JPS63204902A - Cross polarization suppressing system - Google Patents

Abstract

PURPOSE:To suppress the occurrence of cross polarization in remote field directivity and beam diviation by using plural antenna elements as a primary radiator and adjusting the excitation polarization, amplitude and phase in an offset parabolic antenna. CONSTITUTION:In the offset parabola, the cross polarization can be suppressed by using the plural antenna elements as the primary radiator so as to adjust the excitation polarization, the amplitude and the phase because the structure is mechanically simple. For example, by altering the phase of the cross polarizations H1-H7 against main polarizations V1-V7 by 90 deg. and adjusting the excitation coefficient of the cross polarizations H1-H7 in the respective element antennas, the cross polarization in the remote field directivity of the offset parabolic antenna can be suppressed. Namely, the cross polarization in the remote field directivity can be suppressed by giving the cross polarization component opposite to the cross polarization component, which occurs in an offset parabolic reflective mirror R1, as the cross polarizatious H1-H7.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Technology The present invention relates to a cross-polarization suppression method in an offset parabolic antenna.

(2) Prior art In the past, in offset parabolic antennas, cross-polarized components were generated due to their mechanical structure, so offset Cassegrain and Offset Gregorian antennas were designed with sub-reflectors to satisfy cross-polarization cancellation conditions. has been used. Furthermore, when using an offset parabola, a reflector with a large ratio of focal length to reflector aperture diameter has been used, and a horn coupled with a higher-order mode has been proposed as a primary radiator.

However, the method using offset Cassegrain or offset Gregorian has a complicated mechanical structure;
In particular, the conditions are severe when considering installation on satellites, and when the primary radiator is configured with a large number of antenna elements to form a multi-beam, spillover from the sub-reflector increases, making it difficult to obtain good characteristics. There were drawbacks. In addition, the method using an offset parabola with a large ratio of focal length to reflector aperture diameter has the disadvantage of being long in depth due to its mechanical structure, making it difficult to install, especially when space is restricted, such as when mounted on a satellite. Ta. In addition, the method of using a feeding horn coupled with a higher-order mode as the primary radiator of an offset parabola has the drawbacks that it is difficult to obtain a free excitation amplitude and phase distribution in the horn, and that the horn diameter becomes large. The drawback was that it was not suitable for beam formation.

(3) Purpose of the present invention In order to eliminate these drawbacks, the present invention uses a plurality of antenna elements as primary radiators in an offset parabola that has a mechanically simple structure, and the excitation polarization, amplitude,
Cross polarization is suppressed by adjusting the phase.

(4) Detailed description of the present invention The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an offset parabolic antenna using a plurality of antenna elements as primary radiators. The offset parabolic antenna shown in the figure is composed of an offset parabolic reflector R1, a plurality of antenna elements E1 to E7 as primary radiators, a power divider or combiner P1, and an input or output terminal T1. In the example of Fig. 1, the primary radiator is composed of 7 elements, but it is not limited to 7 elements, it may be 4 elements, 19 elements, etc., and is not limited to this value. When considered as a transmitting antenna, the input signal from the input terminal TI is distributed by the power divider P1, given appropriate amplitude and phase, and then fed to each antenna element E1 to E7 to produce an offset parabolic reflection IRI. radiated.

Similarly, when considered as a receiving antenna, the signals input to each antenna element El-E7 via the offset parabolic reflector R1 are given appropriate amplitude and phase, and then combined by the power combiner P1, and the output terminal It is taken out from T1.

FIG. 2 is a configuration diagram of each antenna element in FIG. 1 in a normal embodiment in which cross-polarization suppression is not performed. In FIG. 2, E1 to E7 represent antenna elements as primary radiators, and 1 to v7 represent linearly polarized waves as main polarized waves for each antenna element.

In this conventional method, cross-polarized waves are generated due to the mechanical structure of the offset parabolic reflector R1 shown in FIG.

FIG. 3 shows a specific calculation example of far-field directivity when the antenna element configuration shown in FIG. 2 is used as a primary radiator, that is, when cross-polarization suppression is not performed.

Here, the offset parabolic reflection fiR1 has an offset angle of 48.3 degrees and a line-of-sight angle of 37.5 degrees.

In Figure 3, COI is the far-field directivity of the main polarization, CR1
represents the far-field directivity of cross-polarized waves.

In this case, it can be seen that a large cross-polarization of about -20 dB occurs.

FIG. 4 is a configuration diagram of each antenna element in FIG. 1 in an embodiment of the cross-polarization suppression method according to the present invention. In Figure 4, E1 to E7 are each antenna element as a primary radiator, ■1 to ■7 are linearly polarized waves as the main polarization of each antenna element, and Hl-H7 is added to suppress cross polarization. This is the cross polarization of each antenna element, and the main polarization v1~■
It represents a linearly polarized wave that is orthogonal to 7. In this embodiment, the cross-polarized waves H1 to H7 are changed in phase by 90 degrees with respect to the main polarized waves v1 to v7, and the excitation coefficients of the cross-polarized waves H1 to H7 are adjusted in each element antenna, thereby creating an offset parabolic antenna. The aim is to suppress cross-polarized waves in far-field directivity. In other words, the cross-polarization components opposite to the cross-polarization components generated in the off-cent parabolic reflector R1 in FIG. 1 are the cross-polarization components H1 to H1 in FIG.
7, it is possible to suppress cross polarization in far field directivity.

