In this letter, the bandwidth of high-impedance surfaces (HISs) is discussedby an equivalent circuit approach. Even if these surfaces have been employedfor almost 10 years, it is sometimes unclear how to choose the shape of thefrequency selective surface (FSS) on the top of the grounded slab in order toachieve the largest possible bandwidth. Here, we will show that theconventional approach describing the HIS as a parallel connection between theinductance given by the grounded dielectric substrate and the capacitance ofthe FSS may induce inaccurate results in the determination of the operatingbandwidth of the structure. Indeed, in order to derive a more complete modeland to provide a more accurate estimate of the operating bandwidth, it is alsonecessary to introduce the series inductance of the FSS.We will present theexplicit expression for defining the bandwidth of a HIS, and we will show thatthe reduction of the FSS inductance results in the best choice for achievingwide operating bandwidth in correspondence with a given frequency.
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