000 are set as operating frequency bands, and the target specification is that the return loss is 9.5 dB or more.

  FIG. 5 is a design layout drawing of the planar antenna according to the first embodiment. The diameter of the disk-shaped conductor is 33 mm, the length of the U-shaped linear conductor is 96 mm, and the line width of the U-shaped linear conductor is 1 mm.

  FIG. 6 is a diagram showing a simulation result of the reflection characteristics of the planar antenna shown in FIG. 5 and a measurement result using a prototype sample. The sample was manufactured using a FR4 single-sided copper-clad substrate having a thickness of 0.2 mm. The measurement results for the cdma2000 BC0 were slightly lower than the target specification at the lower end, but the cdma2000 BC6 and GPS band satisfied the target specification with a sufficient margin.

  FIG. 7 is a perspective view schematically showing a production example of the planar antenna according to the first embodiment. In FIG. 7, the planar antenna is produced by the conductor pattern 6 on the substrate 5. The electrical signal is input / output via the feeder line 7 and the connector 8.

  The substrate 5 is preferably a printed circuit board such as a glass epoxy material, but may be another resin material, an acrylic material, a ceramic material, or the like. The conductor pattern 6 is preferably a thin film or a thick film made of copper, aluminum, gold, silver, or an alloy thereof. Most commonly, it is made of a copper foil having a thickness of 18 to 36 μm on an FR4 substrate having a thickness of 0.2 to 2.0 mm. A thin coaxial cable having a diameter of about 1 mm is preferably used as the feeder line 7, but parallel two wires may be used. The connector 8 is preferably a U.S. connector. FL, W.W. FL, H.C. Small coaxial connectors such as FL are used, but SMA, N-type, BNC, PC7, PC-3.5, and parallel two-wire connectors may be used. The feeder line 7 may be directly attached to the antenna terminal of the wireless communication terminal by solder or the like without using a connector.

  Since the planar antenna according to the first embodiment is configured symmetrically with respect to the feeding point 1, it is assumed that a balanced signal is handled. However, in general, since the signal input / output from the antenna terminal of the wireless communication terminal is an unbalanced signal, a balanced-unbalanced conversion is performed by mounting a chip balun in the immediate vicinity of the feeding point on the substrate 5. You may implement. In addition, although the antenna performance is somewhat deteriorated, an unbalanced signal can be directly input to the feeding point 1 without using a balun in order to reduce component costs and simplify the design.

  FIG. 8 is a schematic diagram of a wireless communication terminal unit incorporating the planar antenna according to the first embodiment. The wireless communication terminal unit shown in FIG. 8 houses an antenna substrate 10 and a wireless communication terminal module 11 in a housing 9, and the antenna substrate 10 is joined to an antenna terminal 12 on the wireless communication terminal module via a feeder line. Yes. On the antenna substrate 10, the planar antenna according to the first embodiment is mounted. The housing 9 is preferably made of plastic such as ABS resin or tempered glass such as aluminum silicate glass.

  FIG. 9 is a functional block diagram illustrating an example of a wireless communication terminal to which the planar antenna according to the first embodiment can be applied. Information signals are exchanged between the baseband IC 17 and the RFIC 18, and the RFIC 18 performs modulation and demodulation corresponding to each wireless system. In the example illustrated in FIG. 9, the RFIC 18 transmits and receives cdma2000 BC0 and BC6 and receives GPS signals. The transmission signals of BC0 and BC6 output from the RFIC 18 are amplified by the power amplifier 19 and the power amplifier 20, respectively, and sent to the duplexer 21 and the duplexer 22. The duplexer 21 and the duplexer 22 are generally configured using a high frequency filter such as a SAW filter or a dielectric filter, and play a role of discriminating transmission / reception signals such as FDD. The transmission signal is sent to the triplexer 23 via the duplexer 21 and the duplexer 22. The triplexer 23 is generally configured using a high frequency filter such as a SAW filter or a high frequency switch such as a GaAs switch. The transmission signal is radiated to the outside as a radio wave by the antenna 24 through the triplexer 23. The received signal takes a path opposite to that of the transmitted signal. For example, a GPS signal will be described. The GPS signal taken in from the antenna 24 is amplified by the low noise amplifier 25 via the triplexer 23, and unnecessary signals are removed by the band pass filter 26, and then sent to the RFIC 18.

