Embedded Metallic Structures as Passive Antennas for Sub-GHz IoT

Communication in Smart City

Nurmayanti Zain

, Farhan Rezki Arifin

and Lompo Ramos Emakarim

Department of Electrical Engineering, University of Cokroaminoto Makassar, Tamalanrea-Makassar, Indonesia

Keywords: Embedded Antenna, Smart City, Sub-GHz Wireless, Metallic Structures, Internet of Things (IoT).

Abstract: The increasing demand for robust and scalable wireless infrastructure in smart city has highlighted the

potential of utilizing existing building materials as functional components in communication systems. This

study investigates the feasibility of embedded metallic structures, specifically steel elements such as

galvanized hollow steel and rebars as passive monopole antennas for sub-GHz Internet of Things (IoT)

applications. Focusing on the 700 MHz frequency range, analytical modeling was conducted to examine the

electromagnetic behavior of monopole configurations formed by structural elements in a concrete medium.

Key parameters such as resonance length, impedance matching, and radiation characteristics were derived

based on standard antenna theory. The simulation results confirm that selected metallic structures can support

monopole resonance with acceptable return loss and bandwidth performance for IoT communication. The

integration of antenna functionality into structural elements opens new possibilities for cost-efficient and

unobtrusive wireless systems in smart city environments.

1 INTRODUCTION

The rapid growth of smart city has increased the

demand for pervasive, energy efficient, and reliable

communication infrastructures, particularly for IoT

applications. Wireless communication at Sub-GHz

frequency is a key enabler due to its long-range and

low-power characteristics, making it suitable for large

scale urban deployments. However, deploying

conventional antennas in dense urban areas remains

challenging due to structural integration and aesthetic

constraints (Hussain et al., 2022; Jusoh et al., 2023).

Recent studies have explored embedding antennas

into metallic infrastructure elements, such as steel

beams, hollow sections, and construction frames, to

reduce installation complexity and transform passive

components into active communication elements,

supporting the vision of ambient intelligence (Vähä-

Savo et al., 2022; Kumar et al., 2024). Passive Sub-

GHz designs (700–900 MHz) embedded in metallic

building elements have shown potential for scalable

and covert IoT deployment in smart structures, smart

https://orcid.org/0009-0003-2075-6446

https://orcid.org/0009-0001-3526-6883

https://orcid.org/0000-0002-8005-592X

buildings, and smart composite structures (Albzaie,

2024; Inclán-Sánchez, 2023; Hassan et al., 2024).

While prior works have used load bearing wall

(Vähä-Savo et al., 2022; Vähä-Savo et al., 2024),

SEVA (Structurally Embedded Vascular Antenna)

(Bal et al., 2021) or concrete embedded antenna (Tan

et al., 2022), this study differs by: (1) Employing

galvanized hollow steel tubes as both load-bearing

and radiating elements, (2) Implementing a quarter-

wavelength monopole precisely tuned for 700 MHz

LPWAN (Low Power Wide Area Network) and

optimized via Ansys HFSS (High Frequency

Structure Simulator), and (3) Achieving full structural

integration by embedding the antenna into the main

structural element. These address limitations of

earlier designs reliant on solid conductors, external

mounting, or higher frequency bands.

Research gaps remain, including limited study on

the electromagnetic and mechanical performance of

hollow galvanized steel tubes, minimal focus on

quarter-wavelength resonance at 700 MHz for dense

urban LPWAN, lack of designs where antennas are

embedded within the main structural elements, and

122

Zain, N., Rezki Ariﬁn, F. and Ramos Emakarim, L.

Embedded Metallic Structures as Passive Antennas for Sub-GHz IoT Communication in Smart City.

DOI: 10.5220/0014266500004928

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Research and Innovations in Information and Engineering Technology (RITECH 2025), pages 122-128

ISBN: 978-989-758-784-9

the scarcity of comprehensive simulations with

realistic geometries and full specifications. To

address these gaps, this study employs Ansys HFSS,

a 3D (three-dimensional) electromagnetic solver

based on the Finite Element Method (FEM) that

provides rigorous solutions of Maxwell’s equations

for high-frequency structures. This paper presents a

conceptual and analytical investigation of embedded

galvanized hollow steel monopoles in a concrete

medium for Sub-GHz smart city IoT, focusing on key

design parameters, resonance behavior, and

integration scenarios in typical urban infrastructure.

