This paper expands our previous work on planar tunable capacitive coupling structures in substrate-integrated cavities using lumped components. We demonstrate both frequency and bandwidth tunable filters with adjustable transmission zeros (TZs). By the appropriate choice of the absolute and relative strength of magnetic and electric coupling coefficients, we demonstrate: 1) tunable bandwidth and the ability to maintain either a constant absolute bandwidth or a constant fractional bandwidth; 2) adjustable TZ location at a prescribed bandwidth; and 3) the ability to switch OFF the filter with high isolation. Filter design methodologies based on a dispersive coupling structure are presented using lumped circuit models, coupling matrix, and full-wave simulations. With this planar capacitive coupling, it is also convenient to realize cross-coupling in higher order filters to produce additional TZs for rejecting spurious resonances or interferes. Fabricated two-pole filters with one or two TZs and four-pole filters with three or four TZs validate the filter design. A two-pole filter with tunable center frequency and tunable bandwidth along with a four-pole filter with tunable center frequency and tunable TZs are also demonstrated.

This paper presents the design and characterization of a miniaturized tunable bandpass filter utilizing high-Q ceramic coaxial resonators and commercially available RF-MEMS tunable digital capacitors. A proof-of-concept 2-pole tunable filter occupying only 10 × 10 mm2 is demonstrated with a frequency tuning range of 800-1100 MHz and bandwidth tuning range of 6-13%.

This paper presents octave-tunable resonators and filters with surface mounted lumped tuning elements. Detailed theoretical analysis and modeling in terms of tuning range and unloaded quality factor Qu are presented in agreement with simulated and measured results. Based on the models, a systematic design method to maximize tuning ratio and optimize Qu of the resonator is suggested. A resonator tuning from 0.5 to 1.1 GHz with Qu ranging from 90 to 214 is demonstrated using solid-state varactors. A two-pole filter with a tuning range of 0.5-1.1 GHz with a constant 3-dB fractional bandwidth (FBW) of 4 ± 0.1% and insertion loss of 1.67 dB at 1.1 GHz is demonstrated along with a three-pole filter with a tuning range of 0.58-1.22 GHz with a constant 3-dB FBW of 4 ± 0.2% and insertion loss of 2.05 dB at 1.22 GHz. The measured input third-order intermodulation is better than 17 dBm over the frequency range for the two-pole filter. © 2013 IEEE.