Application of Compact Folded-Arms Square Open-Loop Resonator to Bandpass Filter Design

Abstract

Folded-arms square open-loop resonator (FASOLR) is a variant of the conventional microstrip square open-loop resonator (SOLR) that facilitates further device size miniaturization by having the two arms of the conventional SOLR folded inwards. This paper highlights the benefits of this brand of compact SOLR by implementing a five-pole Chebyshev bandpass filter (BPF) using compact FASOLR. The test BPF is presented, with centre frequency of 2.2 GHz, fractional bandwidth of 10%, passband ripple of 0.04321 dB, and return loss of 20 dB. The design is implemented on a Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7 and thickness of 1.27 mm. The filter device is manufactured and characterised, with the experimentation results being used to justify the simulation results. The presented measurement and electromagnetic (EM) simulation results demonstrate a good match. The EM simulation responses achieve a minimum insertion loss of 0.8 dB and a very good channel return loss of 22.6 dB. The measurement results, on the other hand, show a minimum insertion loss of 0.9 dB and a return loss of better than 19.2 dB. The filter component has a footprint of 36.08 mm by 6.74 mm (that is, 0.26 λg x 0.05 λg), with λg indicating the guided wavelength for the 50 Ohm microstrip line impedance at the centre frequency of the proposed fifth-order bandpass filter.

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

“…However, conventional uniform impedance resonators typically have limited stopband performance with a relatively large overall size. Various small-size planar filter techniques have been previously studied [3][4][5][6][7][8][9][10][11][12][13]. For compact requirements, dual-mode half-wavelength resonators in degenerate [3,4] or non-degenerate modes have been studied [5][6][7].…”

“…These filters are suitable for a bandwidth that is approximately greater than 10% and less than 30%. Also, half-wavelength hairpin-line resonators have been structured in various topologies for compact configurations [8][9][10][11][12][13]. The parallel-coupled half-wavelength resonators are folded to form hairpin resonators as in [8,9].…”

Dual-Band and Wideband Bandpass Filters Using Coupled Lines and Tri-Stepped Impedance Stubs

“…Bandpass filters are mainly transmission line-based passive devices that are used in many RF/microwave circuits and wireless communication and radar systems. They are essential front-end components that can pass signals within a certain frequency range and reject unwanted out-of-band signals [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. There are many parameters to be considered in the design and implementation of a bandpass filter, such as the design structure, size, passband frequency bandwidth, insertion loss, selectivity, roll-off rate, isolation, and stopband rejection.…”

“…This type of filter is excellent for multiple frequency systems such as carrier aggregation or wireless local area network (WLAN) bands. Another method for obtaining a wideband response is by modifying the filter structure or attaching other elements to increase the bandwidth—such a method works well for wideband applications [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ].…”

“…Single-band bandpass filters with a wideband response are another approach for increasing a filter’s bandwidth. Methods for obtaining a wideband response have been demonstrated in the literature and include the use of: folded multiple-mode resonators [ 19 ], dual-mode ring resonators [ 20 ], folded-arms square open-loop resonators [ 21 ], cross-shaped resonators [ 22 ], T-shaped resonators and L-shaped defected microstrip structures [ 23 ], and stepped impedance open stub-loaded ring resonators with a high selectivity response [ 24 ]. A bandpass filter with five poles in the passband and 58.3% 3 dB FBW was developed by employing a ring resonator loaded with stepped impedance open stubs [ 24 ].…”