2 METHODOLOGY

This study adopts a simulation-based methodology

that integrates theoretical modeling, dimensional

resonance analysis, and electromagnetic full-wave

simulation to investigate the feasibility of using

galvanized hollow steel structures embedded in

buildings as passive monopole antennas for sub-GHz

communication in smart city environments. The

analysis targets the 700 MHz frequency band, which

is widely adopted for long-range, low-power Internet

of Things (IoT) applications (Albzaie, 2024; Inclán-

Sánchez, 2023).

2.1 Structural and Electromagnetic

Design

The resonant length of the monopole antenna as a

quarter-wavelength radiator is analytically

determined based on:

L 





λ





(1)

where:

𝑐 is the speed of light (3×10

m/s),

𝑓 is the target frequency (700 MHz).

The nominal resonant length of the hollow steel

monopole is calculated to be approximately 10.7 cm.

Considering the finite conductor diameter, the

effective length is slightly reduced to around 9.7 cm,

in accordance with standard diameter correction

factors, as illustrated in Figure 1.

(a) (b)

Figure 1: Antenna Design: (a) Monopole with Ground

Plane, (b) Top View Antenna Configuration.

The metallic material chosen is galvanized

hollow steel, modeled as the antenna and embedded

within a reinforced concrete structure to represent

realistic construction components and evaluate the

fundamental electromagnetic behavior of the

monopole antenna. Galvanized hollow steel is

selected for its mechanical strength, durability, and

common use in building construction, while its

hollow form enables efficient integration with

structural elements, as illustrated in Figure 2.

(a) (b)

Figure 2: Structural Design: (a) Concrete Column Structure,

(b) Embedded Antenna within Rebar Structure.

The quarter-wavelength monopole antenna is

integrated into a reinforced structural column,

replacing one of the stirrups in an arrangement of

eight stainless steel rebars. Appropriate dielectric

properties are assigned to the surrounding materials

to evaluate their effects on the antenna’s resonant

frequency, impedance matching, and radiation

characteristics.

2.2 Simulation Setup

Electromagnetic simulations are performed using

Ansys HFSS, a full-wave 3D FEM solver widely

employed in antenna design. HFSS is selected due to

its capability to accurately model complex

geometries, account for material properties, and

predict the electromagnetic behavior of antennas

under realistic structural and environmental

conditions.

Figure 3 illustrates the simulation model. The

model consists of an air box with radiation boundary

conditions, a concrete column structure, a ground

plane, and a lumped port located at the monopole base

to emulate excitation from an IoT radio. Adaptive

meshing and a frequency sweep from 100 MHz to

Embedded Metallic Structures as Passive Antennas for Sub-GHz IoT Communication in Smart City

123

1.400 MHz are applied to ensure accurate evaluation

of reflection coefficients and electromagnetic field

distributions.

Figure 3: Simulation Model.

The quarter-wavelength monopole antenna is

positioned above an aluminum ground plane, with a

surrounding vacuum region of approximately 2 cm,

as shown in Figure 4. The vacuum layer is introduced

to prevent direct contact with the concrete, ensuring

that the antenna is not immediately influenced by the

surrounding cement. This configuration allows

precise evaluation of the antenna characteristics,

considering its integration within structural elements

to preserve performance.

Figure 4: Monopole Antenna in Concrete Medium.

The simulation parameters for the embedded

metallic structures are summarized in Table 1. This

setup enables assessment of the antenna’s

performance under realistic structural conditions,

accounting for material properties, geometric

dimensions, and spatial arrangement of the metallic

components. By replicating practical construction

scenarios, the simulation provides insight into the

antenna’s resonant frequency, input impedance, and

radiation characteristics, ensuring the results are

relevant for real-world structural integration.

Table 1: Simulation Parameters.

