Evaluation of wideband leakage cancellation circuit for improved transmit receive isolation

Abstract

The objective of this thesis is to improve the cancellation performance of a wideband leakage cancellation circuit (WLCC). The results of this thesis can be applied to any sensor or communication system that simultaneously transmits and receives, for example, continuous wave (CW) radar, frequency modulated continuous wave (FMCW) radar, or a wirelessly networked distributed digital phased array (WNDDPA), where the isolation is required between the transmit and receive paths. The approach is to investigate leakage cancellation circuit (LCC) techniques in the analog domain. A frequency demultiplexing and multiplexing circuit (FDMC) is adopted for the analog study and is simulated using Advanced Design System 2011.05 (ADS). Both narrowband and wideband LCC models are simulated in ADS to investigate their phase and amplitude balance properties. Methods such as applying grounded stubs to match the phase slopes of the cancellation and leakage paths are also investigated. Two sets of grounded shunt stubs with different characteristics are applied on the leakage and cancellation paths to achieve near coherent cancellation. Using this configuration, the maximum cancellation power of the LCC is about 87 dB, and the 3.0 dB bandwidth of the cancellation is about 56 MHz.