Wideband Transition for Effective Excitation of Second Higher Order Mode in Microstrip Line

In this letter, a wideband transition for exciting the second higher order mode on microstrip line is presented. Different from the traditional excitation method, a systematical design approach is first conducted. The field distribution of higher order modes could be well matched and transformed into quasi-TEM mode by a taper structure. Based on the study of the orthogonal principle of different modes, each mode could be effectively excited by a specific amplitude/phase condition of the feeding network. To meet the wideband amplitude and phase radio requirements among different ports of the feeding network, a multimode resonator-based phase shifter could be utilized to achieve 180° phase difference. To validate this proposal, a wideband EH0-to-EH2 mode transition with 60% bandwidth is proposed, designed, and implemented. Both the extracted propagation constant and the back-to-back S-parameters show good wideband response over the concerned frequencies.