An Octagonal Ring-shaped Parasitic Resonator Based Compact Ultrawideband Antenna for Microwave Imaging Applications

At a Glance

Metadata	Details
Publication Date	2020-03-01
Journal	Sensors
Authors	Amran Hossain, Mohammad Tariqul Islam, Ali F. Almutairi, Mandeep Singh Jit Singh, Kamarulzaman Mat
Institutions	National University of Malaysia, Kuwait University
Citations	44
Analysis	Full AI Review Included

Technical Documentation and Material Solutions for Compact UWB Antennas in Microwave Imaging

Documentation Prepared by 6CCVD Engineering Team

Executive Summary

This paper presents the design and characterization of a compact octagonal ring-shaped parasitic resonator-based Ultrawideband (UWB) antenna optimized for high-resolution Microwave Imaging (MWI) applications. The findings provide a direct rationale for transitioning from conventional lossy substrates to high-performance MPCVD diamond materials offered by 6CCVD.

Performance Achievement: The antenna prototype delivers an exceptional operational bandwidth of 8.7 GHz (2.80 GHz-11.50 GHz) with strong reflection coefficient (S₁₁ < -10 dB).
High Gain and Efficiency: Achieved a maximum gain of 5.80 dBi (at 9.45 GHz) and an average radiation efficiency of 75% (max 82%), critical for penetrating biological tissues.
Design Complexity: Performance relies heavily on intricate design methodologies, including three parasitic ring resonators, diamond-shaped radiating patches, and complex slotting (rectangular and irregular zigzag slots) on the ground plane.
MWI Suitability: The design generates multiple critical resonance frequencies (3.50 GHz, 6.45 GHz, 10.20 GHz) to balance the requirements of high resolution and deep tissue penetration.
Time-Domain Integrity: Demonstrated superb signal integrity with a high Face-to-Face Fidelity Factor of 0.9091, confirming minimal alteration of transmitted pulses.
Material Limitation: The use of FR-4 (Loss Tangent $\delta$ = 0.02) inherently limits the maximum achievable efficiency and gain, demonstrating a clear performance ceiling that MPCVD diamond can overcome.

Technical Specifications

Parameter	Value	Unit	Context
Antenna Dimensions (L x W x h)	29 x 24 x 1.5	mm³	Compact size for integration
Substrate Material	FR-4	N/A	Epoxy resin fiber (low cost)
Relative Permittivity ($\varepsilon_r$)	4.3	N/A	Dielectric constant of substrate
Loss Tangent ($\delta$)	0.02	N/A	Substrate loss factor (high for high-frequency UWB)
Operating Frequency Range	2.80 - 11.50	GHz	Ultrawideband operation
Impedance Bandwidth	8.7	GHz	Bandwidth exceeding $S_{11}$ < -10 dB
Primary Resonance Frequencies	3.50, 6.45, 10.20	GHz	Designed for multi-resolution imaging
Maximum Gain	5.80	dBi	Achieved at 9.45 GHz
Average Radiation Efficiency	75	%	Overall performance across the UWB range
Maximum Radiation Efficiency	82	%	Highest measured efficiency
Fidelity Factor (Face-to-Face)	0.9091	N/A	Indicates high signal correlation
Feed Line Impedance	50	$\Omega$	Matched using SMA connector

Key Methodologies

The high-performance UWB response was achieved through precise manipulation and optimization of both the radiating patch and the ground plane.

Substrate Selection and Initial Design:
- Design was based on low-cost FR-4 (h = 1.5 mm, $\varepsilon_r$ = 4.3, $\delta$ = 0.02).
- Initial dimensions calculated using microstrip patch antenna design formulas (Equations 1-3).
Radiating Patch Geometry:
- A diamond-shaped radiating patch was used, featuring five incremental staircase edges to enhance coupling and bandwidth.
Parasitic Element Integration (Frontside):
- Two octagonal, rectangular slotted ring-shaped parasitic elements were placed alongside the feed line.
- A 0.5 mm gap separated these elements from the feed line to reduce inductive reactance and increase capacitance, widening the bandwidth.
Parasitic Element Integration (Backside):
- One large octagonal, rectangular slotted ring-shaped parasitic element was placed on the backside of the substrate.
- This element, coupled with the partial slotted ground plane, increased directivity and gain.
Ground Plane Slotting and Chamfering:
- Three rectangular slots were cut out at the top of the ground plane to enhance reflection coefficient ($S_{11}$) and gain.
- Two irregular staircase-shaped zigzag slots were cut out at the bottom of the ground plane, crucial for producing the three distinct resonance frequencies and improving directivity.
- Corner Chamfering: The left and right corners of the ground plane were chamfered (length $x=2.83$ mm) to modify current movement and shift the upper operating frequency band from 11.0 GHz to 11.5 GHz.
Simulation and Validation:
- Numerical optimization of 28 parameters performed using CST Microwave Studio 2018.
- Measurements confirmed using an Agilent N5227A PNA network analyzer and the UKM Satimo StarLab system.

