A Novel Corner Etched Rectangular shaped Ultrawideband Antenna Loaded with Truncated Ground Plane for Microwave Imaging

doi:10.21203/rs.3.rs-1598035/v1

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A Novel Corner Etched Rectangular shaped Ultrawideband Antenna Loaded with Truncated Ground Plane for Microwave Imaging

https://doi.org/10.21203/rs.3.rs-1598035/v1

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published 05 Apr, 2023

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Microwave imaging has become a popular research issue in recent decades as a result of its several benefits over traditional imaging technologies. To analyse biological tissues in depth, a microwave imaging instrument is employed.The test determines the presence and location of morphological alterations in specific biological tissues. Ultrawideband (UWB) microwave imaging is a new technique that produces improved results while avoiding the use of ionizing radiation. Antennas play a critical part in these systems, and as a result, antenna optimization has become a hot topic due to the device's proximity to the human body. Recent research has revealed a number of initiatives to improve the electromagnetic sensors employed in these systems, whether as single or array components. In this article, the development of a compact ultrawideband (UWB) antenna functioning in the frequency range of 3.25-14.63GHz is proposed. The reported antenna comprises of a rectangular patch and a modified ground plane “etched on a FR4” substrate excited by a 50Ω feed line. The overall dimension of antenna is \(0.44 {\lambda }_{0}\times 0.38 {\lambda }_{0}\times 0.02{\lambda }_{0}\). The proposed antenna has been fabricated on FR-4 substrate. Measused and simulated results are in good agreement. The proposed antenna is compact and displays good radiation characteristics along with good gain.

1. INTRODUCTION

In recent years, UWB technology has gained significant interest from researchers throughout the globe. In February 2002, the Federal Communication Commission (FCC) released the frequencies of 3.1GHz to 10.6GHz for commercial applications [1]. The design of a UWB antenna requires the antenna to be small and compact, it should have wide bandwidth performance, the radiation pattern has to be Omni-directional and the antenna should be easy to fabricate [2–3].

The benefits of an ultra-wideband antenna are its low complexity and it is inexpensive to manufacture. UWB patch antenna can be designed with various geometries such as circular, triangular, square, or rectangular. UWB technology is applied in several fields such as microwave imaging and radar systems. Microwave imaging utilizes EM waves to see through the inner structure of a tissue. It recognizes tumors based on dielectric properties, which are different compared to normal tissue [4–5]. X-rays, ultrasound, and MRI scans are used in the early detection of cancerous cells [6]. However, these methods pose some disadvantages. X-ray mammography is agonizing for patients, and long exposure to X-ray may cause healthy cells to become cancerous [7]. Another technique used to detect cancerous cells is ultrasound, but this technology is unable to detect deeply buried tumors and it is comparatively expensive [8]. To overcome these limitations, microwave imaging employs low ionizing radiation and is cost-effective compared to other methods [9]. Microwave imaging incorporates the use of UWB pulses which range from “low to high” frequencies in order to generate images of human tissues [10]. The higher frequency band is used to create high-resolution images of the tissue, whereas the lower frequency band is used to detect deeply buried tumors [11].

A microwave imaging system has two parts, a “front end,” which requires the antenna to be inexpensive, compact and it should operate efficiently, whereas the second part requires analyzing the performance of the antenna to detect the tumor and generate the image using the various processing techniques. The need for the antenna to be is compact is because it is to be incorporated into portable microwave imaging systems. This paper overviews the design and optimization of a novel microwave antenna which must serve as an element in a sensor array for early detection. The proposed microstrip patch antenna in this work displays good UWB characteristics and also displays good gain characteristics. The antenna consists of a modified square patch and a ground plane built on a FR4 substrate. Parametric analysis is done on the proposed antenna to observe the effect of various design parameters on the antenna performance, further, the simulations of the current density, gain and radiation pattern are also reported in this paper.

The benefits of an ultra-wideband antenna are its low complexity and it is inexpensive to manufacture. UWB patch antenna can be designed with various geometries such as circular, triangular, square, or rectangular. UWB technology is applied in several fields such as microwave imaging and radar systems. Microwave imaging utilizes EM waves to see through the inner structure of a tissue. It recognizes tumors based on dielectric properties, which are different compared to normal tissue [4-5]. X-rays, ultrasound, and MRI scans are used in the early detection of cancerous cells [6]. However, these methods pose some disadvantages. X-ray mammography is agonizing for patients, and long exposure to X-ray may cause healthy cells to become cancerous [7]. Another technique used to detect cancerous cells is ultrasound, but this technology is unable to detect deeply buried tumors and it is comparatively expensive [8]. To overcome these limitations, microwave imaging employs low ionizing radiation and is cost-effective compared to other methods [9]. Microwave imaging incorporates the use of UWB pulses which range from “low to high” frequencies in order to generate images of human tissues [10]. The higher frequency band is used to create high-resolution images of the tissue, whereas the lower frequency band is used to detect deeply buried tumors [11].

