JPS5928282B2 - Frequency band shared radar antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a radar antenna consisting of a rotationally symmetrical reflector system and a primary radiator system, and is capable of tracking the direction of arrival of radio waves of arbitrary polarization emitted from a tracking target. The present invention relates to a radar antenna that shares another frequency band and has a primary radiator system using a cross dipole antenna as an element antenna.

Conventional antennas for this purpose are Gregorian type antennas, as shown in Figure 1, in which a five-horn antenna is used as the primary radiator system in the tracking frequency band, and the output of the four surrounding horns is are synthesized by a signal processing circuit as shown in internal factor C, and the Az plane, IIJ? In addition to extracting the tracking angle signal of the surface, there was an antenna that placed a cross dipole antenna on the sub-reflector surface as shown in the figure, and used it for other frequency bands as well.

In this type of antenna, the outputs of the horns A, B, C, D, and S of the five horns 3 shown in Figure 1 are combined by a hybrid circuit 6, 6/ as shown in Figure C. AZ direction, EA? A direction angle signal is obtained from one Az terminal.

Next, the phase of the signal at the E717 terminal is changed to 90 by the phase shifter 7.
The signal from the Az terminal is combined with the signal from the Az terminal by the hybrid circuit 6'', and amplified by one receiver 8.

The real part of the signal appearing at the Err terminal is used as a tracking angle signal in the Az direction, and the imaginary part is used as a tracking angle signal in the E7 direction.

In order to track radio waves of arbitrary polarization arriving from the tracking target, solid-liquid long plates 4, 4' and a one-wavelength plate 5 are provided after the horn 11, A, B, C, D, and S. , connect the seven-wavelength plates 4 and 4' to the horn A so that the signals 1 and 1 appearing at the Sum terminals are maximized.

B, C, D, and S rotate by the same amount at the same time.

An antenna with this structure has the advantage of requiring only one receiver, but since the phase of the signal appearing at the Az and El terminals varies depending on the change in the polarization direction of the incoming radio wave, the phase of the signal appearing at the Err terminal changes. The phase of the signal changes,
For example, even though there is actually no signal at the El terminal, an imaginary part appears in the signal at the Az terminal, so that an apparent tracking angle signal in the E1 direction is detected.

There was a drawback that so-called cross-coupling was observed, making the tracking operation unstable.

In order to eliminate such drawbacks, this invention arranges the cross dipole on the sub-reflector as shown in FIG.
One of the elements is parallel to the plane that includes the center of each element horn that extracts the tracking signal and the central axis of the reflector system, and its purpose is to create a frequency band radar antenna that does not cause cross-coupling. The purpose is to provide

Its operation will be explained according to the diagram.

Figure 3 shows the electric field distribution on the sub-reflector surface when a cross dipole is provided on the sub-reflector. In this case, b indicates the case where one element is parallel to the polarization.

Assuming that polarized components parallel to the elements of the crossed dipole cannot reach the mirror surface, a crossed polarized component is generated in case a and not generated in case b, as shown in FIG.

In reality, the component parallel to the cross dipole element also reaches the mirror surface, but its phase is different from the perpendicular component, so
Again, a cross-polarized component is generated in case a, but not in case b.

Figure 4 shows the relationship between the excitation of the primary radiator system used for tracking and the radiation electric field of the antenna. When excitation is performed with vertically polarized wave V as shown in a, horn A The component can be decomposed into a component element 1 parallel to the plane containing the center of the horn and the central axis of the reflecting mirror system, and a component c1 perpendicular to the plane.

Similarly, regarding horn B, r2. Can be decomposed into C2.

As shown in the figure, the radiated electric field in a direction deviated by a certain angle from the center in the Az plane is caused by the polarization components 1. of horns A and B. r
2, C1r R1, R2, C1, C corresponding to C2.

becomes.

When horn A is excited with polarized waves in the rl direction, in the configuration of the present invention shown in FIG. 2, one element of the cross dipole is parallel to the incident polarized wave, so the cross polarized component is generated as shown in FIG. Therefore, the angle α formed by the radiation electric field component R1 in FIG. 4 with the Az plane is close to 45°.

Similarly, the angle β that C1 makes with the Az plane is also close to 45°.

The angle that R2 and C2 make with the Az plane is that R1 and C1 are A
It is equal to the angle formed with the z-plane.

FIG. 4C shows the case of excitation with horizontal polarization, and the radiated electric field in the ■ direction in that case is shown in d.

Since the Az-multiplied signal for tracking is obtained by combining the signals of horns A and B, the combined electric field vector H of the combined electric field vectors V and d in FIG. 4 is α.

Since β is close to 45°, the magnitude and phase are almost equal.

Excitation polarizations v, h are obtained in exactly the same manner for horns C and D.
It can be easily seen that the magnitude and phase of the radiation electric field vectors are equal to each other.

After all, if the cross dipole on the sub-reflector surface is arranged so that one element is parallel to the r-polarized direction, the excitation polarization (■) will be obtained.

The Az-fold signal amplitude and phase do not change much with respect to h, and therefore change little with respect to arbitrary polarization.

The same can be said about the El signal, so the present invention can realize a radar antenna with less cross-coupling even if a simple one-receiver system is used and other frequency bands using cross dipoles are shared.

The above explanation is for the case where the cross dipole is mounted on the sub-reflector, but it is not necessary to install the cross dipole on the main reflector or the tracking mirror.
It can also be applied when installed near the horn.

In addition, as a tracking radiator system, it is not limited to 5 horns, but 4
This also holds true for the horn system or when using something other than a horn as the element antenna.

Also AZ as a tracking signal. It is applicable not only to the E7 direction but also to a format in which signals are extracted in any two orthogonal directions.

The reflecting mirror system is not limited to the Gregorian type, but can also be applied to cases where a Cassegrain type, a parabolic antenna type, or any other number of rotationally symmetrical reflecting mirror systems are used.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional frequency band sharing Gregorian type receiver type radar antenna. FIG. 1C is a block diagram showing the signal processing circuit, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing the arrangement of the cross dipole and the incident polarization according to the present invention. FIG. 4 is a diagram showing the relationship between waves, and is a diagram showing the excitation polarization and radiation electric field components of the primary tracking radiator according to the present invention. In the figure, 1 is a main reflecting mirror, 2 is a sub-reflecting mirror, 3°5 is a horn, and 4 is a crossed dipole. In the drawings, the same or corresponding parts are designated by the same reference numerals.

Claims (1)

[Claims] 1 In a radar antenna consisting of a rotationally symmetrical reflector system and a primary radiator system, the primary antenna is composed of four or more element antennas and extracts the tracking angle signal by combining the outputs of the four element antennas. A reflector system is shared between a frequency band with a radiator system and a frequency band with a primary radiator system using a cross dipole antenna as an element antenna, and one element of the cross dipole antenna is used for the frequency band used for tracking. A radar antenna for frequency band sharing, characterized in that the antenna is arranged parallel to a plane containing the center of an element antenna used for synthesizing tracking angle signals and the central axis of the rotationally symmetrical reflecting mirror system.