A Compact Staircase Rectangular Microstrip Patch Antenna for Microwave Imaging Applications

doi:10.21203/rs.3.rs-1344429/v1

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A Compact Staircase Rectangular Microstrip Patch Antenna for Microwave Imaging Applications

https://doi.org/10.21203/rs.3.rs-1344429/v1

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A Staircase monopole antenna with microstrip line feed for improved bandwidth and high gain. The etching of staircase steps at the bottom and the top of the rectangular patch antenna improves the impedance matching both at lower and at high frequencies. The implementation of the slots at the top of the patch and the ground plane leads to an improved bandwidth ratio of 5.875: 1. The overall size of the proposed antenna is 72 x 63 x 1.588 mm³, and it has multiple resonances at 2GHz, 4 GHz, 5.8GHz and 7.4 GHz. A fractional bandwidth of 141% is achieved for the return loss of less than -10 dB. The antenna accomplishes a gain of 5.87 dBi. The monopole antenna detects the presences of tumor location from the skin layer of the human breast model.

Ultra-Wideband (UWB)

Staircase monopole

Defected Ground Structure (DGS)

Debye model

bandwidth improvement.

The development of UWB antennas at the lowest operating frequency range for medical diagnostics is a challenging task. The electrical length of the antenna should be substantially large at low frequencies. Furthermore, the UWB antennas are required to operate at the broad operating frequency range in the future compact wireless devices. [1] proposed the microstrip slot patch antenna for UWB frequency range. The proposed pentagon lost antenna is placed on the Debye test bed for measuring the scattered field response. However the size of the antenna is larger for applications of the microwave imaging technique. [2] have presented a circularly polarized rectangular monopole antenna for wideband applications. The asymmetric structure of the antenna geometry optimizes the current flow at the top edge of the ground plane and the bottom edge of the radiator. [3] has presented a review of the effects on the ground plane structure to improve bandwidth. [4] have presented a circular disk patch antenna for UWB applications. A band-notch characteristic is created using a rectangular slot to rejected frequency band of 5.15 GHz to 5.825 GHz. The effects of varying feed location and antenna aperture towards the band of operation also are analyzed. [5] have presented an octagonal ring dual band for both Bluetooth (2.4-2.484GHz) and UWB (3.1 to 10.6GHz). The octagonal ring and ground plane modifications provide an enhancement in bandwidth operation. [6] have proposed a compact UWB monopole antenna. The antenna is fabricated using the Roger substrate with a dielectric constant of 2.2. Etching two notches on the patch antenna minimize the electromagnetic coupling effect between the ground plane and the patch. The electromagnetic coupling at the lower corner of patch radiator gets reduced. This modification increases the impedance bandwidth and the antenna provides an omi-directional radiation pattern. [7] have presented a planar disc monopole antenna with high directional on UWB band. This is accomplished from etching the L-shaped ground plane. A miniaturized UWB patch antenna with extended strip is result the antenna to operate at low frequency[8]. The antenna gain is minimum because of lower surface area. A compact high gain antenna operates at UWB band results in high gain and has omnidirectional radiation [9]. A coplanar waveguide fed with conductor backed antenna operates at wide bandwidth and results in average gain of 5 dBi [10]. The different structures of antenna are developed for microwave imaging applications with the major concern in antenna parameter as improvement of bandwidth[11]. After several research it is observed that the antenna applicable for microwave imaging system should have wide bandwidth and better gain. The optimization of the antenna design parameters such as addition of parasitic elements, adjusting feed position, inserting slots and notches improves the antenna bandwidth, directivity and half power beamwidth of the antenna. In recent researches various size reduction techniques are included in the design of UWB antenna which results in a minimum gain and operates only at higher frequency. Hence a staircase monopole antenna is proposed to achieve high gain, wide bandwidth as suitable for microwave imaging applications.

