Real-Time Circuit Optimizations for Dual-Function Radar-Communications

Spectral efficiency has become increasingly important in the modern congested spectral environment. Directional modulation multiplexing helps by using spatial diversity to transmit different messages in different directions at the same frequency. This approach can be used to provide dual-function radar-communication transmissions that are direction-specific. In these transmissions, the vector current excitations of different array elements are calculated to provide the directional transmission, resulting in different output power levels for the different elements. This approach results in varying levels of compression for the element amplifiers, leading to varying distortion and performance. Mutual coupling between elements can change the antenna reflection coefficients, resulting in distortion of the directionally transmitted symbols and further alter element performance. Real-time reconfigurable matching circuitry, placed between each element amplifier device and antenna, ensures that each amplifier is optimized to maximize gain while minimizing distortion when the frequency, intended directions, or directional transmission symbol combinations are changed. An algorithm is proposed and demonstrated in simulation which uses high-speed plasma-switched impedance tuners, in-situ RF current measurements, and amplifier pre-characterization to quickly optimize array circuitry. These optimizations may be completed in microseconds, allowing reconfigurability commensurate with pulse-to-pulse adaptivity relative to the radar function of the transmission.