Width-varying conductor-backed coplanar waveguide-based low-pass filter with a constant signal trace to adjacent grounds separation

In this study, the authors introduce a new and systematic procedure for the design and optimisation of a conductor-backed coplanar waveguide low-pass filter (LPF). The width of the centre conductor (i.e. signal trace) is modelled in a truncated Fourier series, whereas the gap to the adjacent grounds is maintained constant relative to the width variation. Transmission lines theory is adopted to model the LPF and establish an optimisation setup. Three optimisation techniques; namely, trust-region-reflective algorithm, symbiotic organism search, and genetic algorithm are investigated to minimise the developed bound-constrained non-linear objective function. To verify the proposed procedure, an LPF with a cutoff frequency of 2 GHz is optimised, simulated, and measured. The transmission parameter in the passband is found to be in the range −0.3 ± 0.1 dB, and better than −30 dB in the stopband.