Coplanar waveguide filters with floating strips

Coplanar waveguide edge-coupled filters with floating conductor strips dire ctly below the coupled-line sections are investigated. It is demonstrated t hat tight coupling can easily be implemented in this way. A 50% bandpass fi lter with centre frequency at 3GHz was studied. The filter used four couple d-line sections. The floating conductor strips were incorporated into the d esign and the authors have been able to achieve very similar even and odd m ode phase velocities, so that the filter is spurious-free at twice the basi c passband range. The measured passband insertion loss is < 1dB. It also ha s a very good stopband performance.