JPH0377405A - Plane antenna - Google Patents

Abstract

PURPOSE:To obtain a plane antenna of even the inner exciting type with a sufficient efficiency by selecting a coupling coefficient for external radiation higher toward the outer circumference and lower toward the center. CONSTITUTION:A waveguide for the axially symmetrical mode propagation is formed between a an upper disk (radiation disk) 12 and a lower disk 14 and a coaxial cable 16 is connected to the center of the lower disk 14. A radiation slot pair 20 comprising two radiation slots (coupling slots in the case of reception) 20A, 20B arranged on the upper disk 12 so as to be orthogonal spacially and electrically in spiral to the radiation face. Then the length of the radiation slots 20A, 20B, a distance Sr of the radiation slot pair 20 adjacent in the radial direction, a circumferential interval Sa and the thickness of the waveguide or the like are adjusted to make the coupling coefficient higher toward the outer circumference and lower toward the center. Thus, a comparatively flat aperture distribution is obtained and the practical plane antenna of the inner excitation type with a high efficiency is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a planar antenna, and more specifically to a planar antenna called a radial line slot antenna that is excited in an axially symmetric mode.

[Prior art] Regarding radial line slot antennas, there are various documents (for example, Hideo Sasazawa, Makoto Ando, and Naohisa Goto, "Radial line slot antenna arrangement and improvement of efficiency," Institute of Electronics and Communication Engineers IEICE Technical Report, AP86-106), patent application publication No. 57-87603, 60-199201, 6
No. 0-199202, No. 60-199203, 60-2
00602, Heisei 1-46305, etc.

The axially symmetric mode excitation planar antennas described in these publications had a two-layer structure exclusively comprising two propagation layers.

In other words, a radio wave from a power source is supplied to the center of the lower propagation layer, propagated through the lower propagation layer radially outward, guided to the upper propagation layer at the end, propagated within the upper propagation layer toward the center, and then propagated to the upper propagation layer. Radio waves were radiated through a large number of slots during the propagation process through the layers. Circular polarization or linear polarization was determined by the slot arrangement. In such a two-layer structure, radio waves propagate from the outer periphery to the center in the radiation layer (that is, the upper propagation layer) provided with the radiation slot surface. When a radio wave with axially symmetric mode excitation propagates from the outer periphery to the center in this way, the internal electromagnetic field f(r) is f(r) = Aexp ((α+ j k ) r )
It is expressed as /f r. A is a proportionality coefficient, k is a propagation constant, r is a radius, and α is a proportionality coefficient of power radiated per unit length in the radial direction. α is a positive value and is called a coupling coefficient.

On the other hand, the aperture power distribution U(r) at the position of radius r is U (r) = αf2(r) = αexp(2αr)/r, and since α is positive, The configuration is such that it is theoretically easy to obtain an aperture power distribution close to that of the

In addition, the remaining radio waves that are not radiated are absorbed by the central absorbing material, but the cross-sectional area in the direction of radio wave propagation is small near the center, so the amount of radio waves that must be absorbed is small, which increases efficiency. It is true.

[Problems to be Solved by the Invention] However, such a two-layer structure has the drawback that it is extremely difficult to manufacture. That is, it is necessary to maintain the plate material that separates the upper propagation layer and the lower propagation layer so that it does not interfere with radio wave propagation, and it is also necessary to maintain the layer widths of the upper propagation layer and the lower propagation layer at a predetermined value. be.

From this manufacturing point of view, a one-layer structure that emits radio waves in the process of propagating from the center to the outside in the radial direction is advantageous, but when axisymmetric excitation is performed with such a 1@ structure, The feeding radio waves propagate radially outward from the center, and radio waves are radiated little by little during the propagation process. In addition, in this specification, an axially symmetric mode excitation planar antenna in which the excitation radio wave propagates from the outer periphery to the center within a propagation layer having a radiation emitting surface is referred to as an external feeding type (or external excitation type). The one that propagates from the center to the outer periphery is called the inside feeding type (or inside excitation type).

