Cancellation Circuit for Transmit-Receive Isolation

This wireless distributed digital phase array (WDDPA) has been proposed for several military applications in the sensor and communication areas. The idea of WDDPA is to use a wireless network for transmitting and receiving data between a master controller and modules in an active phased array instead of using a conventional wired beamforming network. The WDDPA provides several advantages over conventional networks such as battlefield survivability, digital architecture and flexibility of system installation on platforms. A phase synchronization circuit has been developed in the WDDPA application, allowing coherent processing of the data from all elements. There are limitations encountered due to non-ideal hardware, and the performance of the circuit is limited. One of the major problems is the leakage from the circulator. The leakage disrupts the power distributed from the T/R modules. A cancellation circuit has been developed to cancel out the leakage. The performance of the cancellation circuit was investigated by a series of simulations using Agilent ADS (Agilent Advanced Design System), and hardware tests were conducted to characterize the behavior of the circuit. The performance is limited by the accuracy of the attenuator and phase shifter in the cancelation branch. A method for cancelling the residual leakage signal digitally is discussed.