Paramete

Value

Tar

et Fre

uenc

700 MHz

Frequency Range 100

–

1.400 MHz

Antenna Type

Quarter-Wavelength

Mono

ole

Antenna Material

Galvanized Hollow Steel

Physical Length 10.7 cm

Optimized Length

9.7 cm

Hollow Dimensions

1.5 × 1.5 cm (outer)

1.28 × 1.28 cm (inner)

Wall Thickness 0.11 cm

Ground Plane 21.4 × 21.4 cm Aluminium

Reinforcin

Bar 8 Stainless Steel

Reinforcing Ba

Height 350 cm

Stirrup Spacing 15 cm

Embedding Medium Concrete

Boundary Condition

Radiation (Open)

Excitation Lum

ed Port 50 Ω

(

Base

)

2.3 Performance Metrics

The antenna performance is evaluated based on the

following key electromagnetic parameters: (1) Return

loss (S

) to determine the resonance frequency and

impedance matching, (2) Radiation pattern to assess

the omnidirectional coverage typical of monopole

antennas, (3) Gain to evaluate power conversion

effectiveness and suitability for low-power IoT

devices.

Table 2: Material Properties Used in Simulation.

Paramete

Galvanized Steel Concrete

Relative

Permittivity (εᵣ)

1.0 6.5

Relative

Permeability (μᵣ)

100 1.0

Bulk

Conductivity

(S/m)

1.6 × 10⁶ 0.01

Conductivity

Zinc layer: 1.1×10⁶

Steel core:

6.99×10⁶

Low

Conductivity

Cementitious

Material

Loss Tangent

(

tan δ

)

0 0.02

RITECH 2025 - The International Conference on Research and Innovations in Information and Engineering Technology

124

Paramete

Galvanized Steel Concrete

Densit

(

/m³

)

7850 2400

Metallic and dielectric materials are modelled

with physical parameters closely representing actual

construction materials, including relative

permittivity, permeability, bulk conductivity, and

density, as summarized in Table 2. These parameters

provide a practical reference for future experimental

validation and potential large-scale deployment in

real-world smart city environments. This

methodology enables assessment of the embedded

monopole antenna’s performance using standard

structural geometries and Sub-GHz communication

requirements.

3 RESULTS AND DISCUSSION

The electromagnetic performance of an embedded

metallic monopole antenna, designed using a

galvanized hollow steel in a concrete column

structure, was evaluated through full-wave simulation

in Ansys HFSS. The monopole antenna was modeled

with an optimized height of 9.7 cm, corresponding

quarter-wavelength at the target frequency of 700

MHz, to ensure more efficient performance. This

section presents the return loss characteristics,

radiation behavior, and implications for smart city

communication infrastructure.

3.1 Return Loss and Resonant

Frequency

The simulated return loss of the embedded monopole

antenna is presented in Figure 5.

Figure 5. Simulated Return Loss.

A distinct resonance is observed at 700 MHz with

a return loss of −17.03 dB, indicating efficient

impedance matching and minimal reflection at the

feed point. The −10 dB bandwidth spans

approximately 326 MHz, covering the frequency

range from 526 MHz to 852 MHz, which is

remarkably wide and sufficient to accommodate

multiple LPWAN technologies such as NB-IoT

(Narrowband IoT) and LoRaWAN (Long Range

Wide Area Network). The exceptionally broad

bandwidth ensures robust performance over a wide

range of operating frequencies, enhancing the

antenna’s versatility for sub-GHz applications. The

pronounced return loss together with the accurate

resonant frequency validates the effectiveness of the

antenna’s structural dimensioning and integration

within the concrete medium.

Figure 6: Simulated VSWR.

To further validate antenna matching quality,

simulated VSWR (Voltage Standing Wave Ratio)

values were evaluated as shown in Figure 6. The

antenna achieves a VSWR of less than 1.33 at the

resonant frequency (700 MHz) and maintains VSWR

values well below 2 throughout the operating

bandwidth (526–852 MHz). These results clearly

demonstrate excellent impedance matching and

efficient power transmission, making the antenna

highly suitable for low-power IoT communication in

smart city deployments.

These results confirm the theoretical prediction

based on monopole resonance, validating that the

physical dimension of the structure supports quarter-

wavelength operation. The sharpness of the resonance

peak and low return loss indicate that the structure

behaves as a high quality passive radiator suitable for

sub-GHz IoT applications (Rita et al., 2022).