In the inner excitation type, contrary to the case of the above-mentioned two-layer structure, that is, the ambient feeding type, the internal electromagnetic field f(r) in the waveguide is f(r)=Aexp (-(α+ j k ) r
Even if there is no radiation by the radiation slot (α=0), it is very large at the center and becomes weaker toward the periphery. In addition to this, there is radiation from the radiation slot (α>O), so the electromagnetic field weakens more rapidly toward the outside. Therefore, in such an inside excitation type, it has been thought that it is extremely difficult in principle to make the aperture distribution uniform in the radial direction.

Furthermore, the remaining radio waves that are not radiated are absorbed by the outer peripheral surface to avoid reflection, but the cross-sectional area becomes extremely large compared to the case of the external feeding type.

Since this absorption results in loss, it was theoretically thought that the efficiency of the internal excitation type would be extremely low. For this reason, it has traditionally been thought that it is extremely difficult or impossible to obtain a highly effective and practical planar antenna with the inside excitation type. It is also an area where research into formulas is active.

However, the inventor of the present invention returned to the origins of antenna theory and discovered that it is possible to design a sufficiently efficient planar antenna even with an internal excitation type antenna.

That is, an object of the present invention is to provide an internally excited planar antenna.

[Means for Solving the Problems] The planar antenna according to the present invention is a planar antenna in which radio waves fed to the center are radiated to the outside while propagating in the direction of the outer periphery, and the coupling coefficient of external radiation is I made it higher at the outer periphery and lower at the center. In addition, a region without coupling with the outside was provided at the center of the antenna surface.

Another invention is a planar antenna for circularly polarized waves, in which a spiral slot is provided in the antenna surface of the terminal portion of the axially symmetrical mode waveguide member, and the axially symmetrical mode waveguide member is provided with a spiral slot along the spiral slot. A reflecting member was provided between the inside and outside of the device to reflect radio waves through the spiral slot.

[In the case of central power supply, the internal electromagnetic field is extremely strong in the center,
Although it becomes weaker rapidly toward the periphery, by making the coupling coefficient higher at the outer periphery and lower toward the center as described above, a relatively flat aperture distribution can be obtained. Further, if a non-coupling region is provided in the central portion, the long line effect will be suppressed and the band width will be widened, but on the other hand, the antenna gain will be reduced due to the decrease in the antenna area. However, the increase in bandwidth is more remarkable than the decrease in antenna gain, and more favorable characteristics as an antenna can be obtained.

By using the spiral slot and the reflecting member, the radio wave at the end can be reflected to the front of the antenna while minimizing or substantially eliminating reflection into the inside of the waveguide. Since the spiral slot radiates radio waves that are in phase with the circularly polarized radio waves radiated up to the end, it is possible to effectively utilize the power that would be absorbed when an absorber is used.

[Example code] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view of a circularly polarized planar antenna according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1, and FIG.
The figure is a cross-sectional view taken along line B-B of the construction drawing. In the planar antenna 10 of the illustrated embodiment, a waveguide for axially symmetric mode propagation is formed between a circular upper plate (radiation plate) 12 and a circular lower plate 14.

The upper plate 12 and the lower plate 14 are made of a conductive material, or at least their inner surfaces are coated with a conductor. Top plate 1
2 and the lower plate 14 may be filled with air or a predetermined dielectric material. The distance between the upper plate 12 and the lower plate 14 is determined by a filled dielectric, a member (not shown), or a gap between the upper plate 12 and the lower plate 14.
It is held at regular intervals by its own strength. Lower plate 1
A coaxial cable 16 is connected to the center of the upper plate 12, and a matching reflector 18 is provided at the center of the inner surface of the upper plate 12 (the surface facing the lower plate 14) to direct the radio waves of the coaxial cable 16 outward in the radial direction.
is installed. The matching reflector 18 only needs to have at least its surface as a radio wave reflecting surface.