<Embodiment 1: Summary>
As described above, the planar antenna according to the first embodiment includes the flat antenna and the linear antenna, and the center frequencies F1 and F2 of the radio waves detected by these antennas are different from each other. As a result, it is possible to detect radio waves in the low frequency region using the linear antenna while covering a wide band in the high frequency region using the flat antenna.

  Further, according to the planar antenna according to the first embodiment, since the planar antenna and the linear antenna are used together, it is not necessary for the planar antenna to cover the entire frequency band. Therefore, it is not necessary to make the flat antenna excessively large, and the entire antenna can be made small. Furthermore, since the linear antenna is bent in a U shape, the size of the entire antenna can be further reduced.

<Embodiment 2>
In Embodiment 2 of the present invention, a configuration example in which a part of an antenna is connected to a ground conductor will be described as an example of a planar antenna that detects an unbalanced signal. The ground conductor can be configured by a ground layer formed in the inner layer of the substrate on which the planar antenna is mounted.

  FIG. 10 is a top view of the planar antenna according to the second embodiment. The planar antenna according to the second embodiment includes a feeding point 1, a disk-shaped conductor 2, a U-shaped linear conductor 3, and a ground conductor 13. The disk-shaped conductor 2 is configured as a flat antenna, and the U-shaped linear conductor 3 is configured as a linear antenna.

  One terminal of the feeding point 1 is connected to the disk-shaped conductor 2 via the feeding line 4, the other terminal of the feeding point 1 is connected to the ground conductor 13, and the U-shaped linear conductor 3 is connected to the feeding line 4. It is arranged to branch from. The U-shaped linear conductor 3 has a first straight line part 3-1, a second straight line part 3-2, and a third straight line part 3-3. The first straight line part 3-1 and the second straight line part 3-2 are joined at a substantially right angle, and the second straight line part 3-2 and the third straight line part 3-3 are joined at a substantially right angle. The linear conductor 3 is configured in a U shape.

  The length of the U-shaped linear conductor 3 is configured to be a quarter of the radio wave wavelength at the center frequency F1 of the frequency band detected by the linear antenna. The length of the U-shaped linear conductor 3 is the sum of the length of the first straight portion 3-1, the length of the second straight portion 3-2 and the length of the third straight portion 3-3. That is, the U-shaped linear conductor 3 is designed as a monopole antenna.

  The circumference of the disk-shaped conductor 2 is configured to be a half of the radio wave wavelength at the center frequency F2 of the frequency band detected by the flat-plate antenna. However, similarly to the first embodiment, radio waves in a frequency band in which the center frequency F3 is larger than F2 can be detected.

  The center frequencies F1, F2, and F3 of each frequency band described above have a relationship of F1 <F2 <F3. Therefore, the planar antenna according to the second embodiment functions as a multiband antenna that can detect these three frequency bands. In the second embodiment, preferably, the center frequency F1 is arranged in a frequency band of 1 GHz or less, and the center frequency F2 is arranged in a frequency band of 1 GHz or more, so that the portable radio communication terminal apparatus is An antenna with an optimal dimension can be realized.

  FIG. 11 is a diagram schematically illustrating a configuration example in which the planar antenna according to the second embodiment is integrated with a wireless communication terminal module. The wireless communication terminal module 14 includes a component mounting unit 27 in which a transceiver IC, a microcomputer, a PA, and the like are integrated, and an antenna unit 15 on which a planar antenna pattern according to the second embodiment is formed. The wireless communication terminal module 14 is generally manufactured using a multilayer substrate. The component mounting unit 27 is composed of, for example, four layers, and the second layer is a ground layer. The ground conductor 13 shown in FIG. 10 is substituted by the ground layer of the component mounting portion 27 in FIG. For example, the antenna unit 15 is formed on the first layer of a four-layer substrate, and the second to fourth layers are completely removed. The feeding point of the antenna unit 15 can be directly connected to the antenna terminal of the component mounting unit 27. By integrating the planar antenna with the wireless communication terminal module as shown in FIG. 11, it is possible to realize downsizing and cost reduction.

