JP2007243416A - Communication antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstrip antenna which can be miniaturized easily and can radiate a circularly-polarized wave. <P>SOLUTION: The communication antenna comprises a dielectric substrate, a means for controlling a polarized wave formed on one side of the dielectric substrate, a conductive film as a ground conductor formed on the side of the dielectric substrate opposite to the side for forming a microstrip, and a feed means for electrically connecting the microstrip and the conductive film. This means is a notch, a slit or an active element, and the feed means is formed in the vicinity of the center of gravity of the microstrip. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the structure of an antenna related to communication (hereinafter referred to as “communication antenna”), and particularly belongs to the technical field of a microstrip antenna capable of generating circularly polarized waves.

  Mobile satellite communications, GPS navigation systems, and the like require communication antennas that can radiate circularly polarized waves. In particular, in order to realize a small terminal, a small communication antenna that can be installed in the terminal is required.

  Communication antennas that can radiate circularly polarized waves are generally a cross dipole antenna, a microstrip as a rectangular or circular radiation conductor, a conductive film as a ground conductor (ground), a dielectric substrate, There is a microstrip antenna that is configured to have. Also, among communication antennas, slots and microstrip lines are often used.

  Square and circular microstrip antennas can achieve stable circular polarization characteristics, but downsizing has been a major issue. This is greatly influenced by the conventional design concept. Up to now, circularly polarized radiating elements are basically square or circular elements, and have been circularly polarized using degenerate separation. The current of the mode separated for circular polarization is distributed diagonally, so that it is difficult to shorten the wavelength. Therefore, there is a limit to miniaturization of the communication antenna, and it is difficult to ensure a desired gain and axial ratio even when the communication antenna is miniaturized.

In addition, there is a method of simply using a high dielectric constant substrate for miniaturization of the microstrip antenna, but the reduction in gain and efficiency becomes a problem.

In addition to the design of communication antennas, the use of resonant modes of stacked, back-fed microstrip line planar antennas, such as circular polarization, circular polarization, and multi-polarization sharing, Techniques using a helical antenna or a planar antenna and a rod antenna are described in, for example, Patent Documents 1 to 3 below.

JP 2001-244726 A Japanese Patent Laid-Open No. 9-232849 JP-A-9-98017

However, in the techniques described in Patent Documents 1 to 3, problems remain in miniaturization of the communication antenna, and problems still remain with respect to widening the band, gain, and improvement of the axial ratio.

Accordingly, an object of the present invention is to provide a high-performance microstrip antenna capable of solving the above-described problems and realizing circularly polarized radiation even with a small structure.

A microstrip antenna related to one means for solving the above problem is a microstrip as a radiation conductor in which a notch (or slit) or an active element is loaded on one side of a dielectric substrate and the dielectric substrate, A conductive film as a ground conductor (ground) formed on a surface opposite to the surface on which the microstrip of the dielectric substrate is formed, and a power feeding means for electrically connecting the microstrip and the conductive film. A communication antenna.

In this means, the microstrip is preferably polygonal, more preferably fan-shaped or triangular. In this case, it is also desirable that a notch (or slit) or an active element capable of obtaining the same effect as the notch (or slit) is provided on the element side.

  According to the present invention, the frequency characteristics of the impedance are controlled so that circularly polarized radiation can be obtained with respect to resonance modes generated in a polygonal shape such as a sector or a triangle, and circularly polarized radiation can be generated at a desired frequency. Realize. The frequency characteristics of each resonance mode are controlled by loading a current distributed on the microstrip with a notch (slit). First, the shape of the microstrip is determined, and the current distribution of each mode generated on the microstrip is examined. Next, determine two or more resonance modes of interest. The two resonance modes are preferably as close as possible to the resonance frequency. Next, the main polarization component of the electric field radiated in each resonance mode is examined, and the notches (slits) are appropriately adjusted so as to have equal amplitude and phase difference p / 2 in a desired radiation direction. This is equivalent to controlling the frequency characteristics of the impedance of the antenna as a resonator. The frequency characteristics of the two resonance modes can be freely adjusted within a range in which the circularly polarized radiation conditions (polarization direction, amplitude, and phase) can be matched, thereby realizing a small circularly polarized microstrip antenna.

  The important point of the present invention is not the conventional degenerate separation, but the idea of generating circularly polarized waves by directly adjusting the frequency characteristics of each resonance mode. A fan-shaped microstrip or the like can shorten the wavelength of the two resonance modes almost independently. As a result, the operating frequency of the communication antenna can be set freely, so that circularly polarized radiation can be realized even if the antenna size is reduced.