As a structure for guiding the radio waves of the coaxial cable 16 to the waveguide between the upper plate 12 and the lower plate 14, in addition to the matching reflector 18, a structure as shown in FIGS. 10 and 11 may be used. 10th
A theoretical explanation of the structure shown in the figure can be found, for example, in Natori, Ando, and Goto, "Probe Type Coaxial-Radial Waveguide Converter J, 1989 IEICE Autumn National Conference.

On the upper plate 12, two radiation slots (combined slots in the case of reception) 2OA and 20B arranged so as to be spatially and electrically orthogonal are arranged as a pair, and such a radiation slot pair 20 is provided on the radiation surface. It is arranged in a spiral. For reference, this spiral line is shown as a broken line in FIG.

It is known that when arranged in this way, circularly polarized waves of the same phase can be obtained in front of the antenna (see the above-mentioned literature). As explained above, the axially symmetrical mode radio wave propagating through the waveguide formed by the upper plate 12 and the lower plate 14 has the following formula for the radius r: f(r)=Aexp (-(a + j k) r) /r
It changes with r.

The present inventor has investigated various parameters of the radiation slots 2OA and 20B, specifically the lengths of the radiation slots 2OA and 20B, the distance Sr between the radially adjacent radiation slot pairs 20, the circumferential spacing Sa, and the waveguide thickness ( In other words, it has been discovered that by adjusting the distance between the plates 12 and 14, etc., the coupling coefficient α can be adjusted while maintaining the uniformity of the aperture surface electric field distribution. For example, in the case of an internally fed planar antenna with a diameter of 60 cm, if the coupling coefficient α is varied with respect to the radius r as shown in Fig. 4, a −-like aperture distribution can be theoretically obtained within the allowable range. In order to obtain such a coupling coefficient distribution, the lengths of the radiating slots 2OA and 20B are changed with respect to the radius r as shown in FIG. 5, and the distance between the radially adjacent pairs of radiating slots 20 is What is necessary is to change Sr with respect to the radius r as shown in FIG. Figures 4, 5 and 6
The horizontal axis in the figure is the radius, the vertical axis in FIG. 4 is the coupling coefficient α, the vertical axis in FIG. 5 is the slot length, and the vertical axis in FIG. 6 is the radial spacing Sr between the pairs of radial slots.

The coupling coefficient α theoretically obtained by such numerical calculations
However, it is found that the results are in good agreement with the actual experimental values, Hosou Nibu, Makoto Ando, and Naohisa Goto, "Analysis of the coupling between a radial waveguide and a slot using a periodic structure model," Institute of Electrical Engineers of Japan, Electromagnetism Study Group Materials, May 27, 1989. Reported on a daily basis.

There are radio waves that propagate from the center toward the outer periphery, and during the propagation process, they remain without being radiated to the front. Although such residual radio waves may be absorbed by an absorbing material, it is preferable to radiate them efficiently to the front of the antenna, as explained below. In other words, from the knowledge of externally fed, or two-layer, planar antennas, it is known that the reflector on the approximately 45-degree slope allows radio waves to be reflected in the front direction of the antenna, with almost no reflection in the opposite direction. . Therefore, in this embodiment, a reflective material 22 is arranged around the outer circumference of the planar antenna 10 to direct the propagating radio waves toward the front, and a slot 24 is provided in the upper plate 12 to radiate the reflected radio waves from the reflective material 22 toward the front. has been established. However, the radio waves radiated by the slot 24 must also be in phase with the radio waves radiated by the slot pair 20, and in this embodiment, the slot 24 is a slot extending along the spiral line of the slot pair 20. The slot 24 may be, for example, one slot spanning 360 degrees in the angular direction, as shown in the drawing. A reflective material 22 is arranged along this slot 24.

