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3 years ago in Electrical Engineering By Deep
Can a photonic bandgap (PBG) lattice etched in the ground plane of a microstrip antenna effectively suppress the dominant TM‑ surface wave mode to improve gain and reduce mutual coupling?
I'm designing a densely packed microstrip array at 10 GHz. Mutual coupling via the TM? surface wave is degrading performance. I've read about etching periodic holes (PBG) in the substrate or ground plane. Is this technique specifically effective at suppressing the TM? mode, or is it better for higher-order modes? What determines the lattice period and hole radius for a given substrate (ε?=4.3, thickness=1.5mm) to create a bandgap at 10 GHz? Does this significantly impact the antenna's impedance bandwidth or back-lobe radiation?
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By Raghav V Answered 1 year ago
Yes, a properly designed PBG (more accurately, an Electromagnetic Bandgap - EBG) lattice can suppress the TM? mode. The key is to create a stopband where the surface wave propagation constant β falls within the bandgap. For a square lattice of holes in the ground plane, the period (a) is typically λ_g/2, where λ_g is the guided wavelength in the substrate. For your parameters (ε?=4.3, h=1.5mm @10GHz), λ_g≈14mm, so start with a≈7mm. The hole radius is often 0.2–0.3a. This etching primarily affects the ground plane currents supporting the TM? mode. The trade-offs include a potential reduction in bandwidth (as the effective substrate environment changes) and slightly increased back radiation if the holes become significant radiators. It's very effective for decoupling in arrays but requires full-wave simulation to co-optimize with the patch design.
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