6CCVD Solutions & Capabilities: Enabling Next-Generation MWI Antennas

The exceptional performance demonstrated in this research, despite being limited by standard FR-4 substrate losses, highlights the potential of translating such complex UWB designs onto superior dielectric materials. 6CCVD specializes in providing the MPCVD diamond substrates necessary to maximize performance metrics like gain, bandwidth, and, critically, radiation efficiency for medical and high-frequency applications.

Applicable Materials for MWI Enhancement

The low loss tangent of diamond is orders of magnitude lower than FR-4 ($\delta=0.02$), resulting in significantly higher efficiency, essential for minimizing power consumption and maximizing signal penetration in MWI systems.

6CCVD Material Recommendation	Required Feature	Benefit over FR-4 ($\delta$ = 0.02)
Optical Grade Single Crystal Diamond (SCD)	Ultra-Low Loss, High Dielectric Strength	$\delta \approx 10^{-5}$ to $10^{-4}$. Enables efficiency > 95% at UWB frequencies, crucial for high-power MWI systems.
High Thermal Conductivity PCD Wafers	Large Area, Heat Dissipation (for power handling)	Wafers up to 125mm (suitable for array construction). Thermal conductivity exceeds 1000 W/mK, maintaining performance stability under high microwave load.
Undoped SCD Substrates	Stable & Predictable $\varepsilon_r$	Provides extremely uniform and stable dielectric constant (5.7 $\pm$ 0.1), simplifying frequency tuning and minimizing temperature dependence in sensitive medical sensors.

Customization Potential for Replication and Extension

To replicate the complex slotted resonator architecture and transition it to a robust platform, 6CCVD offers end-to-end processing services far exceeding standard PCB manufacturing capabilities.

Precision Substrate Dimensions:
- The paper uses a specific size ($29 \times 24 \times 1.5$ mm). 6CCVD offers custom dimensions, thicknesses (SCD/PCD from 0.1 µm up to 500 µm), and substrate sizes up to 125 mm.
High-Resolution Patterning and Slotting:
- The design relies on complex staircase zigzag slots and octagonal parasitic elements. 6CCVD provides advanced laser micro-cutting and etching services to achieve the required sub-millimeter precision ($p=0.80$ mm, $i=0.80$ mm, $t=0.90$ mm) directly onto the hard diamond surface.
Advanced Metalization and Connectivity:
- For the feed line and radiating patches, 6CCVD provides internal metalization capabilities, including Au, Pt, Ti, Pd, W, and Cu layers, ensuring low-resistance contacts and robust bonding for high-frequency signal transmission and 50 $\Omega$ impedance matching.

Engineering Support

The success of this UWB antenna depends on the optimized balance of 28 geometric parameters. Transitioning this design to a new dielectric platform (diamond) requires recalculating and re-optimizing these parameters based on the new, superior material properties.

Design Translation: 6CCVD’s in-house PhD team provides expert consultation on optimizing dielectric structures for low-loss environments. We assist researchers in tuning critical parameters (like patch length $L$ or ground plane depth $H$) to achieve optimal impedance matching and resonance profiles on MPCVD diamond.
Application Focus: We offer dedicated material selection guidance for complex applications, ensuring the chosen SCD or PCD grade meets the demands of high-gain, high-efficiency, directional Microwave Imaging (MWI) projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures prompt delivery worldwide.

View Original Abstract

An Ultrawideband (UWB) octagonal ring-shaped parasitic resonator-based patch antenna for microwave imaging applications is presented in this study, which is constructed with a diamond-shaped radiating patch, three octagonal, rectangular slotted ring-shaped parasitic resonator elements, and partial slotting ground plane. The main goals of uses of parasitic ring-shaped elements are improving antenna performance. In the prototype, various kinds of slots on the ground plane were investigated, and especially rectangular slots and irregular zigzag slots are applied to enhance bandwidth, gain, efficiency, and radiation directivity. The optimized size of the antenna is 29 × 24 × 1.5 mm3 by using the FR-4 substrate. The overall results illustrate that the antenna has a bandwidth of 8.7 GHz (2.80-11.50 GHz) for the reflection coefficient S11 < −10 dB with directional radiation pattern. The maximum gain of the proposed prototype is more than 5.7 dBi, and the average efficiency over the radiating bandwidth is 75%. Different design modifications are performed to attain the most favorable outcome of the proposed antenna. However, the prototype of the proposed antenna is designed and simulated in the 3D simulator CST Microwave Studio 2018 and then effectively fabricated and measured. The investigation throughout the study of the numerical as well as experimental data explicit that the proposed antenna is appropriate for the Ultrawideband-based microwave-imaging fields.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s20051354

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