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A modification of the conventional dumbbell-shaped coplanar waveguide defected ground structure (DGS) is proposed. This modification permits the continuous tuning of the rejected frequencies by using reconfiguration technique and it allows the control of the DGS equivalent-circuit model. The modified DGS possesses two-dimensional symmetry, hence, it has been studied under different symmetry conditions and the corresponding equivalent-circuit model in each case has been developed. Based upon this study, a tunable bandstop DGS resonator is proposed. 19% tuning range centered at 3.7 and 7.4 GHz, respectively, is achieved. The equivalent-circuit model of the resonator is also developed. All proposed structures have been fabricated. Measurements as well as three-dimensional simulations are found to be in a very good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

A compact topology for bandpass filters based on coupled slow-wave resonators is demonstrated. A study of fixed band-pass filters leads to design rules and equations. Measurements on a 0.7-GHz fixed bandpass filter, consisting of three coupled slow-wave resonators, demonstrate the validity of the proposed topology and validate the theory, since the agreement between simulations and measurements is very good. Designed for a Q-factor of 5, this filter shows a Q of approximately 5.2. At the center frequency, insertion loss is 0.6 dB and return loss is greater than 20 dB. A 0.7-GHz tune-all bandpass filter is also designed and tested. The performance of this electronically tuned filter, which incorporates semiconductor varactors, is promising in terms of wide continuous center-frequency and bandwidth tunings. For a center-frequency tuning of ±18% around 0.7 GHz, the -3-dB bandwidth can be simultaneously tuned between ∼50 and ∼78 MHz, with an insertion loss smaller than 5 dB and a return loss greater than 13 dB at the center frequency. The surface areas of the fixed and tunable 0.7-GHz filters are, respectively, ∼16 and ∼20 cm². [ABSTRACT FROM AUTHOR]