Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
1999-09-28
2001-11-06
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C455S082000
Reexamination Certificate
active
06313713
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to antenna isolation circuits for transmitters and receivers using the same antenna. More specifically, but without limitation thereto, the present invention relates to an input/output isolation circuit that extracts energy from a radio frequency (RF) output signal to cancel undesired coupling of the RF output signal into one or more RF input devices.
It is often advantageous to couple multiple devices, such as a transmitter and a receiver, to the same antenna. A common approach uses a radio frequency circulator to isolate the transmitted signal from the received signal to avoid overloading the receiver front end. However, current technology for RF circulators limits the degree of isolation to about 25 dB. The conventional methods are therefore not suited to applications that require 50 dB or more of isolation. A need therefore exists for an antenna isolation circuit that attenuates the coupling of undesired RF signals by at least 50 dB.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming the problems described above, and may provide further related advantages. No embodiment of the present invention described herein shall preclude other embodiments or advantages that may exist or become obvious to those skilled in the art.
A matched pair circulator antenna isolation circuit of the present invention provides isolation between an antenna and one or more receivers and transmitters and may also be applied to other RF devices. A portion of the transmit signal is extracted by a first RF circulator and divided into two phase-inverted signals. The first phase-inverted signal is coupled through a first directional coupler to cancel most of the transmit signal present in the receive signal. The second phase-inverted signal is coupled through a second directional coupler to cancel remaining transmit signal in the output of the first directional coupler. The output of the second directional coupler is coupled to the input of the receiver.
An advantage of the matched pair circulator antenna isolation circuit of the present invention is that a high degree of signal isolation may be provided between an antenna and multiple transmitters and receivers.
Another advantage is that the design of the matched pair circulator antenna isolation circuit may readily be scaled to include additional RF devices.
The features and advantages summarized above in addition to other aspects of the present invention will become more apparent from the description, presented in conjunction with the following drawings.
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Hart Stephen M.
Henry Willard I.
Ho Thinh Q.
Kosinovsky Gregory A.
Bettendorf Justin P.
Fendelman Harvey
The United States of America as represented by the Secretary of
Ward James A.
Whitesell Eric James
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