3.2 Radiation Characteristics

The radiation characteristics were evaluated to assess

the antenna’s directionality and gain performance.

The 2D (two-dimensional) patterns provide angular

cuts in the principal planes (E-plane and H-plane) to

analyze radiation symmetry and beamwidth, whereas

the 3D patterns offer a complete spatial visualization

of power distribution. Together, these evaluations

deliver critical insights into the antenna’s coverage

Embedded Metallic Structures as Passive Antennas for Sub-GHz IoT Communication in Smart City

125

efficiency and its capability to radiate power

effectively toward the intended direction.

The radiation characteristics, specifically the 2D

radiation pattern, were evaluated to assess the

antenna’s directionality and gain performance, as

illustrated in Figure 7.

Figure 7: Radiation Pattern.

The 2D polar plots indicate that the H-plane

(Phi=0°–360°) radiation pattern is nearly

omnidirectional, providing predominantly uniform

horizontal coverage around the monopole, which is

advantageous for consistent signal reception in all

azimuthal directions.

Figure 8: Gain 3D Polar Plot.

As shown in Figure 8, the E-plane (Theta) exhibits

a doughnut-shaped pattern with nulls at 0° and 180°,

characteristic of monopole antennas. The 3D

radiation pattern further confirms uniform power

distribution in the horizontal plane, with radiation

concentrated around (θ=90°), while maintaining

symmetry and minimal backlobes.

The peak realized gain of 2.99 dBi, though

moderate, is sufficient for embedded antenna in dense

smart city environments where uniform short-range

coverage is prioritized (Chen & Zheng, 2023). The

combination of nearly omnidirectional H-plane

coverage and typical E-plane behavior ensures

reliable performance for sub-GHz LPWAN

applications, such as NB-IoT and LoRaWAN, within

built environments.

To achieve the radiation performance described

above, the monopole antenna is embedded within a

reinforced concrete column by replacing one of the

stirrups in an eight rebars configuration. Compared to

traditional monopoles fabricated on substrates

(Hussain et al., 2022), this structural integration not

only preserves the desired radiation characteristics

but also provides a mechanically robust solution,

allowing the metallic element to function

simultaneously as reinforcement and as a radiating

antenna. Such an approach aligns with previous

investigations on building and wall integrated

antenna systems (Vähä-Savo et al., 2022; Vähä-Savo

et al., 2024), confirming that embedded antennas can

meet the performance requirements for LPWAN

deployment in smart city environments (Khan et al.,

2024).

3.3 Application Potential in Smart City

The use of galvanized hollow steel as a functional

antenna element enables seamless integration into

urban structures while reducing costs, minimizing

visual clutter, and maintaining both durability and

aesthetics. The specifications summarized in Table 3

demonstrate that the proposed embedded quarter-

wavelength monopole antenna satisfies the required

electromagnetic performance targets as well as the

practical considerations for smart city deployment.

Table 3: Specification and Requirements for Antennas in

Sub-GHz IoT Smart City Applications.

Category Specification /

Requirement

Justification

Operating

Frequency

700–960 MHz

(target 700 MHz

in this study)

Provides long-range

coverage for

LPWAN

Antenna

Type

A quarter-

wavelength

monopole

(embedded in

structure)

Omnidirectional in

H-plane; nulls on

vertical axis E-plane;

uniform street-level

coverage

Impedance 50 Ω nominal;

lumped port or

coaxial feed

Matches standard

IoT radio ports

Return

Loss

≤ −10 dB

across operating

band

Efficient power

transfer and low

reflection losses

VSWR ≤ 2.0 across

operating band

Acceptable

performance

Bandwidth ≥ 100 MHz Complies with

regulations

RITECH 2025 - The International Conference on Research and Innovations in Information and Engineering Technology

126

Peak Gain 0–3 dBi (≥ 1 dBi

desirable)

Adequate link

budget

3.4 Practical Considerations and

Limitations

Passive embedded antennas present notable

advantages such as resilience to weather conditions,

resistance to vandalism, and minimal maintenance

requirements, making them promise for long-term

deployment in smart city infrastructures (Shailesh et

al., 2024).

