Microwave detection apparatus

1. Microwave detection apparatus comprising

an intravascular catheter containing an inner conductor and an outer conductor, each conductor having proximal and distal ends, the distal ends of said conductors forming an antenna at a distal end of the catheter;

means defining a gap in the inner conductor relatively near the antenna thereby forming spaced-apart opposing distal and proximal inner conductor segments, and

an electrical circuit in said catheter and connected electrically between said conductor segments, said circuit including

a temperature reference, and

a Dicke-switch switchable in response to a switching signal between a first condition wherein the switch connects the proximal inner conductor segment to the temperature reference thereby delivering a temperature reference signal from the temperature reference to the proximal ends of the conductors and a second condition wherein the switch connects the proximal inner conductor segment to the distal inner conductor segment thereby delivering an antenna signal from the antenna to the proximal ends of the conductors, and a detector responsive to the antenna signal for providing an indication of microwave emissions picked up at the antenna.

2. The apparatus defined in claim 1 and further including a switching signal source connected electrically to the switching circuit via the inner conductor for applying a switching signal to said switch to toggle the switch between said two conditions.

3. The apparatus defined in claim 2 wherein the switching signal source comprises a switched DC voltage source.

4. The apparatus defined in claim 1 wherein the temperature reference comprises a resistor.

5. The apparatus defined in claim 1 wherein said circuit is comprises an integrated circuit chip which fits entirely within said outer conductor and is electrically grounded thereto.

6. The apparatus defined in claim 5 wherein the chip includes

first and second series-connected diodes, each diode having a cathode and an anode;

a first conductor connecting the cathode of the first diode to the distal inner conductor segment;

a first resistor connecting the cathode of the first diode to the outer conductor, and

a second conductor connecting the proximal inner conductor segment to the anode of the first diode and the cathode of the second diode,

said temperature reference being a resistance connected electrically between the anode of the second diode and the outer conductor.

7. The apparatus defined in claim 1 and further including

a voltage source having an output providing a switched DC bias voltage, and

a filter device connected between said output and the proximal ends of said conductors to isolate the switching signal to the switch from the antenna signal from the antenna.

8. The apparatus defined in claim 1 wherein the detector comprises

a radiometer operating at a selected frequency and having an input, and

connection means electrically connecting the proximal ends of said conductors to said input.

9. The apparatus defined in claim 8 and further including

a voltage source having an output providing a switched DC bias voltage, and

a filter device connected between said output and the proximal ends of the conductors to isolate the switching signal to the switch from the antenna signal to the radiometer.

10. The apparatus defined in claim 9 wherein the filter device comprises

an electrical lead extending through a hole in said outer conductor and connecting said inner conductor to the output of the voltage source, and

a capacitance connected electrically between said outer conductor and the output of the voltage source.

11. The apparatus defined in claim 8 wherein said radiometer is contained within said catheter.