This thesis presents a series of wideband transmitarray (TA) and reflectarray (RA) antennas based on magneto-electric (ME) dipole structure for the future wireless communications. Benefiting from the advantages of high gain, design flexibility, ease of fabrication and lossless feeding, the TA and RA have attracted widespread interest. It’s regarded as a promising candidate in future wireless communication, imaging, sensing and radar systems. The ME dipole antenna has been widely investigated in the past decades due to its merits of simple structure, wide bandwidth, unidirectional patterns and stable gain. Thus, the ME dipole is introduced into the TA and RA designs in this thesis to enhance their performance. For these designs, four aspects are focused, including the wide bandwidth, enhanced aperture efficiency, reduced profile and beam-scanning capability. The common wideband and high-gain characteristics enable them to be attractive for diverse applications in the future wireless communications.

Firstly, two wideband TA designs with enhanced aperture efficiencies are presented. In the first design, the ME dipole is introduced into the TA element. By applying a wideband 90° phase shifter and the polarization-twisting technique, four elements with 90° phase progression are designed for 2-bit resolution. A 12×12 TA operating at the K band is designed, fabricated, and measured. An operating 3-dB gain bandwidth of 38.7% and a peak aperture efficiency of 53% at 23 GHz are achieved. Within the bandwidth of 34%, the achieved aperture efficiencies are higher than 40%. While in the second design, the ME dipole is introduced in the design of feeding source due to its nearly identical beamwidth in all elevation planes. To obtain a uniform amplitude distribution on the TA aperture, a special radiation pattern of the feeding source is extracted based on the Friis Transmission Equation. Then a superstrate is placed above the 2×2 ME dipole array to achieve the required pattern. The measured aperture efficiency of the prototype is enhanced to 72.7% with a peak gain of 29.1 dBi. The measured 1-dB and 3-dB gain bandwidth is 11% and 25.5%, respectively.

Secondly, two wideband TAs with reduced profile are proposed. The first design is linearly polarized (LP) design. By introducing the phase gradient on the reflective polarization-conversion surface (RPCS) in the conventional folded TA scheme, the antenna profile is further reduced. The ME dipole antenna and the true-time-delay (TTD) structure are introduced in the designs of TA and RPCS elements for wide bandwidth. The profile of the fabricated prototype is reduced to 1/5 of the focal length. The measured results show that a peak gain of 25.3 dBi, a peak aperture efficiency of 40%, as well as a 3-dB gain bandwidth of 29% can be achieved. To extend this method, a modified folded scheme is designed for dual LP applications. By placing the feed in TA aperture and employing a phase-gradient reflective surface (PGRS), the profile is reduced to 1/3 of the focal length. The ME dipole structure is used to design the TA and the PGRS element so that they support wide operating bandwidth. The measured gains for x- and y-polarizations can reach their maximum value of 23 dBi at 28 GHz. Furthermore, the fabricated prototype can achieve a bandwidth of 26% and 28% for x- and y-polarizations, respectively. The measured maximum aperture efficiency for the x- and y-polarizations is 21%.

Thirdly, a reconfigurable RA (RRA) and a reconfigurable TA (RTA) are presented for beam-scanning applications. Both of these two designs are based on the ME dipole structure to broaden the bandwidth. In the RRA design, each RRA element is loaded by one single PIN diode to control its resonant types, obtaining a 1-bit reconfigurable reflecting phase. A 16×16 RRA is fabricated at a low cost. A stable gain can be obtained in the bandwidth of 38.4% with a maximum ripple of 3dB. The maximum value of the measured aperture efficiency is around 24%. Within the whole operating bandwidth, the prototype can achieve the scanning range from −60° to +60° in the E-plane and 0° to o +60° in the H-plane. The second design proposed a wideband 2-bit RTA by combing two reconfigurable ME dipole antennas using the receive-and-transmit method. PIN diodes are integrated and controlled to manipulate the current path for 2-bit resolution in transmission phase. A chessboard-like prephase distribution is introduced in the TA aperture to enhance the cross-polarization performance. A 11×11 RTA is designed, fabricated and measured. The fabricated prototype successfully achieves a maximum antenna gain of 21.7 dBi with a peak aperture efficiency of 43%. The gain bandwidth determined by 3-dB ripple is 32%. Within the whole operating bandwidth, scanning angles from -50° to +50° in both E- and H-planes can be obtained. The measured cross-polarization levels are suppressed lower than 20 dB.