Reconfigurable Transmitarray With Near-Field Coupling to Gap Waveguide Array Antenna for Efficient 2-D Beam Steering

A novel array antenna architecture is proposed that can enable 2-D (full-space) radiation pattern control and efficient beam steering. This solution is based on a gap waveguide array antenna and a reconfigurable transmitarray (TA) that are coupled in the radiative near field. An equivalent two-port network model of the coupling mechanism is presented and validated numerically. The desired TA reconfiguration capability is realized by an 8 x 8 array of cavity-backed patch resonator elements, where two AlGaAs p-i-n diodes are integrated inside each element providing a 1-bit phase shift. The TA is implemented in an eight-layer printed circuit board (PCB), which includes radiating elements, fixed phase-shifting inner-stripline sections, impedance matching, and biasing circuitry. The combined antenna design is low profile (similar to 1.7 wavelength) owing to the small separation between two arrays (similar to 0.5 wavelength), as opposed to conventional TAs illuminated by a focal source. The design procedure of the proposed architecture is outlined, and the measured and simulated results are shown to be in good agreement. These results demonstrate 23.5-25.2 GHz -10-dB impedance bandwidth and 23.3-25.3 GHz 3-dB gain bandwidth, a beam-steering range of +/- 30 degrees and +/- 40 degrees in the E- and the H-planes with the gain peak of 17.5 dBi, scan loss <= 3.5 dB, and TA unit cell insertion loss <= 1.8 dB, respectively.