Highly Efficient 30 GHz 2x2 Beamformer Based on Rectangular Air-Filled Coaxial Line

This article introduces a low loss beamformer with a capability of 2-D scanning in elevation and azimuth directions at 30 GHz for 5G applications. The proposed beamformer is based on the broadband and highly efficient rectangular air-filled coaxial line. The beamformer is fed by four standard waveguides (WR-28) as the input ports. Correspondingly, each of the input ports using specific transitions is connected to the coaxial beamformer network. Ultimately, the coaxial transmission lines, in the radiating part of the beamformer, feed a 2 x 2 waveguide antenna array. The structure is aptly called a waveguide-coaxial-waveguide beamformer. The total dimensions of the fabricated prototype are 60 mm x 60 mm (corresponding to 6 lambda x 6 lambda). The beamformer is able to generate four fixed beams, one in each quadrant at an elevation angle of 25 degrees from the broadside to the array axis. The results demonstrate that the proposed passive beamformer has a radiation efficiency greater than 90% over the frequency bandwidth (BW) of interest. Good stability of the radiation pattern and maximum gain over the desired BW were achieved while maintaining the sidelobe level of less than 20 dB.