A microwave ablation system for ablating target tissue, the system comprising: a catheter having a proximal region, a distal region, and at least one lumen extending therebetween; a switching antenna (22, 22') disposed at the distal region of the catheter, the switching antenna comprising: a main antenna (43, 43') comprising first and second microwave radiating elements (44a, 44b, 44a', 44b') configured to emit microwave energy, the main antenna further configured to measure a radiometer temperature and generate signals indicative of the measured radiometer temperature; a reference termination (48, 48') disposed at a junction between the first microwave radiating element and the second microwave radiating element, the reference termination configured to measure a reference temperature and generate signals indicative of the measured reference temperature; and a switch electrically coupled to the main antenna and the reference termination, the switch configured to select between the signals indicative of the measured radiometer temperature from the main antenna and the signals indicative of the measured reference temperature from the reference termination; a generator coupled to the proximal region of the catheter, the generator configured to provide power to the first and second microwave radiating elements via a cable extending through the at least one lumen of the catheter and coupled to the main antenna at a location proximal to the switch and the reference termination; and a processor configured to receive the selected signals indicative of the measured radiometer temperature and the selected signals indicative of the measured reference temperature from the switch, the processor further configured to calculate a target tissue temperature based on the signals indicative of the measured radiometer temperature and the signals indicative of the measured reference temperature. a catheter having a proximal region, a distal region, and at least one lumen extending therebetween; a switching antenna (22, 22') disposed at the distal region of the catheter, the switching antenna comprising: a main antenna (43, 43') comprising first and second microwave radiating elements (44a, 44b, 44a', 44b') configured to emit microwave energy, the main antenna further configured to measure a radiometer temperature and generate signals indicative of the measured radiometer temperature; a reference termination (48, 48') disposed at a junction between the first microwave radiating element and the second microwave radiating element, the reference termination configured to measure a reference temperature and generate signals indicative of the measured reference temperature; and a switch electrically coupled to the main antenna and the reference termination, the switch configured to select between the signals indicative of the measured radiometer temperature from the main antenna and the signals indicative of the measured reference temperature from the reference termination; a main antenna (43, 43') comprising first and second microwave radiating elements (44a, 44b, 44a', 44b') configured to emit microwave energy, the main antenna further configured to measure a radiometer temperature and generate signals indicative of the measured radiometer temperature; a reference termination (48, 48') disposed at a junction between the first microwave radiating element and the second microwave radiating element, the reference termination configured to measure a reference temperature and generate signals indicative of the measured reference temperature; and a switch electrically coupled to the main antenna and the reference termination, the switch configured to select between the signals indicative of the measured radiometer temperature from the main antenna and the signals indicative of the measured reference temperature from the reference termination; a generator coupled to the proximal region of the catheter, the generator configured to provide power to the first and second microwave radiating elements via a cable extending through the at least one lumen of the catheter and coupled to the main antenna at a location proximal to the switch and the reference termination; and a processor configured to receive the selected signals indicative of the measured radiometer temperature and the selected signals indicative of the measured reference temperature from the switch, the processor further configured to calculate a target tissue temperature based on the signals indicative of the measured radiometer temperature and the signals indicative of the measured reference temperature.