A single-layer wideband differential filtering patch antenna for 5G IoT applications is proposed. The proposed antenna features a simple configuration, comprising a pair of T-shaped structures, shorted parasitic patches, and defected ground structures (DGS) etched into the metal ground plane. Two shorted parasitic patches are loaded to achieve λ/4 resonance, and a high-frequency radiation null is introduced. A pair of T-shaped structures, composed of meandered slots, is etched into the main radiating patch, which causes strong current disturbance and excites opposite current components around the slots, thereby introducing a low-frequency radiation null. Moreover, a pair of DGS is incorporated into the ground plane, exciting an additional resonance within the passband to broaden the impedance bandwidth effectively. Finally, a prototype of the proposed antenna is fabricated and measured. The measured results are consistent with the simulated values, demonstrating an impedance bandwidth of 16.8% centered at 4.75 GHz, a peak realized gain of 6.1 dBi, and two controllable radiation nulls near the band edges. The designed antenna achieves a broad bandwidth and filtering response, while maintaining a small electrical size of 0.2 λ20and a low profile of 0.025 λ0. These performance metrics make the proposed wideband differential filtering antenna a promising candidate for 5G IoT applications.

An effective surface plasmon polariton (ESPP) filtering waveguide-fed D-band antenna is proposed for 6G Internet of Things (IoT) applications. Aiming at cross-band interference and link stability in 6G IoT, the design integrates an ESPP filtering structure with a waveguide slot antenna, achieving high selectivity and deep out-of-band suppression while maintaining stable radiation performance. Through ESPP dispersion engineering, the passband (135.9–143.2 GHz) and out-of-band suppression can be independently tuned. Benefiting from ESPPs’ steep asymptotic dispersion and extended modal bandgap, deep out-of-band suppression (>55 dB) and a stable stopband (147–170 GHz) are realized. Notably, the ESPP-based waveguide ensures robust performance against fabrication errors, maintaining frequency consistency between the filtering and radiation responses. The proposed ESPP-based design provides a high-selectivity and fabrication-tolerant solution, effectively mitigating complex interference in ultra-high-speed 6G IoT links and ensuring reliable operation for heterogeneous devices, such as Vehicle-to-Everything (V2X) sensors and smart city terminals.