Enhanced Measurement Sensitivity Using Near-Field Antenna With MMIC Low-Noise Amplifier for Deep Tissue Microwave Thermometry

A monolithic microwave integrated circuit (MMIC) low-noise amplifier (LNA) is incorporated in a passive antenna for noninvasive deep tissue thermometry using a near-field microwave radiometer. An internally impedance-matched high-gain (30 dB) MMIC LNA with 1-dB noise figure (NF) is integrated on the ground plane of a multilayered microstrip patch antenna with a 1.27-mm-thick superstrate. The antenna design parameters were optimized for noninvasive power reception with a sensing depth of 40 mm, return loss of ≥ 30 dB at 1.3 GHz, and a -10-dB bandwidth of 200 MHz. A 1.3-GHz switch-circulator single reference Dicke radiometer with 200-MHz bandwidth was implemented to assess the performance of the active antenna. Microwave circuit simulations were used to optimize the scattering parameters, gain, and NF of the radiometer for unconditional stability. The fabricated microwave radiometer has 38 dB gain, 2.6 dB NF, and input and output port return loss greater than 15 dB over 1.2-1.4 GHz. Radiometer measurements of temperature-controlled tissue phantom indicate improved measurement accuracy with a sensitivity of ±0.18 °C for the proposed active antenna. Enhanced performance observed with the integration of MMIC LNA in the passive antenna is expected to improve noninvasive detection of deep-tissue temperature.