Microwave detection apparatus includes an intravascular catheter containing inner and outer conductors, the distal ends of the conductors forming an antenna at a distal end of the catheter. A gap is provided in the inner conductor near the antenna thereby forming spaced-apart opposing proximal and distal inner conductor segments between which is connected an electrical circuit. That circuit includes 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.