  In the second embodiment, the ground conductor 13 is rectangular, but the shape of the ground conductor 13 is not limited to this. For example, the shape may be a trapezoid. The same applies to Embodiment 3 described below.

<Embodiment 3>
FIG. 12 is a top view of the planar antenna according to the third embodiment of the present invention. The planar antenna according to the third embodiment includes a feeding point 1, a disk-shaped conductor 2, a first U-shaped linear conductor 3a, a second U-shaped linear conductor 3b, and a ground conductor 13. The disk-shaped conductor 2 is configured as a flat antenna, and the first U-shaped linear conductor 3a and the second U-shaped linear conductor 3b are configured as a linear antenna.

  One terminal of the feed point 1 is connected to the disk-shaped conductor 2 via the feed line 4, and the other terminal of the feed point 1 is connected to the ground conductor 13. The first U-shaped linear conductor 3 a is arranged so as to branch from the feed line 4. The second U-shaped conductor 3 b is connected to the disk-shaped conductor 2 at a point farthest from the point where the feed line 4 is connected among the disk-shaped conductors 2.

  The first U-shaped linear conductor 3a includes a first straight line portion 3a-1, a second straight line portion 3a-2, and a third straight line portion 3a-3. The first straight line portion 3a-1 and the second straight line portion 3a-2 are joined at a substantially right angle, and the second straight line portion 3a-2 and the third straight line portion 3a-3 are joined at a substantially right angle. The U-shaped linear conductor 3a is formed in a U-shape. The second U-shaped linear conductor 3b has a first straight line portion 3b-1, a second straight line portion 3b-2, and a third straight line portion 3b-3. The first straight line portion 3b-1 and the second straight line portion 3b-2 are joined at a substantially right angle, and the second straight line portion 3b-2 and the third straight line portion 3b-3 are joined at a substantially right angle. The U-shaped linear conductor 3b is formed in a U-shape.

  The length of the first U-shaped linear conductor 3a is configured to be a quarter of the radio wave wavelength at the center frequency F1U in the frequency band detected by the linear antenna. The length of the second U-shaped linear conductor 3b is configured to be a quarter of the radio wave wavelength at the center frequency F1L of the frequency band detected by the linear antenna. The length of the first U-shaped linear conductor 3a is the sum of the length of the first straight portion 3a-1, the length of the second straight portion 3a-2, and the length of the third straight portion 3a-3. The length of the second U-shaped linear conductor 3b is the sum of the length of the first straight portion 3b-1, the length of the second straight portion 3b-2, and the length of the third straight portion 3b-3.

  The circumference of the disk-shaped conductor 2 is configured to be a half of the radio wave wavelength at the center frequency F2 of the frequency band detected by the flat-plate antenna. However, similarly to the first embodiment, radio waves in a frequency band in which the center frequency F3 is larger than F2 can be detected.

  The center frequencies F1U, F1L, F2, and F3 of each frequency band described above have a relationship of F1L <F1U << F2 <F3. Therefore, the planar antenna according to the third embodiment functions as a multiband antenna that can detect these four frequency bands. In the third embodiment, the length of the first U-shaped linear conductor 3a and the length of the second U-shaped linear conductor 3b are different from each other, so that each linear antenna has a different frequency band. Corresponding to Thereby, the operating frequency of the antenna can be widened.

  In the third embodiment, preferably, the center frequency F1U is arranged in a frequency band of 1 GHz or less, and the center frequency F2 is arranged in a frequency band of 1 GHz or more, so that the portable radio communication terminal apparatus is A planar antenna having an optimal dimension can be realized.

