JP2016058843A - Planar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar antenna which can widen a communicable range.SOLUTION: A planar antenna 1 has: a conductor 12 which forms a microstrip antenna together with a ground electrode 11; a plurality of resonators (13-1 to 13-n) which are arranged to perform electromagnetic coupling with the conductor 12 at prescribed intervals along a longitudinal direction of the conductor 12; switches (14-1, 14-2) provided every prescribed number of sets of two adjacent resonators. The resonator (13-1) nearest an end of the conductor 12 which is open or grounded is arranged in the way that it crosses a node nearest the other end other than the same other end among nodes of stationary waves of current flowing the microstrip antenna. With respect to the respective sets of the prescribed number of resonators, the conductor 12 has at least two partial conductors (12c, 12d) different in length from each other that are arranged in parallel between the two resonators. The respective switches (14-1, 14-2) connect any one of the partial conductors to another part of the conductor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a planar antenna, for example.

  In recent years, Radio Frequency IDentification (RFID) systems have been widely used. Typically, RFID systems include those that use electromagnetic waves corresponding to the UHF band (900 MHz band) or microwaves (2.45 GHz) as communication media, and those that use mutual induction magnetic fields. Of these, RFID systems that use UHF electromagnetic waves are attracting attention because of their relatively long communicable distance.

  As an antenna that can be used for a tag reader to communicate with a wireless IC tag that uses electromagnetic waves in the UHF band, there is a microstrip antenna that uses a microstrip line as an antenna. Hereinafter, the wireless IC tag is referred to as an RFID tag for convenience of explanation. Such a microstrip antenna is incorporated in a shelf as an antenna of a tag reader, and the items placed on the shelf are managed by communicating between the RFID tag attached to the item placed on the shelf and the tag reader. Has been proposed (see, for example, Patent Document 1).

  An antenna incorporated in such a shelf is called a shelf antenna. In the vicinity of the surface of the shelf antenna, the shelf antenna has a specific frequency used for communication so that it can communicate with an RFID tag of an article placed anywhere on the shelf in which the shelf antenna is incorporated. It is preferable that a uniform and strong electric field can be formed. Therefore, the near-field antenna disclosed in Patent Document 1 has at least one resonator within a range that can be electromagnetically coupled to the microstrip antenna in the vicinity of any contact point of the current flowing through the microstrip antenna.

  Depending on the shape of the shelf, the size of the shelf antenna that can be incorporated into the shelf may be smaller than the size of the shelf itself. In addition, depending on the type of shelf, it may be required to customize the size of the shelf antenna in accordance with the size of the shelf in order to appropriately set the range in which the RFID tag can be read. Therefore, it may be preferable that the shelf antenna has a readable range wider than its own size.

  On the other hand, a technique that can change the directivity of an antenna has been proposed (see, for example, Patent Document 2). For example, the antenna device disclosed in Patent Document 2 has an electrical length that resonates at a predetermined frequency, and has a feeding element having a feeding point and a bent first tip portion, and is disposed in close proximity to the first tip portion. And a parasitic element having a bent second end portion. This antenna device changes the directivity by variably controlling the electrical length of the parasitic element by switching on and off at least one switch provided in the parasitic element.

JP 2014-60692 A JP 2006-186851 A

  However, in the antenna device disclosed in Patent Document 2, directivity changes between two directions orthogonal to each other in a plane parallel to the surface of the antenna. Therefore, even if this antenna device is incorporated in the shelf, there is a possibility that the range in which the RFID tag can be read cannot be sufficiently expanded.

  Therefore, an object of the present specification is to provide a planar antenna capable of widening a communicable range.

According to one embodiment, a planar antenna is provided. The planar antenna includes a substrate having a first dielectric layer and a second dielectric layer stacked on the first dielectric layer, a second dielectric layer of the first dielectric layer, A conductor disposed on a surface opposite to the opposite surface and between the first dielectric layer and the second dielectric layer and forming a microstrip antenna with the ground electrode; One end of the conductor is supplied with power, and the other end is open or grounded, and the opposite side of the surface of the second dielectric layer facing the first dielectric layer at a predetermined interval along the longitudinal direction of the conductor And a plurality of resonators disposed so as to be electromagnetically coupled to the conductor, and a switch provided in each of a predetermined number of sets of two adjacent resonators of the plurality of resonators.
The first resonator that is closest to the other end of the conductor of the plurality of resonators flows through the microstrip antenna according to a radio wave having a predetermined design wavelength that is radiated from or received by the microstrip antenna. Of the nodes of the standing wave of the current, it is arranged so as to intersect with the node closest to the other end other than the other end of the conductor. For each of the predetermined number of sets of two adjacent resonators, the conductor has at least two partial conductors of different lengths arranged in parallel between the two resonators of the set, and the switch comprises: Any one of the at least two partial conductors is connected to the other part of the conductor.

