EP0574021A1

EP0574021A1 - Multi-depth corrugated horn antenna

Info

Publication number: EP0574021A1
Application number: EP93109419A
Authority: EP
Inventors: Edwardo H. Villeseca; Donald G. Keppler
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1992-06-12
Filing date: 1993-06-11
Publication date: 1993-12-15

Abstract

A conical corrugated horn antenna (10) is provided with multiple depth corrugation. Antenna (10) includes a corrugated interior surface (14) formed of a plurality of uniform parallel primary conducting members (16) separated by a plurality of uniform parallel slots (18). Each primary member (16) includes a uniform secondary conducting member (20) extending from a top surface (23) of the respective primary member (10). Each secondary member (20) is a plate having a width substantially less than the width of the primary members (16). The secondary members (20) extend parallel with the primary members (16) equidistant between the parallel slots (18).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to antennas and, in particular, to a corrugated horn antenna.

2. Description of Related Art

A wide variety of corrugated horn antenna designs are found in the prior art. Most of the corrugated antenna designs represent an attempt to provide an antenna having equal E- and H-plane beamwidths over a wide frequency range. Among such corrugation designs is dual frequency corrugation, wherein corrugation depth alternates between the two frequencies. Another corrugation design found in the prior art is ring-loaded corrugation, which provides for an extended bandwidth at the expense of low corrugation impedance. Unfortunately, all such prior art antenna designs are difficult to manufacture and have poor overall performance.
As can be appreciated, there exists a need for an improved corrugated horn antenna having equal E- and H-plane beamwidths over a wide frequency range.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an improved antenna;
It is another object of the invention to provide an improved corrugated horn antenna having equal E- and H-plane beamwidths over a wide frequency range;
It is another object of the invention to provide a corrugated horn antenna having a high corrugation impedance over a wide bandwidth;
It is still another object of the invention to provide a corrugated horn antenna having multiple-depth corrugation; and
It is yet another object of the invention to provide a multiple-depth corrugated horn antenna manufactured according to conventional manufacturing techniques.
These and other advantages of the invention are achieved by providing a corrugated horn antenna comprising a conducting surface corrugated to multiple depths. Multiple depth corrugation is achieved by providing a plurality of parallel primary conducting members defining a plurality of parallel slots, with each primary member including at least one secondary conducting member extending perpendicular from a top surface of the respective primary member.
In a preferred embodiment, the conducting surface of the corrugated antenna is conical, with the primary and secondary members formed on an inside surface thereof. The primary members have a rectangular cross-section and are of uniform size. The secondary members are thin plates, likewise of uniform size. Each primary member includes one secondary member integrally formed in the middle of an outer side surface of the respective primary member equidistant between the parallel slots.
Alternative embodiments can include, for example, an embodiment wherein the corrugated antenna includes several secondary members formed on each primary member, or an embodiment wherein the corrugated antenna includes several levels of corrugation, e.g., each secondary member includes at least one tertiary member formed thereon.
Generally, the invention provides for multiple-depth corrugation rather than conventional single-depth corrugation. A conventional single-depth corrugated antenna is analogous to a transmission line terminated by a single shorted stub providing capacitive reactance over the operating frequency range. As with a single stub transmission line, a single-depth corrugated antenna performs well only over a narrow frequency band. With a transmission line an impedance transformer of multistep sections is used to obtain broadband performance. The provision of a large number of multistep sections in the transmission line changes the step impedance to a uniform tapered impedance.
The multiple-depth corrugation of the invention is somewhat analogous to the multistep sections of an impedance transformer. A preferred multiple-depth configuration for the invention was computed to maximize corrugation impedance over a frequency range. The resulting optimal configuration was then modeled and radiation patterns obtained analytically using the Geometrical Theory of Diffraction (GTD). The resulting E-and H-planes at each frequency of the frequency range were found to be almost identical, indicating high corrugation impedance throughout the bandwidth.
Generally, the provision of multiple-depth corrugation achieves a high capacitive reactance over a broad frequency range and thereby yields improved performance over single-depth corrugation antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

The just-summarized invention will now be described in detail in conjunction-with the drawings, of which:

FIG. 1 is a perspective view of a conical antenna having multidepth corrugation constructed in accordance with a preferred embodiment of the invention;
FIG. 2 is a cross-sectional view taken along line 2-2 of the antenna of Claim 1;
FIG. 3 is a close-up cross-sectional view of a portion of the antenna of FIG. 1;
FIG. 4 is a graph showing the far field radiation pattern of the antenna of FIG. 1 for a frequency of 1760 MHz;
FIG. 5 is a graph showing the far field radiation pattern for the antenna of FIG. 1 for a frequency of 2300 MHz; and
FIG. 6 is a graph showing a comparison of the surface reactance of the antenna of FIG. 1 with that of a conventional single-depth corrugated horn antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a corrugated horn antenna having multiple-depth corrugation.
Referring to FIG. 1, a preferred embodiment of a corrugated horn antenna 10 is shown. Antenna 10 includes a conical horn member 12 having an azimuthal axis Z. Conical horn member 12 includes an internal conducting surface 14 facing axis Z. Antenna 10 includes a base 15.
As can be seen from FIGS. 2 and 3, conducting surface 14 is corrugated to include a plurality of integrally-formed parallel rectangular primary members 16. Slots 18 are formed between adjacent primary members 16. Conical horn member 12 feeds into a waveguide 19 which includes an electronics section 21 of conventional design for generating an electromagnetic field. A transmission line 17 connects electronics section 21 to a separate control module (not shown), also of conventional design.
As shown most clearly in FIG. 3, each individual primary member 16 of corrugated surface 12 includes a secondary conducting member 20 extending outward from each primary member 16. Secondary member 20 is a thin plate having a rectangular cross-section with a height much greater than its width.
Each secondary member 20 is formed at the center of a top flat surface 23 of a respective primary member 16 and extends normal thereto.
The provision of secondary conducting members 20 extending from primary members 16 provides multiple-depth corrugation. Unlike single-depth corrugated horn antennas of the prior art, wherein a "step" impedance exists across the corrugations, the multiple-depth corrugation of the invention achieves a uniform "tapered" impedance. As discussed above in the Summary of the Invention, the multiple-depth corrugation is analogous to multistep sections in an impedance transformer.
The provision of multiple-depth corrugation achieves substantially equal E- and H-plane beamwidths over a large frequency range. Further, the multiple-depth corrugation provides a higher capacitive reactance over a large frequency range, thus providing for better antenna performance than single depth corrugated horn antennas of the prior art.