FIG. 5 shows a specific calculation example of far-field directivity when the antenna element configuration shown in FIG. 4 is used as a primary radiator, that is, when cross-polarization suppression is performed.

Here, an offset parabolic reflector R1 similar to that in Fig. 3 is shown.
Calculations are performed using . In FIG. 5, CO2 represents the far-field directivity of the main polarized wave, and CR2 represents the far-field directivity of the cross-polarized wave. In this case, the cross polarization level is -40dB
The cross polarization is about 20 dB compared to Figure 3.
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Furthermore, according to the present invention, since cross-polarized waves are suppressed using multiple antenna elements, the degree of freedom increases according to the number of elements, and the excitation amplitude and phase can be freely set, so cross-polarized waves can be suppressed reliably. be able to.

Furthermore, cross-polarized wave suppression is possible even when each antenna element El to E7 as a primary radiator is out of focus of the offset parabolic reflector R1 in FIG. 1, and multi-beam formation can be supported.

FIG. 6 is a configuration diagram showing an embodiment of circularly polarized wave excitation according to the present invention. In Figure 6, El-ET is each antenna element as a primary radiator, 01 to C7 is a circularly polarized wave of each antenna element as a main polarized wave, and linearly polarized waves C that are orthogonal and have a 90 degree phase difference. (2) Represents circularly polarized waves combined by 1 to CV7 and CHI to CH7. In the case of an offset parabolic antenna, circularly polarized wave excitation is shown in Figures 2 and 4.
Unlike the case of linearly polarized excitation as shown in the figure, a cross-polarized component does not appear in the far-field directivity, but instead a beam shift occurs. In this case, the linearly polarized excitation with cross-polarized wave suppression as shown in FIG. Beam deviation can be suppressed by adjusting the excitation coefficients of C1 to C7. In the case of circularly polarized wave excitation, the centers of the plurality of antenna elements E1 to E7 as primary radiators are offset parabolic reflection m.
It can be seen that if it is at the focus of R1, there is no need to newly add orthogonal polarization to each antenna element, and it is only necessary to control the excitation amplitude of the circular polarization, which is the main polarization. In addition, as in the case of linearly polarized excitation, beam deviation is suppressed using multiple antenna elements in circularly polarized excitation, so the degree of freedom increases according to the number of elements, and the excitation coefficient can be set freely. , beam deviation can be reliably suppressed. Furthermore, when the primary radiator is not at the focal point, multi-beam formation can be supported by controlling the excitation amplitude and excitation phase of each antenna element.

(5) Effects of the present invention As described above, according to the present invention, in an offset parabola, by using a plurality of antenna elements as primary radiators and adjusting their excitation polarization, amplitude, and phase,
It is possible to suppress the occurrence of cross-polarized waves and beam deviation in far-field directivity.

It should be noted that the offset parabolic antenna according to the present invention is not limited to being mounted on a rain leg, but can also be used in a ground antenna such as a broadcasting satellite receiving antenna. Further, an off-cent Cassegrain or an offset D'Agorian can be similarly used to suppress cross-polarization when the sub-reflector does not satisfy the cross-polarization cancellation condition.

[Brief explanation of the drawing]

Fig. 1 shows the configuration of an offset parabolic antenna using multiple antenna elements as primary radiators, and Fig. 2 shows each antenna element as a primary radiator in a normal embodiment without cross-polarization suppression. Figure 3 showing the configuration of
The figure shows an example of calculating far-field directivity when cross-polarization suppression is not performed, and 4th rgJ shows the configuration of each antenna element as a primary radiator in an embodiment of the cross-polarization suppression method according to the present invention. 5 shows an example of calculation of far-field directivity when cross-polarization suppression is performed according to the present invention, and FIG. 6 is a configuration diagram showing an example of circularly polarized wave excitation according to the present invention. . R1...offset parabolic reflector, E1 to E7--
Multiple antenna elements as primary radiators, Pl...
Power divider or combiner, Tl - - human power or output terminal, ■1 to v7 - - linear polarization component for each antenna element as main polarization, H1 to H7 - perform cross polarization suppression Cross polarization component for each antenna element, Cot --- Far field directivity of main polarization, CR1 ---
・Far-field directivity of cross-polarized waves, C02--Far-field directivity of main polarized waves, CR2...Far-field directivity of cross-polarized waves, C1
~C7---Circularly polarized wave component for each antenna element as the main polarized wave, CVI~CV7---One of the orthogonal linearly polarized waves with a different phase of 90 degrees for configuring the circularly polarized waves C1~C7, C
HI to CH7... - one side of linearly polarized waves with orthogonal 90 degree phase differences for configuring circularly polarized waves C1 to C7.

Claims (1)

[Claims] In an offset parabolic antenna composed of an offset parabolic reflector and a primary radiator, when the primary radiator is composed of multiple antenna elements and each antenna element is excited with linearly polarized waves, the main polarization of each antenna element is By adding a linearly polarized wave orthogonal to the wave and adjusting its excitation phase and excitation amplitude, cross-polarized waves caused by the mechanical structure of the offset parabolic antenna are reduced, and each antenna element is excited with circularly polarized waves. cross-polarization suppression method, characterized in that the beam deviation caused by the mechanical structure of the offset parabolic antenna is reduced by means of adjusting the excitation amplitude and excitation phase of each antenna element.