JPS6172403A - Antenna system - Google Patents

Abstract

PURPOSE:To reduce the deterioration in a radiation pattern by adopting a part of a sub reflection mirror as a frequency selective reflection mirror so as to make the beam width of each frequency band nearly equal to each other. CONSTITUTION:The frequency selecting reflection mirror FSR11 acts like reflecting a radio wave in frequency f1 and transmitting that in frequency f2, and a radio wave irradiated to the sub reflection mirror 2 from a primary radiator 3 with an apparent angle of thetam0 of a main reflection mirror 1. The radio wave irradiated with an apparent angle of thetam1 is irradiated in the main reflection mirror Dm1 in an angular range smaller than the angle thetam1 and transmitted through without being reflected on the FSR11 in an angular range larger than the thetam1. Further, the radio wave reflected from the mirror 1 is blocked by the mirror 2 and since the FSR11 shows transmittivity to the f2, the equivalent blocking area is Ds1. Then the relation of Ds0/Dm0approx.=Ds1/Dm1 with respect to the f1, f2 is established. Thus, the relation of lambda1/Dm0approx.=lambda2/Dm1 is obtained, the lambda/D is made nearly equal in the common frequency and the deterioration in the radiation pattern is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an antenna 1 that shares a frequency, and more particularly, to a device that makes antenna beam widths approximately equal at a shared frequency. It is something.

[Conventional technology]

Conventionally, Cassegrain antennas (or Gregorian antennas) have been used for satellite communications or for tracking rockets, mobile satellites, and the like. These antennas typically operate at two or more frequencies (e.g. 6/4GHz, 80/20G
Hz) is used.

On the other hand, these antennas usually require a high G/T in order to receive very weak radio waves.

Here, G is the antenna gain and T is the antenna system noise temperature. Therefore, the first way to increase G/T is to increase the antenna gain (4G) or to lower the noise temperature T of the antenna system.The antenna system noise T is not only the noise of the antenna itself, but also the receiver (e.g. L
It is also related to the noise temperature of NA=Low NoiseAmp, ). Here, consider the antenna gain G, 1.

The general general ζ antenna profit PJG is given as follows.

Here, π=8.1415 (pi), D=antenna diameter, λ: wavelength, η: antenna aperture efficiency.

On the other hand, the 8 dB drop point width θ of the antenna main beam at this time
→ becomes one cycle as shown in the following equation.

λ θ−3=　k　−(2J In this case, k is a constant.

As can be seen from equation (1), <21, the antenna gain G
If the antenna beam width is increased, the antenna beam width will inevitably become narrower.

As the antenna beam width becomes narrower, the precision with which the antenna is pointed toward the target (e.g., satellite, rocket, etc.) must be very strict. However, there is a limit to this precision, and In an antenna that is shared by two frequencies, a problem arises in that even if the usage accuracy is satisfied in one frequency band, the usage accuracy may not be satisfied in the other frequency band.

This problem arises especially when a large-diameter (large D) antenna is used in a place where the frequency is high (where people are short).

・d Figure 1 shows a general conceptual diagram of a conventionally used Cassegrain antenna.

In the figure, (1) is the main reflector% (2) is the sub-reflector, (3
) is the -order radiator, (4) is the power supply device, (6), (6
) is the radio wave heading towards the sub-reflector at line-of-sight angles θm and θml from the -order radiator phase center, (7) and (8) are the radio waves (s),
(a) is a radio wave reflected by the sub-reflector and directed towards the main reflector,
(9) and QO are radio waves (7) and (8) that are reflected by the main reflecting mirror and radiated into space.

In the design of a normal antenna, in order to increase the antenna gain G as mentioned above, the frequency I, which shares the pattern radiated from the primary radiator, is changed as much as possible, as shown in the amplitude characteristics of Figure 2. If we decide to avoid this, the radio waves radiated from the antenna (9),
Since αQ does not change depending on the frequency, the antenna apertures Dm and Dml are used in the same way for any frequency.

By the way, the antenna gain 4G is proportional to Dm/λ and the antenna beam width is proportional to λ/Dm, so as mentioned above, the beam width becomes narrower in proportion to the frequency used, and therefore the pointing accuracy is also proportional to the frequency. The problem arises that it becomes more difficult. On the other hand, as a way to solve this problem, the radiation pattern of the -order radiator is increased by increasing the frequency characteristic at the frequency to be used, as shown in Figure 8, "amplitude characteristic" ζ.
2, the range in which the 1ζ main reflector is effectively used is equivalent to Dm1, and the ratio of the wavelength to the live reflector is equivalently λ/
One possible method is to widen the beam width as D m 1.

