Wideband Transmitarray With Reduced Profile

This letter presents a wideband transmitarray (TA) with reduced profile. A novel unit cell based on a wideband bandpass filter is developed and applied to the design of the TA. The TA consists of two identical trilayer frequency selective surfaces (FSSs), thus it has a lower profile compared to traditional designs that use at least four FSS layers separated by quarter-wavelength air gaps to obtain the <inline-formula><tex-math notation="LaTeX"> $\text{360}^\circ $</tex-math></inline-formula> phase shift range. The FSS has a pair of square patches printed on the top and bottom layers, and a square slot loaded by four microstrip lines printed on the middle layer. The phase shift is achieved by simultaneously adjusting the size of the square patches. Within the frequency band of interest, the developed unit cell shows low insertion loss and sufficient phase shift range. An equivalent circuit model is developed to better understand the operating principles of the FSS. To validate the design concept, one prototype operating at 13.5 GHz is designed, fabricated, and measured. The measurement results show that the designed TA achieves <inline-formula><tex-math notation="LaTeX">$ {\text{16}}\%$</tex-math></inline-formula> 1 dB gain bandwidth and <inline-formula><tex-math notation="LaTeX">$ {\text{60}}\%$</tex-math></inline-formula> aperture efficiency. The developed unit cell has symmetric configurations so it can also be applied to the design of dual-polarized or circularly polarized TAs.