A novel bi-directional amplifier with applications in active Van Atta retrodirective arrays

A novel two-port bi-directional amplifier, which may simultaneously amplify the waves coming from both ports, is proposed and demonstrated in this paper. Using this amplifier, a two-element active Van Atta retrodirective array is implemented and compared to a four-element passive array. The bi-directional amplifier is constructed by two identical one-port reflection-type amplifiers and a 3-dB 90 hybrid. The reflection-type amplifier is designed using an FET with a single-power-supply configuration. A quarter-wavelength microstrip radial stub is connected to the deviceʹs source terminal to narrow down the negative-resistance frequency range so as to avoid oscillation at undesired frequencies. The fabricated bi-directional amplifier provides the transmission gain over the frequency band from 5.76 to 6.88 GHz, with a peak value of 9.1 dB at 6.04 GHz. Printed Yagi antennas with four directors are adopted to build both the active and passive Van Atta arrays. The 3-dB back-scattering beamwidth of the active array is measured as wide as 74. Finally, it is observed from the measurements that, although only half of the antenna elements are used, the active Van Atta array produces a back-scattering field level 4.5 dB, on average, higher than the passive one does. This verifies the performance of the bi-directional amplifier.