JPH0374842B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an improvement in a mode coupler used when a self-tracking function is required in an antenna for an earth station used for satellite communication.

[Description of prior art]

Conventionally, a so-called high-order mode monopulse self-tracking method has been widely used for antenna self-tracking because of its excellent tracking accuracy. As is well known, in this method, among the higher-order modes of a circular waveguide, when the antenna captures the target object, there is no detection, but when the antenna misses the target object, a certain amount of high-order modes are detected within the waveguide. By creating a servo loop that detects something that has the property of exciting the level and drives the antenna so that the detection level of this higher-order mode signal becomes zero, the antenna can accurately capture the target object. It was designed so that it could be used. The higher-order modes used here are preferably as low-order as possible, so circular waveguide TM ₀₁ mode, TE ₀₁ mode,
TE ₂₁ mode and TE ₂₁ ^* mode are widely used. When the arriving wave is linearly polarized, it is necessary to use a plurality of these modes, but when the arriving wave is circularly polarized, it is sufficient to detect one of these higher-order modes. The electric field distributions of these modes are shown in FIG.

Conventional methods for detecting the desired higher-order mode include (1) a method using a multi-hole higher-order mode coupler, and (2) a method of simultaneously detecting the higher-order mode using a coupling hole common to the basic TE ₁₁ mode. , are widely used. In order to increase the detection sensitivity of higher-order mode signals without affecting the fundamental mode, the method described in item (1) above uses a large number of coupling holes at intervals determined by the frequency used and the shape of the waveguide. It has the disadvantage of being expensive as it requires opening in the direction of the tube axis. Furthermore, since the axial length becomes extremely long, there may be an inherent limit to the fact that it cannot be accommodated in the antenna, especially when used in a low frequency band. Further, conventional examples of the method according to item (2) are shown in FIGS. 2a, b, and c. In the figure, the wave arriving at the main waveguide 1 is reflected by the short-circuit surface 4, guided to the sub-waveguide 2 via the coupling hole 3, and separated into each mode through the synthesis circuit shown in figure c. . At this time, for example
If the distance from the coupling hole 3 to the shorting surface 4 is selected so that the degree of coupling is maximized in the TE ₁₁ mode,
Since the cutoff frequency and phase constant of the TE ₁₁ mode and the higher-order modes are different, the coupling of the higher-order modes is low. Also at the same time
Another drawback was that the frequency band of the coupling degree of the TE ₁₁ mode became narrow.

[Purpose of the invention]

The present invention solves the above drawback, and in the method of detecting the fundamental mode and the higher-order mode simultaneously in the above-mentioned item (2), the cut-off frequencies of the fundamental mode and the higher-order mode are almost the same in the main waveguide. The present invention aims to provide a mode coupler having a wide frequency band and good coupling characteristics.

[Features of the invention]

The present invention provides a ridge within the main waveguide.

That is, the present invention provides a main waveguide made of a circular waveguide or a circular tapered waveguide, and a main waveguide formed around the main waveguide through four coupling holes provided in the circumferential direction of the main waveguide. It is composed of four attached sub-waveguides and a hybrid synthesis circuit for synthesizing the sub-waveguides, and the output of the synthesis circuit is directed in the direction of the incoming circularly polarized wave. a terminal for detecting the TE ₂₁ ^* mode, which is a difference signal for antenna self-tracking, and a terminal for detecting the TE ₁₁ mode, which is a communication signal as well as a tracking reference signal, and a ridge is provided in the main wave pipe. Accordingly, the cut-off frequencies of the TE ₁₁ mode and the TE ₂₁ mode are made almost the same.

The above characteristics are based on the following background.

A waveguide loaded with a rod, for example, a rectangular waveguide with narrower spacing at the center of the H plane to concentrate the electric field distribution in the center, lowers the cutoff frequency of the rectangular fundamental TE ₁₀ mode wave and at the same time It is known that cut-off frequencies such as TE ₂₀ and TE ₃₀ modes can be increased. For this reason, the rigid waveguide is used for the purpose of expanding the usable band of the waveguide. It is also used to widen the bandwidth of pyramidal horn antennas and conical horn antennas.

FIG. 3 shows an example of changes in the cutoff frequency of each mode when a ridge is loaded in a circular waveguide. In the figure, the horizontal axis shows the height h of the ridge normalized by the circular waveguide radius a, and the vertical axis shows the height h of the ridge when the ridge is loaded, normalized by the cutoff frequency fco of the circular TE ₁₁ mode without the ridge. Cutoff frequency fc of each mode
shows. The value of the ridge width w normalized by the waveguide radius a is 0.3 in the case of the same figure.