1.1 Related Work

This literature reviews various UWB antennas designed to be used in microwave imaging systems. In the work proposed by Zhang et al [12], the designed micro strip antenna had low gain which was less than 5 dB and had low radiation performance, In order to overcome these limitations several methods were proposed by researchers but it would increase the complexity in designing the proposed antenna for this work. Similarly, Abak et al [13], designed a cavity back Vivaldi antenna which resulted in a compact-sized antenna but displayed low gain characteristics. In order to improve gain characteristics, He et al [14] proposed to fabricate the antenna with planar directors, however in doing so it increased the size of the antenna significantly. M. T Islam et al [15], proposed a low-cost UWB antenna but its dimensions were comparatively larger dimension 51x42 mm² and also displayed low bandwidth. The antenna designs in [12-15] have limitations in size, gain, and bandwidth and the proposed antenna in this report aims to overcome these limitations. A rectangular microstrip patch antenna is developed to function in the UWB frequency range. The detailed analysis of UWB is discussed in the coming sections.

The primary purpose of this work is to develop an inexpensive antenna that operates in the UWB frequency range with optimal performance to be used for microwave imaging applications. To obtain this objective, the evolution of the design stages is depicted in Fig. 1.

The S₁₁ plot of the evolution stages is depicted in Fig. 2. The rectangular microstrip patch antenna proposed is formed on an FR4 substrate with 𝜀_𝑟 =4.4. The dimension of the rectangular patch (in mm) is \(14.5\times 15\). The results obtained for Fig. 1a were substandard, and to achieve better S₁₁ characteristics, the ground plane was modified. The dimensions of the modified ground plane (in mm) are \(12.5\times 30\). To improve the “impedance matching” of the antenna, circular corner cuts are made on the top portion of the ground as illustrated in Fig. 1 (c) and to the top and bottom sections of the “rectangular patch” as shown in Fig. 1 (d). The corner cuts at the lower end of the rectangular patch increase the space between the ground and patch, which tunes the capacitive coupling between them; further adding corner cuts to the top portion of the patch tunes the inductive coupling capacity of the antenna. It cancels out the capacitive coupling between the patch and the ground resulting in “resistive input impedance.”

In contrast, the slots in the ground plane neutralize the “capacitive” effects by the inductive nature of the patch to get purely resistive input impedance.” This proposed antenna depicted in Fig. 3 exhibits good UWB characteristics with S11 < − 10dB and displays good bandwidth characteristics ranging from 3.25 to 14.63 GHz, as represented in Fig. 2. The dimensions for the “proposed antenna” are given in Table 1.

3.1 Analysis of evolution stages.

In the initial design, the S₁₁ value was significantly greater than − 10dB. Hence the ground plane was modified. As a result, the S₁₁ value reduces. To enhance the result, a circular slot is etched on the patch. The corner cuts on the patch significantly bring the S₁₁ value below − 10dB, which is depicted in the plot shown in Fig. 4.

3.2 Effect of corner cuts on Rectangular patch

To analyze the effect of corner cuts on the rectangular patch, each corner cut was simulated individually. The addition of each corner cut is illustrated in Fig. 5. It can be noticed from Fig. 6 that with the addition of each cut, the S₁₁ value decreases even more than the − 10dB mark.

3.3 Effect of truncation on the ground plane.

Figure 7 illustrates the development stage in modifying the ground plane. The S₁₁ characteristics were plotted for each stage of development. It was observed that the addition of corner cuts and modification to the ground plane increased the space between the rectangular patch and the ground, thereby canceling out the inductive and capacitive effects. The proposed antenna displays good S₁₁ < -10 dB bandwidth and impedance matching. The S₁₁ characteristics are plotted and are shown in Fig. 8.

3.4 Parametric Analysis

3.4.1 Effect of corner cuts on rectangular patch

To analyze the effects of corner cuts on the rectangular patch, the addition of each corner cut was simulated and analyzed. The S₁₁ characteristics are represented in Fig. 9. It can be observed that when the radius is 1.5mm, the bandwidth of the antenna is reduced. For a radius of 2.5mm, S₁₁ values are away from the − 10dB mark, but the result is optimum when the radius is 2mm.

3.4.2 Effect of corner cuts on the ground plane.

Optimum results were obtained for a radius of 2.5mm on the corner cuts. Both the corner cuts on the ground plane were varied. They were simulated and analyzed for values of 2mm, 2.5mm, and 3mm. The results obtained were plotted on the graph, and the S11 characteristics displayed optimal results at a 2.5mm radius, as shown in Fig. 10.

3.4.3 Effect of center circular cut on rectangular patch

To increase the space between the ground and the rectangular patch to cancel out the capacitive and inductive effects to produce pure resistive input, the circular cut at the center of the circle (Re) was increased from 1 mm to 2mm in increments of 0.5mm. It is observed that the optimal results were obtained when Re equals 1.5mm. The plot is depicted in Fig. 11.

3.4.4. Effect of Center Ground Cut

The rectangular cut in the center of the ground plane was simulated and analyzed at 2.5mm, 3mm, and 3.5mm. For all three values, the S₁₁ value was significantly less than − 10 dB, but the best results were seen for a width of 3mm, which can be observed in Fig. 12.

