JPH0569322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a broadband antenna that provides a broadband antenna element with unidirectional antenna radiation characteristics.

(Prior Art) Conventionally, as this type of wideband antenna, for example, the one shown in FIG. 5 is known.

In FIG. 5, reference numeral 1 indicates an antenna electrode of a broadband antenna, for example, an antenna electrode of a two-striped planar Archimedean spiral antenna.

As the shape of the antenna electrode 1, a logarithmic spiral antenna, a logarithmic periodic antenna, and a wideband antenna having a self-complementary structure are also used.

Reference numeral 2 denotes a cavity, which is used to make the directional characteristics of the broadband antenna formed by the antenna electrode 1 unidirectional, and the inner wall surface of the cavity 1 is a good electrical conductor.

The function of this cavity 2 is that the radiation characteristic of the antenna electrode 1 itself is a bidirectional characteristic that radiates to both sides of the antenna electrode surface 1a. Therefore, the antenna directivity is made unidirectional.

For example, in Figure 5, the wave traveling into cavity 1 is almost completely reflected because there is almost no loss within the cavity, resulting in an antenna directivity characteristic that is unidirectional in the direction shown by arrow 3. It will be done.

By the way, it is widely known that the radiation characteristics of a broadband antenna equipped with a cavity are determined by the interference between the direct wave radiated directly into free space from the antenna electrode 1 and the indirect wave re-radiated from the cavity 2. It is being In other words, at frequencies where the depth of cavity 2 is an odd multiple of 1/4 wavelength of the antenna excitation wavelength, direct waves and indirect waves constructively interfere with each other in the direction in front of the antenna as shown by arrow 3. It generates a radiation pattern with a narrow beam width and a peak in the direction. Furthermore, at frequencies where the cavity depth is an even multiple of a quarter wavelength, direct waves and indirect waves interfere to cancel each other out, producing a so-called conical pattern with a gain peak in a direction other than the front direction of the antenna.

(Problems to be Solved by the Invention) However, in the case of a conventional wideband antenna equipped with such a cavity, especially a wideband antenna equipped with a cavity 2 that serves as a lossless reflector as shown in FIG. As mentioned above, strong interference between direct waves and indirect waves occurs, so the antenna radiation pattern exhibits strong frequency dependence, and is suitable for applications where the shape of the radiation pattern must be kept approximately constant over a wide band. The problem was that I couldn't use it.

This problem is caused by the existence of the cavity itself, and therefore cannot be solved no matter how wide-band characteristics the antenna element exhibits. In reality, with the structure shown in FIG. 5, the limit for maintaining a substantially constant radiation pattern is one octave.

On the other hand, fill cavity 2 with a radio wave absorber,
Another possible method is to absorb all the energy traveling inside the cavity and eliminate indirect waves.

However, in this case, although the radiation pattern can be maintained approximately in the same shape over several octaves, another problem occurs in that the antenna gain is significantly reduced due to absorption.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems in the prior art. The purpose is to provide a broadband antenna that can maintain a pattern.

In order to achieve this objective, the present invention includes:
Abbreviation of the depth of the cavity 2 converted to the equivalent electrical length from the aperture of the cavity 2 to the bottom in a wideband antenna that provides antenna radiation characteristics in a single direction to the broadband antenna element 1 placed on the aperture of the cavity 2 Plate-shaped electric field absorption type radio wave absorbers 4 and 5 are loaded at a position of 1/2N (where N is a positive integer).

(Function) According to the configuration of the present invention, since the plate-shaped electric field absorption type radio wave absorber is mounted at the position of 1/2 of the cavity depth given by the equivalent electrical length, for example, 1 The maximum amplitude part (antinode part) of the standing wave generated by the /2 wavelength resonance is the position where the electro-absorption type radio wave absorber is placed, and therefore the maximum radio wave absorption effect is obtained, and the cavity due to the half wavelength resonance is It is possible to attenuate and absorb the indirect waves to such an extent that it does not affect the radiation pattern caused by the unidirectional direct waves.

This point also applies to 1/1 wavelength resonance, which is an integer multiple of 1/2 wavelength resonance.
By loading an electro-absorption type radio wave absorber at position 4, the maximum radio wave absorption is achieved at one wavelength resonance, and the unidirectional radiation pattern is maintained approximately constant over a wide frequency band. can.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention.