The essential parameters to design a rectangular patch antenna are the resonance frequency (fr), FR4 dielectric substrate with the dielectric constant of 4.4 and the dielectric thickness of 1.6 mm. The selection of a suitable substrate is the first step in the design of microstrip patch antenna for the required applications. The selection of the substrate material depends on its dielectric constant ∈_r, loss tangent tanδ and material thickness. Various types of materials such as polyphenylene, alumina, polyolefin, Polytetrafluoroethylene (PTFE), polystyrene, sapphire, quartz, ferromagnetic and semiconductor substrates have considerable flexibility in the selection of substrates for a particular application. From the above-specified substrate materials, quartz and PTFE result in excellent radiation efficiency at microwave frequencies, but they are expensive. Hence the FR4 substrate material is widely selected for the microwave applications since it is cost effective and readily available. The mathematical modeling of the proposed rectangular microstrip patch antenna is summarized below from Equations (1) to (7)

a) The width of the patch (W_p)

$${W}_{p}=\frac{{v}_{0}}{2{f}_{r}}\sqrt{\frac{2}{{\epsilon }_{r}+1}}$$

b) The effective dielectric constant (ε_reff) of the substrate

$${\epsilon }_{reff}=\frac{{\epsilon }_{r}+1}{2}+\frac{{\epsilon }_{r}-1}{2}{\left[1+12\frac{h}{W}\right]}^{\frac{-1}{2}}$$

c) The extension length (ΔL) is calculated as

$$\frac{\varDelta L}{h}=0.412{\left[\frac{{\epsilon }_{reff}+0.2\left(\frac{w}{h}+0.264\right)}{{\epsilon }_{reff}-0.258\left(\frac{w}{h}-0.8\right)}\right]}^{\frac{-1}{2}}$$

d) The effective length (${ L}_{eff}$) is calculated as

$$L{e}_{ff}=\frac{{v}_{0}}{2{f}_{r}\sqrt{{\epsilon }_{eff}}}$$

e) The actual length of the patch (${L}_{p})$ can be determined from

$$\left({L}_{p}\right)= {L}_{eff}-2\varDelta L$$

f) The ground plane length (${L}_{g}$) and width (${W}_{g}$) are determined from

$${L}_{g}=6h+{L}_{p}$$

$${W}_{g}=6h+{W}_{p}$$

where is the free space velocity and ${\text{f}}_{\text{r}}$ is the frequency of resonance.

Initially, a rectangular patch radiator is designed and simulated with the calculated dimensions of proposed antenna results in a narrowband resonance. A human body is made up of several layers with different thickness and dielectric constant. Hence, an UWB antenna with wide bandwidth is suitable to examine the defects at different layers at various frequencies.

The staircase steps at the patch edges and Defective Ground Structure (DGS) improve the impedance bandwidth and increase the directivity of the antenna. Varying the gap between the bottom of the patch edge and the ground plane varies the fringing fields. Hence there is an increase in the electrical length of the antenna, and the proposed antenna resonates towards the low frequency. Figure 1 depicts the development of the proposed UWB in different stages. The optimal dimensions of the proposed UWB antenna are listed in Table 1.

Table 1

Dimensions of the proposed UWB Staircase monopole antenna
Antenna Parameters	Antenna dimensions (in mm )	Antenna Parameters	Antenna dimensions (in mm)
Lp	34	L4	17
Wp	36	W4	7
L1	4	L5	4
W1	2	W5	7.5
L2	4	Lg	25.7
W2	5	Wg	58.5
L3	5	Ls	72
W3	4	Ws	63

2.1 UWB Monopole Antenna with Various Staircase Steps of Stage 2

In Stage 2, the geometry with multiple staircase steps at both the edges is shown in Figure 1(b). [12] proposed that the optimization of planar antenna width, feed line height and feed line width results in an improved impedance bandwidth. The rectangular patch antenna is excited by the 50Ω transmission line via various staircase steps. The implementation of three staircase steps of dimensions L1xW1, L2xW2 and L3xW3 of the patch antenna results a perfect impedance matching. Figure 2 shows the effect of staircase steps on the impedance bandwidth of Stage 2. The proposed UWB antenna resonates on both the lower edge frequency at 1.88 GHz and the upper edge frequency of 8.3 GHz. From the return loss plot, it is found that the antenna with staircase steps makes a shift in the upper edge resonant frequency from 8.3 GHz to 7.4 GHz compared to the simple rectangular patch antenna. In addition, the lower edge frequency of stage 1 and stage 2 antenna layouts remains unchanged.

2.2 UWB Monopole Antenna with DGS Ground Plane of Stage 3

The patch radiator with varaitions at the edges resonates only at the lower frequency of 1.88 GHz with narrow bandwidth. The return loss |S11| less than -10 dB is found at the higher frequencies of 5.4 GHz to 9 GHz with banwidth improvement of 3.6 GHz. To improve the resonance at the mid-band from 3 GHz to 6.5 GHz, a rectangular slit of width 10 mm and length of 1mm is etched in the ground plane at the bottom of the feed line. Figure 3 depicts that the defective ground structure introduces the multi-resonance with the value of |S11| which is well below -10 dB at the frequencies of 1.88 GHz, 3.7 GHz, 5.7 GHz and 8 GHz. There is also an improvement in the bandwidth of 5 GHz from 1.6 GHz to 6.7 GHz.

2.3 UWB Monopole Antenna with Top Loaded Staircase Steps of Stage 4

Figure 4 depicts that the addition of a staircase steps on the top of the radiator results in a significant shift of the return loss curve towards the higher frequency. Since the resonance frequency is directly proportional to the length of the antenna, the decrease in the patch length shifts the resonant frequency from 1.8 to 2.2 GHz. Hence there is an improvement in the return loss curve at the higher frequency with an increase in bandwidth.

2.4 UWB Monopole Antenna with Ground Plane Slot of Stage 5

In microwave imaging applications, the maximum depth of penetration in UWB signals is required to identify the location of a tumor inside a dense breast tissue. A rectangular slot etched at edges of the ground plane varies the surface wave distribution between the ground plane and the patch radiator. The variation in the fringing field at the edges of the patch makes the antenna to resonate at 1.9 GHz with the |S11| of -37.32 dB and achieves a wide bandwidth of 7.1 GHz as shown in Figure 5.

2.5 UWB Monopole Antenna with Curved Edges of Stage 6

From Figure 5, it is obvious that the Stage 5 with staircase steps at the edges and at the top regions of the patch antenna results in a improved reflection coefficient only at the low frequency. [13] have done a study on the rectangular and circular patch antennas. They have reported that the circular patch antenna results in an improved bandwidth and proper impedance matching compared to rectangular patch antenna. Hence the increase in the surface area of the flat edges into curved surface introduces resonances at the higher frequencies with improvement in bandwidth. Figure 6 depicts that the reflection coefficient at the higher frequencies is well below -10 dB than the antenna with flat edges in Stage 5. It implies that there is an increase in the impedance bandwidth of the antenna after creating curved edges when comparing with flat edges.

2.6 Current Distribution of the Proposed UWB Antenna

The current distribution in the proposed antenna is shown in Figure 7. From the general principle of antenna design, at a lower frequency of operation, the length of the antenna is significantly large and the current distribution is found at the edges of the patch.

As the frequency of resonance increases, the current distribution approaches the sharp edges of the antenna. Besides this, the optimization of surface wave current in the ground plane by introducing the slots varies the fringing fields the implementation of slots at both ends of the ground plane varies the fringing fields obtains an improved impedance matching. The slot below the feed line improves the impedance bandwidth.

2.7 Simulated and Measured Results of the Proposed UWB Antenna

The Staircase UWB antenna resonates from 1.6 GHz to 9.4 GHz which has a broad bandwidth. The layout of the proposed antenna fabricated antenna is shown in Figure 8. As it provides a wide bandwidth of 7.8 GHz, the antenna can able to transmit and receive the reflected signals from various layer of the object under test. Hence, the proposed antenna is suitable for microwave imaging applications. The introduction of staircase steps at the top and bottom edges provides an improved impedance matching at higher lower and lower frequencies. The proposed UWB antenna results in a return loss |S11| of –40 dB at 1.9 GHz as shown in Figure 9.

The fabricated staircase monopole antenna is tested with the Vector Network Analyser (VNA) for parameter measurements. Figure 10 depicts that the proposed UWB patch antenna has proper impedance matching with the feed line over the frequency range of 1.6 GHz to 9.4 GHz with a value of VSWR<2. The shift in the lower frequency resonance is because of the soldering RF connector with the feed line. Since the antenna resonates for wide bandwidth, it is used in microwave imaging applications.

