Fundamental-mode EMSIW for miniaturized differential antenna with high CM rejection

This letter proposes a novel miniaturization approach for differential antennas using fractional-mode substrate integrated waveguide (SIW) fundamental-mode. Symmetrically arranging dual miniaturized cavities, in-phase DM magnetic currents are constructed to superimpose differential-mode (DM) E-fields for enhanced radiation while simultaneously constructing reverse common-mode (CM) magnetic currents to cancel the CM E-fields and suppress the CM signal. Three kinds of eighth-mode SIW differential antennas with boundary symmetry are designed to verify the approach. Analysis of the equivalent circuit models reveals that the DM resonant frequency is lower than the CM resonant frequency, effectively suppressing CM signal within the DM passband through impedance mismatch reflection and radiation E-fields cancellation. The measured and simulated results show good agreement. The size of the miniaturized antenna is 0.46x0.42x lambda(3)(0) with a high CM rejection of 31.4 dB achieved.