Single-Fed $3\times3$ Substrate-Integrated Waveguide Parasitic Antenna Array for 24 GHz Radar Applications

A novel substrate-integrated waveguide parasitic compact antenna array without feeding network is proposed for operation in the 24 GHz Industrial, Scientific, and Medical (ISM) band. Inductive windows are exploited to couple adjacent array elements, eliminating the need for a conventional elaborate feeding network, consisting of multiple stages of power dividers. As such, this coupling technique results in an extremely compact design, facilitating integration in close proximity with active devices. Moreover, the insertion loss and the parasitic radiation from the feeding network are significantly reduced, improving the overall energy efficiency. The amplitude distribution is optimized by tuning the amount of coupling between the adjacent array elements, effectively eradicating the side lobes in the radiation pattern’s H-plane and minimizing them in the E-plane. An impedance bandwidth of 315 MHz is obtained, covering the entire 24 GHz ISM band. A 3 dB beamwidth of 43° and 46° in the H-plane and E-plane, respectively, is measured, with a broadside array gain of 10.2 dBi.