Chi-Yang Chang

Microwave active filters based on coupled negative resistance method

A novel coupled negative resistance method for building a microwave active bandpass filter is introduced. Based on this method, four microstrip line end-coupled filters were built. Two are fixed-frequency one-pole and two-pole filters, and two are tunable one-pole and two-pole filters. In order to broaden the bandwidth of the end-coupled filter, a modified end-coupled structure is proposed. Using the modified structure, an active filter with a bandwidth up to 7.5% was built. All of the filters show significant passband performance improvement. Specifically, the passband bandwidth was broadened by a factor of 5 to 20. >

A modified parallel-coupled filter structure that improves the upper stopband rejection and response symmetry

A modified parallel-coupled microstrip line filter structure is presented. Using this new structure improves the filter upper stopband rejection by at least 15 dB, and the filter response symmetry is also improved. Compared with the traditional parallel-coupled filter, the modified filter used less space and is easy to lay out owing to its inline structure. Several examples show the performance improvement of the filters fabricated in both low-dielectric-constant (2.55) and high-dielectric-constant (10.2) substrates. >

Miniaturized spurious passband suppression microstrip filter using meandered parallel coupled lines

A novel meandered parallel coupled-line structure is proposed to suppress the first spurious passband of a microstrip bandpass filter. The meandered parallel coupled line can equalize the modal transmission phases at any interested frequency such as first spurious passband frequency due to its dispersive response. Several filters are designed and fabricated on a substrate with a dielectric constant of 10.2 and a thickness of 50 mil (1.27 mm) to demonstrate the validity of the proposed method. The example filters are chosen to be of large fractional bandwidth and with a relatively high dielectric-constant substrate where, in these cases, the first spurious passband near twice of the passband frequency (2fo) seriously degrades the conventional parallel coupled filters upper stopband performance. The upper stopband performance of the proposed filters drastically improves that the measured first spurious passband are suppressed to better than -50 dB for all example filters. Besides, a meandered coupled line not only suppresses the filters first passband, but also largely shrinks its length. The characteristics of the proposed structure and the design procedures of the filter are described in detail

Analytical Design of Microstrip Short-Circuit Terminated Stepped-Impedance Resonator Dual-Band Filters

This paper proposes an analytical method to design a dual-band Alter using the short-circuit terminated half-wavelength stepped-impedance resonator (SIR). The SIR has an advantage to easily control the first and second resonances by adjusting its structural parameters. In the proposed method, the structural parameters of the SIR are obtained analytically according to the two passband center frequencies and bandwidths of the filter. As a result, the achievable specifications of the dual-band filter can be rapidly determined. The coupling between adjacent SIRs is realized by a short-circuited stub, which is characterized as a K-inverter network. The dual-frequency transformer incorporated with the tapped-line input/output structure is used for the external coupling. Applying the analytical equations in the design process, a dual-band filter can be easily and quickly realized. More importantly, compared to the published dual-band filters, the proposed method is easier to design, especially for a relatively high-order dual-band filter. Two fourth-order and one sixth-order dual-band filters are designed and fabricated to demonstrate the proposed method.

Design of microstrip quadruplet filters with source-load coupling

Quadruplet microstrip filters with source-load coupling are proposed to achieve similar skirt selectivity and/or in-band flat group delay as that of a sixth-order canonical form or an extracted pole microstrip filter. The diagnosis method of unwanted effects such as asynchronous resonant frequencies and unwanted couplings, which often occurs in the microstrips open environment, is described in detail. A systematic design flow to implement a quadruplet microstrip source-load coupled filter with proper filter response is also provided. Two trial filters exhibited quasi-elliptical and flat group-delay response are designed and fabricated. Both theoretical and experimental results are presented.

Miniaturized microstrip cross-coupled filters using quarter-wave or quasi-quarter-wave resonators

Miniaturized microstrip filters using quarter-wave or quasi-quarter-wave resonators with cross-coupling are presented. The quarter-wavelength resonators enable very compact positively or negatively cross-coupled filters to be realized. The combination of quarter-wave and quasi-quarter-wave resonators facilitates the cross-coupling with a proper coupling phase. A new explanation for the coupling phase between the main-coupling and cross-coupling paths is proposed. Different filters that use the proposed resonators are realized and may have either quasi-elliptical or flat group-delay responses. Measurement results correlate well with theoretical predictions.

A novel coupling structure suitable for cross-coupled filters with folded quarter-wave resonators

A new class of coupling structure for cross-coupled filters with folded quarter-wave resonators is presented. The cross coupling mechanism is realized by magnetic coupling from the short ends of the resonator. The proposed magnetic coupling solves the problem of response limitation of folded quarter-wave resonator cross-coupled filters that were introduced previously using electrical cross coupling. Several quadruplet and trisection filters are proposed and fabricated. The measured results matched well with the theoretical prediction.

Novel planar, square-shaped, dielectric-waveguide, single-, and dual-mode filters

This paper presents a novel concept of a square-shaped dielectric-waveguide resonator, which can easily realize a dielectric-waveguide cross-coupled filter or a dielectric-waveguide dual-mode filter, using the conventional printed circuit board (PCB) process. This planar dielectric-waveguide resonator has a higher Q value than a microstrip resonator. The physical mechanisms of both single- and dual-mode filters are elucidated. Some new coupling structures are developed for undergoing the PCB process. Filter design procedures are detailed. Design curves for the coupling coefficients of internal- and external-coupling structures are determined by full-wave finite-element-method electromagnetic calculations. Measurement results are highly consistent with theory for all trial filters. This study offers an effective means of producing low-cost high-performance planar circuit filters.

A semi-lumped balun fabricated by low temperature co-fired ceramic

A new chip-type multi-layer ceramic balun is presented in this paper. This balun is designed in the ISM band and fabricated using low temperature co-fired ceramic (LTCC) technology. It involves the semi-lumped concept and the multi-layer structure to realize the LTCC-MLC balun. The symmetric structure provides the excellent characteristics of phase balance and amplitude balancing. Measured results of the LTCC-MLC balun match well with the computer simulation.

A new class of wideband multisection 180/spl deg/ hybrid rings using vertically installed planar couplers

A new class of wideband multisection 180deg hybrid rings using the vertically installed planar (VIP) coupler is proposed. On the basis of the reconfigured ideal single-section 180deg hybrid ring (i.e., the 180deg hybrid ring with an ideal phase inverter), the multisection 180deg hybrid rings can be realized by properly cascading of single-section 180deg hybrid rings. Compared with the conventional hybrid ring, the two-section hybrid rings exhibit wide bandwidth, size reduction, and easily achievable high power-division ratios. Design equations based on the equal-ripple functions are derived. Design curves for the equal and unequal power-division ratio are also described. In addition, a cascade of single-section cascadable hybrid rings with a unit element at each I/O port can be used for bandwidth enhancement. Good agreement is obtained between the experimental and simulated results