Miniaturized Wideband Bandpass Filter Utilizing Square Ring Resonator and Loaded Open-Stub

Abstract

In this paper, a miniaturized wideband bandpass filter utilizing a square ring resonator and loaded open-stubs is proposed. One pair of bent open-stubs characterized as perturbations is installed outside the diagonal corners of the ring, and another pair of loaded open-stubs is added inside the ring resonator. By stretching the perturbation stubs more than half-wavelength of the ring, three pairs of degenerated modes in a ring are split for wideband operation. The first two split modes form the dominant passband. Meanwhile, the loading effect introduced by the loaded open-stubs could move the third split mode into the dominant passband. At the same time, an additional transmission zero is generated by the loaded openstub, which improves the skirt selectivity. Due to the applying of the perturbation stubs as long as more than half-wavelength, this kind of wideband microstrip ring resonator filter occupies a smaller size than those conventional ones that based on ring resonator. To verify the mechanism above, a wideband bandpass filter centered at 3.5 GHz is designed, implemented, and fabricated. Measured results of experimental circuit show good agreement with simulated responses.

Microstrip Wideband Bandpass Filter Based on Square Ring Loaded Resonator

“…Two bent open stubs are used as perturbations to split the degenerated modes in the ring. The first even-and odd- order split modes form a wideband passband under a proper external coupling, and two square patches are added in the corners of the ring to equalize the in-band ripple [8]. Two open stubs are parallel loaded with the perturbation stubs in order to control the second odd-order split mode.…”

“…[8], two loaded open stubs are loaded outside the ring in this work, whereas two loaded open stubs are added inside the ring in Ref. [8]. The third split resonant mode can be moved into the dominant passband by stretching the loaded open stubs, leading to an extra bandwidth of the passband.…”

“…Distinct from the layout in Ref. [8], two loaded open stubs are loaded outside the ring in this work, whereas two loaded open stubs are added inside the ring in Ref. [8].…”

“…The concept of combining a SRLR and two loaded open stubs was employed in [8] to form a wideband BPF. In that design, a pair of perturbation stubs as long as more than half-wavelength of the square ring was installed to the ring, making up the so-called SRLR.…”

“…In all these structures, ring resonator filters can provide a small circuit size and thus being attractive for designer. A square ring loaded resonator (SRLR) with loaded open stubs was described for wideband BPF operation in [8], which achieves a smaller circuit size than conventional ring resonator wideband BPFs [9][10][11][12][13][14].…”