Co-Circularly Polarized Van Atta Array Enabled by Quasi-Monostatic STAR Antennas

A true in-band full-duplex (IBFD) co-circularly polarized (CP) Van Atta array with the active enhancement of the radar cross section (RCS) at 2.45 GHz is demonstrated for the first time. This operation is enabled by a quasi-monostatic simultaneous transmit and receive (STAR) element consisting of two quadrifilar helix antennas (QHAs) counter wound with respect to each other and placed coaxially. Co-CP operation is realized by operating one helix in the forward mode and the other in the backward mode, which increases the isolation between the transmit (Tx) and receive (Rx) layers at the antenna level. To further enhance the isolation, the Van Atta array beamforming network (BFN) is formed from a reduced complexity CP configuration featuring only 90° hybrids and amplification. The concept of operation is verified through measurement of a two-element array and simulated eight-element array with aid from a novel method for the synthesis of Van Atta array performance from conventional range and bench measurements. The effect of mutual coupling in the array is examined along with the role of the phase delay in the BFN.