REVIEW
Six-Pole Dual-band Bandpass Filter for WiMAX Applications
Signal Processing · Submitted 8 Jul 2026 · 23 references
Pith's verdict: Competent but incremental dual-band filter design; the synthesis claim is underspecified.
Why Pith says this
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Referee report
The paper
The paper claims
Three-Pole Filter Doubled to Six-Pole Dual-Band at 2.3 GHz
The reading
What carries the argument
FASOLR (Folded-Arms Square Open-Loop Resonator): a microstrip resonator formed by folding the arms of a square open-loop resonator inward, reducing side length to ~λg/10; admittance inverter (J-inverter) replaced by capacitor-only coupling network; Chebyshev low-pass prototype with element values g0=g4=1.0, g1=g3=0.8516, g2=1.1032; frequency-splitting technique for extracting practical coupling coefficients from EM simulation.
Extended reading notes
Core claim
The central claim is that a dual-band bandpass response can be structurally derived from a single-band prototype by duplicating the three-resonator chain and coupling the duplicate set to the main line, raising the filter order from three to six and splitting the single passband into two symmetric bands. The FASOLR geometry serves as the enabling physical structure: by folding the arms of a square open-loop resonator inward, the side length shrinks to roughly one-tenth of a guided wavelength, achieving approximately 20% size reduction over the unfolded version. The paper reports that this synthesis route produces two passbands symmetric about the 2.3 GHz design frequency, each carrying three
Load-bearing premise
The paper assumes that coupling three additional resonators to the main signal path will naturally produce the intended dual-band behavior with three poles per band, without requiring independent tuning of the inter-pair coupling. The realized bandwidths deviate from the 7% design target, which the authors attribute to the approximation of ideal admittance inverters and physical coupling adjustments—indicating the synthesis route does not yield target specifications without
Editorial extensions
If this is right
- The single-to-dual-band conversion principle could extend to tri-band or multi-band filters by adding further resonator sets coupled to the main chain, each set contributing additional poles.
- The FASOLR geometry's compactness (~λg/10 side length) on high-permittivity substrates makes it a candidate for filter miniaturization in space-constrained RF front-ends beyond WiMAX.
- The discrepancy between designed (7%) and realized (5.09–6.17%) fractional bandwidths suggests that the capacitor-only admittance inverter approximation introduces systematic bandwidth compression that could be characterized and compensated in future designs.
- Higher-order dual-band filters (e.g., four poles per band) could be explored using the same duplication-and-coupling approach, potentially improving selectivity further at the cost of larger footprint.
Original abstract
Recent advances in multi-band wireless communication systems have driven the increasing need for dual-band bandpass filters. These types of filters are capable of isolating a small section of the frequency spectrum within a broader spectrum. Over the years, coplanar waveguide, microstrip, slotline, stripline, and other planar transmission line technologies have been widely employed in the design of microwave circuits and systems. This work employs a Folded-Arms Square Open-Loop Resonator (FASOLR) microstrip planar structure, designed and simulated using PathWave Advanced Design System (ADS). A third order (three-pole) single bandpass filter is transformed into a sixth order (six-pole) dual-band bandpass filter. The proposed six-pole dual-band bandpass filter is centred at 2.3 GHz, with a fractional bandwidth of 7% and produces two passbands centred at approximately 2.2 GHz and 2.4 GHz. The design is implemented on a commercially available Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7, a loss tangent of 0.0023, a substrate thickness of 1.27 mm, and 35 micro meter copper cladding on both sides. The overall filter component has a compact footprint of 30.56 mm by 20.56 mm. The design is validated through comparison of circuit-level and electromagnetic (EM) simulation results, which show good agreement. The EM simulation responses indicate a return loss better than 10 dB on the first band and better than 19 dB on the second, and an insertion loss better than 1.5 dB, demonstrating its suitability for WiMAX applications.
Figures
Showing 4 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:2607.07661 by the authors.
References
Discussion
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