ELO-STRIP BASED IMPEDANCE TUNING FOR DUAL-BAND SIW CAVITY-BACKED ANTENNAS FOR MMWAVE APPLICATIONS

Dual-band impedance matching at millimeter-wave frequencies remains challenging due to elevated dielectric losses and limited control over multiple resonances beyond 20 GHz. This work introduces the ELOngated strip (ELO-strip), a compact, substrate-less copper strip galvanically connected to a substrate-integrated waveguide (SIW) cavity-backed slot antenna for controlled dual-band operation at 27 GHz and 39.8 GHz. It perturbs the cavity current distribution by extending the effective electrical path and introducing distributed inductive-capacitive loading within the SIW resonator. This electromagnetic redistribution enhances impedance coupling and significantly broadens the achievable impedance bandwidth while maintaining compact cavity dimensions. The integration of two shorting pins modifies the electromagnetic boundary conditions to enable controlled excitation of the second resonant mode without requiring additional substrate layers. An asymmetric U-slot provides selective fine-tuning of inter-band frequency spacing. The conventional SIW configuration, achieves 9.83 dBi and 7.93 dBi with bandwidths of 5.85% and 1.28% at 27 GHz and 39.8 GHz. While the ELO-strip improves the reflection coefficient by 7 dB and 9 dB,  maintaining gains of 9.03 dBi and 7.81 dBi, bandwidths of 5.74% and 1.97%, with radiation efficiency ranging from 83 to 94% across both bands. This demonstrates a controlled gain-impedance trade-off enabling application-specific designs.