Leakage Power Canceling Module with a Negative Capacitor for a Circulator’s Isolation

In this study, we developed a leakage power canceling module (LPCM) incorporating a negative capacitor (NCAP). The NCAP provided the circulator with a wide bandwidth, rendering it suitable for retrodirective short-range wireless power transfer applications. The proposed LPCM consisted of a directional coupler, a hybrid coupler, and a low-pass filter network with an NCAP that exhibited the frequency response required to realize leakage power cancellation from the transmitter output to the receiver input. The two couplers were fabricated in an FR4 printed circuit board, and the NCAP was implemented using Samsung LR6LP 65 nm RF CMOS IC technology. The NCAP chip provided a capacitance of -2 pF and consumed a DC voltage and current of 3 V and 13 mA, respectively. The size of the fabricated LPCM was 41 mm × 37 mm. The application of the proposed LPCM was demonstrated with a commercial circulator. The S-parameter measurements indicated that the leakage cancellation was 20‒46 dB at a frequency range of 2.29–2.515 GHz. The bandwidth was defined considering a leakage cancellation of more than 20 dB, and the actual and fractional bandwidths were 222 MHz and 9.25%,