Fully tunable filter with cross coupling and reconfigurable transmission zero

Abstract

In this article, a novel coupling structure is proposed. The surface voltage and current distribution on this structure can be tuned by changing the ratio of the two capacitances so that the central frequency and coupling coefficient can be tuned. The coupling structure can also be tuned to change the sign of coupling coefficient, which is utilized to control the transmission zero of cross coupled tunable bandpass filter. A second order bandpass filter with tunable central frequency and bandwidth is designed and measured. The measurement shows that the central frequency tuning range is 0.768 to 1.512 GHz and the fractional bandwidth tuning range is 0.052 to 0.18 at 1.14 GHz. It shows that the filter can also be tuned with constant fractional bandwidth or constant absolute bandwidth. A tunable cascaded triple bandpass filter with tunable central frequency and bandwidth is designed and measured, as well. The crosscoupled transmission zero can be configured to locate at either high side or low side of the passband by changing the coupling type of the filter topology.

A Novel Switchable Dielectric Bandpass Filter With Reconfigurable Transmission Zeros

“…Tunable/switchable filters have been widely used in modern communication systems due to their potential to reduce volume and design complexity. Many tunable microstrip bandpass filters with center frequency or/and in-band bandwidth control have been published [1][2][3][4], and there are some articles about the bandpass filters with reconfigurable or controllable TZ(s) [5][6][7][8][9][10]. In [5], one switchable TZ is realized by only tuning the resonant frequencies of waveguide resonators.…”

“…In [5], one switchable TZ is realized by only tuning the resonant frequencies of waveguide resonators. In [6], the reconfiguration of TZs of a third-order cross coupled openloop bandpass filter is realized by changing the ratio of the two capacitances to tune coupling coefficient and the sign of coupling coefficient, which makes the transmission zero of the filter locate at either high side or low side of the passband. In [7], a reconfigurable asymmetric frequency response bandpass filter using a dual-mode open-loop resonator was demonstrated experimentally, and two cases are designed by controlling the resonant frequencies of the odd-mode and even-mode.…”

“…In [7], a reconfigurable asymmetric frequency response bandpass filter using a dual-mode open-loop resonator was demonstrated experimentally, and two cases are designed by controlling the resonant frequencies of the odd-mode and even-mode. The positions of TZs are the same as [6]. In [8], one TZ of a three-pole tunable combline bandpass filter can be controlled by a varactor loaded I/O network, and the TZ can be tuned from 1.37 to 1.64 GHz in the lower stopband of the filter.…”

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.…”