First, to explain the configuration, 1 is an antenna electrode, 2
is a cavity, and as the antenna electrode 1, for example, as shown in FIG. 5, a two-strand planar Archimedean spiral antenna, a multi-strand log spiral antenna, a log-periodic antenna, or another antenna with a self-complementary structure is used. .

The inner wall surface of the cavity 2 is a good electrical conductor, and the waves traveling from the antenna electrode 1 into the cavity 2 are almost completely reflected because there is almost no loss within the cavity 2.

Reference numeral 4 denotes a resistor sheet as an electric field absorption type radio wave absorber provided in the cavity 2 at a position d/2 with respect to the cavity depth d. Further, 5 is a resistor sheet serving as an electric field type radio wave absorber, and this resistor sheet 5 is provided at a position approximately d/4 of the cavity depth from the bottom surface of the cavity.

That is, in the present invention, a plate-shaped electric field absorption type radio wave absorber is placed at a position approximately 1/2N of the cavity depth d (where N is a positive integer such as 1, 2, 3, 4, etc.),
That is, since it is basically the case that a resistor sheet is installed, in the embodiment shown in FIG. It is installed at the /4 position.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, in the broadband antenna equipped with the cavity of the present invention, in order to maintain the radiation pattern of the antenna, which has been made unidirectional by the cavity, substantially constant over a wide frequency band, half-wavelength resonance must be generated within the cavity 2. It is important to avoid this. That is, the present invention requires a structure that selectively absorbs energy at frequencies where the cavity depth is an integral multiple of a half wavelength.

FIG. 2 shows the electric field distribution of the standing wave 6 when half-wavelength resonance occurs within the cavity 2 shown in the embodiment shown in FIG. As is clear from the standing wave 6 generated within the cavity by this half-wavelength resonance, there is an antinode portion where the amplitude of the standing wave 6 is maximum at a position of 1/2 of the cavity depth d. Resistor sheet in position 4
is provided. Therefore, the resistor sheet 4 exhibits the maximum radio wave absorption effect for the standing wave 6 generated at half-wavelength resonance, and by appropriately selecting the surface resistance value of the resistor sheet 4, By absorbing and attenuating indirect wave components, the influence on the radiation pattern can be suppressed to a level that does not pose a practical problem.

Furthermore, Fig. 2 shows a standing wave 7 generated by one-wavelength resonance, which is twice the half wavelength.
The resistor sheet 4 placed at a position half of
Since the resistor sheet 5 is placed at a position that is 1/4 of Since the sheet 5 exhibits the maximum radio wave absorption for the standing wave 7 of one wavelength resonance, the influence of the standing wave 7 caused by one wavelength resonance on the antenna pattern can be suppressed to a level that does not pose a practical problem.

Figure 3 shows 1/4 wavelength in cavity 2 of the present invention.
This shows standing waves when resonance occurs at a wavelength that is an odd number multiple of that wavelength, and standing wave 8 shows 1/4 wavelength resonance, and standing wave 9 has 3 times the 1/4 wavelength. The case of /4 wavelength resonance is shown.

In this case, the antinode portion of the standing wave 8 or 9 having the maximum amplitude is shifted from the position of any of the resistor sheets 4 and 5, and therefore does not exhibit a large absorption effect.
Of course, the resistor sheets 4 and 5 exhibit a slight absorption effect on the standing waves 8 and 9, but this absorption weakens the emphasis on the direct waves and indirect waves and minimizes the beam width. This is advantageous in maintaining the characteristics of the antenna pattern, which suppresses fluctuations in the antenna radiation pattern and maintains it substantially constant.

Here, in the embodiment shown in FIG. 1, the arrangement of the resistor sheets 4 and 5 that produces an absorption effect for the half-wavelength resonance or one-wavelength resonance shown in FIG. 2 was taken as an example; When used up to this range, a resistor sheet may be similarly placed at a position corresponding to the antinode of the maximum amplitude of the standing wave generated in the cavity at the operating frequency.

In other words, in resonance that is an integer multiple of 1/2 wavelength, that is, N/2 wavelength resonance, N standing waves are generated in the cavity 2, and the position of the antinode of the maximum amplitude of this standing wave is at the depth of the cavity. It can be placed in the position m・d/2N (where m is a positive integer such that m≦N) for the distance d.

