Compact and Wideband U-Slotted Microstrip Antenna for Modern IoT Devices at ISM Band

Abstract

This paper presents the design and analysis of a compact U-slotted microstrip patch antenna with a truncated feed, optimized for IoT applications. The antenna is realized on an FR4 substrate with a thickness of 1.6 mm, offering a low-cost and mechanically stable platform. The proposed design achieves a wide operational bandwidth ranging from 1.8 GHz to 3.2 GHz, corresponding to a fractional bandwidth of up to 40%, making it suitable for multiple wireless standards such as Wi-Fi, Zigbee, and Bluetooth. Detailed simulations are performed to evaluate the antenna’s performance, including reflection coefficient (S11), voltage standing wave ratio (VSWR), input impedance, radiation pattern, and gain. Results demonstrate efficient impedance matching, stable omnidirectional radiation, and satisfactory gain across the operating band. The integration of the U-slot with the truncated feed enhances multi-resonant behavior while maintaining a compact footprint, making the antenna suitable for smart home devices, wearable sensors, and industrial IoT systems. The proposed antenna design provides a reliable, wideband, and low-profile solution, addressing the size and performance constraints inherent in IoT device integration.

Introduction

???? Objective

To design a compact, efficient, and cost-effective microstrip patch antenna for Internet of Things (IoT) applications that:

• Operates across multiple wireless standards (e.g., Wi-Fi, Bluetooth, Zigbee)

• Offers wide bandwidth, high radiation efficiency, and good impedance matching

• Fits within small, wearable, or embedded IoT devices

???? Context and Importance

• IoT ecosystems rely on wireless connectivity, making antennas critical for performance.

• Antenna performance impacts:

  • Range

  • Data throughput

  • Energy efficiency

• Microstrip patch antennas are ideal for IoT due to their:

  • Low profile and weight

  • Compatibility with PCBs

  • Simple fabrication and low cost

???? Literature Review Highlights

???? Common Designs and Trade-Offs:

• Substrates:

  • FR4: Cheap, but lossy at high frequencies

  • Rogers RT/duroid, Taconic: Low loss, better efficiency

• Feeding Techniques:

  • Microstrip line feed: Easy integration

  • Coaxial feed: Better matching, but bulkier

???? Key Challenges:

• Achieving multi-band operation in a small form factor

• Maintaining high gain, low return loss, and stable radiation

• Managing environmental impacts (e.g., metal enclosures, human proximity)

????? Antenna Design Methodology

???? Step-by-Step Design Process:

1. Set resonant frequency: 2.4 GHz

2. Choose substrate: FR4, εr = 2.2, thickness = 1.6 mm

3. Calculate width & length: Based on standard equations for rectangular patches

4. Apply correction for fringing fields

5. Design inset feed: For 50-ohm impedance matching

6. Introduce U-shaped slot: For bandwidth enhancement and multi-resonance

7. Use EM Simulation (e.g., HFSS): For optimization

???? Final Design Specs:

• Patch size: L = 28 mm, W = 36 mm

• Feed width: 4 mm

• U-slot: Main slot width = 18 mm, inner slot = 12 mm

• Ground plane: L = 30 mm

• Achieved bandwidth: ~40% (1.8 GHz – 3.2 GHz)

• Peak gain: Moderate, suitable for short/medium IoT range

???? Simulation Results

? Advantages of Proposed Antenna

• Wideband performance for supporting multiple IoT protocols

• Compact and low-cost using FR4 substrate

• Good impedance matching and low reflection losses

• Omnidirectional radiation, suitable for portable/wearable devices

• Simple fabrication with integrated microstrip feed

? Research Gaps & Future Directions

• Still no universal design balancing compactness, multi-band support, and fabrication ease

• Need for:

  • Advanced geometries (e.g., fractal-meander hybrids)

  • Low-loss, flexible materials

  • Improved feeding schemes

  • Environmentally robust designs

• Continued simulation-based optimization using tools like HFSS or CST

Conclusion

A compact U-slotted microstrip antenna with a truncated feed has been successfully designed and analyzed on an FR4 substrate of 1.6 mm thickness for IoT applications. The antenna operates efficiently over a wide frequency range of 1.8 GHz to 3.2 GHz, achieving a bandwidth of up to 40%, which demonstrates its capability to support multiple wireless communication standards. Simulation results, including S11, VSWR, impedance, radiation pattern, and gain plots, confirm that the antenna maintains good impedance matching, stable radiation characteristics, and satisfactory gain across the operating band. The U-slot configuration, combined with the truncated feed, enhances the overall performance by providing multi-resonant behavior while maintaining a compact and cost-effective design. Overall, the proposed antenna proves to be a promising solution for integration into IoT devices, offering wide bandwidth, reliable radiation performance, and ease of fabrication.

References

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Copyright

Copyright © 2025 Rajeev Kumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.