The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

  The planar antenna disclosed in this specification can widen a communication range.

2 is a transmission plan view of a shelf antenna according to one embodiment of a planar antenna. FIG. It is side surface sectional drawing of a shelf antenna seen from the direction of the arrow about the line shown by AA 'in FIG. (A) is the elements on larger scale of the conductor between two adjacent resonators, (b) is a circuit block diagram regarding control of the switch provided between the two resonators. (A) to (c) respectively radiate from each resonator when the length of the conductor between two adjacent resonators is equal to the design wavelength, longer than the design wavelength, or shorter than the design wavelength. It is a figure which shows the direction of the main lobe of the electromagnetic wave to be performed. It is a top view of the shelf antenna which shows the dimension of each part utilized for simulation. It is a figure which shows the simulation result of the frequency characteristic of S parameter of a shelf antenna. (A) And (b) is a figure which shows the simulation result of the gain of a shelf antenna. It is a figure which shows the simulation result of the electric field formed in the surface vicinity of a shelf antenna when the longer partial conductor is connected to the conductor main body. It is a figure which shows the simulation result of the electric field formed in the surface vicinity of a shelf antenna when the shorter partial conductor is connected to the conductor main body. It is a permeation | transmission top view of a shelf antenna by a modification.

Hereinafter, the planar antenna will be described with reference to the drawings.
This planar antenna uses a microstrip line including a linear conductor, one end of which is connected to a feeding point and the other end is an open end or is grounded, as a microstrip antenna. For this reason, in this planar antenna, the current flowing through the microstrip line is reflected by the other end of the conductor, so that the current becomes a standing wave. Then, at a nodal point of a standing wave generated at an interval that is an integral multiple of the wavelength of the current, the flowing current is minimized and the intensity of the electric field around it is maximized. Therefore, in this planar antenna, a resonance that electromagnetically couples to the microstrip line at a predetermined interval in order from the node of the standing wave closest to the end of the conductor forming the microstrip line, except for the open or grounded end of the conductor. A vessel is placed. Thereby, this planar antenna enables radiation or reception of radio waves from each resonator, and improves the uniformity and strength of the electric field in the vicinity of the antenna surface.

  Further, in this planar antenna, the conductor forming the microstrip line has two partial conductors having different lengths between the resonators and arranged in parallel. And this planar antenna changes the length of the conductor between resonators by connecting the two partial conductors with other parts of the conductor alternately at a predetermined switching frequency so as to be able to conduct electricity. Thereby, the directivity in the longitudinal direction of the conductor (that is, the direction parallel to the straight line connecting the feeding point of the microstrip line and the other end point) is temporally changed at the switching frequency.

  In the embodiments described below, the planar antenna disclosed herein is formed as a shelf antenna. However, the planar antenna disclosed in the present specification may be used as various near-field antennas used for applications other than the shelf antenna, for example, for communication with the RFID tag.

  FIG. 1 is a transparent plan view of a shelf antenna according to one embodiment. FIG. 2 is a side cross-sectional view of the shelf antenna as seen from the direction of the arrow along the line indicated by AA ′ in FIG.

  The shelf antenna 1 is provided on a substrate 10, a ground electrode 11 provided on the lower surface of the substrate 10, a conductor 12 provided between two dielectric layers of the substrate 10, and an upper surface of the substrate 10. The plurality of resonators 13-1 to 13-n (where n is an integer of 2 or more).

  The substrate 10 supports the ground electrode 11, the conductor 12, and the resonators 13-1 to 13-n. Further, the substrate 10 includes a lower layer 10-1 that is a dielectric layer positioned relatively below, and an upper layer 10-2 that is a dielectric layer stacked above the lower layer 10-1. Have. Thereby, the ground electrode 11, the conductor 12, and the resonators 13-1 to 13-n are insulated from each other. For example, the lower layer 10-1 and the upper layer 10-2 are each formed of a glass epoxy resin such as FR-4. Alternatively, the lower layer 10-1 and the upper layer 10-2 may be formed of other dielectrics that can be formed in layers. Further, the lower layer 10-1 and the upper layer 10-2 may be formed of the same dielectric material, or may be formed of different dielectric materials. Further, the thickness of the lower layer 10-1 of the substrate 10 is determined so that the characteristic impedance of the shelf antenna 1 becomes a predetermined value, for example, 50Ω or 75Ω.