  13 and 14 show specific design examples of the planar antenna according to the third embodiment. In this design example, BC0 (825-875 MHz), BC6 (1920-2130 MHz), and GPS band (1575 MHz) of cdma2000 are set as operating frequency bands, and the target specification is that the return loss is 9.5 dB or more.

  FIG. 13 is a design layout drawing of the planar antenna according to the third embodiment. The diameter of the disk-shaped conductor 2 is 29 mm, the length and line width of the first U-shaped linear conductor 3a are 74 mm and 1 mm, respectively, and the length and line width of the second U-shaped linear conductor 3b are 97 mm, respectively. 1 mm.

  FIG. 14 is a diagram showing the simulation results of the reflection characteristics of the planar antenna shown in FIG. 13 and the measurement results of the prototype sample. A sample was made by attaching a copper foil tape to an acrylic plate having a thickness of 2.0 mm. Both simulation results and measurement results satisfied the target specifications for all three frequency bands.

  The present invention is not limited to the embodiments described above, and includes various modifications. The above embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment. The configuration of another embodiment can be added to the configuration of a certain embodiment. Further, with respect to a part of the configuration of each embodiment, another configuration can be added, deleted, or replaced. For example, in the case of manufacturing a planar antenna for millimeter wave communication in the above first to third embodiments, an antenna pattern can be formed on a semiconductor substrate by using a film forming process or a photolithography technique.

  1: feeding point, 2: disk-shaped conductor, 3: U-shaped linear conductor, 4: feeding line, 13: ground conductor.

Claims (9)

A flat antenna,
A linear antenna electrically connected to the planar antenna;
With
The planar antenna and the linear antenna are configured so that center frequencies of frequency bands to be detected are different from each other. The planar antenna according to claim 1, wherein the linear antenna is formed in a linear shape that branches from a feed line that supplies power to the flat antenna. The flat antenna is formed in a disc shape,
The total length of the linear antenna along the linear shape is configured to be a quarter wavelength of the detected radio wave at the center frequency of the frequency band detected by the linear antenna,
The planar antenna according to claim 2, wherein a circumference of the flat antenna is configured to be a half wavelength of a detected radio wave at a center frequency of a frequency band detected by the flat antenna. . The planar antenna is
A disc-shaped second flat plate antenna electrically connected to the flat plate antenna via the feeder line;
A linear second linear antenna branched from the feeder line;
With
The linear antenna and the second linear antenna are respectively branched from the feed line between the flat antenna and the second flat antenna,
The total length along the line shape of the second linear antenna is configured to be a quarter wavelength of the detected radio wave at the center frequency of the frequency band detected by the second linear antenna;
The circumference of the second flat antenna is configured to be a half wavelength of a detected radio wave at a center frequency of a frequency band detected by the second flat antenna. The described planar antenna. The planar antenna includes a ground conductor electrically connected to the planar antenna via the feeder line,
The planar antenna according to claim 3, wherein the linear antenna is branched from the feeder line between the flat antenna and the ground conductor. The planar antenna includes a linear second linear antenna that is connected to the planar antenna at a position farthest from the contact point between the feeder line and the planar antenna on the planar antenna,
The total length along the line shape of the second linear antenna is configured to be a quarter wavelength of the detected radio wave at the center frequency of the frequency band detected by the second linear antenna;
The planar antenna according to claim 3, wherein a center frequency of a frequency band detected by the linear antenna and a center frequency of a frequency band detected by the second linear antenna are different from each other. . The planar antenna includes a ground conductor electrically connected to the planar antenna via the feeder line,
The planar antenna according to claim 6, wherein the linear antenna is branched from the feeder line between the flat antenna and the ground conductor.   The planar antenna according to claim 1, wherein the linear antenna is formed in a U-shape surrounding at least a part of an outer periphery of the flat antenna.   The planar antenna according to claim 1, wherein the center frequency is arranged in a frequency band of 1 GHz or less.

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