As you can see from the figure, TE ₂₁ ^* mode is TE ₁₁
As the height h of the ridge increases with the mode, the cutoff frequency decreases and matches that of the TE ₁₁ mode at point A in the figure. Therefore, if a ridge shaped to be near point A is loaded into a circular waveguide, the cutoff frequencies of the TE ₁₁ mode and the TE ₂₁ ^* mode can be made to almost match.

[Explanation based on examples]

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

FIG. 4a shows rectangular sub-waveguides 2 which are orthogonal to the circular main waveguide 1 with ridges 5 provided on the inner surface and which are orthogonal to each other.
A coupling hole 3 is provided between the mode coupler and the waveguide 2, and a terminal 1' for feeding power in a frequency band higher than the frequency band in which the mode coupler is detected is provided.
In Figure 4, b is a BB arrow view of figure a, and figure c is B-B.
FIG. The bridge 5 is determined so as to satisfy the condition shown at point A in FIG. 3, that is, the cutoff frequencies match. As a result, TE ₁₁ and
The cutoff frequencies of the TE ₂₁ ^* mode are almost the same, and the coupling of both modes to the sub waveguide 2 can be maximized. The signal detected in the sub waveguide 2 is
It is separated into each mode by the synthesis circuit shown in Figure c.

FIG. 5 shows a case where the main waveguide is a circular tapered waveguide. In this case, the inner diameter changes according to the change in the axial direction, but at the rear of the coupling hole 3, the third
The shape of the ridge 5 must be changed so as to maintain the condition at point A in the figure. In this case, as in the case of FIG. 4, the signal detected by the sub-waveguide 2 is separated into each mode by the combining circuit of FIG. 2c.

In addition, in FIGS. 4 and 5, the terminal 1' is used to feed a frequency band higher than _f1 , for example, _f2 , which is detected by this mode coupler, but in this case, the sub waveguide 2 is It is necessary to provide a filter or the like having a characteristic of blocking f ₂ so that the coupling hole becomes a short-circuit surface for f ₂ .

The reason why both ends of the ridge 5 are tapered in both FIGS. 4 and 5 is to prevent deterioration of the VSWR characteristics of the ridge 5 that passes through the main waveguide 1 due to the loading of the ridge 5.

〔Effect of the invention〕

As explained above, if the Ritsugi waveguide is used as the main waveguide for the TE ₂₁ ^* higher-order mode monopulse antenna self-tracking method, the cutoff frequencies of the TE ₁₁ mode and TE ₂₁ ^* mode will almost match, and the phase of both modes will be The constants can be made approximately equal. As a result, TE ₁₁
The short-circuit surface where the mode coupling is maximum is equal to the short-circuit surface where the TE ₂₁ ^* mode coupling is maximum, which has a remarkable effect on expanding the frequency band of the mode coupler and improving the degree of higher-order mode coupling. be.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the electric field distribution of each mode used in the high-order mode monopulse antenna self-tracking method. FIG. 2 is a diagram showing a conventional mode coupler. A is an external view, b is a vertical sectional view, and c is a composite circuit block configuration diagram. FIG. 3 is a diagram showing changes in cutoff frequency when changing the shape of the ridge. a...radius of circular waveguide, fco...when no ridge is loaded
Cutoff frequency of TE ₁₁ mode, fc……cutoff frequency,
h...Height of the ridge, w...Width of the ridge, A...
The point where the cut-off frequencies of TE ₁₁ mode and TE ₂₁ ^* mode match. FIG. 4 is a diagram showing an embodiment of the present invention in which the main waveguide is a circular waveguide. a is external view, b is B
- An external view in the B direction, c is a BB sectional view. FIG. 5 is a diagram showing an embodiment of the present invention in which the main waveguide is a circular tapered waveguide. 1... Main waveguide, 1'... Terminal for feeding a frequency band higher than the frequency band for detecting the main mode coupler, 2... Sub-waveguide, 3... Coupling hole, 4... Short circuit surface, 5 ...Rip, 6...Hybrid, 7...
90° transfer device, 8...Reflection-free terminator, 9...TE ₁₁ mode right-handed circularly polarized wave output terminal, 10...TE ₁₁ mode left-handed circularly polarized output terminal, 11...TE ₁₂ mode output terminal.

Claims (1)

[Claims] 1. A main waveguide made of a circular waveguide or a circular tapered waveguide; It includes four attached sub-waveguides and a hybrid synthesis circuit for synthesizing the sub-waveguides, and further includes a terminal for detecting TE ₂₁ ^* mode at the output of the synthesis circuit; A mode coupler comprising a terminal for detecting TE ₁₁ mode, and a ridge configured to substantially match the cut-off frequency of the TE ₁₁ mode and the cut-off frequency of the TE ₂₁ ^* mode in the main waveguide. A mode coupler characterized by: