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Electromagnetic Modeling of Deformation-Based Pinching Antennas

Dimitrios Tyrovolas, Nikos C. Sagias, Ke Guan, George K. Karagiannidis, Stylianos D. Asimonis

arXiv:2610.30906v1eess.SP

TL;DR

A finite PA perturbation changes both guided-wave scattering and radiation, motivating a unified electromagnetic model. The model derives these responses from PA geometry and is validated against MEEP simulations. Geometry affects power, phase, and radiation patterns, while SNR results show that distance or total radiated-power fraction alone does not determine the best outcome.

  • Problem

    Existing studies mainly characterize PA effects through power-coupling or radiation-oriented formulations, rather than jointly relating one finite perturbation to complete complex scattering and three-dimensional radiation.

    Source: B. Motivation & Contribution · p. 2

  • Method

    The model derives complex reflection and transmission coefficients and three-dimensional radiation characteristics from the same finite PA geometry.

    Source: §III · p. 6, §V · p. 9

  • Results

    Case 3’s joint position-and-geometry optimization improves received SNR by 2.38 dB over Case 1 and 11.32 dB over Case 2.

    Source: §IV · p. 9

  • Takeaways & Limitations

    Pinching ratio and pinched-section length jointly shape the PA’s transmitted power and phase, radiation power-fraction, and radiation pattern, making geometry a design degree of freedom.

    Source: §V · p. 9

Abstract

from arXiv · show

Pinching-antenna systems (PAS) rely on local perturbations of a guiding structure to radiate part of the guided electromagnetic energy, making the physical response of the resulting pinching antenna (PA) fundamental to both guided-wave propagation and free-space radiation. To capture this coupled behavior, we develop an electromagnetic model of a finite deformation-based PA that directly relates the applied waveguide perturbation to its complex reflection and transmission responses and three-dimensional radiation characteristics. Full-wave MEEP simulations validate the model and demonstrate how the pinching ratio and pinched-section length jointly affect the transmitted power and phase, radiation power-fraction, and radiation pattern, thereby establishing PA geometry as a degree of freedom for controlling the radiation response. Importantly, this geometric dependence extends to communication performance, as the received signal-to-noise ratio (SNR) results reveal that neither minimizing the PA--user distance nor maximizing the radiation power-fraction necessarily yields the highest SNR, since the applied perturbation also determines the realized gain toward the user.

I. INTRODUCTION

Emerging wireless applications demand reliable, low-latency, high-rate service that adapts to users and propagation conditions. Pinching-antenna systems use guided signals and positionable radiation points, but their physical response also affects communication performance.

I. INTRODUCTION

  • Immersive applications and the metaverse impose stringent reliability, latency, and data-rate requirements while requiring infrastructure to adapt to user locations and propagation conditions.Source: §I · p. 1
  • Flexible-antenna architectures dynamically modify antenna configurations and wireless channels using spatially reconfigurable radiating elements.Source: §I · p. 1
  • Conventional architectures face feeding complexity, deployment cost, and propagation losses, motivating low-loss guiding structures with configurable radiation points.Source: §I · p. 1
  • PAS radiates signals from activated positions along a dielectric waveguide, enabling radiation points near users and favorable line-of-sight links.PA location also affects free-space distance and communication-link phase, while the PA’s interaction with the guided field redistributes power between the waveguide and radiation.Source: §I · p. 1

A. State-of-the-Art

Prior PAS research addresses communication-level design, hardware power coupling, and radiation characteristics. Together, these lines of work motivate models that account for coupling, network response, and directional radiation.

A. State-of-the-Art

  • PAS communication studies optimize PA positions and resources, characterize frequency-selective multi-PA transmission, and analyze array gain, outage, rate, and PA placement,.Source: A. State-of-the-Art · pp. 1–2
  • Deployment studies extend PAS to vertical waveguides for UAV communications [13] and curved waveguides [14], alongside analyses of PA number, spacing, and placement [12],.Source: A. State-of-the-Art · p. 2
  • Hardware and electromagnetic studies model power coupling,, multiport interactions, and radiation patterns through theory, simulation, measurement, and measured-pattern system models, [17]–[19].These studies establish the relevance of jointly accounting for PA power coupling, network response, and directional radiation when relating physical behavior to communication performance.Source: A. State-of-the-Art · p. 2

B. Motivation & Contribution

The paper addresses the lack of a unified model linking a finite PA perturbation to both complex guided-wave scattering and three-dimensional radiation. It develops and validates such a model, showing that geometry affects radiation and received SNR.

B. Motivation & Contribution

  • No prior work was known to jointly relate the same finite physical PA perturbation to complete complex guided-wave scattering and three-dimensional radiation characteristics.PA geometry can affect radiated power, the amplitude and phase of the downstream signal, and spatial radiation characteristics.Source: B. Motivation & Contribution · p. 2
  • The model derives complex reflection and transmission coefficients and three-dimensional radiation characteristics from the same finite PA geometry, with accuracy validated against MEEP simulations.Source: B. Motivation & Contribution · p. 2
  • Pinching ratio and pinched-section length jointly affect transmitted power and phase, radiation power-fraction, and radiation pattern, making geometry a design degree of freedom.Source: B. Motivation & Contribution · p. 2
  • Minimizing PA–user distance or maximizing total radiation power-fraction does not necessarily maximize received SNR because the perturbation also determines realized gain toward the user.Source: B. Motivation & Contribution · p. 2

II. WAVEGUIDE PROPAGATION AND PINCHING-ANTENNA RESPONSE

The section models guided propagation and the finite PA response using the HE11 mode in unperturbed and pinched waveguide sections. The response accounts for the two radius transitions and propagation through the pinched section.

II. WAVEGUIDE PROPAGATION AND PINCHING-ANTENNA RESPONSE

  • The section first characterizes the fundamental HE11 mode in unperturbed and pinched waveguide sections.Source: §II · p. 2
  • The mode description yields radius-dependent propagation constants and normalized modal fields for characterizing the PA response.Source: §II · p. 2
  • The finite PA response arises from two radius transitions and propagation between them.Source: §II · p. 2

A. Propagation in a Cylindrical Dielectric Waveguide with Pinching Antennas

The section models pinching as a finite, axisymmetric reduction of waveguide radius and characterizes propagation using the fundamental HE11 mode in the unperturbed and pinched sections. The resulting modal fields and propagation constants provide the basis for analyzing the PA response.

A. Propagation in a Cylindrical Dielectric Waveguide with Pinching Antennas

  • The PA is represented by a finite section whose radius changes from a to bk = κk a over length LP,k, capturing the perturbation magnitude and extent.The structure includes two radius transitions with propagation through the intervening pinched section.Source: A. Propagation in a Cylindrical… · pp. 2–3
  • Within the single-mode regime, the fundamental HE11 mode is characterized for each radius using the normalized frequency and transverse wavenumbers, then its boundary condition yields the propagation constant.The boundary-condition relation reduces to a one-dimensional nonlinear equation for u(r), whose HE11-branch root determines w(r) and β(r).Source: A. Propagation in a Cylindrical… · p. 3
  • Evaluating the modal solution at r = a and r = bk gives the propagation constants and fields for the unperturbed waveguide and pinched section.These quantities describe guided phase evolution through both sections and support characterization of scattering at the radius transitions.Source: A. Propagation in a Cylindrical… · pp. 3–4
  • The HE11 fields are normalized to unit guided power so their amplitudes can be compared consistently across the unperturbed and pinched sections.Equal field coefficients before normalization do not generally correspond to equal guided powers.Source: A. Propagation in a Cylindrical… · p. 4

B. Pinching Antenna Response

A finite PA response combines interactions at two radius transitions with propagation through the pinched section, including coupling through radiative and evanescent fields. Its geometry determines the complex reflected and transmitted guided signals, and the section length changes their coherent interaction.

B. Pinching Antenna Response

  • At each radius transition, projecting interface fields onto the adjoining HE11 modes characterizes the local reflected and transmitted guided components.Reversing the transition preserves the local transmission amplitude and reverses the reflection amplitude under the same modal projection.Source: B. Pinching Antenna Response · p. 4
  • Radiative and evanescent fields excited at each radius transition can propagate or decay across the pinched section and recouple into the guided HE11 mode.Their interaction is represented through the continuous cylindrical-mode spectrum and contributes to the length-dependent response.Source: B. Pinching Antenna Response · pp. 4–5
  • For a PA characterized by κk = bk/a and LP,k, the model determines its complex reflection and transmission coefficients from the finite-geometry response.The incident guided power is redistributed among reflected, transmitted, and radiated channels.Source: B. Pinching Antenna Response · pp. 4, 6
  • Changing LP,k changes phase accumulation and cylindrical-spectrum propagation or decay between the transitions, modifying the transmitted signal's amplitude and phase.The model treats finite pinched sections with two separated transitions, rather than the LP,k → 0 limit.Source: B. Pinching Antenna Response · p. 6

III. FAR-FIELD RADIATION AND PINCHING ANTENNA GAIN

The PA’s scattering response does not specify the angular and polarization characteristics of its radiation, so its far field is derived from the electric field over the finite pinched geometry. The resulting radiation power-fraction and directivity jointly determine gain, with both depending on the pinching ratio and pinched-section length.

III. FAR-FIELD RADIATION AND PINCHING ANTENNA GAIN

  • The PA’s scattering response alone does not determine the angular and polarization characteristics needed to describe its radiated field.Because the pinched section is the radiating region, the far-field response is derived from the electric field over that same finite geometry.Source: §III · p. 6
  • The reduced-radius section is modeled as an equivalent polarization-current distribution in the annular perturbation region, whose radiation integral yields the complex vector far field.The perturbation occupies the region between radii bk and a over the finite pinched-section length.Source: §III · pp. 6–7
  • Integrating the radiation intensity over the complete solid angle gives the fraction of incident guided power radiated by the PA.The incident HE11 mode is normalized to unit guided power.Source: §III · p. 7
  • The pinching ratio and pinched-section length jointly determine radiated-power fraction and angular redistribution, whose combination sets PA gain.Directivity describes the angular distribution of radiated power.Source: §III · p. 7

IV. SIMULATION RESULTS

MEEP-validated results show that pinching ratio and pinched-section length jointly shape a PA’s guided-wave response, radiation, and received SNR. Geometry-dependent directional gain means proximity or total radiated power alone does not determine the highest SNR.

IV. SIMULATION RESULTS

  • For κ = 0.75, |S21|^2 falls from 0.842 to 0.822 as LP,k rises from 2λ0 to 4λ0, then rises to 0.870 at 10λ0; |S11|^2 stays below −25 dB.Analytical scattering results closely follow MEEP; the non-monotonic transmission reflects phase-dependent partial recoupling at the second radius transition.Source: §IV · p. 7, Figure 1 · p. 8
  • Longer pinched sections reshape the far-field pattern more strongly, producing narrower angular features and more pronounced sidelobes at LP,k = 10λ0.The analytical and MEEP patterns agree closely; changes in κ also alter the dominant radiation region and secondary-lobe strengths.Source: §IV · p. 8
  • For LP,k = 10λ0, Arg{S21} spans [0, 2π) as κ varies, with longer sections producing larger geometry-dependent phase excursions.The phase accumulated in the PA is carried by the transmitted HE11 mode downstream; analytical phase results closely follow MEEP.Source: §IV · pp. 7–8, Figure 2 · p. 9
  • Radiation power-fraction rises as κ decreases and tends to zero as κ → 1, while its dependence on pinched-section length is non-monotonic and κ-dependent.Length changes the relative phase of contributions radiated along the finite section, so the length yielding the largest fraction varies with κ.Source: §IV · p. 9
  • Case 3’s joint optimization improves received SNR by 2.38 dB over Case 1 and 11.32 dB over Case 2; Case 2 is 8.94 dB below Case 1.Case 2 minimizes PA–user distance and maximizes total radiated-power fraction, while Case 3 also accounts for directional gain.Source: §IV · p. 9

V. CONCLUSION

The paper presents a finite deformation-based PA model validated with full-wave MEEP simulations. Its results link PA geometry to guided-wave and radiation responses, and show that optimizing received SNR requires accounting for directional gain.

V. CONCLUSION

  • The model relates finite dielectric-waveguide perturbations to complex reflection and transmission coefficients and three-dimensional radiation characteristics, with accuracy validated by full-wave MEEP simulations.The formulation derives the guided-wave and radiation responses from the same finite PA geometry.Source: §V · p. 9
  • Pinching ratio and pinched-section length jointly control transmitted power and phase, radiation power-fraction, and radiation pattern, with non-monotonic responses establishing geometry as a design degree of freedom.The conclusion identifies these geometric effects as relevant to shaping PA radiation characteristics.Source: §V · p. 9
  • In the considered single-PA evaluation, minimizing PA–user distance or maximizing total radiation power-fraction does not necessarily maximize received SNR because perturbation also determines directional gain.The framework is presented as a basis for extending physics-compliant modeling to multi-PA deployments, multi-mode operation, and other physically realizable perturbations.Source: §V · p. 9

APPENDIX A PROOF OF PROPOSITION 2

The proof derives the PA’s far-field radiation by modeling the finite pinched section’s guided fields and evaluating their overlap with a reciprocal field over the perturbation volume.

APPENDIX A PROOF OF PROPOSITION 2

  • The radiated far field is obtained from the overlap of the pinched-section field and a reciprocal field over the annular perturbation volume.The volume-equivalence formulation uses the reference waveguide’s outgoing Green function; reciprocity maps it to illumination from the observation direction.Source: Appendix A · pp. 10–11
  • The finite pinched section is modeled by forward- and backward-propagating HE11 fields whose amplitudes incorporate interactions between its two radius transitions.The interaction includes propagation or decay across the section and recoupling into the guided state.Source: Appendix A · p. 11
  • The proof evaluates the reciprocal-field overlap for both spherical polarizations and combines their components to form the far-field radiation pattern.The derivation uses cylindrical harmonics and boundary matching for the reciprocal field, then reduces the overlap to radial and longitudinal terms.Source: Appendix A · pp. 11–13
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