  The ground electrode 11, the conductor 12, and the resonators 13-1 to 13-n are formed of, for example, a metal such as copper, gold, silver, nickel, an alloy thereof, or other conductive material. The ground electrode 11, the conductor 12, and the resonators 13-1 to 13-n are fixed to any surface of each layer of the substrate 10 by, for example, etching or adhesion.

  The ground electrode 11 is a grounded flat conductor and is provided so as to cover the entire lower surface of the lower layer 10-1 of the substrate 10.

  The conductor 12 is a linear conductor provided between the lower layer 10-1 and the upper layer 10-2 of the substrate 10, and is disposed along the longitudinal direction of the substrate 10. One end of the conductor 12 serves as a feeding point 12 a and is connected to a communication circuit (not shown) that processes a radio signal superimposed on a radio wave radiated or received via the shelf antenna 1. On the other hand, the other end 12b of the conductor 12 is an open end. The conductor 12, the ground electrode 11, and the lower layer 10-1 of the substrate 10 form a microstrip line that functions as a microstrip antenna.

  Since the end point 12b of the conductor 12 is an open end, the current flowing through the conductor 12 by the radio wave radiated from the microstrip antenna or the radio wave received by the microstrip antenna becomes a stationary wave. Therefore, the node of the standing wave is formed at a position away from the end point 12b of the conductor 12, that is, the open end of the microstrip antenna, by a distance corresponding to an integral multiple of 1/2 of the wavelength of the radio wave. In addition, since the conductor 12 is disposed between the lower layer 10-1 and the upper layer 10-2, the wavelength of the radio wave depends on the relative dielectric constant of the lower layer 10-1 and the ratio of the upper layer 10-2. Note that it decreases with the dielectric constant. At each node of the standing wave, the current has a minimum value, and a relatively strong electric field is formed around the node. In the following, for convenience, the wavelength of radio waves radiated from the microstrip antenna or received by the microstrip antenna is referred to as a design wavelength. The design wavelength is represented by λ.

  In addition, the conductor 12 is perpendicular to each other between the two resonators for each of the two adjacent resonators 13-m and 13- (m + 1) (where 1 ≦ m <n). It is formed in a meandering shape that is bent. Thereby, since the space | interval between two adjacent resonators, ie, a linear distance, becomes shorter than design wavelength (lambda), the electromagnetic waves radiated | emitted from each resonator can mutually strengthen.

  Furthermore, in order to change the directivity of the shelf antenna 1 over time, the conductor 12 is set between the two resonators for each of the two adjacent resonators 13-m and 13- (m + 1). Has two partial conductors formed in parallel. Details of the directivity of the partial conductor and the shelf antenna 1 will be described later.

  The resonators 13-1 to 13-n are each formed of a linear conductor having a length substantially equal to the design wavelength λ or an integral multiple thereof, and the longitudinal direction of the conductor 12 so that the conductor 12 can be electromagnetically coupled. Are provided on the surface of the upper layer 10-2 of the substrate 10 at predetermined intervals. Therefore, each of the resonators 13-1 to 13-n can also radiate or receive a radio wave having the design wavelength λ. In the present embodiment, the length of each resonator is approximately equal to the design wavelength λ.

  As described above, the position along the conductor 12 away from the open end 12b of the microstrip line by a distance corresponding to an integral multiple of 1/2 of the design wavelength λ is the design wavelength λ closest to the open end 12b. It becomes a node of the standing wave of the current flowing through the conductor 12 according to the radio wave that it has. Therefore, a relatively strong electric field is formed around the conductor 12 at that position. Therefore, the resonator 13-1 is disposed along the conductor 12 from the open end 12 b at a distance that is ½ of the design wavelength λ. Thereby, the resonator 13-1 is electromagnetically coupled to the conductor 12 satisfactorily by the electric field generated by the current flowing through the conductor 12 by the radio wave having the design wavelength λ.

