JPH0119642B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna that can control side lobes of the antenna in order to reduce interference from a certain direction. More specifically, the present invention relates to an antenna that uses a reflecting mirror and that can lower side lobes in a particular direction in an antenna that shares two or more frequency bands.

Taking the case of a conventional receiving antenna as an example, as shown in Figure 1, in addition to the main antenna, a sub-antenna is provided whose main radiation direction is directed toward the interference wave source, and the main antenna and the sub-antenna are connected to each other. By combining the interference waves received in such a way that they cancel each other out, the sidelobes of the main antenna in the direction of the interference wave source are apparently lowered.

That is, in FIG. 1, the interference wave received by the sub-antenna 2 whose main radiation direction is directed toward the interference wave source passes through the variable attenuator 3 and the variable phase shifter 4, and is transferred to the main antenna 1 by the combining circuit 5. The side lobe in the direction of the interference wave source is combined with the received interference wave. At this time,
If the variable attenuator 3 and the variable phase shifter 4 are adjusted so that the interference wave output becomes zero at the output 6 of the combining circuit 5, no interference wave will be output and only the desired wave will appear at the output 6.

However, in the configuration shown in Figure 1,
If the main antenna 1 is a multi-frequency band antenna of two or more, a sub antenna 2, a variable attenuator 3, a variable phase shifter 4, and a combining circuit 5 are provided for each frequency band, or the sub antenna 2 is also connected to the main antenna. As the same multi-frequency band antenna as in 1, it is necessary to install a variable attenuator 3, a variable phase shifter 4, and a synthesis circuit for each frequency band after splitting into each frequency band using a demultiplexer, resulting in a complicated configuration. Therefore, it had the disadvantage of being economically expensive. Furthermore, it is almost impossible to match the electrical lengths between the main antenna 1 and the combining circuit 5 and between the auxiliary antenna 2 and the combining circuit 5 over a wide band, and performance can only be obtained in a narrow band. Furthermore, when the direction of the interference wave source changes, it is necessary to change the direction of the sub-antenna 2 and readjust the variable attenuator 3 and variable phase shifter 4 for each frequency band. .

In order to solve these drawbacks, the present invention employs a reflective phased array antenna configuration for the secondary antenna, and installs the secondary antenna so that its aperture approximately coincides with a part of the inner surface of the reflector of the main antenna. A frequency-selective element is attached to the aperture of the phased array antenna, which allows only radio waves in the target frequency band to pass through and reflects radio waves in other frequency bands. By using part of the radio waves in the target frequency band, the direction of the interference wave source can be changed by eliminating the need for a synthesis circuit, and by controlling the phase shifter and attenuator in the phased array antenna. Even if there is a problem, it can be handled without moving the antenna.
The drawings will be explained in detail below.

FIG. 2 shows an embodiment of the present invention, in which the main antenna is a horn reflector antenna and the number of frequency bands for controlling side lobes is one. In the figure, 10 is a multi-frequency primary horn, 11 is a parabolic reflector, 12 is a sub-array antenna with a reflective phased array antenna configuration, and 12a is a channel through which radio waves in one frequency band pass and radio waves in other frequency bands are transmitted. It is a frequency-selective element that reflects most of the light, and is fitted into a cutout in a portion of the mirror surface so that it is almost flush with the mirror surface. 12b is a phase shifter, 12c is an attenuator, and 12d is a shorting surface for reflection, which are installed in a hierarchical manner on the selective element on the back surface of the reflecting mirror. FIG. 3 is a front view of FIG. 2.

In the figure, most of the multi-frequency radio waves emitted from the primary horn 10 are reflected by the parabolic reflector 11 and have the same phase at the aperture surface, forming a main beam in the front direction. On the other hand, the frequency selective element 12
The radio waves incident on A are reflected by this surface, except for the radio waves in one frequency band that pass through, forming the main beam.
2b, attenuator 12c, is reflected at short-circuit surface 12d, passes through attenuator 12c and phase shifter 12b again, and is reflected to the outside through frequency selective element 12a. By electronically controlling the phase shifter 12b and the attenuator 12c from the outside to give the radio waves the necessary phase shift and attenuation, it is possible to obtain the desired radiation directivity for the sub-array antenna 12. Further, when only the direction of radiation directivity of the sub array antenna 12 is changed, the attenuator 12c may be a fixed attenuator set in advance, or may not be used.

