A fully tunable two‐pole bandpass filter using the resonator with asymmetrical capacitances

Abstract

A fully tunable second-order bandpass filter based on novel resonator is proposed. The resonating frequency and the coupling coefficient between the resonators can be controlled by two varactor diodes. Theoretical expressions have been derived for the coupling coefficient. Four types of filter responses can be reconfigured by setting different bias voltage combinations, including tunable bandwidth filter, constant absolute bandwidth filter, constant fractional bandwidth filter, and decrease bandwidth filter. The simulation and measured results of the four responses are in good agreement with each other, and excellent tunable characteristics are achieved. K E Y W O R D S asymmetrical capacitances, bandpass filter, fully tunable

A novel resonant‐type tunable group delay controller based on third‐order fully tunable topology

“…Therefore, both the group delay and its central frequency can be tuned by tuning the coupling coefficients and the resonating frequency of the resonant topology, and the reconfigurable GDC with both tunable group delay and central frequency may remedy the weakness of the narrow resonant bandwidth. In recent years, fully tunable filters with tunable coupling coefficients and resonating frequency were studied to achieve tunable bandwidth and central frequency, however, most of the reported fully tunable filters are with second‐order topology and the coupling coefficient tunable range is about two times, which cannot be used for implementing wide‐range tunable GDC 15–18 …”

“…In recent years, fully tunable filters with tunable coupling coefficients and resonating frequency were studied to achieve tunable bandwidth and central frequency, however, most of the reported fully tunable filters are with second-order topology and the coupling coefficient tunable range is about two times, which cannot be used for implementing wide-range tunable GDC. [15][16][17][18] In this letter, a novel GDC is designed based on thirdorder resonant topology, and the coupling structure is realized by coupled line resonators loaded with two shunt capacitors for coupling coefficient tuning, and a series capacitor for resonant frequency tuning. The structure has the advantage of a large range of tunable coupling coefficients and breaks through the group delay tunable range of traditional delay circuits.…”

Fully tunable filter with cross coupling and reconfigurable transmission zero

“…Since the coupling coefficient is normally small, the varator's capacitance should be very small for resonator, which limits the filter design. In References 18, 19, additional varactors can be added to central frequency tunable half wave‐length resonator to tune bandwidth by changing the field distribution, but they can only achieve magnetic coupling.…”

A tunable cross‐coupled trisection bandpass filter with constant bandwidth based on dual‐mode resonators

“…Electrical tunable microwave filters are the key components for multiband or reconfigurable wide band radio systems for rejecting the out of band interference . Cross‐coupling topologies with extra transmission zeros (Tzs) beside the passband of microwave bandpass filters (BPFs) are widely used in modern radio systems for improving the frequency selectivity .…”

“…Electrical tunable microwave filters are the key components for multiband or reconfigurable wide band radio systems for rejecting the out of band interference. [1][2][3] Cross-coupling topologies with extra transmission zeros (Tzs) beside the passband of microwave bandpass filters (BPFs) are widely used in modern radio systems for improving the frequency selectivity. [4][5][6][7] Recently, tunable cross-coupled bandpass filters based on singled mode tunable resonator are reported, [8][9][10] it shows that the cross-coupled topologies with Tzs can improve the frequency selectivity of the tunable passband.…”