3.4.5 Effect of the width of transmission line

The width of the transmission line was simulated and analyzed at 2.5mm, 2.85mm, and 3mm. Better results were obtained for a width of 2.5mm but at the cost of bandwidth. Hence, for optimal results, 2.85mm is selected as the width of the transmission line. The result can be observed in Fig. 13.

3.5 Current Distribution

The current distribution is simulated and analyzed, as shown in Fig. 14, to realize the operation of the proposed UWB antenna. The resonance characteristics are analyzed at the 3.5, 5.2, 5.8, 8.0, 10.0, and 12.0 GHz frequencies. It is observed that at 5.2 GHz, the entire patch and the ground plane are conducting with a value of 1 Amp/m. Similar results are seen at the other frequencies. It can be observed from Fig. 14 that different parts of the antenna have different resonance paths for different operating modes.

The suggested antenna was designed and manufactured using the FEM approach on the HFSSv.13.0 simulator. The suggested UWB antenna is shown in Fig. 15.

4.1 Simulated and measured S₁₁:

The comparison of the models and observations of S₁₁ is shown in Fig. 16. The ROHDE & SCHWARZ ZVL network analyzer was used to determine S₁₁. At the S₁₁<-10 dB level, the simulated impedance bandwidth is 3.25–14.63 GHz. At the S₁₁<-10 dB level, the measured operating impedance bandwidth is 3.1–13.9 GHz. There is a little disparity between S₁₁ simulations and measurements.. It's because to soldering, failing to account for the SMA connector during simulation, errors in the substrate's dielectric constant, and fabrication tolerances.

4.2 Gain

The “gain of the Ultrawideband antenna is shown in Fig. 17. It is observed that the gain ranges from 2.98–9.68 dB. Under simulation, the antenna displays a minimum gain of 2.98 dB at 3.5 Hz and 9.68 dB at 14 GHz. Figure 18 shows the 3D polar gain of proposed antenna.

4.3 Radiation Pattern

The radiation pattern for the antenna is illustrated in Fig. 19 for different frequencies. From Fig 19, it is observed at 3.5 GHz, the pattern is directional. The radiation pattern for 5.2 and 5.8 GHz is directional. At 8 GHz, the pattern observed is bi-directional). The reported antenna exhibits a “bidirectional pattern in the E-plane” and an “omnidirectional pattern in the H-plane” at frequencies below 5.8 GHz. At frequencies greater than 5.8 GHz, the radiation pattern distorts. These distortions can be attributed to higher-order modes.

A comparative analysis is done to know how improved the proposed antenna is compared to the current literature available, as shown in Table 2.

A rectangular microstrip patch antenna is developed to function in the UWB frequency range in this paper for microwave imaging. Further developments are made to the ground and patch and to enhance the antenna performance. The antenna also displays good frequency bandwidth from 3.25 GHz – 14.63 GHz. Parametric analysis on the antenna shows that a slight change in the dimensions can affect the UWB characteristics. The proposed antenna is compact and displays good radiation characteristics while being cost-effective.

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Tables 1 and 2 are available in the Supplementary Files section

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Journal Publication

published 05 Apr, 2023

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Editorial decision: Minor revisions
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You are reading this latest preprint version

A Novel Corner Etched Rectangular shaped Ultrawideband Antenna Loaded with Truncated Ground Plane for Microwave Imaging

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Design Of Ultrawideband Antenna

3. Design Analysis Of The Ultrawideband Antenna

3.1 Analysis of evolution stages.

3.2 Effect of corner cuts on Rectangular patch

3.3 Effect of truncation on the ground plane.

3.4 Parametric Analysis

3.4.1 Effect of corner cuts on rectangular patch

3.4.2 Effect of corner cuts on the ground plane.

3.4.3 Effect of center circular cut on rectangular patch

3.4.4. Effect of Center Ground Cut

3.4.5 Effect of the width of transmission line

3.5 Current Distribution

4. Result Of Uwb Antenna

4.1 Simulated and measured S₁₁:

4.2 Gain

4.3 Radiation Pattern

5. Conclusion

References

Tables

Supplementary Files

Status:

Journal Publication

Version 1

A Novel Corner Etched Rectangular shaped Ultrawideband Antenna Loaded with Truncated Ground Plane for Microwave Imaging

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Design Of Ultrawideband Antenna

3. Design Analysis Of The Ultrawideband Antenna

3.1 Analysis of evolution stages.

3.2 Effect of corner cuts on Rectangular patch

3.3 Effect of truncation on the ground plane.

3.4 Parametric Analysis

3.4.1 Effect of corner cuts on rectangular patch

3.4.2 Effect of corner cuts on the ground plane.

3.4.3 Effect of center circular cut on rectangular patch

3.4.4. Effect of Center Ground Cut

3.4.5 Effect of the width of transmission line

3.5 Current Distribution

4. Result Of Uwb Antenna

4.1 Simulated and measured S11:

4.2 Gain

4.3 Radiation Pattern

5. Conclusion

References

Tables

Supplementary Files

Status:

Journal Publication

Version 1

4.1 Simulated and measured S₁₁: