In this paper, a novel multilayer structure using the double-sided parallel-strip line with an inserted conductor plane is investigated. A conductor plane is inserted into the middle of the substrate of the double-sided parallel-strip line in the proposed structure, which can function as virtual ground to isolate the nonidentical circuits on the top and bottom layers effectively. On the other hand, the conductor plane can be negligible for the identical circuits. Based on the new structure, a dual-band stub can be realized using the isolation characteristic of the conductor plane, where the stub can be treated as a combination of two back-to-back microstrip stubs operating at different frequencies. The common ground of the two microstrip stubs is provided by the inserted conductor plane. For demonstrating this idea, a bandpass filter with two transmission zeros is optimized, fabricated, and tested. The simulated and measured results are presented and show good agreement. The size of this filter is reduced approximately by half, as compared with that of the similar type of microstrip filters.

Double-Sided Parallel-Strip Line With an Inserted Conductor Plane and Its Applications

The procedure of attaining a compact bandpass filter (BPF) with dual band-notch function for ultra-wideband (UWB) applications is presented and discussed. In the proposed BPF, defected ground structure is used in order to improve the out-of-band performance of the filter. Also, four short-circuited bent stubs are employed in order to improve the selectivity of the filter at its cutoff frequencies. Dual band-notch function is added to the performance of the filter by coupling two short-circuited inverted T-shaped stubs to the filter main resonator. The fabricated filter satisfies well the demands of the Federal Communications Committee with two narrow band-notch functions at 5.5 and 8 GHz, which eliminates the interference of the UWB system with wireless local area network (WLAN) and satellite communication systems, respectively. The improved upper stop-band of the proposed filter with more than 20 dB attenuation level extends up to 20 GHz.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2014.0484

New design of compact dual band-notch ultra-wideband bandpass filter based on coupled wave canceller inverted T-shaped stubs

Novel quasi-elliptic coupled-resonator bandpass filters with wider fractional bandwidth are proposed. By using the broadside-coupled mechanism to couple the half-wavelength microstrip resonators and the quarter-wavelength coplanar-waveguide (CPW) resonators together with introducing two CPW shorted stubs, the required mixed and magnetic couplings associated with the resonators may be enhanced so that a wider bandwidth cross-coupled filter may be realized. Specifically, a fourth-order quasi-elliptic broadside-coupled bandpass filter with a center frequency at f0=1.48 GHz, a minimum insertion loss of 0.68 dB, and a wider 3-dB fractional bandwidth of 34.6% is implemented, and its stopband is extended up to 6 GHz (4f0) with a rejection better than 20 dB

Novel Broadside-Coupled Bandpass Filters Using Both Microstrip and Coplanar-Waveguide Resonators

This paper presents a design methodology for realizing broadside-coupled microstrip bandpass fllters on multilayer substrates to reduce the size of the fllter. The new fllter conflguration consists of broadside coupled split-ring resonators on two layers backed by a ground plane. With the proposed new method, miniaturization to a greater extent can be achieved compared to the conventional method of realizing microstrip multilayer fllters. In addition, coupling apertures in the ground plane used to achieve coupling among the resonators in conventional multilayer structures are eliminated. The proposed design is more ∞exible compared to traditional multilayer fllters. Layers can be easily added to increase the fllter order. To demonstrate the method, a miniaturized two-layered bandpass fllter centered at 728MHz with low insertion loss is implemented and investigated. Miniaturization of more than 25% is achieved compared to the conventional broadside coupled structure and more than 40% miniaturization compared to the edge coupled structure. The new microstrip fllter discussed in this paper can be realized using simple fabrication techniques.

/pdf/compact-two-layer-microstrip-bandpass-filters-using-65oc3viwp7.pdf

Compact two-layer microstrip bandpass filters using broadside-coupled resonators

In this paper, compact multilayered helical resonators and various coupled resonator pairs with a mixed electric and magnetic coupling structure were developed. A multilayer structure is suitable for miniaturization and enhances mutual coupling. A pair of transmission zeros (TZs) can be created using mixed coupling between two coupled helical resonators, achieving superior frequency selectivity. An equivalent circuit model was proposed to analyze the creation of TZs. The planar helical structure provides design flexibility in control of TZs. Eight coupled resonator pairs were proposed for synthesizing various filter responses. An experimental second-order helical filter was fabricated using low-temperature cofired ceramic technology. The measurement results of this second-order filter showed the center frequency to be 0.976 GHz, with two TZs located at 0.8 and 1.4 GHz. The insertion loss was lower than 1.96 dB, and the return loss was 25 dB at $f_{0}$ . The size of this filter was only $5.7~\textrm {mm} \times 3.4$ mm ( $0.051~\lambda _{g}\times 0.031~\lambda _{g}$ ), which is highly compact compared with filters from other published studies. In addition, the proposed coupled pairs have potential in the construction of high-order filters with superior frequency selectivity by cascading multiple coupled helical pairs.

LTCC Multilayered Helical Filters With a Mixed Electric and Magnetic Coupling Structure

A four-pole quasi-elliptic function bandpass filter for a compact low-temperature cofired ceramic is proposed in this paper. The filter is constructed by the open-loop resonators and the miniaturized hairpin resonators that can be coupled through the apertures on the common ground plane, and the 0/spl deg/ feed structure adds two extra transmission zeros to the filter response. It is shown that the filter occupies a very small size. As a result, the proposed structure of the filter occupies a very small circuit area and has a good out-of band rejection.

Tsung-Wen Chen

Papers

A miniaturized multilayer quasi-elliptic bandpass filter with aperture-coupled microstrip resonators