Phased array impedance tuning, secure transmission, and nonlinear spatial intermodulation suppression for next-generation radar and communications systems.

Simultaneously transmitting radar and communications signals from the same multi-beam phased array system, using spatial diversity, allows multiple functions to use the same frequency and can alleviate spectral congestion. An issue arises, however in a transmitter array that consists of power amplifiers connected to the antenna elements. Undesired spatial intermodulation beams are transmitted as a result of the nonlinearities in these power amplifiers and can degrade both radar and communications mission abilities. The research presented in this dissertation resolves the nonlinear intermodulation products caused by these power amplifier nonlinearities by element-wise impedance tuning between each power amplifier and antenna element to reverse the nonlinear distortion effects. To emphasize the importance of the flexibility that elementwise impedance tuning provides, the analysis of a single-beam phased array transmitter is presented to demonstrate the dynamic improvement in range for both radar and communications scenarios individually. The improvement results from resolving the mismatch between the antenna elements due to mutual coupling as the array scan angle changes. Finally, to ensure secure communications messages while maintaining radar capabilities, a directional modulation technique is presented, as well as Barker code sequencing, to maintain communications security in the transmit and receive mode of the radar.