• A miniaturized HMSIW-based diplexer using TE101/TE301 dual-mode resonator achieves wide stopband up to 2.16f1 with >20 dB out-of-band rejection.
• The TE202 mode is effectively suppressed in HMSIRCs due to magnetic wall symmetry, overcoming the conventional 2f1 stopband limitation.
• The second-order prototype at 10.34/13.90 GHz exhibits a compact footprint of only 1.363λg², enabled by eliminating T-junctions and reducing resonator count.
• The proposed design offers high isolation and low insertion loss with simplified manufacturing, making it suitable for advanced wireless communication systems.