JPS6340486B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention is used as a primary radiator of a reflector antenna or as a single horn antenna, and is excited by multiple modes including higher-order modes in addition to the TE ₁₁ mode, which is the fundamental mode of a circular waveguide. The present invention relates to a multi-mode horn antenna.

Conventionally, such a multi-mode horn antenna is composed of a conical horn 1, a straight circular waveguide 2, a step 4, and a feeding waveguide 3, as shown in a side view in FIG. 1a and a front view in FIG. 1b. The TM ₁₁ mode is generated from the discontinuities at both ends of the straight circular waveguide 2, or the conical horn 1 and the straight circular waveguide are shown in the side view in Figure 1c and the front view in Figure 1d. There was also a type in which the TM ₁₁ mode was generated from both ends of the straight circular waveguide 2, which was composed of a tube 2, a tapered waveguide 5, and a feeding waveguide 3.

In these types of antennas, if the inner diameter of the straight circular waveguide 2 is selected so that modes higher than the TM ₁₁ mode will not occur, the phase characteristics of the TM ₁₁ mode in the conical horn 1 will change as the frequency changes. The problem was that good radiation characteristics could not be obtained over a wide band.

In addition, if the inner diameter of the straight circular waveguide 2 is increased in order to reduce the change in the phase characteristics of the TM ₁₁ mode in the conical horn 1 due to frequency, the TM ₁₁ mode will change at the discontinuous parts at both ends of the straight circular waveguide 2. Higher-order modes (for example, TE ₁₂ mode) may occur. Therefore, in the case of such a configuration, the generation amount of the TM ₁₁ mode and the generation amount of the TE ₁₂ mode cannot be controlled simultaneously, so there is a drawback that good radiation characteristics cannot be obtained over a wide band.

In order to eliminate these drawbacks, this invention
TM ₁₁ mode generator only in high frequency band
It consists of two parts: a part where the TM ₁₁ mode occurs and a part where the TM ₁₁ mode occurs in both the low frequency band and the high frequency band, and will be explained in detail below using the drawings.

FIG. 2 shows an embodiment of this invention, and FIG.
2b shows a side view, and FIG.
b, the tapered waveguide 5b, and the feeding waveguide 3b are connected in this order. This multi-mode horn antenna has two frequencies: a high frequency band excited from the feeding waveguide 3b and a low frequency band excited from the feeding waveguide 3a attached to the feeding port 6 in the middle of the tapered waveguide 5a. used in the frequency band.

The feed port 6 used for excitation in the low frequency band must be provided near the diameter where the TE ₁₁ mode in the low frequency band is cut off, and must be installed in the straight circular waveguide 2b.
The TM ₁₁ mode in the high frequency band needs to propagate within. That is, in the straight circular waveguide 2b, TE ₁₁ at the highest frequency in the low frequency band
No mode should propagate, and the TM ₁₁ mode at the lowest frequency of the high frequency band should propagate. Therefore, the inner diameter of the straight circular waveguide 2b is D, the highest frequency in the low frequency band is e, and the lowest frequency in the high frequency band is
When h is assumed, the following relational expression holds true.

e<Ck _TE11 /πD ...(1) h>Ck _TM11 /πD ...(2) where C is the speed of light, k _TE11 (=1.8412) is the cutoff wave number of TE ₁₁ mode, and k _TM11 (=3.8317) is TM Shows the cutoff wave number of ₁₁ modes.

Therefore, from equations (1) and (2), ek _TM11 /k _TE11 = 2.08e<2.1e<h...(3), and the lowest frequency e in the high frequency band is The frequency h needs to be 2.1 times or more.

Here, the diameter of the straight circular waveguide 2b is selected so that the TM ₁₁ mode propagates in the high frequency band and the TE ₁₂ mode does not propagate, and the diameter of the straight circular waveguide 2a is selected so that the TM ₁₁ mode propagates in the low frequency band. I have chosen to do so. With this configuration, the TM ₁₁ mode occurs only in the high frequency band at the discontinuous parts at both ends of the straight circular waveguide 2b, and both TM 11 modes occur at the discontinuous parts at both ends of the straight circular waveguide 2a. TM ₁₁ mode occurs in the frequency band.