However, in this method, the ratio of the sub-reflector to the main reflector at frequency ftlζ = Ds/Dm For Gζ, the frequency 12 (
The ratio of the sub-reflector to the main reflector when fl<fl) is Ds/
Dm2Ds/I)ml. This ratio DS/Dm is usually selected to be optimal at 110 frequencies. In this way, at the frequency of fl, it becomes equivalently Ds/Dml, for example, at the frequency of fl with the relationship 2:h=f2,
To make the beam width the same, Dm = 20ml, and D
s/Dml = 2D s/Dm.

Therefore, at the frequency fl, Ds/Dm1 becomes 1ζ, which is twice the optimum value Ds/Dm, causing deterioration of the gain, axis, and wide-angle radiation pattern.

[Summary of the invention]

In view of the above drawbacks, the present invention uses a part of the sub-reflector as a frequency selective reflector (hereinafter abbreviated as FSR),
Optimal iζ as long as the beam widths are almost the same for the two shared frequencies and the ratio of the main reflector to the sub-reflector is equivalent.
This is an attempt to eliminate deterioration of the gain radiation pattern by making the gain radiation pattern closer.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 4 and 5.

FIG. 4 is an explanatory diagram of the radiation pattern of the primary radiator in one embodiment of the present invention.

FIG. 6 shows an embodiment of this invention.

In Fig. 6 1ζ, (1) is the main reflecting mirror, (2) is the sub-reflecting mirror, (3) is the -order radiator, (4) is the power feeding section, (5),
(6) is the angle of view θm from the phase center of the −order radiator, respectively.
0. The radio waves radiated at θm1 (7) and (8) are the radio waves (5) and (6) that are reflected by the sub-reflector and head towards the main reflector, and (9) and 013 are the radio waves (7).

(8) is a radio wave reflected by the main reflector and radiated into space, (
b) is FSR. Note that the FSR may be, for example, a wire mesh having a mesh of a predetermined size that reflects the signal of frequency fl and allows the signal of frequency f2 to pass (provided that fI<h).

Next, the operation will be explained. Now, in FIG. 5, it is assumed that a radiation pattern as shown in FIG. 4 is radiated from the -order radiator (3). Note that this radiation pattern is the primary radiator (3)
The radiation pattern corresponds to the angle of view θm6 +θml from the phase center of .

FSR (b) reflects the frequency 1 of fl,
For the frequency of f2, when it acts to transmit, the sub-reflector (2) has a line of sight angle θm6 from the primary radiator (3).
The radio waves blown onto the main reflector (1) are effective - the Dm of the main reflector (1)
,) is irradiated.

On the other hand, the radio waves blown at the line-of-sight angle θm are
Within the angle range smaller than m1, the main reflector D is effectively
The light is irradiated onto a circle m1, and the angle range larger than θml is transmitted without being reflected by the FSR (6).

In addition, the electric current reflected from the main reflector (1) and directed toward space.
The waves are also proking by the secondary reflector (February ζ, but F
Since SR (b) is transparent to the frequency of fo, the equivalent blocking area is Dsl, and the ratio of the main reflector pair to the sub-reflector is Ds/Dm for the frequency of 1s-h.
6 = Dsl 70m1 1 can be done.

Therefore, let the frequency fl-ft and Dmt/Dm6 be ft
/ j”2 = Dm 1/Dm6, it becomes ^t/Dm6;λz/Dmt, and λ/D can be almost the same Iζ at the shared frequency, and as mentioned in t, D
s/Dmoz Dsl/Dml lζ name 1ζFS
By determining the magnitude of R, the decrease in gain and the deterioration of the radiation pattern can be reduced.

Although the above explanation has been about sharing two frequencies, the same idea can be applied to a large number of frequencies.

Furthermore, although the explanation has been given using a horn feeding system as an example of a -order radiator, the present invention can also be applied to a focused beam feeding system ■ζ.

〔Effect of the invention〕

As described above, according to the present invention Iζ, by arranging the FSR in a part of the sub-reflector, the beam width of two or more frequency sharing antennas can be made almost the same at any frequency lζ, and the radiation characteristics This has the effect of reducing the deterioration of

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of a conventional Cassegrain antenna; Figure 2 is a conceptual diagram of a conventional Cassegrain antenna;
FIG. 8 is a diagram for explaining the radiation pattern of the -order radiator, FIG. 4 is a diagram for explaining the radiation pattern of the primary radiator in the embodiment of the invention, and FIG. 6 is a diagram for explaining the radiation pattern of the primary radiator in the embodiment of the invention. A conceptual diagram of such a Cassegrain antenna is shown. (1) is the main reflector, (2nd J sub-reflector, (3) is the -order radiator, (4) is the feeder, (506) is the radio wave radiated from the -order radiator, (7) ( 8) is the radio wave (5) (6) is the radio wave reflected by the sub-reflector, (9) αQ is the radio wave < 7)
(8) shows the radio wave reflected by the main reflecting mirror, and (b) shows the FSR. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] An antenna device that uses two or more frequencies in common, characterized in that a part of the sub-reflector is a frequency-selective reflector so that the beam widths of the respective frequency bands that are shared are made approximately equal.