Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-12-21
2001-10-16
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S001100, C333S024200
Reexamination Certificate
active
06304155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the isolation of radio frequency (RF) signal amplifiers from returned signals using circulator-based isolators.
2. Background and Related Art
Circulators are generally ferrite devices composed of permanent magnets. Circulators used as isolators pass RF signals and block returned signals. Some of the power in the RF signal, and nearly all of the power in the blocked returned signals, is dissipated as heat. Dissipating power as heat raises the temperature of a circulator. The performance characteristics of ferrite devices composed of permanent magnets change with temperature. In particular, the frequency response of ferrite, and the coercive effect of permanent magnets, changes as temperatures rise. Uncompensated changes in the frequency response of ferrite and the coercive effect of permanent magnets cause a circulator to suffer higher return losses, or “drift”, in all of its ports. Drift manifests itself as a change in impedance. Changed impedances cause mis-matched impedances, which cause power to be reflected rather than transferred, which leads to further heating, further losses, and ultimately failure of the circulator. Failure of a circulator means upstream components such as amplifiers are no longer being isolated from returned signals, which jeopardizes their lives as well.
In general, the higher the temperature a circulator is able to withstand, the higher its rated power level. Circulators used as isolators are normally temperature-compensated to increase the temperature they are able to tolerate. Temperature compensation is costly. Higher operating temperatures, and hence higher rated power levels, may be achieved in return for higher cost and greater complexity. Still, there is a finite limit to the amount of power that can be passed safely through any circulator-based isolator.
SUMMARY OF THE INVENTION
The present invention provides a solution to the shortcomings of the prior art as discussed above.
In particular, the present invention provides an apparatus for doubling the amount of power that can be safely applied to a circulator-based isolator, which is made up of an input hybrid which receives an RF signal and outputs two divided RF signals, a circulator that receives one of the divided RF signals at one of the circulator ports and outputs it at another circulator port, an output hybrid that receives the two divided RF signals, combines them, and sends them on, an output hybrid that simultaneously receives a returned signal, divides it, and outputs two divided returned signals, one divided returned signal going to the circulator and the other divided returned signal going directly to the input hybrid, and a phase retarding circuit that takes the one-half of the divided returned signal that went back to the circulator and retards its phase by 180 degrees and sends it back to the circulator, where it goes to the input hybrid as well, to be recombined with the other half of the returned signal and there attenuated.
DESCRIPTION OF THE DRAWINGS
The invention will be described in detail with reference to the following drawings, in which:
FIG. 1
is a schematic diagram of a hybrid junction used in connection with the present invention;
FIG. 2
is a schematic diagram of a Y-junction circulator used in connection with the present invention;
FIG. 3
is a schematic diagram of the Y-junction circulator shown in
FIG. 2
configured as an isolator;
FIG. 4
is a block diagram of the forward signal path of a first embodiment of a circulator-based isolator power capacity doubling apparatus according to the present invention;
FIG. 5
is a block diagram of the reverse signal path of the embodiment of a circulator-based isolator power capacity doubling apparatus shown in
FIG. 4
;
FIG. 6
is a block diagram of the forward signal path of a second embodiment of a circulator-based isolator power capacity doubling apparatus according to the present invention;
FIG. 7
is a block diagram of the reverse signal path of the embodiment of a circulator-based isolator power capacity doubling apparatus shown in
FIG. 6
;
FIG. 8
is a block diagram of the forward signal path of a third embodiment of a circulator-based isolator power capacity doubling apparatus according to the present invention; and
FIG. 9
is a block diagram of the reverse signal path of the embodiment of a circulator-based isolator power capacity doubling apparatus shown in FIG.
8
.
REFERENCES:
patent: 3622896 (1971-11-01), Pircher
patent: 4902983 (1990-02-01), Fujiki et al.
Bettendorf Justin P.
Rothwell Figg Ernst & Manbeck
Thomcast Communications, Inc.
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