  Furthermore, the longitudinal directions of the resonators 13-1 to 13-n are arranged so as to be orthogonal to the conductor 12. Therefore, each of the resonators 13-1 to 13-n can form an electric field having a spread in a different direction from the electric field generated by the microstrip antenna. As a result, the electric field near the surface of the shelf antenna 1 is more uniform and stronger than the electric field generated by the microstrip antenna alone.

Hereinafter, the directivity and the communicable range of the partial conductor and the shelf antenna 1 will be described.
FIG. 3A is a partially enlarged view of the conductor 12 between two adjacent resonators, and FIG. 3B is a circuit block diagram relating to control of a switch provided between the two resonators. For each pair of two adjacent resonators 13-m and 13- (m + 1), between the two resonators, the conductor 12 has two lengths different from each other and formed in parallel. Partial conductors 12c and 12d are provided. One end of each of the partial conductors 12c and 12d is connected to the main body on the open end 12b side of the conductor 12, which is another part of the conductor 12, so as to be energized. On the other hand, the other end of the partial conductor 12c is connected to the main body on the feeding point 12a side of the conductor 12, which is another part of the conductor 12, via the switch 14-1. The other end of the partial conductor 12d is connected to the main body of the conductor 12 on the power feeding point 12a side through the switch 14-2 so as to be energized.

  In the present embodiment, the partial conductor 12c is longer than the partial conductor 12d. When the switch 14-1 is turned on and a current flows through the partial conductor 12c, the length of the conductor 12 serving as a current path length between two adjacent resonators is longer than the design wavelength λ. In addition, the partial conductor 12c is formed. On the other hand, when the switch 14-2 is turned on and a current flows through the partial conductor 12d, the length of the conductor 12 serving as a current path length between two adjacent resonators is shorter than the design wavelength λ. Thus, the partial conductor 12d is formed. Note that the length of the conductor 12 between two adjacent resonators is longer than (1/2) λ, regardless of which of the partial conductor 12c and the partial conductor 12d is connected to the conductor 12 body, and It is preferably shorter than (3/2) λ. When the length of the conductor 12 between two adjacent resonators becomes a length obtained by adding an integral multiple of the design wavelength to ½ of the design wavelength, the phases of the currents flowing through the two resonators are inverted from each other. Therefore, the electric fields generated by the two resonators cancel each other. Therefore, the lengths of the partial conductors 12c and 12d are set so that the length of the conductor 12 between the two resonators is longer than (1/2) λ and shorter than (3/2) λ. This suppresses the electric fields generated from the two resonators from canceling each other.

Each of the switch 14-1 and the switch 14-2 is turned on and the other is turned off at a predetermined switching frequency according to a control signal from the control circuit 15. In this manner, ON and OFF are alternately repeated. The switching frequency may be any frequency that does not interfere with communication of a device (for example, an RFID tag) that receives radio waves from the shelf antenna 1 or transmits radio waves received by the shelf antenna 1. Is set. As a result, the shelf antenna 1 can alternately form an electric field directed toward the feeding point 12a and an electric field directed toward the open end 12b, so that the device located outside the feed point 12a and located outside the open end 12b. Communication with the device is also possible.
In order to appropriately adjust the directivity of the shelf antenna 1, the control circuit 15 adjusts the timing at which the partial conductor 12c is connected to the conductor 12 for each pair of two adjacent resonators. It is preferable to control the switch 14-1 of the resonator set. Similarly, the control circuit 15 controls the switch 14-2 of each resonator set so that the timing at which the partial conductor 12d is connected to the conductor 12 is synchronized for each of the two adjacent resonator sets. Is preferred.

  Further, the switch 14-1 and the switch 14-2 can be, for example, single pole, single throw (SPST) type RF switches formed of diodes. Alternatively, instead of the switch 14-1 and the switch 14-2, one single pole, dual throw (SPDT) for connecting any one of the partial conductor 12c and the partial conductor 12d to the main body of the conductor 12 on the feeding point 12a side. A type of switch may be used. In this case, the switch can be, for example, an SPDT type RF switch formed of a field effect transistor.

