Abstract

Digital linearization of a phased array transmitters is usually based on feedback measurements. Various arrangements can be used to measure multiple transmit paths by using conducted or radiated methods. We propose a technique for measuring any pair of transmit paths simultaneously by using a common feedback connected to two receivers, and a cancellation method that can make the measurements independent. Together with the feedback cancellation, a single feedback line with two output ports can be used to measure different transmit chain pairs coherently under varying load conditions present in phased arrays. The cancellation filters are trained by using a fifth-generation (5G) new radio waveform and verified by over-the-air (OTA) measurements along with the predistortion performance evaluation of a 28 GHz 8-element phased array transmitter. The method achieved 30 dB cancellation between the paths and the DPD trained with the feedback cancellation achieved 4.2 % EVM and -40.8 dBc ACPR.