A low-profile wideband planar phased array of cavity-backed slot microstrip elements for two-dimensional beam scanning applications

A low-profile wideband planar phased array, working in X band and with two-dimensional (2-D) beam scanning characteristic is presented. In order to meet the requirements of wideband 2-D beam scanning and low-profile performance, a cavity-backed slot stacked microstrip element is introduced. The array element is mainly composed of the open-ended microstrip line printed on the bottom substrate, which backed by a rectangular metal cavity, and dual layer patches etched on the middle substrate and the top substrate, respectively. A vertical transition structure is used to feed the microstrip line and connect the active T/R module, which is similar to the coaxial probe. The thickness of the proposed element is only 4.5 mm (0.12 lambda(L), lambda(L) is the wavelength of the lowest frequency). Based on the simulated design, an 8 x 8 planar phased array prototype has been fabricated and measured. The experimental results show that the proposed array have achieved the maximum scanning angle of +/- 45 degrees in theH-plane and +/- 30 degrees in theE-plane across the frequency range of 8 similar to 12 GHz. Therefore, the proposed array can be used as a sub-array of larger low-profile wideband phased arrays for 2-D beam scanning applications, and also validate the introduced design concept.