Nevertheless, several practical considerations and

limitations must be carefully addressed. From a

material perspective, galvanized hollow steel,

although highly conductive, is still vulnerable to

corrosion over time, particularly in humid or coastal

environments where gradual deterioration of the zinc

layer may contribute to increased RF losses. When

antennas are embedded in concrete, the relatively

high dielectric constant (εᵣ = 6.5) and loss tangent (tan

δ = 0.02) introduce dielectric loading that shifts the

resonance frequency and decreases radiation

efficiency.

Moreover, variability in concrete composition,

moisture content, and curing conditions leads to

inconsistent dielectric properties, thereby

complicating accurate antenna tuning. Consequently,

antenna dimensions require careful optimization to

preserve resonance at the desired frequency despite

the dielectric loading effect.

Beyond electromagnetic aspects, structural and

mechanical factors also pose challenges. Embedded

antennas must withstand long-term mechanical

loading, thermal expansion, and vibrations within the

building structure, while any misalignment during

installation can permanently alter the radiation

pattern or coverage area since repositioning is not

possible once integrated. Environmental influences,

such as seasonal humidity variations, temperature

cycling, and pollution, further exacerbate these

challenges by modifying both the conductivity of

metals and the dielectric characteristics of concrete.

In addition, proximity to reinforcement bars,

electrical wiring, or other metallic components may

introduce parasitic coupling and electromagnetic

interference that detune the antenna and degrade

system performance.

To mitigate these limitations, several strategies

have been proposed, including the adoption of

reconfigurable antenna designs, adaptive impedance

matching, and AI-based optimization techniques to

dynamically maintain resonance under varying

environmental conditions (Spachos et al., 2021;

Mishra et al., 2022).

However, such approaches require further

validation through long-term experimental studies,

especially under real-world loading and

environmental stresses. Therefore, while passive

embedded antennas hold significant promise for

smart city communication systems, their practical

deployment demands careful material selection,

robust design methodologies, and rigorous durability

testing. Comprehensive experimental investigations

will be addressed in future studies as a critical part of

the research roadmap to ensure reliable performance

over extended operational lifetimes (Majumder et al.,

2025).

4 CONCLUSIONS

This study has demonstrated, through rigorous full-

wave electromagnetic simulations, the novel

contribution of employing galvanized hollow steel as

an embedded passive monopole antenna within

reinforced concrete columns for sub-GHz IoT

communication in smart city infrastructure.

By utilizing the inherent conductivity of

galvanized hollow steel within structural elements, a

9.7 cm monopole designed for operation at 700 MHz

achieved efficient impedance matching (−17.03 dB

return loss), a wide operational bandwidth (526–852

MHz), and an nearly omnidirectional radiation

pattern with a peak gain of 2.99 dBi.

These findings confirm the feasibility of

integrating communication functionality directly into

construction materials, thereby supporting the

development of smart urban infrastructure with

minimal additional cost and adaptive structural

modification.

This research demonstrates the embedding of

passive antennas within concrete column structures,

preserving their structural function while enabling

sub-GHz IoT communication. The approach

addresses practical urban challenges such as limited

space, aesthetic integration, and efficient deployment,

thereby supporting the development of scalable,

resilient, and low-profile IoT networks for smarter

and more sustainable urban environments.

Future research will focus on experimental

validation of the embedded antenna and the

evaluation of their performance under realistic

environmental conditions. These studies aim to

bridge the gap between theoretical design and

practical implementation in complex urban scenarios,

Embedded Metallic Structures as Passive Antennas for Sub-GHz IoT Communication in Smart City

127

ensuring the embedded antenna operates reliably and

maintains long-term durability.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the availability

of Ansys HFSS under an academic research license

provided by Department of Electrical Engineering

University of Cokroaminoto Makassar, which was

instrumental in conducting the electromagnetic

simulations presented in this study.

This research was funded by the Ministry of

Higher Education, Science, and Technology of the

Republic of Indonesia, through the Directorate

General of Research and Development, under the

Basic Research Scheme for the 2025 Fiscal Year.