2.8 Radiation Pattern of the Staircase Monopole UWB Antenna

The radiation characteristics of antenna at various resonance frequencies at 2 GHz, 4GHz, 5.8GHz and 7.4 GHz is shown in Figure 11. It is observed that from the figure that the E plane of antenna has omnidirectional radiation pattern at low frequencies and bidirectional pattern at high frequency. The monopole UWB antenna results a high gain of 5.87 dBi. At the higher frequencies, the antenna has a decrease in the broadside radiation. The performance of the proposed radiator is compared with the existing microstrip patch antennas as shown in Table 2. The proposed staircase monopole antenna is of optimum size and resonantes at multiple frequencies at 2 GHz, 4 GHz, 5.8GHz and 7.4GHz. The proposed staircase patch antenna achieved a wide bandwidth of 7.8 GHz, fractional bandwidth of 141% and the gain of 5.87 dBi over the frequency range of 1.6GHz to 9.4GHz which is better than the existing antenna design.

Table 2

Comparison of the proposed Staircase UWB antenna with the existing UWB antennas
Ref	Antenna parameters
Ref	Dimensions in mm	Resonant frequency, GHz	Bandwidth in GHz	Fractional Bandwidth %	Gain dBi
[14]	78 x 70.4	0.5-5.5	5	163.6	-
[1]	80 x 50	4.6, 7.5	6.8	124	3.25
[7]	55 x 40	4.6, 7.5, 9.4	7	108	6
[8]	17x22	3.4, 6.5, 9.5	9	122	2
[15]	51x42	3, 4.77, 5.78	3.2	85.74	<5
[10]	43 x 43	2, 4, 6, 8	6.52	127.6	5.27
Proposed UWB patch antenna	72 x 63	2, 4, 5.8, 7.4	7.8	141	5.87

The present research is to design a UWB patch antenna which is suitable for breast cancer diagnosis in the UWB microwave imaging system. The human breast consists of skin layer, breast tissue and cancerous tissue. The fabricated UWB monopole antenna is tested with the equivalent dielectric breast model. It reveals the presence of the tumor and its resolution stages, which is easy to differentiate the healthy tissue from cancerous tissue. The equivalent materials of breast tissue are taken to develop the human breast phantom model which is prepared based on the survey of the existing researches. [16] have proposed the system configuration with low and high dielectric coupling medium with the breast phantom. They have proposed the effect of small antennas at microwave frequencies on the breast phantom. The image of the tumor is reconstructed from the backscattered signals received from the breast phantom. The received signals are time aligned at the receiver system before image formation. Subtraction algorithm is used to remove the artifacts from the breast skin. [17] have proposed a measurement setup for breast phantom model and defined a confocal microwave imaging algorithm to detect the tumor. [18] have reported the dielectric permittivity and conductivity of corn syrup and glycerin material using cavity perturbation technique. It is noted that the corn syrup and glycerin act as a good coupling medium in the preparation of breast phantom model. [19] have proposed the characteristics of dielectric properties of various tissue mimicking phantom materials under narrow band and UWB frequency ranges. The mixture of tissue materials is tested at various conditions and concentrations. [20] have studied the heterogeneous and homogeneous breast phantom preparation. The effect of both the heterogeneous and the homogeneous breast models is tested with the UWB system for its permittivity and conductivity. Likewise, [15, 21–23] have proposed an equivalent dielectric human breast model preparation with various material compounds. The growing and major stages of the cancer tissue are identified from different tumor sizes. The proposed human breast model of various tumor sizes is tested with the UWB antenna to detect the depth of the tumor location.

3.1 Experimental Measurement of Microwave Dielectric Constant of Materials

The microwave test bench setup for the dielectric strength measurement of solid materials using a solid dielectric cell is shown in Figure 12. It consists of klystron source and klystron mount which generate the X band signals. The X band signal propagates through the isolator, variable attenuator, slotted line and final incident on the solid dielectric cell. The material under test is placed at the opening end of the solid dielectric cell as shown in Figure 13. The measurement is observed from the tunable probe by connecting coaxial Bayonet Navy Connector (BNC) to the VSWR meter and Cathode Ray Oscilloscope (CRO). The dielectric strength of the liquid materials such as glycerin, vegetable palm oils and distilled water is measured using the liquid dielectric cell test bench setup shown in Figure 14. The measured dielectric strength is compared with the standard range listed in Table 3.

