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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.

T0 · AI review

How this review was made: An AI referee (glm-5.2) read the paper on July 9, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID2607.07661 (version 1)
Pith IDGYIHA6AR, Pith's permanent record of this paper and its review
CitationAugustine O. Nwajana, Halimat Olamide Yusuf. "Six-Pole Dual-band Bandpass Filter for WiMAX Applications." arXiv:2607.07661 (2026). https://pith.science/paper/GYIHA6AR
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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

This paper presents a method for converting a standard three-pole single-band bandpass filter into a six-pole dual-band bandpass filter by adding three additional resonators coupled to the main signal path. The authors use a Folded-Arms Square Open-Loop Resonator (FASOLR) microstrip structure—a compact variant of the conventional half-wavelength resonator—to implement the design on a Rogers RT/Duroid 6010LM substrate. The resulting filter produces two passbands centered at approximately 2.2 GHz and 2.4 GHz, with three transmission poles allocated to each band, yielding sharper selectivity than typical second-order dual-band designs. The approach is validated through circuit-level and electromagnetic simulations that show good agreement, with return loss better than 10 dB in the first band and 19 dB in the second, and insertion loss below 1.5 dB across both bands.

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
Figure 2. a, in which the shunt resonators are formed by equal capacitance C and inductance L, and the inter-resonator coupling is provided by the capacitor networks C01 and C12. The single-band network is then converted into the corresponding six-pole dual-band configuration shown in Figure 2b. The conversion is achieved by extending the circuit, with an additional set of three resonators coupled to the main-line resonators through a similar capacitor-only mutual-coupling network, thereby raising the filter order from three to six and producing the dual-band response. The resulting capacitor…
Figure 3. Filter coupling arrangements: (a) three-pole single-band; (b) six￾pole dual-band. K = FBW √g1g2 = 0.0722 (1) Qext = g0g1 FBW = 12.17 (2) With the coupling arrangements of
Figure 4. Microstrip layout of the proposed six-pole dual-band bandpass filter (dimensions in mm). IV. RESULTS AND DISCUSSION This section presents and discusses the simulation results for the proposed six-pole dual-band bandpass filter. The circuit-level (theoretical) response is examined first, followed by the electromagnetic (EM) (practical) response. A comparison between the theoretical and practical responses is then presented to validate the microstrip realisation. The theoretical S-parameter response is shown in Figure 5a. The filter exhibits two passbands positioned symmetrically…
Figure 5. b. As in the theoretical case, the filter exhibits two passbands positioned symmetrically about the 2.3 GHz design frequency, separated by a deep inter-band rejection at the centre, with the first passband centred near 2.2 GHz and the second near 2.4 GHz. The return loss remains better than 10 dB across the first passband and better than 19 dB across the second, with an insertion loss better than 1.5 dB in both bands, confirming that the practical microstrip implementation preserves the dual-band response established at the circuit level. The theoretical and practical responses are…

Showing 4 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:2607.07661 by the authors.

References

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