It is already known that circularly polarized radio waves are emitted from spirally extending slots, but because it is difficult to finely adjust the amount of emitted radio waves, radiation from multiple slots was considered. There is a history. In the slot 24 of this embodiment, since it is not necessary to adjust the amount of radiation by the slot 24 and it is sufficient to radiate all the radio waves by the reflecting material 22, the slot 24 may have a width corresponding to this. The termination structure with the reflector 22 and the slot 24 is applicable only in the case of circularly polarized waves, and not in the case of linearly polarized waves. Furthermore, although the effect obtained is small, the termination structure with the reflector 22 and the slot 24 can also be applied to an externally fed planar antenna. In this case, a spiral slot in the center of the radiation layer and a reflection materials will be placed.

For linearly polarized waves, the remaining radio waves that are not radiated may be absorbed by a radio wave absorbing material.

As shown in FIG. 4, the coupling coefficient α may be very small in the central portion of the antenna plane. As an extreme case, if the radiation slots 2OA and 20B are not provided in the central part of the antenna surface, the coupling coefficient α in that part becomes zero. Therefore, as a second embodiment of the present invention, the center of the antenna surface is
It is proposed that the area be a non-radiating area that does not include the radiating slots 2OA and 20B. FIG. 7 shows a front view of the second embodiment. A non-radiation area of radius r is provided at the center of the antenna surface,
Radiation slots 2OA and 20B are provided on the outer circumferential side thereof so as to have the coupling coefficient distribution shown in FIG. As a result, the coupling coefficient α is completely zero up to the radius r, as shown in FIG. 8, and becomes the same curve as in FIG. 4 between the radius r and the radius R.

The antenna gain G is the area S of the radiation surface, that is, the antenna radius R
On the other hand, the bandwidth B is approximately inversely proportional to the propagation distance of the waveguide, that is, the antenna radius in the case of an axially symmetrically excited planar antenna. The latter is due to the so-called long line effect, in which the longer the line length, the narrower the frequency band.

FIG. 9 shows the antenna radius R and the radius r of the non-radiation area,
This is a graph illustrating the relationship between the bandwidth B and the gain G. Since the antenna area is reduced due to the non-radiating region, the gain G is slightly reduced, but the radio wave propagation distance is reduced from R to (R-r
), and the band width becomes wider due to the long line effect.

In other words, to compensate for the decrease in gain G due to the provision of a non-radiating region, the antenna radius R should be increased so that the radiation area increases by πr2, but even with this increased antenna radius, the radio wave propagation distance (line long) is the initial value (R
), and therefore a larger bandwidth B can be obtained. For example, if the diameter is 60 cm, the radius r = 1
If a non-radiating area of 0 cm is provided, the gain is approximately 0.5 dBL.
The bandwidth is increased approximately 13 times without any loss in performance.

The disadvantage of having such a non-radiating region is that the main lobe is slightly lowered and the odd-numbered sidelobes are slightly increased, but these disadvantages are outweighed by the advantage of increased bandwidth. isn't it. .

In Fig. 8, the coupling coefficient changes stepwise to the characteristic curve shown in Fig. 4 at the contact point between the non-radiating region and the radiating region, but such a rise in side lobes causes the coupling coefficient to change gradually. Therefore, it is not necessarily necessary to change the coupling coefficient α stepwise at the boundary between the non-radiating region and the radiating region as shown in FIG. 8, but gradually from the boundary as shown in FIG. The characteristic curve may be made to approach the characteristic curve of

Note that the configuration in which a non-radiating region is provided at the center of the antenna surface as shown in Figure 7 can be applied to general planar antennas with internal excitation in an axially symmetric mode, and is not limited to types of polarization such as circularly polarized waves and linearly polarized waves. .

To summarize the above, in the internal feeding system, the strong electromagnetic field in the center is a major factor that prevents the formation of a -like aperture distribution, but in the present invention, by changing the coupling coefficient in the radial direction, It was shown that a flat aperture distribution can be obtained.