Also, when N = 2 or more, m = 2 or more, so the positions of the antinodes that give the maximum amplitude of the standing wave exist at multiple locations in the cavity, but the resistor sheet is placed on the side closer to the antenna electrode 1. When placed, it causes a loss to the current flowing on the antenna electrode 1, so
It is desirable to arrange the resistor sheet as far away from the antenna electrode 1 as possible. In this way, if there are multiple positions for placing the resistor sheet due to N/2 wavelength resonance within the cavity, the antenna gain can be reduced by placing the resistor sheet as far away from the antenna electrode 1 side as possible. can be kept to a minimum.

FIG. 4 is a sectional view showing another embodiment of the present invention, in which the resistor sheet 4 shown in the embodiment of FIG.
Since the material 5 is extremely thin, its mechanical strength may be insufficient by itself.

Therefore, in the embodiment shown in FIG. 4, mechanical strength can be ensured by filling the space between the resistor sheets 4 and 5 with a dielectric material 10.

When the resistor sheets 4 and 5 are embedded in the dielectric 10 in this way, the position of the antinode that gives the maximum amplitude of the standing wave generated in the cavity due to half-wave resonance or resonance with a wavelength that is an integral multiple thereof is determined. changes due to the presence of the dielectric 10, the positions of the resistor sheets 4 and 5 are approximately 1/2N of the cavity depth expressed in electrical length (however, the positive value of N=1, 2, 3,...) will be placed at the position (an integer of ).

Further, as the dielectric material 10 for embedding and fixing the resistor sheets 4 and 5, a foam such as urethane foam, a honeycomb structure, or the like can be used, so that the weight of the antenna itself increases only slightly.

Furthermore, it has been experimentally confirmed that in the embodiment of the present invention shown in FIGS. 1 and 4, the shape of the antenna radiation pattern can be kept substantially constant over a wide frequency band of nearly three octaves. There is.

(Effects of the Invention) As described above, according to the present invention, in a wideband antenna that provides antenna radiation characteristics in a single direction to the broadband antenna element 1 disposed on the aperture of the cavity 2, from the aperture of the cavity 2 to the bottom. Cavity 2 converted to equivalent electrical length up to
Because the plate-shaped electromagnetic wave absorbers 4 and 5 are loaded at approximately 1/2N of the depth (N is a positive integer), there is little change in the antenna radiation pattern over a wide frequency band. It is possible to realize antenna characteristics, and at the same time, it is possible to minimize the decrease in antenna gain due to the radio wave absorber installed inside the cavity.Furthermore, the radio wave absorber installed inside the cavity is made of a very thin resistor sheet, etc. Therefore, the weight of the cavity can be reduced, and even if the absorber is embedded and fixed with a dielectric material such as urethane to ensure mechanical strength, urethane foam or honeycomb is used as the dielectric material. , the mechanical strength can be increased without significantly increasing the weight of the cavity.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG. 2 is a half-wavelength resonance and one-wavelength resonance in the embodiment of FIG.
An explanatory diagram showing each standing wave of wavelength resonance, Fig. 3 is an explanatory diagram showing standing waves of 1/4 wavelength resonance and 3/4 wavelength resonance in the embodiment of Fig. A sectional view showing another embodiment of the invention, and FIG. 5 is an explanatory view showing a conventional example. 1: antenna electrode, 2: cavity, 4, 5:
Resistor sheet (electromagnetic wave absorber), 6:1/2
Standing wave with wavelength resonance, standing wave with 7:1 wavelength resonance,
8: Standing wave with 1/4 wavelength resonance, 9: Standing wave with 3/4 wavelength resonance, 10: Dielectric material.

Claims (1)

[Claims] 1. In a wideband antenna that provides antenna radiation characteristics in a single direction to a wideband antenna element 1 placed on the aperture of the cavity 2, the length is converted into an equivalent electrical length from the aperture of the cavity 2 to the bottom surface. A broadband antenna characterized in that plate-shaped electromagnetic wave absorbers 4 and 5 are loaded at positions approximately 1/2N of the depth of the cavity 2 (where N is a positive integer).