Miniaturised multi-beam-controlled circular eight-port beamforming network for long-range UHF RFID hemispheric coverage

In this paper, a miniaturised multi-beam-controlled circular eight-port beamforming network for long-range ultra-high-frequency radio-frequency identification (UHF RFID) hemispheric beam-coverage systems (e.g. unmanned aircraft systems) is proposed. For multi-beam control and compact implementation, the proposed eight-port feeding network consists of an integrated beam-control block with a two-stage RF switch block, 12 quadrature hybrid couplers, and 12 90 degrees phase shifters, and was designed and fabricated on a circular three-layer 1.2mm FR-4 substrate. The diameter of the fabricated network is approximate to 0.47 (0) at 915MHz. The measured maximum insertion loss, and amplitude and phase imbalances of the fabricated network at the authorised UHF RFID frequency band (902-928MHz) are approximate to 4.5dB,+/- 1.3dB, and +/- 17.5 degrees, respectively. An eight-element dipole antenna array with the proposed feeding network shows feasibility of hemispheric beam coverage by generating multiple beams simultaneously regarding port controls. Beam coverages, where the simulated realised gain is higher than 3dBi, are approximate to 180 degrees and 130 degrees at phi=90 and 0 degrees, respectively.