  As described above, the present invention can provide a circularly polarized microstrip antenna having a small structure.

(Embodiment 1)
FIG. 1 is a schematic perspective view of a microstrip antenna (hereinafter referred to as “the present antenna”) according to this experimental embodiment. This antenna is formed on the dielectric substrate 3, the microstrip 2 formed on one surface side of the dielectric substrate, and the surface of the dielectric substrate 3 opposite to the surface on which the microstrip 2 is formed. One of the characteristics is that it includes a conductive film 4 as a ground conductor (ground), a microstrip 2, and a power feeding means 1 that electrically connects the conductive film.

  The microstrip 2 is formed on the dielectric substrate 3, but air may be used instead of the dielectric substrate 3, and a notch (or slit) 5 is provided on the element side. Alternatively, it is formed by loading an active element 6 having the same effect as a notch (or slit). The microstrip is not particularly limited as long as the notch (or slit) 5 or the active element 6 having the same effect is loaded, but the shape is preferably a fan shape or a polygonal shape, for example. In particular, the fan shape is not only close to the two resonance modes and easy to control the frequency, but also when a plurality of microstrip antennas are formed on one dielectric substrate 3, a normal square or circular micro This is more advantageous in terms of miniaturization than using strip elements.

  In addition, it is desirable that at least one or more notches (or slits) 5 or active elements 6 having the same effect are loaded on any side. There is no particular limitation on the shape of the notch (or slit) 5. In an example of the present embodiment, the microstrip 2 is formed in a sector shape, and notches (or slits) 5 are loaded on both hypotenuses. The dielectric substrate 3 is not particularly limited as long as insulation between the conductive film 4 and the microstrip 2 described later can be achieved, and a known substrate can be employed. In addition, the material of the microstrip 2 is not particularly limited as long as it has electrical conductivity. For example, metals such as copper and aluminum and alloys thereof can be preferably used.

The conductive film 4 is used as a ground conductor (ground) or as an input for supplying a potential to the microstrip 2. In this embodiment, the surface of the dielectric substrate 3 on which the microstrip is formed. Arranged on the opposite side. The material is not particularly limited as long as it is conductive, and can be made of the same material as that of the microstrip 2.

The power supply means 1 is means for electrically connecting the conductive film 4 and the strip line 2 and is not particularly limited as long as it can be electrically connected. 3 can be formed by forming a through hole and filling the through hole with a conductive material. It is also desirable as an aspect that the power supply means 1 according to the present embodiment is provided at a position offset from the center of gravity of the microstrip 2. In particular, in this embodiment, since the microstrip 2 and the conductive film 4 are arranged on each surface of the dielectric substrate 3 and supply means for penetrating the substrate is used, a small and thin circularly polarized antenna is realized. I can do it.

By adopting such a configuration, this antenna has a small structure, radiation of circularly polarized waves, improvement of gain axis ratio, and further, sharing of multipolarization and multifrequency by loading active elements. I can do it. Here, the operation of this antenna will be described with reference to FIGS.

FIG. 2 is a schematic diagram of current distributions in two resonance modes appearing in a fan-shaped patch antenna having no notch or the like. FIG. 2A shows the current distribution in mode # 1 having the lowest resonance frequency. FIG. 2B shows the current distribution in mode # 2, which has the next lowest resonance frequency after mode # 1. Taking the fan shape with an inner angle of 90 ° as shown in the figure as an example, the difference between the two frequencies without the notch is about 21%, but the polarization directions of each other are orthogonal. Therefore, this antenna performs circular polarization of the antenna using these orthogonal modes. First, the notches (and slits) are loaded on the sides AB and AD in FIG. 2 so that the resonance frequency of mode # 2 is substantially the same as that of mode # 1. At this time, the shape and position of the notches (and slits) are arbitrary, but the polarization directions of the modes # 1 and # 2 are not changed as much as possible. Finally, circularly polarized radiation is realized by appropriately adjusting the notch so that the phase difference between the two modes # 1 and # 2 is π / 2 at a specific frequency. In the fan shape of this example, as is clear from the current distribution, the resonance frequency of mode # 1 can be controlled by a notch (or slit) loaded on the arc CBD, and the resonance frequency of mode # 2 is And the notch loaded on the side AC can be adjusted as appropriate.
FIG. 3 is a diagram for explaining the operation of the circularly polarized antenna, for example, when the antenna receives a left-handed circularly polarized wave. This figure shows a sector shape as an example. It is a top view at the time of seeing the microstrip 2 from a dielectric substrate upper surface. In the case of this figure, it is explanatory drawing in the case of receiving a left-handed circularly polarized wave, FIG. 3 (a) shows the case where the phase of this wave is 0, and FIG. 3 (b) shows that the phase is p / 2. FIG. 2 (c) shows a case where the phase is p, and FIG. 3 (d) shows a case where the phase is 3p / 2.

