JPS62190903A - Multiple mode horn antenna - Google Patents

Abstract

PURPOSE:To prevent the opening efficiency of a parabolic antenna from decreasing by filling a dielectric in a mode generator. CONSTITUTION:A dielectric matching element 5 is a matching circuit which has a cylindrical dielectric projecting into a hollow circular waveguide 3 from a dielectric loaded waveguide 4 along the center axis of the waveguide. The TE11 mode in the hollow circular waveguide 3 is coupled with the TE11 mode in the dielectric loaded circular waveguide 4 without disordering an electric field distribution while an electromagnetic field is converged on the center of the waveguide by the circular dielectric. This multiple mode horn antenna is reducible in shape to one over the square root of the dielectric constant of the filled dielectric and the width of a 10dB down antenna beam can be expanded to >=90 deg., so it operates as the primary radiator of a parabolic antenna which has a >=120 deg. opening angle normally to obtain excellent radiation directivity without decreasing the opening rate of the parabolic antenna.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is a parabolic antenna for radar production.
”Dual ・Vlode Small-Ap
erture Antennas” (Egh;E
tras, AP-15no, 21967, P
There are antennas introduced on pages 307-308).

FIG. 3 shows a cross-sectional view of an example of a conventional multi-mode horn antenna. l is the mode generator, 2 is the aperture surface, 3 is the circular waveguide, θ is the angle of the conical taper of the mode generator 10, l is the length of the circular waveguide portion of the mode generator 1, and D is the aperture diameter. be.

This multi-mode horn antenna generates the internal KTE of the mode generator 1 by adjusting the width and phase of the two modes.

The antenna beam widths of the radiation directivity of the E-plane and the H-plane are matched.

(Problem that the invention attempts to solve) However, the 'I''Mll mode is in a hollow circular waveguide.

If the diameter is less than 1.22 wavelengths, the light will not propagate, so it is advisable to make the aperture diameter of the multimode horn antenna smaller than 1.25 wavelengths. Therefore, with the conventional double-mode horn antenna, it was not possible to widen the +10 dn down antenna beam width from approximately 90 degrees to more than 90 degrees. Normal magnetic bolet antennas are used with an aperture angle of 120 degrees or more,
If a conventional ring mode horn antenna was used as the primary radiation 4 of a parabolic antenna having this aperture angle, the aperture efficiency of the parabolic antenna would be reduced due to the narrow antenna beam width of the -order radiator.

(Means for Solving the Problems) The present invention has the advantage of filling the inside of the mode generator with a dielectric material, so that even if the aperture diameter is 1.25 wavelength or less, the Tg and
, and TM , are the propagation modes, and the antenna beam widths of the E plane and the 1-1 plane are the same and narrow (so that they are not
Even when used as the primary radiator of a parabolic antenna with an aperture angle of 120 degrees or more, it does not reduce the aperture efficiency of the parabolic antenna. Since impedance mismatching occurs between the waveguide and the waveguide, matching is achieved by protruding a dielectric material along the central axis within the hollow waveguide.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention. 1 is a mode generator, 2 is an aperture, 3 is a circular waveguide, 4 is a dielectric-loaded circular waveguide, 5 is a dielectric matching element, ε is the permittivity of the dielectric, 0 is the mode generator 10 cone The angle of taper, l is the length of the circular waveguide section of mode generator l, and D is the aperture diameter.

(Operation) In FIG. 3, the power ratios of the TM11 mode and the 'rg, mode generated in the mode generator l are related to each other by the taper angle θ as follows.

Here, PtM+1. Pti+tHTMo, TE
o Mo)”) is the force, λ is the wavelength in free space, λp
TM11+λ9TE+l is TM II, T E +
rE is the internal wavelength of the pipe. The TMth mode generated by the mode generator 1 is 'rg.

Since the phase advances by 90 degrees with respect to the mode, 2
In order for the phases of the two modes to be in phase, the length l of the circular waveguide portion of the mode generator 10 must satisfy the following relationship.

In FIG. 1, the shape of the horn antenna is reduced to 1 unit q by filling it with a dielectric material having a dielectric constant C.

The width and phase relationship between the two modes immediately before the aperture 2 of the mode generator 1 is exactly the same as that of a conventional hollow multi-mode horn antenna. But on the other hand.

Since the characteristic impedance and free space impedance of each mode differ at the aperture surface 2, impedance mismatch occurs.

Therefore, TM, , mode and tp generated in the mode generation 51
B,, taking the square root of the mode power ratio, the first
Expressing the S parameter between AA' and B-13' in the figure,
Due to the unitary property of the matrix, it becomes as follows.

Here l”lt2 is an independent phase, and 811 is A
- TE incident on the A′ plane from the left, , reflection coefficient of the mode,
82□ is the reflection coefficient of the TLI mode incident on the B-B' plane from the right, S, 3 is the reflection coefficient of the TM11 mode incident on the B-r3' plane from the right, Stg and Szt are A
-X.

Amount of transmission in TE mode between B and B', SI2. S
! I is TtV1n between A-A and B-B')
”No transmission it 8tx.

S12 is TE' on the B-B' plane, mode and TM
, , is the amount of transmission between modes. Also, since the reflection coefficient of the "rE■ mode incident on the A-A plane from the left is small, 8.I
-O.

Due to the impedance mismatch with the free space at the aperture surface 2,
The radiated electric field from the aperture surface 2 in a steady state when reflection occurs in each mode is set at 1°, and the reflection coefficient of the TEII mode at the aperture surface is defined as the FT4 transmission coefficient by T.
If the reflection coefficient of the TE, TM, mode is rTM, and the transmission coefficient is 'rTM, then ETm++° and ETM mouth° can be expressed as follows using the S parameter of equation (4).

&E++・=i”Tr,・S+□+i″tg・(/'7
2・SH・St 2+l'ru・Sxz・Slx)+
1"Tto(/'trs226(r?t1St z+s
+ z+/″TMH8zs 8Sr s) 10rTM-
82,・(rTM-83,・SI3+/″T6・S, 2
・S1□))+...(5)&Mt+'=T7M-81
3l'1・(FTM-83,・Sl,±rTt-8,
2・Sl□)+TTM・(FTM-8s s ・(/'
TM″8ss°Sti%5iz−8+2)+ /’rz
・ss'x ・(/'rz-8z□・8.2+/'?M
”s23 '81 m )) +... (61 where, (
4) Equation 12: If tnπ, then two modes of electromagnetic fields are radiated from the aperture 2 of the multimode horn antenna at the ratio generated by the mode generator.

(4) Formula 8s3c, B - B' side right side TM+
This is the reflection coefficient when +Mo1-' is incident, and its phase is t2+π. 'ls incident from the B-B' plane
The M, mode is reflected at the diameter where the TM, mode is blocked due to the narrowing of the diameter of the circular waveguide within the mode generator.

At this time, the phase is reversed. Therefore, from the B-B' plane, TM
,,If the propagation phase to the plane where the mode is blocked is nπ, then the phase of S,3 becomes 20π+π.

By setting the value, even if impedance mismatch occurs at the aperture surface 2, the ratio of the TM, 1 mode and the rpE, mode radiated from the aperture surface 2 is determined from the relationship in equation (1). be able to. For this reason, while keeping the radiation directivity of the E plane and H plane the same by loading a dielectric,
It became possible to widen the antenna beam width. The antenna beam width can be adjusted by changing the dielectric constant of the loaded dielectric.

Furthermore, when a dielectric material is loaded into the waveguide, an impedance mismatch occurs at the connection surface with the hollow waveguide. The input side of the belly mode horn antenna is 'rg.

The waveguide diameter is such that only the mode can propagate, but in order to radiate 9 circularly polarized waves or both horizontal and vertical waves, it is necessary to
Two orthogonal TEs, one mode, need to propagate. For this reason, it is necessary for impedance matching to use a matching circuit that is symmetrical with respect to the two Tg modes and has no coupling between the modes.

The dielectric matching element 5 shown in FIG. 1 is a matching circuit in which a cylindrical dielectric is protruded from the dielectric-loaded waveguide 4 into the hollow circular waveguide 3 along the central axis of the waveguide. . In the '■'r!311 mode in the hollow circular waveguide 3, the electromagnetic field is concentrated at the center of the waveguide by the 9 cylindrical dielectric, and the dielectric-loaded circular waveguide 4 is generated without greatly disturbing the electromagnetic field distribution. Figure 2 shows the change in impedance of a dielectric-loaded multi-mode horn antenna due to the dielectric matching element 5. Point P in Figure 2 shows the dielectric resistance when no matching circuit is used. The impedance of the loaded re-mode horn antenna, the three circular arcs are the diameters of the three types of dielectric matching elements 5, and represents the locus of impedance when the length is changed.

Since the change in diameter and the change in length are almost orthogonal, matching can be achieved easily. A matching circuit using this dielectric matching element.

Compared to the matching method using a circular iris, there is no risk of reduction in discharge withstand voltage, so it can be used as an antenna for high-output radar IIT.

(Effects of the Invention) The multi-mode horn antenna according to the present invention can be reduced to 1/square root of the permittivity of the dielectric material filling its shape, and has an IQ d that cannot be obtained with conventional multi-mode horn antennas.
B Down Antenna Because the beam width can be expanded to over 90 degrees, it can be used as the primary radiator for parabolic antennas with a normal aperture angle of 120 degrees or more, allowing circular polarization and horizontal/vertical polarization without reducing the aperture efficiency of the parabolic antenna. Good radiation directivity characteristics can be obtained for both side waves. In addition, by using a dielectric matching element that protrudes along the central axis inside the hollow waveguide for impedance matching between the hollow waveguide and the dielectric-filled waveguide, good input stability is achieved. There is an advantage that a wave ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and a cross-sectional view showing an example of a second multi-mode antenna. DESCRIPTION OF SYMBOLS 1...Mode generator, 2...Aperture surface, 3...Circular waveguide, 4...Dielectric-loaded circular waveguide, 5...Dielectric matching element.

Claims (1)

[Claims] A dielectric matching element is provided in a shape that projects from a dielectric-loaded waveguide filled with a dielectric material into a hollow waveguide along a central axis, and the dielectric-loaded waveguides are connected and filled with a dielectric material. A multi-mode horn antenna comprising a mode generator with a reduced aperture.