TX to RX Compact Leakage Cancellation Impedance Tuner for 60 GHz Monostatic Doppler Radar

Monostatic radar shares a single antenna between the transmitter (TX) and receiver (RX) and offers an advantage of the reduced sensor size. However, due to the limited isolation of the coupler, the TX signal leaking into the RX significantly degrades the performance of the monostatic doppler radar. This paper presents the design of an ultra-compact impedance tuner (IT) which is connected to the lumped Rat-Race coupler to minimize the TX to RX leakage signal. The IT offers 5-bit phase control and 8-bit magnitude control via the Serial Peripheral Interface (SPI); moreover, it uses SiGe transistors in reverse saturation to enhance the impedance tuning performance. The size of the IT is only 0.04 mm² and its power consumption is 4 mW at 3.3V power supply. A two-channel 60 GHz monostatic doppler phased array radar chip has been designed and fabricated in 130 nm SiGe BiCMOS technology for vital signs monitoring application. The measured TX to RX isolation due to the Rat-Race coupler is 22 dB; moreover, IT provides the additional isolation of 27 dB, giving total TX to RX isolation of 49 dB at 60 GHz. The design, simulation and measurements of the IT and its measured leakage cancellation performance is reported in this paper.