Wenxing Tang

Varactor-Tuned Dual-Mode Bandpass Filters

This paper presents a new type of varactor-tuned dual-mode bandpass filter. Since the two operating modes (i.e., the odd and even modes) in a dual-mode microstrip open-loop resonator do not couple to each other, the tuning of the passband frequency becomes simple with a single dc-bias circuit while keeping nearly constant absolute bandwidth. Design equations and procedures are derived, and two two-pole tunable bandpass filters of this type are demonstrated experimentally.

Tunable microstrip quasi-elliptic function bandpass filters

In this paper, a new type of varactor-tuned microstrip quasi-elliptic function bandpass filter based on dual-mode open-loop resonator is investigated. By employing the unique characteristic of the dual-mode open-loop resonator, i.e. whose two operating modes (odd-and even-modes) do not couple to each other, tuning the passband frequency becomes simple with a single DC bias circuit. Two finite-frequency transmission zeros on each side of the passband are tunable along with the center frequency, resulting in high selective frequency response. A designed four-pole tunable bandpass filter of this type is demonstrated experimentally.

Dual-band filter based on non-degenerate dual-mode slow-wave open-loop resonators

This paper presents a new class of dual-band filters based on non-degenerate dual-mode microstrip slow-wave open-loop resonators, which support two non-degenerate modes that do not couple. Different feed schemes that affect the filtering characteristics are investigated. Examples of dual-band filters of this type are described with simulation and experiment results.

Compact Tunable Microstrip Bandpass Filters with Asymmetrical Frequency Response

A new type of electronically tunable asymmetric frequency response bandpass filter based on dual-mode open-loop resonator is investigated. By employing the unique characteristic of the dual-mode open-loop resonator, that is, whose two operating modes (odd-and even-modes) do not couple to each other, tuning the passband frequency becomes simple with single DC bias circuit. Two designed tunable bandpass filters of this type are demonstrated experimentally, which show more than 10 dB of return loss and less than 3 dB insertion loss over a tuning range of 12% from 0.83 to 0.93 GHz.

Design of Microstrip Lossy Filter Using an Extended Doublet Topology

A lossy three-pole microstrip bandpass filter using an extended doublet network is proposed in this letter. Nonuniform Q distribution is considered by reducing the Qu of one resonator, resulting in a flatter passband with an enhanced selectivity. Also, the novel feeding network adopted brings about two extra transmission zeros and a wide stopband that further improve the filter performance. Good agreement between the simulated and measured results can be observed to validate the design.

Quasi-elliptic function doublet filters without cross coupling

This paper presents a recent investigation of miniature microstrip doublet dual-mode filters that exhibit quasi-elliptic function response without using any cross coupling. It shows that a single two-pole filter or the doublet can produce two transmission zeros resulting from a double behavior of the dual-mode resonator of this type. Electromagnetic (EM) simulation and experiment results are described. A four-pole filter of this type is demonstrated.

Microstrip cross-coupled stepped-impedance line bandstop filter

This paper presents a novel design of a wide spurious-free bandstop filter using cross-coupled stepped impedance lines. A measured bandstop filter with 10-dB bandwidth of 160 MHz is designed at the center frequency of 1.0 GHz, and it shows no spurious responses up to 5.2 GHz. As a preliminary investigation, the filter is tuned electronically using ferroelectric thin film varactors.