Compact Microstrip Wideband Cross-Coupled Inline Bandpass Filters With Miniaturized Stepped-Impedance Resonators (SIRs)

Abstract

This paper presents a class of reduced footprint inline microstrip bandpass filters capable of covering bandwidth up to 20% as well as good flexibility in establishing various cross-couplings for creating transmission zeros. The resonating elements are quarter-wave stepped-impedance resonators (SIRs), which have a wide upper stopband in nature. To achieve size miniaturization, the low-impedance segment of each SIR is implemented as a thick-trace ring and configured in spiral form, and the highimpedance section is deformed to accommodate the low-impedance section. An interlaced coupling structure is proposed to enhance the coupling limited by the downsized coupled segments of adjacent resonators. In addition, by properly routing the associated shorted stubs, the structure can easily establish cross-coupling between nonadjacent resonators. Thus, compact SIR filters in an inline arrangement can be achieved to have either narrow or wide passbands with plural transmission zeros. Two such circuits with sharp transition bands and upper stopband extension are synthesized, fabricated, and tested. The measured results show good agreement with simulated data. The circuit areas together with the performances of the experimental filters are compared with those in existing literature.

A New Compact Wideband Filter Based on a Coupled Stepped Impedance Resonator

“…The bandwidth is mainly determined by the following: (1) the coupling coefficients between the filter resonators; and (2) the external quality factor between the terminations and the adjacent resonators. The coupling coefficient and the external quality factor can be calculated based on the methods presented in [17,28]. The coupling coefficients between the coupled resonators depend on the separation distance S between the resonators.…”

“…Therefore, cascading can be performed through the coupling between resonators two and three. The coupling is performed by a 50 Ω quarter-wavelength line as suggested and discussed in [28]. Very minor adjustments may be needed to compensate for the minor changes in g's.…”

“…In [27], a new coupling mechanism is introduced that allows for the design of filters with narrow and wideband performance. A short-circuit quarter-wavelength SIR is also suggested in [28] in a very compact spiral form at the cost of high insertion loss. In general, SIRs can be used as a compact part to design small-size components such as a triplexer [19], filtering power divider [29], and dual-band filters [30].…”

Globalized simulation-driven miniaturization of microwave circuits by means of dimensionality-reduced constrained surrogates

“…Miniaturization is essentially a two-stage process. Initially, a basic circuit architecture is selected to ensure compact dimensions 16 , 17 , often with the use of techniques such as transmission line (TL) folding/meandering 18 , utilization of the slow-wave phenomenon 19 (typically, in the form of compact microwave resonant cells, CMRCs 20 ), multi-layer realizations 21 , or incorporation of various supplementary components (stubs 22 , defected ground structures 10 , substrate-integrated waveguides 23 , shorting pins 24 ). All of these methods result in geometrically complex structures, whose accurate evaluation requires full-wave electromagnetic (EM) analysis due to the presence of cross-coupling effects in densely arranged circuit layouts.…”

Novel Stepped Impedance Microstrip Bandpass Filters for Radar Applications

“…In these designs, stepped impedance resonators are used to get a Bandpass Response. The SIR which are having an Open Circuit on one end and the Input and output ports are kept on the other ends acts as a Bandpass Filter [9][10].…”