Improved HMSIW Cavity-Cascaded Array With High Front-to-Back Ratio Based on Complementary Element

A new complementary element based on half-mode substrate integrated waveguide (HMSIW) cavity and loaded monopole technology is presented. By slightly breaking the shorting wall of the HMSIW cavity and loading a printed monopole, the resonance characteristics of the HMSIW cavity can be made intact while the additional monopole can be excited. The open edge of the HMSIW cavity is equivalent to a magnetic current. This equivalent magnetic current is orthogonal to the electric current introduced by the monopole, thus they form a pair of complementary sources. Because the backward radiation of the complementary sources can be canceled out, a remarkable unidirectional radiation performance is achieved. To improve the symmetry of the radiation pattern and enhance the antenna gain, a cascaded cavity array is then studied. By alternately connecting the complementary elements, all equivalent magnetic currents of the HMSIW cavities and all electric currents of the monopoles can work in-phase, thus a broadside radiation can be achieved. In this communication, a 1 × 5 array based on the proposed complementary element and a corresponding array based on the classical HMSIW cavity cell are comparatively analyzed. It is found that the impedance characteristics and radiation gain of the HMSIW cavity can be kept intact by the proposed structure. Meanwhile, a 20 dB enhancement in front-to-back ratio can be attained.