Various shapes and arrangements of the radiation slots have been proposed, for example, as described in the above-mentioned publications, but the present invention, which is characterized by changing the coupling coefficient in the radial direction, is based on the above-mentioned publications. It goes without saying that the invention is also applicable to the various shapes and arrangements of the radiation slots described. In addition, by making the central part of the antenna surface a non-radiating area, the influence of the strong internal electromagnetic field in the central part on the aperture distribution can be significantly reduced or eliminated, which not only makes it easier to obtain a flat aperture distribution, but also makes it possible to The width can also be expanded.

In the case of circularly polarized waves, there is a spiral slot 2 on the outer periphery.
4 and the reflective material 2.2 along the slot 24, the radio waves that propagate from the center to the outer periphery and remain without being radiated to the outside can be efficiently radiated to the front of the antenna as circularly polarized waves. Therefore, very high efficiency can be expected.

Although the case of emitting radio waves, that is, the case of transmission, has been explained as an example, the same argument holds true in the case of receiving radio waves due to the antenna reciprocity theorem. The scope of the claims should also be understood as such.

[Effects of the Invention] As can be easily understood from the above description, according to the present invention, it is possible to provide a highly efficient single-layer planar antenna with an axially symmetrical excitation mode. Since only one radio wave propagation layer is required, the antenna can be manufactured at a lower cost than a two-layer planar antenna that is externally powered. In addition, in a circularly polarized planar antenna with a one-layer or two-layer structure, unradiated radio waves can be efficiently radiated by the spiral slot and the reflective member placed along it, providing a planar antenna with higher efficiency. can.

[Brief explanation of drawings]

FIG. 1 is a front view of an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1, FIG. 3 is a cross-sectional view taken along line B-B in FIG. 1, and FIG. The distribution diagrams of the coupling coefficient α to obtain a flat aperture distribution, FIGS. 5 and 6, respectively show the slot length and slot spacing Sr to obtain the coupling coefficient distribution of FIG. 4.
7 is a front view of a modified example in which a non-radiation region is provided in the center of the antenna surface, and FIG. 8 is a distribution diagram of the coupling coefficient α when a portion with a radius of 10 cm is set as a non-radiation region. Figure 9 is a characteristic diagram of gain G and bandwidth B, Figure 10 and
Figure 1 shows another example of the structure of the central power feeding section. 10: Planar antenna (example) 12: Upper plate 14: Lower plate 16: Coaxial cable 18: Matching reflector 2OA,
20B: Radiation slot 20: Radiation slot pair 22:
Reflective material 24: Spiral slot

Claims (5)

[Claims] (1) An axially symmetrical mode waveguide, a receiving or transmitting radio wave connection means connected to the center of the axially symmetrical waveguide, and an axially symmetrical waveguide such that the coupling coefficient is high at the outer periphery and lower at the center. A planar antenna characterized in that it comprises a plurality of coupling slots formed and arranged on one side of the means. (2) Claim No. 1 (1) characterized in that an area without the coupling slot is provided in the center of the antenna surface.
) The planar antenna described in section 2. (3) A planar antenna for circularly polarized waves, which includes an axially symmetrical mode waveguide member in which an axially symmetrical mode is excited, and a spiral slot provided in the antenna surface of the terminal portion of the axially symmetrical mode waveguide member. A planar antenna, characterized in that a reflecting member is disposed along the spiral slot and reflects propagating radio waves between the inside and outside of the axially symmetric mode waveguide member. (4) The planar antenna according to claim (3), wherein the axially symmetrical mode waveguide member is a one-layer waveguide in which transmitted radio waves propagate from the center toward the outer periphery. (5) The axially symmetrical mode waveguide member includes a first waveguide layer in which the transmitted radio waves propagate from the center toward the outer periphery, and a second waveguide layer in which the radio waves in the first waveguide layer propagate from the outer periphery toward the center. The planar antenna according to claim 3, wherein the spiral slot and the reflective member are arranged at the center of the second waveguide layer.