UWB Antenna with All Band Suitable Radiation Pattern for Breast Cancer Detection

T. G. Abouelnaga , A. F. Desouky *2 # Researcher, Microstrip Circuits Department, Electronics Research Institute, Giza, Egypt # Assistant Professor, Communication Department, Higher Institute of Engineering and Technology, Kafr El-Shiekh, Egypt 1 tamer@eri.sci.eg * Teacher Assistant, Communication Department, Higher Institute of Engineering and Technology, Kafr ElShiekh, Egypt asmaa.fereg@gmail.com

tumor. The field distribution inside the breast phantom is discussed. The proposed antennas are fabricated, measured and the obtained results are discussed.

II. CONVENTIONAL ANTENNA DESIGN
The conventional antenna is designed based on [13]. Fig.1. shows the antenna structure. FR-4 material has been considered as antenna substrate with dielectric constant of 4.65 and height of 1.27 mm. Given the lowest frequency ( ), substrate thickness (h) and dielectric constant ℰ . The width (W) and length (L) of the antenna can be calculated using the following equation Where c is the speed of light in free space. The antenna structure is formed from the intersection of quarters of two ellipses. The major radii ( and ) and the minor radii ( and ) of the two ellipses as shown in Fig.1. The two ellipses are chosen according to the following equations [14] = 2 + 2 , (2) = 2 − 2 , = , = 0.5 .
The width of the microstrip transmission feeder for a characteristic impedance, = 50 Ω, can be calculated using the following equations [15] Where the effective dielectric constant for the transmission line, ℰ is given by Figure 2 shows the return loss of the conventional antenna and it's noticed that this antenna suffers from mismatch at lower frequency band which extends from 3 GHz to 9.5 GHz. The conventional antipodal Vivaldi antenna doesn't cover the UWB. To improve the performance, conventional antipodal Vivaldi antenna is modified. Conventional antenna feeding line is modified to improve the characteristic impedance of the antenna [16].  Figure 3 shows the simulated proposed antipodal Vivaldi antenna with modified feed line using CST Microwave Studio 2014. Figure 4 shows the simulated return loss. The modified feed antipodal Vivaldi antenna (AVA) operates in the frequency range 3.1-11.6 GHz. Figure 5 shows the radiation patterns at different low frequencies. It has been noticed that the main beam direction at low frequencies changed from the end fire direction to a broad side direction. This, indeed make the antenna radiation deviate from the end-fire direction which is required all over the entire band. This is the major disadvantage of this structure. From the previous two sections, one can notice that the radiation pattern direction is a broadside at low frequencies and at 4 GHz and higher frequencies, the radiation pattern is an end-fire. This problem is solved in the next two proposed structures of antipodal Vivaldi antenna by adding slits in the radiating structure to transfer the radiation direction from broad side to end fire direction. Figure 6 shows the proposed antipodal Vivaldi antenna with rectangular slits which are added to the antenna's outer edge. CST Microwave Studio 2014 is used to optimize the slits dimensions. Table 2 shows the antenna's optimized dimensions. Figure 7 shows the simulated return loss of the conventional and proposed antipodal Vivaldi antenna with rectangular slits. One can notice that an enhancement of about 10 dB is obtained. The proposed antenna operates in the frequency range 2.6-11 GHz. The proposed antenna is fabricated using FR4 material with dielectric constant ℰ = 4.65, height of 1.5 mm and loss tangent = 0.025, Fig.8. Figure 9 shows the measured return loss of the proposed antenna which agrees well with the simulated one. Figure 10 shows the radiation pattern direction of the proposed antipodal Vivaldi antenna with slits at lower frequency band. It can be noticed that the obtained radiation pattern are end-fire and in the same direction as all higher frequencies.

C. Antipodal Vivaldi Antenna With Slits and Meandered Edge
In this structure the antenna edge is meandered, Fig.11. This meandering enhances the matching better than the previous structure as shown in Fig.12. Matching enhancement of about 5 dB at 7.5 GHz, 3 dB at 5 GHz and about 5 dB at 4GHz are obtained. The proposed structure is fabricated using FR-4 material as substrate, Fig.13. Figure 14 shows both simulated and measured return loss of the proposed structure. Also, good agreement is obtained. Figure 15 shows that the radiation pattern direction is end-fire and in the same direction as all higher frequencies. So, the last two structures where rectangular slits are added, successfully solve the broad-side radiation problem that appears from the first structure at lower frequencies.

III. PROPOSED BREAST PHANTOM
For detection purpose, a hemispherical breast phantom of radius 50 mm is built. The phantom consists of two layer tissues and tumor. The phantom is implemented and measured to have a dielectric constant similar to the real dielectric constant of real breast tissues and tumor. The breast phantom tissue is a mixture of water (39.77%), Sugar (53.41%) and Gelatine (6.82%). The permittivity and conductivity of the breast phantom and tumor are measured using DAK system and Vector Network Analyzer (VNA). The results are very close to that were predicted in [17][18]. Figure 16 shows the dielectric constant curves of both tissues and tumor.

IV. BREAST CANCER DETECTION USING THE PROPOSED ANTENNAS
It had been demonstrated in [18] that one antenna pair was sufficient to classify tumors sizes in phantoms but had little success with the clinical trial. In this section, only one antenna is used to demonstrate the idea of microwave breast cancer detection. The proposed antennas with two layers phantom (tissues and tumor) are simulated. The electric field distribution inside the breast phantom with and without tumor are monitored with considering the dispersive phantom materials that were measured in Fig. 16. Figures 17 to 46 show the electric field distribution inside the two phantoms with and without tumors using the two proposed antennas. Also, these figures show that the electric field distribution changed inside the phantom especially in the tumor presence due to the high contrast between the breast tissue and tumor dielectric constant. In the tissue layer the output field from the antenna partially passed inside the tissue layer, but in tumor the field was exceedingly low due to its high permittivity and this simulation make the detection process sufficient and easy to notice the tumor position. V. CONCLUSIONS In this paper the idea of microwave breast cancer detection using UWB antenna was demonstrated. Vivaldi antipodal antenna was considered as a basic structure due to its well-known UWB characteristics. For bandwidth enhancement the feeding line was modified and an UWB performance was obtained. The problem arose from the broadside radiation pattern at the lower frequency band. This problem was solved by adding slits at the antenna's edge. The proposed antennas bandwidth extended from 2.6 GHz to 11.6 GHz. Also, two breast phantoms with and without tumor were considered. The fields' distribution inside the phantom with and without tumor were investigated. The proposed antennas were fabricated and measured. Good agreement was obtained between simulated and measured results.