A broadband double-layer U-shaped slot patch antenna based on SIW technology with air resonant cavity

This paper proposes a broadband double-layer "U"-shaped slot patch antenna based on Substrate Integrated Waveguide (SIW) technology with the integration of an air resonant cavity. The antenna adopts a three-layer dielectric substrate laminated structure. By leveraging the low-loss and easy-integration characteristics of the SIW structure, an air resonant cavity is introduced to reduce dielectric loss. Additionally, the coupling design of the double-layer "U"-shaped slot radiating patches creates multiple resonant frequency points, thereby expanding the bandwidth and optimizing radiation performance. Simulation results demonstrate that the antenna achieves a Voltage Standing Wave Ratio (VSWR) < 2 within the frequency band of 25.21–35.07 GHz, corresponding to a relative bandwidth of 32.87%. Within this band, the reflection coefficient |S₁₁| < −10 dB (with |S₁₁| < −15 dB in 25.32–32.30 GHz), the peak gain reaches 7.67 dB at 30 GHz, and the half-power beamwidths (HPBWs) of the E-plane and H-plane at 30 GHz are 68.7° and 88.4°, respectively. Compared with traditional SIW back-cavity antennas, its impedance bandwidth is increased by 27.87% with key innovations including: (1) independent tuning of dual resonant modes via double-layer "U"-shaped slots; (2) synergistic design of air cavity and SIW for low loss and broadband operation. These features confirm its suitability for 5G millimeter-wave communication and radar applications.