High-Resolution Digital Beamforming Receiver Using DDS-PLL Signal Generator for 5G Mobile Communication

This article presents a signal generator and a digital beamforming receiver (DBR) with high phase control resolution and high beam control resolution, respectively. The signal generator is designed based on a direct digital synthesizer (DDS) and a phase lock loop (PLL). In the DDS-PLL signal generator, the conventional divider in PLL is replaced with a mixer, comb generator, and a doubler to utilize high phase control resolution of DDS (14 bit, 0.022°) as it is to synchronize the DDS-PLL signal generator with the entire system. In the DBR, the output signals of the DDS-PLL signal generators are used as the second local oscillator (LO) signal, and the beamforming technique is implemented through the change of the phase of the second LO signals. Also, for sophisticated beamforming, all signal generator components in the DBR are synchronized for generating same and fixed frequency and phase. Finally, the DBR has the same phase control resolution as the DDS, and the phase of each chain of the DBR can be adjusted up to 0.022° (14 bit). The DBR using the DDS-PLL signal generator is designed and fabricated. The DBR consists of a 1 \times 8 array tapered slot antenna (TSA) part, a first and second frequency conversion part, a 1 \times 8 data acquisition and combiner part, DDS-PLL signal generator part, and a reference signal generator part. The phase control performance of the DBR was verified by measuring the phase change of the chain in the DBR according to the DDS phase change. Also, to verify the beamforming performance of the DBR with high beam control resolution, the radiation pattern of the DBR when the angle of the main lobe was 0°, 0.2°, 0.4°, 15°, and 30° was measured in the 28 GHz band. At the main lobe, the gain error is within 1 dB and the beam angle error is within 0.2°. The simulation results are in good agreement with the measured results. A high-resolution beamforming performance is achieved in the DBR using the DDS-PLL signal generator.