# Modified 16-Quasi Log Periodic Antenna Array for Microwave Imaging of Breast Cancer Detection
## 5 Microwave Imaging Setup  
With the aid of CST and HFSS simulation software, the 16-antenna array is tested for its ability to detect breast tumor by means of a breast phantom, seen in Figure 9. The top and slant view of the antenna array system around the breast phantom is depicted in Figure 9a,b, respectively. In this study, two breast phantoms are examined. The phantom is made of different layers of skin and fat tissue with an inserted tumor. The antenna array is placed in a circular manner around the phantom of radius 60 mm with an air gap of 20 mm, thus the sensor elements are not in direct contact to the breast phantom. The dielectric constant of the skin, fat, and tumor are 38, 5.14, and 67, respectively. In the first phantom, a cylindrical tumor with a radius of 5 mm and a height of 20 mm is inserted at location x = 30 mm and y = 30 mm (position A) from the center of the phantom. In  
Figure 8: Peak gain of the proposed PLPA. Figure 7: 2D and 3D radiation patterns of the PLPA at (**a**) 3.5 GHz and (**b**) 5 GHz. the second phantom, an identical tumor is inserted at location x = -30 mm and y = 30 mm (position B) from the center of the phantom. Different configurations of 3D circular antenna arrays were initially simulated; after optimization, 16 element array is selected. The main idea is to incorporate as many elements as possible to the extent that the coupling between elements is in the acceptable range. Data collection at several angular positions will be less complex if there are more elements and hence avoids the unnecessary rotation of the system. However, with the increase of the array elements, the simulation time will increase dramatically. Due to the large number of mesh cells to resolve, it is difficult to optimize this large array by HFSS or CST domain solver. Using optimization and symmetry techniques to reduce the simulation time, the 16-array configuration was selected and it helped in successfully reconstructing images  
Figure 9: Microwave Imaging System (**a**) Top view and (**b**) Slant view. from the collected data using MATLAB. Figure 10 illustrates the array bandwidth range for a 16 element array ranging from 2 to 5 GHz. Approximately 8 cm separates the antennas from the center of the phantom. The array elements are spaced at 22.5 degrees apart, which results in transmission coefficients below \(-20\) dB in the presence of the breast phantom. As shown in Figure 10, the antenna array exhibits reflection and transmission coefficients with less than \(-10\) dB over a bandwidth of 2 to 5 GHz. In the proposed MIS, there are 16 antennas, one of which acts as a transmitter, while the remaining 15 antennas act as receivers to collect scattered signals from the phantom. The entire process is repeated for all antennas, resulting in 240 (16 \(\times\) 15) scanned data points from the breast phantom. The collected backscattered signals are then analyzed using DAS algorithm with a suitable computing system to determine the presence of tumor. A picture of the imaging result can be seen in Figure 11 for two different locations of tumor in breast phantom. The ranges for x, y, and z are measured in meters. The 3D phantom is in hemispherical shape. As we move along the z axis the radius of the circular slice starts decreasing till it reaches the apex point. The results are obtained at different horizontal planes as slices along the z axis. The Figure 11 shows 2D images at z = 0.005 m and z = 0.02 m positions (i.e., a slice of image at z location of 5 mm and 20 mm). Therefore, if the tumor is located along the z axis it will be detected and shown in the horizontal slices at that z-location. As can be seen, the proposed system successfully detects the presence of tumor with a dark red color. A comparison of different MIS in literature with the proposed one is presented in Table 1. In this regard, the system designed proves to be a good method for detecting breast cancer using microwave imaging. Figure 10: Scattering matrix of 16 PLPA elements: S1,1-S2,1-S3,1-S4,1-S5,1-S15,1-S16,1.