Capacity Enhancement of Ad Hoc Networks Using a New Single-RF Compact Beamforming Scheme

This paper proposes a new single-radio-frequency (RF) compact beamforming scheme that forms the beam by adjusting variable loads. In a conventional phased-array beamformer, half-wavelength antenna spacing is required in order to achieve a reasonable performance without taking into account the mutual coupling. On the other hand, a conventional electronically steerable parasitic array radiator (ESPAR) system requires smaller antenna spacing, but it provides a lower beamforming performance compared to the phased-array beamformer. The proposed method delivers a beamforming performance close to that of a phased array, without having any constraints on the antenna spacing. In the proposed structure, the RF front-end is connected to each antenna via a tunable load, whereas all antenna elements are also terminated by other tunable reactive loads. Simulation results confirm that the proposed scheme provides better interference suppression and achieves more average capacity compared to ESPAR technique. To further validate the beamforming ability of the proposed method, a testbed with 1/20 of the wavelength antenna spacing was fabricated. A good agreement is observed between the measurement and simulation results.