Therefore, in the case of a low frequency band, the optimum amount of TM ₁₁ mode generation can be obtained by using the length of the straight circular waveguide 2a and the opening angle of the tapered waveguide 5a as design parameters. In the case of a high frequency band, higher-order modes such as TM ₁₁ mode and TE ₁₂ mode occur at the discontinuities at both ends of the straight circular waveguide 2a. The length of the wave tube 2b and the opening angle of the tapered waveguide 5b can be designed, and the amount of TM ₁₁ mode generation can be controlled, so the optimal amount of higher-order modes can be generated even in high frequency bands. Obtainable.

As explained above, by adopting such a configuration, it is possible to obtain the optimal amount of higher-order modes generated in both the low frequency band and the high frequency band, so it is possible to obtain a good amount of generation over a wide band. Radiation characteristics can be obtained.

FIG. 3a shows another embodiment of the present invention, in which, in addition to the configuration explained in FIG. 2, a tapered waveguide 5c is provided between the tapered waveguide 5a and the straight circular waveguide 2b. The configuration has been inserted. The structure other than the tapered waveguide 5c is the same as described above. The diameter of the connecting portion between the tapered waveguide 5a and the tapered waveguide 5c is set to TE ₁₂ in the high frequency band.
mode is generated, and the TM ₁₁ mode is selected so that it does not occur in the low frequency band.

Therefore, in the case of a high frequency band, the TE ₁₂ mode generated at the discontinuous portions at both ends of the straight circular waveguide 2a is replaced by the TE ₁₂ mode generated from the connection between the tapered waveguide 5a and the tapered waveguide 5b. Since the waveguide can be controlled, the linear circular waveguide 2b and the tapered waveguide 5b need only be designed by considering only the TM ₁₁ mode, which has the advantage of increasing the degree of freedom in design.
Furthermore, since the TM ₁₁ mode and TE ₁₂ mode can be controlled separately, good radiation characteristics can be obtained over a wide band.

FIG. 3b shows the tapered waveguide 5c shown in FIG. 3a.
An iris 7 is inserted in place of the . In this case as well, effects similar to those described above can be obtained. Furthermore, straight circular waveguides 2a, 2b
A similar effect can be obtained when a tapered waveguide with a small opening angle is used instead, or when an iris is provided in the middle of the straight circular waveguides 2a and 2b.

As explained above, in the multi-mode horn antenna according to the present invention, the TM ₁₁ mode generating part is divided into a part where the TM 11 mode is generated only in the high frequency band and a part where the TM ₁₁ mode is generated only in the high frequency band, and a part where the TM ₁₁ mode is generated in both the low frequency band and the high frequency band. By configuring the mode into two parts, it is possible to obtain the optimal amount of higher-order modes to be generated in both frequency bands, and therefore to obtain good radiation characteristics over a wide band. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional multi-mode horn antenna, FIG. 2 is a block diagram of a multi-mode horn antenna according to the present invention, and FIG. 3 is a block diagram of a multi-mode horn antenna according to another embodiment of the present invention. . In the figure, 1 is a conical horn, 2 is a straight circular waveguide,
3 is a feeding waveguide, 4 is a step, 5 is a tapered waveguide, 6 is a feeding port, and 7 is an iris. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] 1. A multi-mode horn antenna that is excited in multiple modes including higher-order modes in addition to the TE ₁₁ mode, which is the fundamental mode of a circular waveguide, in which the antenna is excited in a low frequency band and a high frequency band. The TM ₁₁ mode generator of the above antenna is used in two frequency bands.
It consists of two parts: a part where the TM ₁₁ mode occurs only in the high frequency band and a part where the TM ₁₁ mode occurs in both frequency bands, and excites the low frequency band between the two TM ₁₁ mode generating parts. A multi-mode horn antenna characterized by having a power feeding port for 2. The multi-mode horn antenna according to claim 1, characterized in that the lowest frequency in the high frequency band is 2.1 times or more the highest frequency in the low frequency band.