In the case of FIG. 3A, that is, when the phase is 0, the total current distribution occurs in the direction from C to D of this microstrip. This changes with the phase change of the left-handed circularly polarized wave as shown in FIGS. 3 (b), (c), and (d). By detecting this via the conductive film 4, reception becomes possible. In particular, since this antenna circulates the notches (or slits) 5 loaded on the side AC and the side AD, circularly polarized radiation can be realized with a small structure.

In this embodiment, the reception of the left-handed circularly polarized wave has been described, but it goes without saying that it can also be used for transmission. In addition, this antenna can be realized for right-handed circularly polarized waves by substantially the same principle by changing the position of the feeding point. An example of this is shown in FIG.

In the case where the shape of the element is a fan shape, the antenna of Embodiment 1 was analyzed with respect to the vertical in-plane radiation directivity (f = 0 °) of the gain and the axial ratio by the measurement system as shown in FIG. As shown in FIG. FIG. 5 shows the result of numerical calculation using the moment method (MoM) and the measurement result using a prototype. It can be confirmed that circularly polarized radiation can be satisfactorily realized by the above method.

Note that the shape of the microstrip 2 is similar to that of the circularly polarized wave by selecting the position of the notch (or slit) 5 appropriately even when the length of the hypotenuse, interior angle, and arc is different from the sector shape. Radiation can be obtained. For example, when the sector-shaped inner angle is narrow (when the length of the arc is short), a notch (or slit) 5 is made in the arc in order to cause the same total current distribution as described above. An example of this is shown in FIG.

Note that the shape of the microstrip 2 is not limited to the above-mentioned sector shape, and may be a polygonal shape. As described above, if the notch (or slit) 5 can be appropriately adjusted according to the shape of the element, circularly polarized radiation can be easily obtained. An example in which the shape of the element is a triangle is shown in FIG.

The shape, number, and position of the notch (or slit) 5 can be adjusted as appropriate, and are not limited. If the notch is adjusted according to the size of the target microstrip antenna, circularly polarized radiation can be easily obtained. 8 and 9 show examples of realizing a circularly polarized wave element smaller in size than that in FIG. 1 on the basis of a sector shape. In this way, by using a plurality of notches (slits), if the wavelength is actively shortened for each of the two modes, a smaller circularly polarized microstrip antenna can be realized.

(Embodiment 2)
This embodiment is substantially the same as the first embodiment except that the active element 6 is formed instead of the microstrip notch (or slit) 5. FIG. 10 is a schematic perspective view of the microstrip antenna according to this embodiment.

As the active element 6, for example, a diode, a capacitor, a reactance, an inductance, or the like can be suitably used. As a result, the phase relationship of the current distribution can be controlled to realize sharing of right / left-handed polarization and linear polarization. In addition, since the frequency characteristics of the two modes can be directly controlled by the active element, a broadband circularly polarized antenna can be realized. Note that FIG. 10 shown above is an example applied to a fan-shaped microstrip antenna. As with the first embodiment, the shape of the element is not particularly specified.

(Embodiment 3)
This structure is substantially the same as in the first and second embodiments, but the connection relationship between the microstrip 2 and the power feeding means 1 is different. FIG. 11 is a schematic exploded perspective view of this antenna. As shown in the figure, this antenna is provided with another layer in a dielectric substrate, and a feeding microstrip line 7 and feeding means 1 are provided. The input impedance is adjusted according to the position of the microstrip line 8, and matching can be easily performed. By using this structure, the antenna can be easily realized with only a laminated structure. In addition, since the antenna unit and the power feeding unit can be disassembled, each of them can be partially maintained.