Therefore, in the frequency band where the side lobes are controlled, if you want to lower the side lobes in a certain characteristic direction in the radiation directivity from the parabolic reflecting mirror surface 11 other than the auxiliary array antenna 12 to avoid interference, the auxiliary array antenna This can be realized by directing the directional main beam in the direction of the side lobe, matching the amplitudes, and making the phases opposite to each other. The size of the sub array antenna 12 is determined by the direction and level of the side lobes of the main antenna to be lowered to avoid interference waves.
In a normal horn reflector antenna, the sidelobe level is approximately -20dB or less, so
The size of the sub-array antenna 12 can be made considerably smaller than the parabolic reflector 11, and there will be no problems in terms of configuration and structure.

FIG. 4 shows another embodiment of the present invention, in which the main antenna is a horn reflector antenna,
A case is shown in which there are two frequency bands for controlling side lobes. In the figure, reference numeral 13 denotes a sub-array antenna for controlling side lobes in a frequency band different from that of the sub-array antenna 12, and its configuration and operation are the same as those of the sub-array antenna 12. FIG. 5 is a front view of FIG. 4.

Therefore, in this case, in the radiation directivity of the main antenna in this frequency band, side lobes in the same direction or in different directions can be lowered to avoid interference waves.

As explained above, according to the present invention, the conventional system which required a sub-antenna in addition to the main antenna and a circuit for adjusting and synthesizing the amplitude and phase of the interference waves between the two antennas can be Even in the case of a frequency band shared antenna, by providing a sub-array antenna in a part of the parabolic reflecting mirror surface, using a frequency-selective element in its opening, and making this sub-array antenna a reflective phased array antenna, This eliminates the need for a circuit that adjusts and synthesizes the amplitude and phase, making it possible to lower the side lobe in the direction of the interference wave source in the frequency band corresponding to the frequency selective element, and when changing the direction in which you want to lower the side lobe. It is only necessary to electronically control the phase shifter and attenuator in the sub-array antenna from the outside,
There is an advantage that changing the installation direction of the antenna does not require any additional steps. Furthermore, even if the number of frequency bands to control side lobes increases, since the sub-array antenna is provided through the frequency-selective element, a sub-array antenna can be provided for each frequency band without affecting other frequency bands. Another advantage is that sidelobes in different directions for each frequency band can be lowered.

In addition, the frequency selective element of each sub-array antenna almost coincides with the parabolic reflecting mirror surface, which serves as the aperture of the sub-array antenna, eliminating the need for a feed line and further reducing the length of the phase shifter and attenuator. By making it even shorter, the frequency characteristics of the radiation waves from the sub-array antenna can be made close to the frequency characteristics of the main antenna, which has the advantage of providing broadband characteristics.

Although the above explanation has been given for the embodiment of a horn reflector antenna, it can also be applied to other types of antennas using reflectors, such as parabolic antennas, Cassegrain antennas, offset antennas, etc. , the same effect can be obtained.

In this way, the antenna device according to the present invention that can reduce interference waves has multiple frequency bands, can easily change the direction in which side lobes are desired to be lowered, and can obtain broadband characteristics, making it practical for practical use. is of great value.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional antenna device, FIG. 2 is a sectional view showing an embodiment of the antenna device according to the present invention, FIG. 3 is a front view of the antenna device shown in FIG. 2, and FIG. FIG. 5 is a sectional view showing another embodiment of the invention, and FIG. 5 is a front view of FIG. 4. 1...Main antenna, 2...Sub antenna, 3...
Variable attenuator, 4... Variable phase shifter, 10... Primary horn, 11... Parabolic reflector, 12, 13...
Sub-array antenna, 12a, 13a... frequency selective element, 12b, 13b... phase shifter, 12c,
13c...Attenuator, 12d, 13d...Short circuit surface.
It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Scope of Claims] 1. A primary horn that transmits or receives radio waves, a reflecting mirror that reflects radio waves facing the primary horn, and a part of the reflecting mirror surface that is provided substantially flush with the mirror surface. 1. An antenna device comprising a frequency selective element and a plurality of reflection type array elements each comprising a phase shifter, an attenuator, and a shorting surface attached to the selective element in a hierarchical manner. 2 A plurality of reflective array elements each consisting of a frequency selective element, a phase shifter, an attenuator, and a shorting surface are provided for each of two or more different frequency bands. An antenna device according to claim 1, characterized in that: