JPH02280403A - Corrugated horn - Google Patents

Abstract

PURPOSE:To expand the operating frequency band by selecting a slot pitch in the direction of the inner wall face to be 1/2 wavelength at a high frequency portion of the operating frequency band. CONSTITUTION:Teeth 41,42 provided nearly in parallel with a horn axis 2 and slots 61, 62 having grooves 51, 52 provided nearly perpendicularly to the horn axis 2 are provided to the inner wall face and the pitch of the slots 61, 62 in the direction of the inner wall face is selected to be a pitch corresponding to a half the wavelength of the high frequency portion of the frequency band of an electromagnetic wave to be propagated or over. Thus, the TM11 mode is selected in the inside of the grooves 51, 52, the property of the zero admittance at the virtual inner wall face is utilized when the depth of the grooves is equal to lambda/4 depending on the boundary condition of the electric field RE11 in the inside of the horn, the electric field enters the slots 61, 62 at a frequency when the depth reaches the depth lambda/2 or over, the effective depth of the grooves is made shallow equivalently, and when the depth of the groove is lambda/4 at a low frequency portion, the condition is closer, and the excellent frequency characteristic is kept over a wide frequency band.

Description

[Detailed description of the invention] [Industrial application field] The present invention is utilized in a primary radiator of an antenna.

Especially regarding corrugated horns with wide apex angles.

〔overview〕

The present invention provides a corrugated horn with a half apex angle of 30 degrees or more and 60 degrees or less, by providing slots with a shape that is easy to process at a predetermined pitch, thereby producing a horn with a wide usable frequency band at a low cost. It was made so that it could be done.

[Conventional technology]

Conical corrugated horns have excellent axial symmetry over a wide band and provide radiation characteristics with low side lobes, so they are widely used as the primary radiator of various reflector antennas.

As shown in FIG. 6, the conical corrugated horn has grooves cut repeatedly in the circumferential direction on the inner wall surface of the conical horn. The operating principle of such a corrugated horn will be explained.

In the electromagnetic field propagating inside the corrugated horn as shown in Figure 6, if the width of the groove is smaller than λ/2 (λ is the wavelength), the TE mode component cannot exist, but the TM mode component cannot exist. The component can exist even if the width of the groove is small.

Further, both TE and TM mode components can exist inside the horn other than inside the groove. For the commonly used fundamental mode, TM is inside the groove.

mode exists, and both the T E r 1 mode and the TM, □ mode exist inside the horn. The mode inside the horn is HE, which is a composite mode of T E + + and TM11 modes, and can be regarded as a special mode called a hybrid mode. The wall admittance when looking at the inner wall surface of the horn from inside the horn for the HE mode can be determined based on the matching condition between the TM11 mode inside the slot at the population of the slot and the HE mode inside the horn, and its value is It is. Here, zo is the free space impedance, p and a are the slot pitch and groove width, and d is the groove depth. From equation (1), when the depth d of the groove is equal to λ/4, the admittance becomes zero and the electromagnetic field inside the horn becomes completely axially symmetric.

Further, when it becomes equal to λ/2, the admittance becomes infinite and equivalent to a conical horn without a groove.

When the depth d of the groove is between λ/4 and λ/2,
Since the inner wall admittance becomes capacitive and a fast wave condition is established, good radiation characteristics can be obtained. Therefore, in a normal corrugated horn, the slot pitch is set to about λ/2 or less, and the groove depth is set between λ/4 and λ/2.

In addition, as shown in equation (1), the admittance has periodicity with respect to frequency, and the groove depth is between 3λ/4 and λ, and between (2n+1) λ/4 and (n+1) λ/2. Fast-wave conditions can be obtained even in a frequency band of is the same as the case between λ/4 and λ/2, so next, only the case of this lowest order will be explained. A corrugated horn with a large apex angle, for example, an opening angle of about 90 degrees, is often used for antennas such as offset parabolic antennas and parabolic antennas where the primary radiator has a large viewing angle. In this case, by cutting the groove perpendicularly to the inner wall surface as shown in FIG. 7, good radiation characteristics can be obtained in the same frequency band as in the case where the apex angle is small. In addition, as shown in Figure 8, in a structure where the groove is cut perpendicular to the horn axis, the frequency band is slightly narrower than when the groove is cut perpendicular to the inner wall surface, but the frequency band is about the same. performance can be obtained.

FIGS. 8 and 9 show structures of other conventional examples.

Here, the frequency band can be expanded by loading rings on all teeth as shown in FIG. In this case, it is not possible to cut the horn from the inside using a lathe, and the structure is such that a large number of disks are made and inserted into the cylinder.

[Problem that the invention seeks to solve]

However, such a conventional corrugated horn has a drawback that the frequency band in which good radiation characteristics can be obtained is limited to a band where the groove depth d is 1/4 wavelength or more and 1/2 wavelength or less. Furthermore, when the band is expanded, the structure becomes complicated and the price rises.

The present invention aims to eliminate these drawbacks, and aims to provide a corrugated horn that has a simple structure and can provide good radiation characteristics over a wide frequency band.

[Means for solving problems]

The present invention provides a corrugated horn having a half-vertex angle of 30 degrees or more and 60 degrees or less, with teeth provided substantially parallel to the horn axis of the own device and grooves provided substantially perpendicular to the horn axis. A slot having a pitch length in the direction of the inner wall surface of the slot is a length equivalent to half of the wavelength corresponding to this high frequency region in the frequency band of the electromagnetic wave to be propagated. It is characterized by the above.

[Effect]

The corrugated horn of the present invention generates TM and □ modes inside the groove, and when the boundary conditions between the electric field HE inside the horn, the E mode and the TM11 mode inside the groove are such that the depth of the groove is equal to λ/4, Utilizing the property that the admittance becomes zero on the virtual inner wall surface, the electric field enters the slot at frequencies above λ/2 (i.e., high frequency region), equivalently reducing the effective depth of the groove, and In the section, the depth of the groove is λ
In the case of /4, the condition becomes closer and good frequency characteristics are maintained over a wide frequency band.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing the shape of this embodiment. The corrugated horn 1 has an opening angle of about 90 degrees and is rotationally symmetrical about the horn axis 2. The inner wall has grooves 51.52 cut perpendicular to the horn axis and teeth 41.4 horizontal to the horn axis.
The virtual inner wall surface 30 is a surface connecting the tips of the teeth 41, 42, and serves as a boundary surface between the inside of the horn and the inside of the slot. The corrugated horn l is connected to a straight waveguide section 8 via a matching section 7 of the tapered waveguide. That is, in this embodiment, the half apex angle is 30 degrees or more and 60 degrees or less, and the teeth 41, 42, - are provided almost parallel to the horn axis of the own device.
and a groove 51.5 provided approximately perpendicular to this horn axis.
Slots 61, 62, - having 2, . The length is equivalent to one-half of the wavelength.

FIG. 2 shows details of one of the slots 61, 62. Virtual inner wall surface 3 at the apex of teeth 41 and 42
The distance in the 0 direction is P, and at a frequency where P is 172 wavelengths or more, the distance between the surface of the tooth 41 parallel to the horn axis 2 and the side surface of the tooth 42 in a direction parallel to the virtual inner wall surface 30 is λ/2 (λ is the wavelength) is defined as the boundary surface 31.

The corrugated horn generates the TM mode inside the groove, and the electric field HE mode inside the horn and the TM mode inside the groove.
, the mode boundary condition utilizes the property that when the depth of the groove is equal to λ/4, the admittance becomes zero at the virtual inner wall surface 30, and if the width of the groove is λ/2 or less, the inside of the groove is Since only the TM mode exists in , this boundary condition holds true. However, in the case of the full-gate horn of the present invention, at frequencies where P is λ/2 or more, the electric field inside the horn penetrates to the boundary surface 31, that is, the width of the groove in the wall direction becomes λ/2. This is equivalent to the effective depth of the groove becoming shallower. Here, in a normal corrugated horn, the groove depth is close to λ/4, and as the frequency increases, the groove depth approaches λ/2, and the radiation characteristics approach that of a conical horn without grooves, and as the frequency increases, the groove depth approaches λ/2. However, in the case of the present invention, the equivalent depth of the groove is approximately λ/4 in the low frequency part of the frequency band used.
In addition, if the pitch is set to λ/2 or less and the pitch is set to λ/2 or less in the high frequency region, it will have radiation characteristics equivalent to a normal corrugated horn in the low frequency region, but with high frequency In the frequency section, the equivalent depth of the groove becomes shallower as the electric field enters the slot, and when the groove depth is λ/4, radiation characteristics closer to each other can be obtained; Even in a band of 2 or more, the effective depth of the groove becomes λ/2 or less due to the effect of the electric field entering the slot, making it possible to expand the frequency band with good radiation characteristics.

FIG. 3 shows the frequency characteristics of the equivalent admittance of the slot of a corrugated horn. The vertical axis represents the admittance of the slot in terms of the equivalent depth in the direction perpendicular to the inner wall surface, and the horizontal axis represents the frequency normalized by the frequency f1 at which the equivalent depth is equal to λ/4. The frequency range where the equivalent depth is from λ/4 to λ/2 becomes the usable frequency band. Curve I is a calculated value for a normal corrugated horn, and curve 2 is a calculated value for an embodiment of the present invention. In the case of the present invention, the usable frequency band is expanded in the high frequency region.

In this embodiment, a tapered waveguide is used as the matching section 7, but the matching section 7 can be a corrugated slot whose depth is gradually changed as shown in FIG. 4, or a ring loaded as shown in FIG. The present invention can also be practiced using a corrugated slot.

The present invention is also applicable to a corrugated horn that can be used in multiple frequency bands, where the groove depth d is shared between the frequency range from λ/4 to λ/2 and the range from 3λ/4 to λ or more. can do.

That is, in the first region where the groove depth d changes from λ/4 to λ/2, the pitch is λ/2 or less, and in the second region where the groove depth d changes from 3λ/4 to λ, the pitch becomes λ/2 or more. If selected as such, the frequency band can be expanded in the second region.

〔Effect of the invention〕

As explained above, the present invention has the effect of expanding the usable frequency band because the pitch in the direction of the inner wall surface of the slot is set to 1/2 wavelength in the high frequency part of the usable frequency band. In the corrugated horn of the present invention, the slot of the corrugated horn has a shape consisting of teeth parallel to the horn axis and grooves cut perpendicular to the teeth, so it can be cut from the inside of the horn with a lathe etc. In addition, the cutting direction during cutting is only horizontal and perpendicular to the horn axis, which is the rotation axis of the lathe, and it has the advantage of being cheaper to manufacture than conventional corrugated horns.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the structure of an embodiment of the present invention. FIG. 2 is a detailed diagram of a slot according to an embodiment of the present invention. Figure 3 is a bluff showing the frequency characteristics of the electrically equivalent groove depth of various corrugated horns. FIGS. 4 and 5 are longitudinal cross-sectional views showing the structure of another embodiment of the present invention. FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are longitudinal sectional views showing the structure of a conventional example. 1... Corrugated horn, 2... Horn shaft, 7...
- Matching part, 8... Straight waveguide part, 11... Cylinder, 3
0...Virtual inner wall surface, 31...Boundary surface, 41.42.
... Teeth, 51.52 ... Groove, 61.62 ... Slot, 71.72 ... Matching part slot, 91.92 ...
·disk.

Claims (1)

[Claims] 1. In a corrugated horn whose half-vertex angle is 30 degrees or more and 60 degrees or less, a slot having teeth provided approximately parallel to the horn axis of the own device and a groove provided approximately perpendicular to the horn axis is provided. Provided on the inner wall surface of the own device, the pitch length of this slot in the direction of the inner wall surface is equal to or longer than one-half of the wavelength corresponding to this high frequency region in the frequency band of the electromagnetic wave to be propagated. A corrugated horn featuring