The Table 3 depicts the dielectric strengths of various breast equivalent materials. Here the petroleum jelly of dielectric constant ${\in }_{\text{r}}$= 9 is considered as breast tissue. The glass blow of 1.6 mm thickness with ${\in }_{\text{r}}=12$ is considered as skin layer of breast. The mixture of wheat flour and water is considered as cancer tissues. In the development of phantom, the dielectric strength value of the solid materials is very important. Only the concentration of water controls the amount of electromagnetic signal reflection as observed from the previous studies. The concentration of water in the mixture of wheat flour and water mimics various cancer tissue resolution stages. In the present research, two types of tumor stages like malignant and benign are considered in the validation process.

Table 3.3

Comparison of standard and measured ε_r value of breast equivalent materials
S. No	Dielectric materials	Breast contents	Standard εr Value	Breast content equivalent materials	Measured εr value
1	Human Breast model	Breast tissue	9 - 15	Petroleum jelly (Vaseline)	9
2		Skin layer	10 - 30	Glass bowl	12
3		Cancerous tissue	10 - 56	Wheat flour & water mixture	30
4	Coupling liquid material	Glycerin	30 - 45	Glycerin	42
5	Coupling liquid material	Vegetable palm oil	3.75	Vegetable palm oil	3.5

These two materials differ majorly from their property of viscosity. The malignant tumor is more viscous than the benign tumor, hence the concentration of liquidity is more in malignant tissues. From the dielectric property measurement taken on different tissue equivalent material properties reported by [19] the malignant tumor has higher permittivity than benign. From the report, it is infered that the malignant tumor has permittivity between from 30 to 55, and the benign tumor has permittivity lesser than 30. In the experimental setup of the present research, the equivalent dielectric strengths of homogenous breast contents are taken in the glass container. The hemispherical shaped glass bowl consists of 120 mm diameter, 50 mm height and 1.6 mm thickness used as the breast phantom skin layer. Since the glass has only 1.6 mm thickness, its effect on microwave signal radiation is lossless.

3.2 Validation of the Staircase UWB Antenna with the

Human Breast Model Developed

[24] employed various researchers on the dielectric characteristics of the human organs at microwave frequencies. The fabricated antenna layout is tested on the developed human breast Debye model. A 1x4 array antenna setup is arranged surrounding the developed Debye model to validate the scattering effects of the breast model is shown in Figure 15. The array antenna setup is connected to the network analyzer to measure the scattering parameters over the operating frequencies. The cancer tissues stages are developed according to the report from the American Society of Clinical Oncology (ASCO 2018). The stages of the tumor sizes from 1 cm to 4 cm is further categorized as malignant and benign. The tumor with high water content is considered as malignant and it is referred as stage III (3 cm) and stage IV (4cm). The benign tumor is of lower water content and is referred as stage I (1 cm) and stage (2 cm) in the Debye model. Here the composition of the wheat flour with ratio of water defines the stages of tumor from stage 1 to 4.

The antenna array of 1 x 4 is placed around the human breast model for measurement of scattered response from human breast model. For each pair of measurements, two ports are considered; one as transmitter and the other as a receiver. The scattered responses observed from the debye model considering single transmitter and other receivers with the setup of presence and absence of tumor. This process is repeated on considering each one of them as transmitter and receiver. The scattered field response on low and high dielectric is shown in Figure S1 and S2 (see supplementary information). Generally, the scattered field response comprises the details of skin, breast tissue and tumor Figure S2. The subtraction of the scattered responses observed from the Debye model in the conditions of with and without tumor depicted in Equation (E1) gives the details about the tumor. The response of the various stages of the tumor is shown in Figure S3. The absorption of scattered field response below -85 dB do not reveal the clear information of the tumor. An average of the scattered response is calculated to estimate the presences of tumor at various stages is shown in Figure S4. The depth of tumor located inside the Debye model is evaluated from the observed average value of scattered responses.

