In-Situ Measurements in Reconfigurable Phased-Array Transmitters

In reconfigurable array transmissions, a phased-array transmitter changes its characteristics, yet must still be able to control its transmission while optimizing its performance. To enable full reconfiguration while transmitting predictably, performing accurate, real-time measurements within the transmit chain is useful. This recently developed in-situ measurement approach, shown in multiple previous contributions, is summarized in this paper. It serves two purposes: (1) informing the real-time optimization algorithm whether changes in transmitter characteristics improve or worsen performance, and (2) updating the array calibration to obtain the desired transmit array pattern. This will enable real-time, “on the fly” optimizations of transmitters to coexist with other wireless devices in an increasingly congested spectral environment. A four-port coupler, with two monitoring outputs, is used to monitor the total voltage and current between a reconfigurable impedance tuner and the antenna in each element of a transmit array chain. Experimental work from the different prior contributions shows the overall trajectory, reliability, and proposed applications of this in-situ measurement technique. Less than 1 mV of error vector magnitude is shown in vector network analyzer methods compared with simulations using the in-situ coupler approach. The integration and calibration of a software-defined radio to perform antenna input current in-situ measurements has been implemented, with an average current error vector magnitude of 258 µA when comparing the software-defined radio measurements with simulations. Simulation results have shown that in-situ measurements can successfully correct input voltage waveforms for accurate directionally modulated transmissions, lessening reliance on fixed transmitter array pre-calibrations.