In the present embodiment, the resonators 13-1 to 13-n can radiate or receive radio waves, respectively. Therefore, the directivity in the longitudinal direction of the shelf antenna 1 can be considered in the same manner as the directivity of the array antenna when the resonators 13-1 to 13-n are one antenna. In this case, the array factor is given by
Here, α represents a phase difference between currents flowing through the conductor 12 at the positions of two adjacent resonators. d represents a linear distance between two adjacent resonators. Β is a propagation coefficient. Ψ represents the direction of the electric field formed by each resonator.
From the equation (1), the relationship between the direction ψm of the main lobe of the electric field formed by each resonator and the phase difference α is expressed by the following equation.
Therefore, if the phase difference α is 0 °, the direction of the main lobe of the electric field formed by each resonator is a direction perpendicular to the direction in which the resonators are arranged, that is, a method with respect to the surface of the substrate 10. Line direction. On the other hand, when the phase difference α is smaller than 0 ° or larger than 0 °, the direction of the main lobe of the electric field formed by each resonator is a conductor with respect to the normal direction to the surface of the substrate 10. 12 in the longitudinal direction, that is, along the longitudinal direction of the shelf antenna 1. Therefore, by changing the length of the conductor 12 between two adjacent resonators, the phase difference between the currents at the positions of the two resonators changes, so that the shelf antenna 1 has directivity in the longitudinal direction. Can be changed.

  4A to 4C show the case where the length λm of the conductor 12 between two adjacent resonators is equal to the design wavelength λ, or longer than the design wavelength λ, than the design wavelength λ. It is a figure which shows the direction of the main lobe of the electric field formed by each resonator in the case where is also short.

  As shown in FIG. 4A, when the length λm is equal to the design wavelength λ, the phase of the current flowing through the conductor 12 at the position of each resonator is the same. Therefore, the direction of the main lobe of the electric field formed by each resonator is substantially parallel to the normal direction to the surface of the substrate 10 as indicated by an arrow 401.

  On the other hand, when the partial conductor 12c is connected to the conductor 12 body, the length λm becomes longer than the design wavelength λ. Therefore, when the phase of the current flowing through the conductor 12 at the position of the resonator closer to the open end 12b of the two adjacent resonators is used as a reference, the conductor 12 at each position of the two resonators is The phase difference between the flowing currents is negative. Therefore, the direction of the main lobe of the electric field formed by each resonator is directed toward the open end 12b rather than the normal direction n to the surface of the substrate 10, as indicated by the arrow 402 in FIG. As the length λm is longer than the design wavelength λ, the inclination angle in the direction of the main lobe of the electric field formed by each resonator with respect to the normal direction to the surface of the substrate 10 increases, and in the vicinity of the surface of the substrate 10. The communicable range outside the open end 12b becomes wider.

  Conversely, when the partial conductor 12d is connected to the conductor 12 body, the length λm becomes shorter than the design wavelength λ. Therefore, when the phase of the current flowing through the conductor 12 at the position of the resonator closer to the open end 12b of the two adjacent resonators is used as a reference, the conductor 12 at each position of the two resonators is The phase difference between the flowing currents is positive. Therefore, the direction of the main lobe of the electric field formed by each resonator is directed to the feeding point 12a side from the normal direction n to the surface of the substrate 10, as indicated by an arrow 403 in FIG. As the length λm is shorter than the design wavelength λ, the inclination angle of the direction of the main lobe of the electric field formed by each resonator with respect to the normal direction to the surface of the substrate 10 increases, and in the vicinity of the surface of the substrate 10. The communicable range outside the feeding point 12a becomes wider.

  In this way, the partial conductor 12c and the partial conductor 12d are alternately connected to the conductor 12 main body so that energization is possible, so that the direction of the main lobe of the electric field formed by each resonator of the shelf antenna 1 is the feeding point 12a side. And the open end 12b side alternately. As a result, the shelf antenna 1 can extend its communicable range in the longitudinal direction of the shelf antenna 1 to either the outside of the feeding point 12a or the outside of the open end 12b. Therefore, the communicable range of the shelf antenna 1 becomes wider than the size of the shelf antenna 1 in the longitudinal direction.

Hereinafter, simulation results of the antenna characteristics of the shelf antenna 1 will be described.
FIG. 5 is a plan view of the shelf antenna 1 showing the dimensions of each part used in the simulation. In FIG. 5, for convenience of explanation, the longitudinal direction of the shelf antenna 1 is parallel to the surface of the shelf antenna 1 and the longitudinal direction of the shelf antenna 1 is parallel to the surface of the shelf antenna 1 and is perpendicular to the x axis. . The normal direction of the surface of the shelf antenna 1 is taken as the z axis. FIG. 6 is a diagram illustrating a simulation result of the frequency characteristics of the S parameter of the shelf antenna 1. FIG. 7A and FIG. 7B are diagrams showing simulation results of the gain of the shelf antenna 1. Further, FIGS. 8 and 9 are diagrams showing simulation results of the electric field formed in the vicinity of the surface of the shelf antenna 1.

