Generalized Odd-Even Mode Theory and Mode Synthesis Antenna Design Approach

In this article, studies on the multimode excitation problem of waveguides and antennas, the balance/unbalance mechanism and the balanced feeding techniques in dipole antenna systems are first briefly historically reviewed. In this context, generalized odd-even mode theory is advanced to quantitatively and approximately describe the mutual coupling effect between a feed line and an antenna. As is mathematically deduced and demonstrated, the modal parity mismatch between the feed line and the antenna should ultimately dominate the unbalance phenomenon in antenna systems. Thus, an elegant, closed-form formula is derived to approximately calculate the “unbalance degree” of a straight dipole off-center fed by a symmetric twin-wire line. Design approaches for the simplest, linear, 1-D multimode resonant antennas are introduced. Moreover, the “falling tone excitation” law gauged based on prototype dipoles is revealed and used to develop a mode synthesis design approach for microstrip patch antennas (MPAs) and 2-D sectorial electric dipole antennas. Design examples with distinctive radiation performance are presented and discussed. Finally, possible development trends of multimode resonant antennas are prospected.