This paper presents a thorough review of the techniques involved in the enhancement of the efficiency performance of the reflectarray antenna. The effect of the selection of a suitable patch element or a proper feeding mechanism on efficiency improvement is studied in detail. Reflectarray loss quantification is examined in relation to the design techniques involved in the efficiency improvement. A low loss patch element with a wide reflection phase range and a properly illuminated reflectarray aperture are supposed to offer high efficiency performance. Additionally, the placement, the orientation and the position of a patch element on the reflectarray surface can also affect its efficiency performance. Mathematical equations were developed to estimate the efficiencies of circular and square aperture reflectarray antennas by considering their feed footprints. Moreover, a step by step practical method of predicting and measuring the total efficiency of a reflectarray antenna is presented. The two selected apertures of the reflectarray consisting of the square patch element configuration are fabricated and measured at a frequency of 26 GHz. Their measured efficiencies have been estimated using the derived equations, and the results were compared and validated using the efficiencies obtained by the conventional gain-directivity relation.

This paper presents an investigation for the performance comparison of three different unit cell configurations operating at 26 GHz for 5G applications. The unit cells are cross shape dielectric resonator, cross microstrip patch and cross hybrid dielectric resonator. Verification of the comparison has been done by simulations using commercial Computer Simulation Technology Microwave Studio (CST MWS). The simulated results for reflection phase, slope variation, reflection loss and 10% bandwidth were analyzed and compared. The results indicate that the optimum configuration to be deployed for the reflectarray’s unit element in order to fulfill the 5G requirements of a wide bandwidth is the cross hybrid DRA. This configuration is a combination of cross DRA with cross microstrip patch as the parasitic element in order to tune the phase and provide a wide phase range with smooth variation slope. Cross hybrid DRA provided a wide phase range of 520° with 0.77 dB loss and 10% bandwidth of 160 MHz.

The performance of a proposed cross hybrid dielectric resonator antenna (DRA) element for dual polarization configuration operating at 26 GHz for 5G applications is presented in this paper. The new cross hybrid DRA unit cell is introduced which combines a cross shape DRA with a bottom loading cross microstrip patch. This technique of a bottom loading cross microstrip patch is chosen as the tuning mechanism (varying the length of the microstrip to tune the phase) instead of changing the DRA dimensions because of their ease of implementation and fabrication. By doing so, high reflection phase range with low reflection loss performance can be obtained, which is essential for a high bandwidth and high gain reflectarray for 5G applications. The design and simulation have been done using commercial software of CST MWS. The reflection loss, reflection phase and slope variation were analyzed and compared. A metallic cross microstrip patch of varying length placed beneath the DRA to act as the phase shifter to tune the phase and give smooth variation in slope with a large phase range. The proposed cross hybrid DRA unit cell provides a high reflection phase range of 342º and 1.8 dB reflection loss. The computed results are compared with experimental results revealing reasonable agreement, thereby confirming the viability of the design.