An X-Band Dual Function Transceiver Utilizing Digital Predistortion for Radar and Communication in 250 nm GaN HEMT

Abstract

We present an X-band transceiver with memory polynomial digital predistortion (MP-DPD) and neural network digital predistortion (NN-DPD) for a dual-function radar and communication (DFRC) system targeting 6G FR3 in $0.25\mu $ m GaN High Electron Mobility Transistor (HEMT) technology. In the implemented transceiver, we integrated a transmit and receive switch (T/R switch), high-power amplifier (HPA), and low noise amplifier (LNA) into a single-chip. By utilizing shunt switches and quarter-wave transmission-lines ( $\lambda $ /4 T-lines) without series switches, the T/R switch achieved an insertion loss of 0.69dB, and the input 0.2dB compression point was 44 dBm. In the transmit (Tx) path, the HPA and T/R switch achieved a bandwidth of 8.4 - 10GHz, an output power (P ${}_{\mathrm {out}}$ ) of 40.8dBm, and a power added efficiency (PAE) of 33.1% at 9GHz. By eliminating a limiter and circulator in the receive (Rx) path owing to the superior breakdown performance of the GaN HEMT, the designed MMIC achieved a noise figure of 2.14dB at 8.5GHz, which is comparable with that of the Rx using a GaAs LNA with a limiter and circulator. The bandwidth of the LNA with T/R switch was 7.3GHz - 10.6GHz, and the power gain was 33.5dB. To mitigate the nonlinearity of GaN HEMTs for 16-QAM and 64-QAM signals, NN-DPD was adopted. At 10GHz carrier frequency and 1GHz bandwidth, the NN-DPD improved the 16-QAM EVM from -24.0dB to -32.4dB and ACLR from 29.3dB to 39.3dB. Similarly, the 64-QAM performance rose from -25.1dB to -34.6dB in EVM and from 28.7dB to 45.4dB in ACLR while transmitting a 6Gbps signal. The fabricated X-band MMIC has outstanding performance and is perfectly suitable for implementing high-performance DFRC applications.