In this simulation, the design wavelength λ is a wavelength corresponding to a frequency of 919 MHz. In addition, the lower layer 10-1 and the upper layer 10-2 of the substrate 10 are formed of FR-4 (relative permittivity εr = 4.3, dielectric loss tangent tanδ is 0.01). All of the ground electrode 11, the conductor 12, and the resonators 13-1 to 13-n are made of copper (conductivity σ = 5.8 × 10 ⁷ S / m).

As shown in FIG. 5, the length of the substrate 10 along the longitudinal direction of the conductor 12 is 730 mm, and the length in the direction orthogonal to the longitudinal direction of the conductor 12 is 200 mm.
Furthermore, the length of each resonator 13-1 to 13-n is 178 mm, and the linear distance between two adjacent resonators is 45 mm. Further, between two adjacent resonators, the lengths of the four portions of the conductor 12 parallel to the x-axis direction were each 13 mm. When the partial conductor 12c is connected to the conductor 12 body, the length h of the longest portion parallel to the y-axis direction among the bent portions of the conductor 12 is 73 mm, and the conductor between two adjacent resonators The length of 12 is 192 mm. On the other hand, when the partial conductor 12d is connected to the conductor 12 main body, the length h is 61 mm, and the length of the conductor 12 between two adjacent resonators is 174 mm. In this example, regardless of which of the partial conductor 12c and the partial conductor 12d is connected to the conductor 12 body, the path of the current flowing through the conductor 12 has a shape bent between the resonators, so that it extends in the y-axis direction. An electric field with is formed.

  In FIG. 6, the horizontal axis represents the frequency [GHz], and the vertical axis represents the value [dB] of the S11 parameter. A graph 600 represents the frequency characteristic of the S11 parameter of the shelf antenna 1 obtained by simulation of the electromagnetic field by the finite integration method. As shown in the graph 600, it can be seen that the shelf antenna 1 has a S11 parameter of −10 dB or less, which is a measure of good antenna characteristics, within the 900 MHz band used in the RFID system. In particular, it can be seen that the S11 parameter has the lowest value in the vicinity of 920 MHz.

  In FIG. 7A and FIG. 7B, the direction of the arrow representing the x axis represents the direction toward the open end 12b. FIG. 7A shows a gain distribution 700 of the shelf antenna 1 when the longer partial conductor 12c is connected to the conductor 12 body. When the partial conductor 12c is connected to the conductor 12 body, the length λm of the conductor 12 between two adjacent resonators is longer than the design wavelength λ. Therefore, since the direction of the main lobe of the electric field formed by each resonator is inclined toward the open end 12b, the gain closer to the open end 12b is larger than the normal direction of the substrate 10 as shown in the distribution 700. Get higher.

  FIG. 7B shows a gain distribution 710 of the shelf antenna 1 when the shorter partial conductor 12d is connected to the conductor 12 body. When the partial conductor 12d is connected to the conductor 12 main body, the length λm of the conductor 12 between two adjacent resonators is shorter than the design wavelength λ. Therefore, since the direction of the main lobe of the electric field formed by each resonator is inclined toward the feeding point 12a, the gain closer to the feeding point 12a is larger than the normal direction of the substrate 10 as shown in the distribution 710. Get higher.

  FIG. 8 is a diagram showing a simulation result of an electric field formed in the vicinity of the surface of the shelf antenna 1 when the longer partial conductor 12c is connected to the conductor 12 body. In FIG. 8, the direction of the arrow representing the x-axis represents the direction toward the open end 12b. 8, distributions 801 to 803 indicate the surface of the shelf antenna 1 at a position 20 cm upward from the surface of the shelf antenna 1 when the phase of the electric field at the reference point is 180 °, 240 °, and 300 °, respectively. Represents the intensity distribution of the electric field in a plane parallel to However, in each distribution, the higher the concentration, the stronger the electric field. As shown in the distributions 801 to 803, as the phase advances, the position where the electric field becomes stronger is toward the open end 12b, and this indicates that the main lobe of the electric field is toward the open end 12b. . For this reason, when the longer partial conductor 12c is connected to the conductor 12 body, it can be seen that the communicable range of the shelf antenna 1 extends outward from the open end 12b.

