Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-09-27
2001-06-05
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S772000, C343S776000, C343S725000
Reexamination Certificate
active
06243049
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to antennas and more particularly, to an antenna which provides a plurality of antenna patterns at a plurality of frequencies from a single aperture with the characteristics of each antenna pattern being independently controllable.
Antennas are used on spacecraft to provide multiple uplink and downlink communication links between the spacecraft and the ground. The downlinks operate at one frequency, for example around 20 GHz, and the uplinks operate at a second higher frequency, for example around 30 or 44 GHz. It is usually desirable for a single spacecraft to provide multiple uplink and downlink antenna patterns with each antenna pattern having specific characteristics such as gain and beamwidth. It is also desirable to provide both an uplink and downlink antenna pattern which have the same beamwidth so that a user on the ground can both receive and transmit to the same spacecraft. The method typically used to provide multiple uplink and downlink antenna patterns from a single spacecraft is to provide separate reflectors for each uplink and downlink antenna. This requires a large amount of space on a spacecraft, is expensive and extracts a weight penalty. Therefore, it is desirable to save weight by coupling multiple antennas together in a single structure.
One method used to save weight is to couple one uplink antenna and one downlink antenna together in a single reflector structure where the uplink and downlink antennas share a common reflector. Typically, a single feed horn is configured to simultaneously illuminate a reflector with two RF signals, each at different frequency. The two RF signals are reflected by the reflector which transforms each RF signal into a separate antenna pattern. A disadvantage with this structure is that adjustments to the feed horn affect the characteristics of both antenna patterns making it difficult to provide a plurality of antenna patterns having preselected characteristics at different frequencies from a single feed horn. To decouple the adjustment of each RF signal typically requires using a plurality of adjacently located feed horns positioned about the focus of the reflector where each RF signal is generated by a separate feed horn. The disadvantage with this design is that the feed horns occupy a significant amount of space and create blockage and losses in the antenna patterns.
What is needed therefore is a single, compact antenna which provides a plurality of antenna patterns, where each antenna pattern characteristic is independently controllable and can be adjusted without affecting the pattern characteristics of another antenna pattern, but does not require multiple adjacently positioned horns.
SUMMARY OF THE INVENTION
The preceding and other shortcomings of the prior art are addressed and overcome by the present invention which provides a multi-pattern antenna for generating a first antenna pattern at a first frequency of operation and a second antenna pattern at a second frequency of operation from first and second RF signals, respectively. The antenna included a horn which is dimensioned to generate the first antenna pattern from the first RF signal.
A conduit is located within the horn and is configured to propagate the second RF signal in a waveguide mode. A corrugated rod having a first and a second portion is positioned so that the first portion of the rod is located inside the conduit and the second portion of the rod protrudes from the conduit into the horn. The rod is configured to be responsive to the second RF signal and is operative to transition the second RF signal from a waveguide mode to a surface wave mode and propagate the second RF signal in a surface wave mode along the rod. The rod is configured to generate a second antenna pattern having second antenna pattern characteristics from the second RF signal propagating in a surface wave mode.
In a first aspect, changes in the dimensions of the horn will alter the pattern characteristics of the first antenna pattern but will have substantially no effect on the characteristics of the second antenna pattern.
In a second aspect, changes in the length of the second portion of the rod will alter the pattern characteristics of the second antenna pattern but have substantially no effect on the pattern characteristics of the first antenna pattern generated by the horn.
REFERENCES:
patent: H584 (1989-02-01), Schwering et al.
patent: 4489331 (1984-12-01), Salvat et al.
patent: 5038151 (1991-08-01), Kaminski
patent: 5041840 (1991-08-01), Cipolla et al.
patent: 5109232 (1992-04-01), Monte
Modern Antenna Design, Milligan pp. 179-213, Chapter 7.
Thousand Connie M.
TRW Inc.
Vo Tuyet T.
Wong Don
Yatsko Michael S.
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