3.3 Evaluation of Depth of Tumor in Human Breast Model for Various Stages

The depth of the tumor inside the human phantom is numerically determined. [25] have proposed a numerical approach to examine the average scattered field response plot using statistical approaches. The simple relationship among speed, distance and total time taken for the signal to travel from the antenna to hit the target and return to the antenna aperture is used to determine the location of a tumor inside the human breast model. Let $v$ be the velocity of propagation electromagnetic wave into the human breast tissue as given in Equation (8).

$$v=c/\sqrt{{\in }_{r}}$$

where c = free space velocity of 3 x 10^8 m/sec

${\in }_{r}$ = dielectric strength of the breast tissue

Likewise, let Δt be the time travelled by the electromagnetic wave from source to target. It is determined from the inverse of the frequency displacement between the location of the tumor and the early time response from the skin layer. The time travelled Δt is represented in Equation (9).

${\Delta }\text{t}=1/({\text{f}}_{\text{e}\text{a}\text{r}\text{l}\text{y} \text{t}\text{i}\text{m}\text{e} \text{r}\text{e}\text{s}\text{p}\text{o}\text{n}\text{s}\text{e}}- {\text{f}}_{\text{t}\text{u}\text{m}\text{o}\text{r} \text{r}\text{e}\text{s}\text{o}\text{l}\text{u}\text{t}\text{i}\text{o}\text{n} \text{s}\text{t}\text{a}\text{g}\text{e}}$ ) (9)

where, f_etr =${\text{f}}_{\text{e}\text{a}\text{r}\text{l}\text{y} \text{t}\text{i}\text{m}\text{e} \text{r}\text{e}\text{s}\text{p}\text{o}\text{n}\text{s}\text{e}}$

f_tr =${\text{f}}_{\text{t}\text{u}\text{m}\text{o}\text{r} \text{r}\text{e}\text{s}\text{o}\text{l}\text{u}\text{t}\text{i}\text{o}\text{n} \text{s}\text{t}\text{a}\text{g}\text{e}}$

The location of the tumor is twice the distance travelled by the signals from the antenna position to hit the tumor inside the human breast model. It is the total distance travelled by the

wave to and far within the human tissue from the antenna aperture represented in Equation (10).

$$2d=2\text{*}v\text{*}\varDelta t$$

Table 4

Comparison of the depth of tumor of the proposed Staircase UWB antenna with the Existing patch antenna with Debye testbeds
Proposed Staircase UWB antenna with Test bed		Tumor Stages	f_etr in GHz	f_tr in GHz	$\varDelta \mathbf{t}\left(\mathbf{n}\mathbf{s}\right)$	ε_r	Velocity of propagation v (mm/sec)	Tumor depth by numerical analysis d (mm)	Physical distance of Tumor from UWB antenna (mm)
		Stage I 1 cm	7.16	2.85	0.232	9	10¹¹	46.4	50
		Stage II 2 cm	7.16	2.85	0.232	9	10¹¹	46.4	50
		Stage III 3 cm	7.16	2.86	0.233	9	10¹¹	46.6	50
		Stage IV 4 cm	7.16	2.85	0.232	9	10¹¹	46.4	50
Existing antenna with Test bed	[21]	Tumor size 1cm	3.48	2.417	0.94	48.5	4.3x10¹⁰	80.84	129.8
		Tumor size 2 cm	3.48	2.417	0.94	48.5	4.3x10¹⁰	80.84	127.4
		Tumor size 2.5 cm	3.48	2.417	0.94	48.5	4.3x10¹⁰	80.84	109.2
		Tumor size 3 cm	3.48	2.417	0.94	48.5	4.3x10¹⁰	80.84	110.4
	[1]	Tumor size 0.5cm	10.9	3.6	0.137	50	10¹¹	27.4	25
		Tumor size 1cm	11	3.5	0.133	50	10¹¹	26.6	27.5
		Tumor size 1.5cm	10.9	3.6	0.137	50	10¹¹	27.4	30
	[14]	Tumor size 1cm	2.62	1.8	1.21	20 to 40	5.3x10¹⁰	128.26	129.24
	[14]	Tumor size 2cm	2.43	1.34	0.926	60 to 80	3.1 x 10¹⁰	98.156	109.24

[1] have proposed the tumor resolution stages using different dielectric strength materials. Six pentagonal-shaped patch antennas are arranged in the z-axis to measure the signal propagation on opposite sides and the depth of tumor of various tumor sizes is determined. [14] have evaluated the depth of tumor using the printed dipole and Vivaldi antenna on the Debye breast model developed. The numerical analysis of tumor depth is done for various dielectric strength of tissue from ${\in }_{\text{r}}$=40 to 80 and dielectric strength of tumor from ${\in }_{\text{r}}=$20 to 40. [21] also has examined the depth of the tumor by considering the coal piece as a tumor. The velocity of wave propagation is determined by taking the dielectric constant value of the coal piece. Since the wave is propagating only through the breast tissue, considering the tumor dielectric constant may not result in the actual depth of tumor location.