  FIG. 9 is a diagram showing a simulation result of an electric field formed in the vicinity of the surface of the shelf antenna 1 when the shorter partial conductor 12d is connected to the conductor 12 body. In FIG. 9, the direction of the arrow representing the x axis represents the direction toward the open end 12b. 9, distributions 901 to 903 indicate the surface of the shelf antenna 1 at a position 20 cm above the surface of the shelf antenna 1 when the phase of the electric field at the reference point is 180 °, 240 °, and 300 °, respectively. Represents the intensity distribution of the electric field in a plane parallel to However, in each distribution, the higher the concentration, the stronger the electric field. As shown in the distributions 901 to 903, as the phase advances, the position where the electric field becomes stronger is directed toward the feeding point 12a, and this shows that the main lobe of the electric field is directed toward the feeding point 12a. . Therefore, it can be seen that the communicable range of the shelf antenna 1 extends outward from the feeding point 12a.

  As described above, in this shelf antenna, the length of the conductor between the two adjacent resonators among the plurality of resonators electromagnetically coupled to the conductor forming the microstrip line is a predetermined switching frequency. It can be switched with. Therefore, in this shelf antenna, the directivity in the longitudinal direction of the shelf antenna is switched at the switching frequency. Therefore, this shelf antenna can extend the communicable range in comparison with the size of the antenna body along the longitudinal direction.

  According to the modification, the end point 12b of the conductor 12 opposite to the feeding point 12a may be grounded by being short-circuited to the ground electrode 11 via a via formed in the substrate 10, for example. In this case, the end point 12b is a fixed end for the current flowing through the microstrip line. Therefore, the position of the node of the current flowing through the conductor 12 is specified with the end point 12b as a fixed end. That is, a position that is separated from the end point 12b by a distance of (1/4 + n / 2) λ (n is an integer of 0 or more and λ is a design wavelength) along the longitudinal direction of the conductor 12 is a node. Therefore, the resonators are arranged along the longitudinal direction of the conductor 12 at predetermined intervals in order from the end point 12b to (1/4) λ, which is the node closest to the end point 12b except for the end point 12b.

According to another modification, even when any of the partial conductor 12c and the partial conductor 12d is connected to the main body of the conductor 12, the length λm of the conductor 12 between two adjacent resonators is longer than the design wavelength λ. The partial conductor 12c and the partial conductor 12d may be formed so as to be shorter. In this case, regardless of which partial conductor is connected to the conductor 12 main body, the direction of the main lobe of the electric field formed by each resonator is directed to the feeding point 12a side with respect to the normal of the surface of the substrate 10. It will be. On the contrary, even when any of the partial conductor 12c and the partial conductor 12d is connected to the main body of the conductor 12, the length λm of the conductor 12 between two adjacent resonators is longer than the design wavelength λ. The conductor 12c and the partial conductor 12d may be formed. In this case, regardless of which partial conductor is connected to the conductor 12 body, the direction of the main lobe of the electric field formed by each resonator faces the open end 12b side with respect to the normal of the surface of the substrate 10. It will be.
Further, when one of the partial conductor 12c and the partial conductor 12d is connected to the conductor 12 body, the length λm of the conductor 12 between two adjacent resonators is made equal to the design wavelength λ. The partial conductor may be formed. In this case, when the partial conductor is connected to the conductor 12 body, the direction of the main lobe of the electric field formed by each resonator is substantially parallel to the normal of the surface of the substrate 10.

  Thus, the position of the communicable range of the shelf antenna 1 changes according to the lengths of the two partial conductors 12c and 12d. Therefore, the lengths of the two partial conductors 12c and 12d may be set according to the positional relationship between the required communicable range and the shelf antenna 1.

According to still another modification, the conductor 12 has three or more partial conductors having different lengths arranged in parallel between the resonators for each set of two adjacent resonators. May be. Furthermore, a switch may be disposed between each partial conductor and the conductor body. Each switch may be controlled such that any one of the partial conductors is alternately connected to the conductor 12 body at a predetermined switching frequency.
In this case, since the shelf antenna 1 can change the direction of the main lobe of the radio wave radiated from the shelf antenna 1 between three or more different directions, the communicable range can be further widened. .

  Further, the conductor forming the microstrip line may be formed to have a shape other than the meandering shape between two adjacent resonators.

