Single frequency duplex radio link

Abstract

A radio link with two communicating transceivers each having a system for isolating incoming and outgoing radio signals to permit simultaneous transmit and receive by each transceiver on the same frequency or in the same frequency range. This is done so that in-coming receive signals received by each of the transceivers from the other transceiver is much stronger than the portion of its own transmitted signal that is coupled back into its antenna. The invention uses a special electronic circuit, termed the iso-circulator, to couple the antenna to both the co-located receiver and the transmitter. The iso-circulator circuit includes a simulated antenna load with an impedance matched to the antenna impedance. The circuit also includes a transformer with its primary side fed asymmetrically by the antenna so that it can pass the desired receive signal with minimum attenuation. The transformer's primary is on the other hand fed symmetrically from both sides by equally small portions of the transmit power from the co-site transmitter, but these signals are 180 degrees out of phase and cancel almost completely in the transformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art circulator.

FIG. 2 shows a prior art circulator located in a transceiver system.

FIG. 3 shows features of a prior art Wilkinson divider.

FIG. 4 is a block diagram showing features of the present invention.

FIG. 5 shows more details an embodiment of the present invention.

FIGS. 6 a, 6b and 6c show how radio energy circulates in the present invention.

FIG. 7 shows test results showing isolation of more than 70 dB in an idealized situation.

FIG. 8 shows a preferred radio link according to the present invention.

FIG. 9 shows more details of a preferred embodiment of the present invention.

Claims

1. A radio link radio link with two communicating transceivers each having a system for isolating incoming and outgoing radio signals to permit simultaneous transmit and receive by each transceiver in the same frequency range, said radio link comprising: A) a transmitter,B) an antenna, defining an antenna electrical impedance within said radio frequency range,C) a iso-circulator comprising: 1) a matched electrical load having an electrical impedance substantially matched to said antenna electrical impedance,2) a radio signal splitter adapted to split incoming radio power signals into two substantially equal outgoing radio power signals,3) a transformer defining a primary and a secondary coil,4) a circulator coupling said antenna to said splitter and said transformer, and5) a second circulator coupling said matched electrical load to said splitter and said transformer. wherein the three radio signal splitters and said transformer are arranged produce: (i) a circulation within said iso-circulator of about one-half of output power of said co-located transmitter in a first direction and a circulation of about one-half of said output power of said co-located transmitter in a second direction opposite said first direction and(ii) a circulation within said iso-circulator of about one-half of input power received by said antenna in said first direction and a circulation of one-half of said input power received by said antenna said second direction; with said transformer positioned within said quasi-circulator so that substantially all output power of said transmitter that is not otherwise transmitted or dissipated is cancelled in said transformer, andD) at least one receiver adapted to receive remote radio power signals from the other transceiver at an output of said secondary coil of said transformer, wherein said remote radio power signals received by said receiver is significantly greater than radio power signals received by said receiver from said transmitter.

2. The radio link as in claim 1 wherein said iso-circulator also comprises two radio signal amplifiers for amplifying radio signals at two inputs to the primary side of said transformer.

3. The radio link as in claim 1 and further comprising a radio signal amplifier positioned to amplify output signals from said secondary side of said transformer.

4. The radio link as in claim 1 wherein said radio signal splitter is a Wilkinson divider.

5. The radio link as in claim 4 wherein said Wilkinson divider is a three-port divider with each port having a 50-Ohm characteristic impedance and each divider having a port connected to two other ports with a quarter-wave transmission line transformer of about 70.7 Ohm characteristic impedance, wherein the other two ports are separated by an isolation resister with an impedance of about 100 Ohms.

6. The radio link as in claim 1 wherein said transformer is a balun transformer.

7. The radio link as in claim 6 wherein one of two secondary terminals of said transformer is grounded.