The numerical calculation of the tumor location is reported in Table 4 and compared with the existing UWB antenna with Debye testbeds. It is noted that the proposed antenna reveals the relative position of the tumor inside the human breast phantom. The proposed Staircase UWB antenna identifies the approximate tumor location of 46.4 mm instead of 50 mm from the human breast model. The percentage accuracy of tumor depth estimation is 92.8% which is better than the existing test bed setup.

In the proposed microwave imaging method, antenna size reduction and wider bandwidth operation are the primary requirements in the design of antenna. A staircase patch antenna is proposed for operating in the Ultra-Wideband (UWB) frequency range. The FR4 substrate is chosen with a dielectric constant of 4.4 and a thickness of 1.6 mm. The proposed UWB microstrip patch antenna is designed using the mathematical model. Introducing the staircase at the edges of the patch antenna improves the gain and bandwidth of the proposed antenna. The antenna accomplishes a better impedance matching over the operating frequency of 1.6GHz to 9.4 GHz for -10dB reflection coefficient. The proposed patch achieves an improved gain of 5.87 dBi. The fabricated staircase patch antenna is used to identify the depth of the tumor using scattering mapping algorithm. The resolution of tumor sizes is evaluated using the basic relationship of the speed, distance and time taken the signal travel. The estimated results are tabulated and compared with the existing approaches where the proposed antenna detects the approximate depth of the tumor with 92.8% accuracy. However, the staircase monopole antenna is dimensionally large, results in a lower bandwidth and better impedance matching only around lowest resonant frequency.

ACKNOWLEDGEMENTS

Not applicable

AUTHOR CONTRIBUTIONS

V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi: Conceptualization; V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi: investigation; V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi, Balwinder Raj: resources; V.Dinesh: Original draft preparation; V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi: review and editing; V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi: Visualization; V.Dinesh, Manoharan Arun Kumar and J.Vijayalakshmi, Balwinder Raj: Supervision;

AUTHORS AGREEMENT

Not applicable

DATA AVAILABILITY

Not applicable

FUNDING

Not applicable

CONFLICT OF INTEREST

The authors declare that they have no conflict of interest.

HUMAN AND ANIMAL RIGHTS

This article does not contain any studies with human or animal subjects.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

Authors freely agreed and gave their consent for the publication of the paper.

CONSENT FOR PUBLICATION

All the authors declare their consent for publication of the article on acceptance.

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Reviewers agreed at journal
11 Sep, 2022
Reviewers invited by journal
05 Sep, 2022
Editor assigned by journal
10 Feb, 2022
First submitted to journal
09 Feb, 2022

You are reading this latest preprint version

A Compact Staircase Rectangular Microstrip Patch Antenna for Microwave Imaging Applications

Status:

Version 1

Abstract

Figures

1 Introduction

2 Design of a staircase UWB microstrip patch antenna

2.1 UWB Monopole Antenna with Various Staircase Steps of Stage 2

2.2 UWB Monopole Antenna with DGS Ground Plane of Stage 3

2.3 UWB Monopole Antenna with Top Loaded Staircase Steps of Stage 4

2.4 UWB Monopole Antenna with Ground Plane Slot of Stage 5

2.5 UWB Monopole Antenna with Curved Edges of Stage 6

2.6 Current Distribution of the Proposed UWB Antenna

2.7 Simulated and Measured Results of the Proposed UWB Antenna

2.8 Radiation Pattern of the Staircase Monopole UWB Antenna

3 Developing Dielectric Equivalent Human Breast Model

3.1 Experimental Measurement of Microwave Dielectric Constant of Materials

3.2 Validation of the Staircase UWB Antenna with the

Human Breast Model Developed

3.3 Evaluation of Depth of Tumor in Human Breast Model for Various Stages

4 Conclusion

Declarations

References

Supplementary Files

Status:

Version 1