  FIG. 10 is a transmission plan view of a shelf antenna according to a modification. In FIG. 10, the same reference numerals as those of the corresponding components of the shelf antenna 1 shown in FIG. The shelf antenna 2 according to this modification is different from the shelf antenna 1 shown in FIG. 1 in the shape of the conductor forming the microstrip line. Therefore, hereinafter, the shape of the conductor forming the microstrip line will be described.

  Also in this modified example, the conductor 12 forming the microstrip line includes two partial conductors 12c having different lengths arranged in parallel between the two resonators for each set of two adjacent resonators. 12d. However, in this modification, when the relatively short partial conductor 12d is connected to the conductor 12 body, the conductor 12 is a straight line between two adjacent resonators. On the other hand, the relatively long partial conductor 12c is formed in a U shape and is disposed adjacent to the partial conductor 12d. The partial conductor 12c and the partial conductor 12d are alternately connected to the main body of the conductor 12 by a switch (not shown) so as to be energized.

  In this modification, the distance between two adjacent resonators is long, and the conductor 12 is also substantially linear. Therefore, the readable range in the short direction of the shelf antenna 2 is the short range of the shelf antenna 1 according to the above embodiment. It becomes narrower than the readable range in the hand direction. However, the shelf antenna 2 requires fewer resonators than the shelf antenna 1.

  Moreover, it is not necessary to provide a plurality of partial conductors arranged in parallel between the two resonators for all the groups of two adjacent resonators. For example, for a predetermined number of sets of at least one of two adjacent resonator sets, a plurality of partial conductors arranged in parallel as in the above embodiment, and any one of these partial conductors is a conductor A switch connected to the main body may be provided. Also in this case, the directivity of the shelf antenna can be changed by switching the partial conductor connected to the conductor body.

  All examples and specific terms listed herein are intended for instructional purposes to help the reader understand the concepts contributed by the inventor to the present invention and the promotion of the technology. It should be construed that it is not limited to the construction of any example herein, such specific examples and conditions, with respect to showing the superiority and inferiority of the present invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the present invention.

1, 2 Shelf antenna (planar antenna)
DESCRIPTION OF SYMBOLS 10 Board | substrate 10-1 Lower layer 10-2 Upper layer 11 Ground electrode 12 Conductor 12a Feeding point 12b Open end 12c, 12d Partial conductor 13-1 to 13-n Resonator 14-1, 14-2 Switch 15 Control circuit

Claims (4)

A substrate having a first dielectric layer and a second dielectric layer stacked on the first dielectric layer;
A ground electrode disposed on a surface of the first dielectric layer opposite to the surface facing the second dielectric layer;
A conductor disposed between the first dielectric layer and the second dielectric layer and forming a microstrip antenna together with the ground electrode, wherein one end of the conductor is fed and the other end of the conductor Is an open or grounded conductor,
A plurality of the second dielectric layers arranged at predetermined intervals along the longitudinal direction of the conductor and disposed on the surface opposite to the surface facing the first dielectric layer so as to be electromagnetically coupled to the conductor. A resonator of
A switch provided in each of a predetermined number of sets of two adjacent resonators of the plurality of resonators;
The first resonator closest to the other end of the conductor of the plurality of resonators is radiated from the microstrip antenna or received by the microstrip antenna according to a radio wave having a predetermined design wavelength, Of the nodes of the standing wave of the current flowing through the microstrip antenna, arranged to intersect the node closest to the other end other than the other end of the conductor,
For each of the predetermined number of sets of resonators, the conductor has at least two partial conductors of different lengths arranged in parallel between the two resonators of the set, the switch comprising: Connecting any one of the at least two partial conductors to the other part of the conductor;
Planar antenna.   When one of the at least two partial conductors is connected to the other part of the conductor, the length of the conductor between the two resonators is longer than the design wavelength, and the at least two parts The at least two partial conductors such that the length of the conductor between the two resonators is shorter than the design wavelength when another one of the conductors is connected to another part of the conductor. The planar antenna according to claim 1, wherein the length of is set. The plurality of resonators are arranged so that the predetermined interval is shorter than the design wavelength,
The conductor has a shape in which a path through which the current flows on the conductor is bent between the two resonators, regardless of which of the at least two partial conductors is connected to another part of the conductor. The planar antenna according to claim 1, wherein the planar antenna is formed as follows.   A control circuit for controlling the switch for each of the predetermined number of sets of the resonators to alternately connect each of the at least two partial conductors with other portions of the conductor at a predetermined switching frequency; The planar antenna as described in any one of Claims 1-3.