Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1998-04-09
2001-03-13
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S767000, C343S770000, C333S137000
Reexamination Certificate
active
06201507
ABSTRACT:
BACKGROUND
The present invention relates generally to radiators, and more particularly, to the use of a centered longitudinal shunt slot disposed in a broadwall of a rectangular waveguide that is fed by an offset ridge resonant iris.
An advanced seeker under development by the assignee of the present invention requires a common aperture dual polarized antenna. There are several ways to provide a dual polarized antenna having a common aperture. To provide a large aperture, a dipole array and slot array combination is very attractive. For this combination, centered longitudinal shunt slots must be used because an offset longitudinal shunt slot excites not only a desired lowest parallel plate mode but also undesirable higher order modes in the parallel plate region created by the dipole array. The centered longitudinal shunt slot excites only the desired lowest mode (TEM).
However, a centered longitudinal broadwall slot in a rectangular waveguide does not radiate because the centered longitudinal slot does not disturb the current flow of the TE10 mode. The prior art used an L-shaped offset resonant iris to excite the centered longitudinal slot.
Centered longitudinal broadwall slots fed by L-shaped resonant irises have heretofore been used to produce a linear antenna array. This antenna array is disclosed in a paper by R. Tang, entitled “A slot with variable coupling and its application to a linear array:, IRE Trans. AP-8, p. 97, 1960. This linear antenna array has a relatively inefficient layout, exhibits an undesirable phase change in terms of offset variation, has a somewhat unstable conductance range, and is relatively difficult to machine and dip braze.
Accordingly, it is an objective of the present invention to provide for the use of a centered longitudinal shunt slot disposed in a broadwall of a rectangular waveguide that is fed by an offset ridge resonant iris, and which is particularly well adapted for use in a common aperture dual polarized antenna.
SUMMARY OF THE INVENTION
To meet the above and other objectives, the present invention provides for a radiator comprising a centered longitudinal shunt slot disposed in rectangular waveguide that is fed by an offset ridge resonant iris having a finite thickness. Depending upon the application, the rectangular waveguide has one or more centered longitudinal shunt slots that are fed by corresponding offset ridge resonant irises that are centered on each respective slot. Typically the offset ridge resonant irises are oriented opposite to each other within a particular waveguide to change the radiating phase by 180 degrees.
The present radiator provides for an improved common aperture antenna layout, for example, compared to a conventional antenna array using offset shunt slots fed by a rectangular waveguide. The antenna array constructed using centered longitudinal shunt slots disposed in a rectangular waveguide that is fed by offset ridge resonant irises in accordance with the present invention reduces undesirable phase changes in terms of the offset variation compared to conventional antenna arrays having centered longitudinal shunt slots fed by L-shape offset resonant irises of the same finite thickness at a higher frequency. An antenna array constructed in accordance with the present invention has a more stable conductance range than one that uses L-shaped irises. Furthermore, an antenna array employing the offset ridge resonant irises and centered longitudinal shunt slot is easy to machine and dip braze.
The present invention improves upon the prior art in the following three ways. The use of centered longitudinal shunt slots fed by an offset ridge resonant irises makes it possible to design a low sidelobe antenna by having a large range of radiating conductance with constant radiating phase. The present invention reduces the undesirable phase advances due to the use of offset L-shaped irises. The offset ridge resonant irises are easy to fabricate because ridge irises are easy to machine and the ridge irises provide a salt drain path for dip brazing processes. The use of centered longitudinal shunt slots fed by rectangular waveguides is desirable because it produces a low sidelobe antenna pattern when used in a dual polarized common aperature antenna.
REFERENCES:
patent: 4491810 (1985-01-01), Saad
patent: 4839663 (1989-06-01), Kurtz
patent: 5010351 (1991-04-01), Kelly
patent: 5543810 (1996-08-01), Park
patent: 5619216 (1997-04-01), Park
Kim Sang H.
Park Pyong K.
Collins David W.
Lenzen, Jr. Glenn H.
Phan Tho
Raytheon Company
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