Stepped-impedance Filter Research Articles

A Waveguide to Unenclosed Coplanar Waveguide Transition

A transition from rectangular waveguide to unenclosed coplanar waveguide (CPW) is designed and tested at W -band. Full-wave finite-element analysis is applied to the design and optimization trends are shown for the critical parameters. A stepped-impedance filter suppresses a parasitic mode, which is generated as the circuit emerges from the waveguide block, and a rejection of -20 dB is achieved. A back-to-back structure is used to characterize the performance of the transition and an insertion loss of 1.6 dB from 75 to 100 GHz is measured. Removing line losses, a single transition insertion loss of 0.46 dB is obtained.

Analysis of the periodic superconducting CPW transmission line with stepped-impedance for on-chip microwave filter applications

This paper investigates the filter properties of a superconducting coplanar waveguide (CPW) periodically loaded with stepped-impedances. The unit cell of the stepped-impedance filter is a cascade of two transmission lines (TLs) with different characteristic impedances. This impedance difference is obtained by step changing on the width of the center strip of the CPW. We use the ABCD matrix representation together with the Floquet analysis to derive the dispersion relation of the infinitely long periodic structure. Scattering matrix analysis along with impedance calculation is performed for an arbitrary number of unit cells. Complex propagation constant, scattering parameters and the input impedance of the structure are expressed in a closed-form equations. The results display the low-pass filtering property. Also, the effect of changing geometrical parameters on the cut off frequency, rejection bandwidth and attenuation in rejection band of such a filter are shown and discussed in this paper.

Compact planar and vialess composite low-pass filters using folded stepped-impedance resonator on liquid-Crystal-polymer substrate

A compact composite low-pass filter, designed by the image parameter method and semilumped component approach, will be described and results for cutoff frequency ranging from C- to V-band will be presented. This composite design combines four filter sections and the presence of a strong attenuation pole near the cutoff frequency provides an extremely sharp attenuation response, while ensuring good matching properties in the passband, making this filter design very attractive for harmonic spurious response suppression or diplexing. The lumped-element schematic of the filter has been implemented using a combination of a stepped-impedance filter and folded stepped-impedance resonators. The overall folded layout has been optimized using full-wave simulation and occupies an ultra-compact area of only 5/spl times/5 mm/sup 2/ for a C-band filter. Measured results exhibit rejection of the attenuated pole greater than 40 dB. Similar filter designs have been realized for C- and V-bands. These filters have been fabricated on a liquid-crystal-polymer substrate demonstrating a high performance, ultra-compact, and very low-cost solution for RF and millimeter-wave applications.

Microstrip stepped impedance filters with variable dielectric or variable width

A stepped impedance filter has been realised on a modified substrate. The change in impedance was achieved by varying the dielectric constant in the substrate while maintaining a constant width of the microstrip. In contrast to conventional stepped impedance filters the impedance is varied by the dielectric constant instead of the microstrip line width. The manufactured filter was measured and compared with an equivalent conventional stepped impedance filter. It is shown that the modified substrate technology could offer an alternative to the standard approach for the stepped impedance filter. In combination with new materials with a high permittivity the technology could also offer a denser package since the microstrip width could be controlled as desired.

A New Approach in the Computation of Ultrahigh Degree Equal-Ripple Polynomials for 90°-Coupler Synthesis

An improved efficient numerical method for the computation of ultrahigh degree equal-ripple polynomials, necessary for the synthesis of multielement 90° coupler, is presented. The highest degree computed was N=201 with an accuracy better than 10/sup -20/. For the calculation of the impedances of the equivalent stepped impedance filter an optimization procedure is also described. Finally, based on the N coupling factors k/sub i/ of the sections, the continuous coupling curve is achieved using spline interpolation. Experimental results of a continuously tapered 8.34-dB coupler constructed in three-layer polyolefin stripline are presented.

A uniformly coupled asymmetric TEM-mode transmission-line directional coupler

An analysis of an asymmetric coupled four-port transmission-line coupler in terms of a two-port transmission line corresponding to two normal modes is presented. This method permits the use of a transmission matrix approach which simplifies considerably the derivation of an expression for coupling and also establishes the mathematical equivalence of such couplers to transmission-line stepped impedance filters. The coupling as well as the terminating impedances required for an impedance match and infinite directivity have been determined in terms of self and mutual immittance parameters, expressions for which have been determined as explicit functions of the line parameters. The method of design of a coupler for specified values of coupling and terminating impedances is also presented.

The analytical equivalence of TEM-mode directional couplers and transmission-line stepped-impedance filters

The coupling of two parallel transmission lines is utilized in directional couplers and filters which are simple to construct and have excellent electrical characteristics from high frequencies to microwave frequencies. The paper establishes the mathematical equivalence of such couplers to transmission-line stepped-impedance filters.It also places new demands on that theory in so far as new insertion-loss functions, having, for instance, equi-ripple characteristics in the stop-band, will be required.A new directional filter circuit, or channel-dropping filter, is suggested.