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I’m trying to suppress surface waves in a high-frequency patch antenna to improve gain and reduce mutual coupling. How effective are Photonic Bandgap (PBG) structures, and what’s a practical implementation?

My patch antenna on a thick, high-dielectric substrate suffers from poor gain and pattern distortion due to surface wave excitation. I've read about etching PBG lattices in the ground plane. Does this really work for a single patch, or is it more suited for arrays? What are the key design parameters—lattice period, hole/pattern shape—and how do they relate to my operating frequency (say, 28 GHz)? Are there significant trade-offs, like increased back-lobe radiation or fabrication complexity?

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By Debashis Mohapatra Answered 2 months ago

PBG (or more accurately, EBG - Electromagnetic Bandgap) structures are highly effective for surface wave suppression in a single patch, especially on thick substrates. From my mmWave work, the key is designing the EBG lattice to have a bandgap that covers your operating band. The period (a) is typically λ_g/2, where λ_g is the guided wavelength in the substrate. At 28 GHz on Rogers 5880, this is roughly 3-4mm. I often use a mushroom-type EBG (patches with vias) or a simpler uniplanar compact EBG (UC-EBG) etched in the ground plane. The trade-offs are real: they increase board area, add fabrication steps (especially for via-based types), and can slightly narrow the impedance bandwidth. However, the gain improvement (2-3 dB is common) and drastic reduction in mutual coupling for arrays are often worth it. For a single patch, a tapered ground plane corrugation can be a simpler alternative.

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