The paper presents a consideration of the optimum initial phase distribution for 1-bit transmitarrays with near-field coupling feeding technique. The study is based on the array factor decomposition into a series of continuous aperture distributions, which naturally includes the phase quantization errors. The previously proposed virtual focus approach is compared with the optimum quadratic initial phase distribution. Both methods are found to be very similar for specific values of distribution parameters in terms of farfield performance. Some further sidelobes level improvement is proposed.

Energy-efficient and highly-compact beam-steering array antennas at W-and D-band frequencies are considered as future enabling technologies for beyond-5G applications. However, most existing solutions at these frequencies are limited to the fixed-beam and frequency-dependent beam-steering scenarios. This paper aims to fill in this knowledge gap by investigating various types of antenna elements as potential candidates for wideband and wide-scan arrays at W-band. We consider openended ridge and ridge gap waveguide radiating elements that could overcome the physical complexities associated with the integration of elements in large-scale electronically scanned arrays. An infinite array approach is used, where we have adopted a triangular array grid and introduced E-and Hplane grooves to the element design to enhance the scan and bandwidth performance. Cross-comparison of several simulated array designs leads to the final array elements with 25% impedance bandwidth over the scan range of ±40 • in both the E-and H-planes.Index Terms-phased array antennas, beam steering, W-band, waveguide antenna element, ridge gap waveguide.

A novel array antenna architecture is proposed that can enable 2D (full-space) radiation pattern control and efficient beam steering. This solution is based on a fixed-beam gap waveguide (GWG) 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 8×8 array of cavity-backed patch resonator elements, where two AlGaAs PIN-diodes are integrated inside each element providing a 1-bit phase shift. The TA is implemented in an 8-layer PCB, which includes radiating elements, fixed phase-shifting inner-stripline sections, impedance matching and biasing circuitry. The combined antenna design is low-profile ( 1.7 wavelength) owing to the small separation between two arrays ( 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° and ±40° in the E-and the H-plane with the gain peak of 17.5 dBi, scan loss ≤ 3.5 dB and TA unit cell insertion loss ≤ 1.8 dB.

A new antenna element type based on the openended ridge gap waveguide (RGW) is proposed for phased array applications. This element type is of a particular interest at high mm-wave frequencies (≥ 100 GHz) owing to a contactless design alleviating active beam-steering electronics integration. The key challenge addressed here is a realization of a wide fractional bandwidth and scan range with high radiation efficiency. We demonstrate a relatively simple wideband impedance matching network comprised of an aperture stepped ridge segment and a single-pin RGW section. Furthermore, the E-and H-plane grooves are added that effectively suppress antenna elements mutual coupling. Results demonstrate a wide-angle beam steering (≥ 50 • ) over ≥ 20% fractional bandwidth at W-band with ≥ 89% radiation efficiency that significantly outperforms existing solutions at these frequencies. An experimental prototype of a 1×19 W-band array validates the proposed design concept through the embedded element pattern measurements.