REFERENCES

Albzaie, M. (2024). Smart materials and smart structures:

Transforming engineering and infrastructure.

International Journal of Civil and Structural

Engineering Research, 12(2), 42–47.

Bal, A., Baur, J. W., Hartl, D. J., Frank, G. J., Gibson, T.,

Pan, H., & Huff, G. H. (2021). Multi-layer and

conformally integrated structurally embedded vascular

antenna (SEVA) arrays. Sensors, 21(5), 1764.

Chen, X., & Zheng, Z. (2023). A wideband bow-tie slot

antenna embedded in dielectric for 5G communication.

IEEE International Conference on Microwave and

Millimeter Wave Technology (ICMMT), 1–3.

Hassan, O. S., Saif ur Rahman, M., Mustapha, A. A., Gaya,

S., Abou-Khousa, M. A., & Cantwell, W. J. (2024).

Inspection of antennas embedded in smart composite

structures using microwave NDT methods and X-ray

computed tomography. Measurement: Journal of the

International Measurement Confederation, 226, Article

114086.

Hussain, R., Alhuwaimel, S. I., Algarni, A. M., Aljaloud,

K., & Hussain, N. (2022). A compact Sub-GHz wide

tunable antenna design for IoT applications.

Electronics, 11(7), 1074.

Inclán-Sánchez, L. (2023). 3D-printed transparent mesh

antenna for smart buildings. In Antenna designs for

5G/IoT and space applications (pp. 1308–1320). MDPI.

Jusoh, A. Z., Husain, N. F., Abdul Malek, N. F., Mohd Isa,

F. N., & Mohamad, S. Y. (2023). Design of

miniaturized antenna for IoT applications using

metamaterial. IIUM Engineering Journal, 24(1), 122–

137.

Khan, S., Mazhar, T., Shahzad, T., Bibi, A., Ahmad, W.,

Khan, M. A., Saeed, M. M., & Hamam, H. (2024).

Antenna systems for IoT applications: A review.

Discover Sustainability, 5, 412.

Kumar, N., Kumar, P., & Sharma, M. (2024).

Reconfigurable MIMO antenna for IoT wireless

applications controlled by embedded system. Journal of

Telecommunications and Information Technology,

96(2), 32–40.

Majumder, K., Pramanik, S., Goswami, J. (2025).

Implementation of Smart Building Using Internet of

Things (IoT). In: Acharyya, A., Dey, P., Biswas, S.

(eds) Real-World Applications and Implementations of

IoT. Studies in Smart Technologies. Springer,

Singapore.

Mishra, M., Lourenço, P. B., & Ramana, G. V. (2022).

Structural health monitoring of civil engineering

structures by using the internet of things: A review.

Automation in Construction, 132, 103936.

Rita, J., Salvado, J., Rocha, H. d., & Espírito-Santo, A.

(2025). A comprehensive review of IoT standards: The

role of IEEE 1451 in smart cities and smart buildings.

Smart Cities, 8(4), 108.

Shailesh, Srivastava, G., & Kumar, S. (2024). A flexible

reconfigurable MIMO antenna for IoT-enabled smart

systems. International Journal of Antennas and

Propagation, 2024, Article 7557178.

Spachos, P., Papapanagiotou, I., & Plataniotis, K. (2021).

Microlocation for smart buildings in the era of the

Internet of Things: A survey. arXiv preprint.

Tan, J., Shao, Y., Zhang, J., & Zhang, J. (2022). Empirical

formulas for performance prediction of concrete

embedded antenna. The University of Sheffield.

Vähä-Savo, L., Haneda, K., Icheln, C., & Lü, X. (2022).

Electromagnetic-thermal analyses of distributed

antennas embedded into a load bearing wall. arXiv

preprint.

Vähä-Savo, L., Veggi, L., Vitucci, E. M., Icheln, C., Degli-

Esposti, V., & Haneda, K. (2024). Analytical

characterization of a transmission loss of an antenna-

embedded wall. IEEE Open Journal of Antennas and

Propagation, 5(6), 1765–1772.

RITECH 2025 - The International Conference on Research and Innovations in Information and Engineering Technology

128