The multiple-depth configuration of the invention was analyzed according to conventional electromagnetic theory and antenna specifications were determined to maximize corrugation impedance over a large frequency range. Optimized specifications for maximized corrugation impedance are provided in Table I.

Table I

Interior length of antenna (along azimuthal axis)	25.5"
Maximum internal width of antenna (perpendicular to azimuthal axis)	13.9"
Maximum external width of antenna (perpendicular to azimuthal axis)	18.0"
Height of a primary member	0.49"
Height of a secondary member	1.59"
Width of a secondary member	0.01"
Distance separating adjacent primary members	0.1"
Distance separating adjacent secondary members	0.57"

The thus-optimized antenna 10 was modeled using the Geometrical Theory of Diffraction (GTD). Radiation patterns obtained via the GTD analysis are provided in FIGS. 4 and 5.
FIG. 4 shows the far field radiation pattern for the optimized configuration of Table I obtained at a frequency of 1760 Mhz with a directivity of 15.62 dBi, and with a beamwidth of 29.4 degrees. As can be seen from FIG. 4, the E- and H-plane bandwidths, represented by reference numerals 30 and 32, respectively, are substantially similar. The greatest extent of variation between the E- and H-plane fields occurs between 18 degrees and 36 degrees.
FIG. 5 provides the far field radiation pattern for the optimized configuration of Table I obtained at a frequency of 2300 MHz with a directivity of 17.46 dBi and a beamwidth of 24 degrees. As can be seen, the E- and H-plane bandwidths, both represented by reference numerals 34, are substantially identical.
FIG. 6 shows a comparison of the corrugation surface reactance of a conventional single-depth corrugated horn antenna 35 with the surface reactance for the optimized configuration of Table I, the latter being identified by reference numeral 36. As can be seen from FIG. 6, multiple-depth corrugation achieves a higher capacity reactance over the entire frequency range shown, thus achieving improved performance.
The multiple-depth corrugated antenna thus far described includes two corrugation depths. However, alternative embodiments may provide corrugation to an arbitrary number of depths. Thus, for example, each secondary member 20 can further include an additional tertiary member (not shown) to achieve three levels of corrugation depth. Of course, in such an embodiment, the secondary members require greater thickness than those shown in the drawings.
Antenna 10, including primary members 18 and secondary members 20, is constructed of conventional horn antenna materials, and is manufactured and operated according to conventional techniques. As these various techniques and materials are well understood by those skilled in the art, neither will be discussed in further detail here.
Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

A corrugated horn antenna (1) characterized by:
a conducting surface (14);
a plurality of parallel conducting primary members (16) provided on the conducting surface (14) extending substantially perpendicular to the surface; and
a plurality of conducting secondary members (20) provided on each primary member (16), the secondary members (20) extending substantially perpendicular to the conducting surface (14) and extending parallel to the primary members (16), such that multiple-depth corrugation is achieved.
The corrugated horn antenna (10) according to Claim 1, characterized in that the primary members (16) are equally spaced along the conducting surface (14).
The corrugated horn antenna (10) according to Claim 1, characterized in that the secondary members (20) of each respective primary member (16) are equally spaced along the respective primary members (16).
The corrugated horn antenna (10) according to Claim 1, characterized in that each primary member (16) includes one respective secondary member (20).
The corrugated horn antenna (10) according to Claim 4, characterized in that each respective secondary member (20) is formed at a center of a top surface (23) of a respective primary member (16).
The corrugated horn antenna (10) according to Claim 1, characterized in that the primary members (16) have substantially rectangular cross-sections.
The corrugated horn antenna (10) according to Claim 1, characterized in that the secondary members (20) have substantially rectangular cross-sections.
The corrugated horn antenna (10) according to Claim 1, characterized in that the primary members (16) are of a uniform size and shape and the secondary members (20) are of a uniform size and shape.
The corrugated horn antenna (10) according to Claim 1, characterized in that the conducting surface (14) has a substantially V-shaped cross-section with the primary members (16) provided on an interior surface thereof.
The corrugated horn antenna (10) according to Claim 1, characterized in that the corrugated horn antenna (10) is a conical antenna.