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PIER PIER B PIER C PIER M PIER Letters PIER Photonics
2026-09-21
A Concentric Multi-Ring Circular Monopole Antenna Designed by Characteristic Mode Analysis for Continuous Sub-6 GHz 5G Coverage
By
Immanuel Prabaharan Soundararajan,

    Mr. Immanuel Prabaharan Soundararajan

    Department of Electrical and Electronics Engineering

    Academy of Maritime Education and Training (AMET), Deemed to be University

    India

    Homepage

Muthurajan Subramoniam,

    Dr. Muthurajan Subramoniam

    Department of Electrical and Electronics Engineering

    Academy of Maritime Education and Training (AMET), Deemed to be University

    India

    Homepage

Arul Kulandaivel,

    Dr. Arul Kulandaivel

    Department of Marine Engineering

    Academy of Maritime Education and Training (AMET), Deemed to be University

    India

    Homepage

Lakshmi Dhandapani,

    Dr. Lakshmi Dhandapani

    Department of Electrical and Electronics Engineering

    Academy of Maritime Education and Training (AMET) Deemed to be University

    India

    Homepage

Rajeshkumar Dhandapani

    Dr. Rajeshkumar Dhandapani

    Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology

    India

    Homepage

Progress In Electromagnetics Research C, Vol. 173, 321-330, 2026
doi:10.2528/PIERC26080901 | Google Scholar

Abstract
This paper presents a single-port concentric multi-ring circular monopole in which each ring is a separate characteristic-mode resonator, and cross spokes force the ring currents in phase so that the individual ring resonances merge into one continuous impedance band. This ring-per-mode partitioning distinguishes the design from single-mode monopoles, and characteristic mode analysis (CMA) is used to place and order the modes rather than explain a finished geometry. The radiator occupies 0.27λ0 × 0.39λ0 on a 33 × 23 × 0.8 mm3 RT/Duroid 5880 substrate (εr = 2.2, tan δ = 0.0009), a low-permittivity laminate that resists miniaturisation. A central disc of radius 5.5 mm and three concentric rings of mean radii 6.27, 7.79, and 10.14 mm are excited by a 50 Ω microstrip line whose 2.465 mm width follows directly from Hammerstad synthesis, and a triangular tapered partial ground of height 10.66 mm - one quarter-wavelength at band centre completes the match. Closed-form ring resonances of 3.72, 4.84 and 6.02 GHz agree with the modal spectrum and with the measured lower resonance at 3.65 GHz to within 1.9%. The measured impedance band spans 3.50-6.15 GHz, a fractional bandwidth of 54.9% centered at 4.83 GHz, and covers the 5G NR n77, n78 and n79 bands together with the 5.5 GHz WLAN band in one continuous match. A physically partitioned equivalent circuit, one series-RLC branch per ring with every branch resonance fixed to its closed-form value, reproduces the full-wave reflection response with a 0.72 dB RMS error. The design gives a compact, single-layer, single-feed route to full sub-6 GHz coverage with an analysis chain that ties every dimension to a resonant mechanism.
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Citation
Immanuel Prabaharan Soundararajan, Muthurajan Subramoniam, Arul Kulandaivel, Lakshmi Dhandapani, and Rajeshkumar Dhandapani, "A Concentric Multi-Ring Circular Monopole Antenna Designed by Characteristic Mode Analysis for Continuous Sub-6 GHz 5G Coverage," Progress In Electromagnetics Research C, Vol. 173, 321-330, 2026.
doi:10.2528/PIERC26080901
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