Influence of air gaps in single-layer bandpass FSS structures

The air gaps in compound structures of frequency-selective-surface(FSS) and dielectric slab were investigated by computation, based on modal matching method, and experimentation, taking slot arrays as illustrative examples. The results show that the influence of air gaps on the transmission properties have a close relationship with the air gap and dielectric thickness. The resonant frequency of FSS with air gap is higher than without air gap. The transmission properties would change periodically with the air gap thickness, if the air gap is thicker than a specific value. The change of transmission properties in one period is determined by dielectric thickness. Mechanism analysis is also carried out. Based on these results, the concept of stealth shield radome is developed, which provides a new thought for application of FSS radome with large angle incidence and low loss.