(Embodiment 4)
This structure is substantially the same as in the first and second embodiments, but the connection relationship between the microstrip 5 and the power feeding means 1 is different. FIG. 9 shows a schematic exploded perspective view of this antenna. As shown in FIG. 9, a feeding slot 8 is inserted into the conductive film 4, and another dielectric substrate is provided under the conductive film 4, and the feeding microstrip line 8, the feeding means 1, and further below it. The dielectric substrate 10 and the conductive film 11 are provided on the lowermost layer. Thus, the antenna can be easily manufactured only by stacking the substrates. Furthermore, in this embodiment, the power supply microstrip line 7 and the microstrip 2 as the radiation conductor can be electrically separated by the conductive film 4 as the ground conductor. As a result, unnecessary radiation from the power supply microstrip line 8 and unnecessary coupling between the element and the power supply line can be reduced, and power transmission loss can be reduced. The thickness of the dielectric substrate is appropriately adjusted according to the purpose. The shape and number of slits are not specified as long as energy can be efficiently transmitted to the radiation conductor. Similarly, the number and shape of the microstrip lines are not specified. FIG. 12 shows an example in which the microstrip line is linear and the slot 8 is cross-shaped. For example, in order to improve the characteristics of the axial ratio, the microstrip line may be arranged so as to go around a cross-shaped slot.

(Embodiment 5)
This structure is almost the same as in the first and second embodiments, but the structure of the microstrip 2 as a radiating element is different. FIG. 10 shows a schematic exploded perspective view of this antenna. As shown in FIG. 10, the difference is that a microstrip 9 as a dielectric substrate and a parasitic radiation element is laminated on the microstrip 2. The shape of the microstrip 9 is not particularly specified, but is preferably the same shape as the microstrip 2. By adopting such a structure, it is possible to expand the specific bandwidth in which circularly polarized light can be radiated even with a single power supply, and to improve the circularly polarized wave gain and the axial ratio. The thickness of the dielectric substrate is appropriately adjusted to obtain a desired gain and specific band characteristics.

Since the present invention has a thin, light, and robust structure and can be easily designed and prototyped, it can be installed in the interior of a car, roof, etc., such as a portable terminal, automobile, airplane, ship (boat), train, etc. It can be used as an antenna for applications using circular polarization.

Further, the communication microstrip antenna according to the present invention can be easily miniaturized, so that it can be applied as a terminal built-in antenna.

The communication microstrip antenna according to the present invention can be used not only for communication but also for receiving applications such as GPS and mobile satellite broadcasting.

In addition, the communication microstrip antenna according to the present invention is also suitable for an array structure in which several elements are arranged, and can be significantly reduced in size as compared to a microstrip antenna having a square or circular structure. .

Further, the communication microstrip antenna according to the present invention can be used for many applications such as mobile satellite communication, medical care, and disaster countermeasures. With this antenna, mobile satellite communications using portable terminals and mobile satellite broadcasting services including moving images can be implemented, and the Internet can be used in passenger cars.

1 is a schematic perspective view of a communication microstrip antenna according to Embodiment 1. FIG. FIG. 5 is a diagram for explaining the operation of the communication microstrip antenna according to the first embodiment. FIG. 5 is a diagram for explaining the operation of the communication microstrip antenna according to the first embodiment. FIG. 3 is a schematic perspective view of an example in which the characteristic analysis of the communication microstrip antenna according to the first embodiment is performed. FIG. 3 shows radiation characteristics of the communication microstrip antenna according to the first embodiment. FIG. 4 is a schematic perspective view of another example of a communication microstrip antenna according to the first embodiment. FIG. 4 is a schematic perspective view of another example of a communication microstrip antenna according to the first embodiment. FIG. 4 is a schematic perspective view of another example of a communication microstrip antenna according to the first embodiment. FIG. 4 is a schematic perspective view of another example of a communication microstrip antenna according to the first embodiment. 3 is a schematic perspective view of a communication microstrip antenna according to Embodiment 2. FIG. 4 is a schematic perspective view of a communication microstrip antenna according to Embodiment 3. FIG. 5 is a schematic perspective view of a communication microstrip antenna according to Embodiment 4. FIG. 6 is a schematic perspective view of a communication microstrip antenna according to Embodiment 5. FIG.

Claims (6)

A dielectric substrate;
Means for controlling the polarization formed on one side of the dielectric substrate;
A conductive film as a ground conductor formed on the surface opposite to the surface on which the microstrip of the dielectric substrate is formed;
A communication antenna comprising: a power feeding means for electrically connecting the microstrip and the conductive film. 2. The communication antenna according to claim 1, wherein the means is a notch or a slit or an active element. The communication antenna according to claim 1 or 2, wherein the microstrip has a sector shape with a notch or a slit. The communication antenna according to claim 1 or 2, wherein the microstrip has a circular fan shape with a notch or slit. The communication antenna according to claim 1, wherein the microstrip has a polygonal shape with a notch or a slit. The communication antenna according to claim 1, wherein the power feeding unit is formed near a center of gravity of the microstrip.