Beamforming networks using the Nolen matrix for 5G applications

Abstract

A design of a wideband low loss 3 × 3 Nolen matrix is presented at 3.5 GHz. The proposed Nolen matrix is designed with the implementation of three branch-line couplers and two phase shifters. The interdigital capacitor unit cell is implemented in both the coupler and phase shifter to reduce the size and improve the bandwidth. The proposed 3 × 3 Nolen matrix is simulated using computer simulation technology (CST) software and then fabricated on the FR4 substrate with . The 3 × 3 Nolen matrix performance is achieved with a fractional bandwidth of 49% and operates at 2.52–4.2 GHz. The coupling factor of the 3 × 3 Nolen matrix across outputs at 3.5 GHz is −6 ± 0.98 dB with phase differences of 3.37° at port 1, 125.6° at port 2, and −117.8° at port 3. Then, the proposed Nolen matrix is attached with three standard microstrip antennas to prove the property of a unique beam scanning. The measured results approve the concept of three different phases scanning at 0°, 45°, and −40° with a reflection coefficient below −10 dB. Compared to the conventional Nolen matrix, the 3 × 3 Nolen matrix with a modified coupler is achieved with a low loss characteristics with phase error up to 2.2° and a compact size of 0.82 λ × 0.75 λ. The proposed Nolen matrix is suitable to be used in future 5G antenna beamforming applications.