Simple Analytical Approximations for a Gap in Coplanar Waveguide

Series gaps in the central strip of a coplanar waveguide (CPW) are characterised experimentally and theoretically. 50 Ohm coplanar waveguides are fabricated on a 1.27 mm thick Duroid substrate (¿r = 10.5) with a 17 ¿m thick copper layer. Gap widths range from 0.2 to 3.0 mm. The measured equivalent ¿-network capacitances are compared with proposed simple analytic models in the frequency band 1.5 to 4.5 GHz. The discrepancies in the modelled and measured magnitude of Si1 and S21 are within ± 0.01 and ± 0.2 dB respectively, while the discrepancy in the modelled and measured phases of S11 and S21 are within ± 1 degree in both cases.