# Defining Breast Tumor Location Using a Four-Element Wearable Circular UWB MIMO Antenna Array
###### Abstract  
The objective of this paper is to develop a wearable circular UWB MIMO antenna array, consisting of four elements, that is capable of detecting and locating tumor cells within a heterogeneous breast phantom. The antenna element operates within a bandwidth from 2.4 GHz to 10.6 GHz when FR4 is used as the substrate, and extends from 2.57 GHz to 12.6 GHz when a Dacron fabric is used instead. The antenna is fabricated and measured, yielding highly similar results to the simulated outcomes. In the suggested detection system, one antenna is used for transmission, while the other antennas receive the transmitted signal. The employed antenna demonstrates gains of 5.49 dBi, 9.87 dBi, 11.9 dBi, and 14.7 dBi at resonant frequencies of 2.84 GHz, 3.87 GHz, 5.83 GHz, and 8.24 GHz, respectively, when a Dacron fabric is used as the substrate. Moreover, the proposed antenna exhibits a flexible shape with minimal vertical and horizontal bending effects across the entire operating frequency band. The antenna has a compact size of 42.85 \(\times\) 42.85 mm\({}^{2}\) and is printed on an FR4 substrate with a dielectric constant of 4.5 and a thickness of 1.6 mm for testing purposes. The S-parameters of the suggested system can effectively identify and precisely locate small tumors. Furthermore, the SAR findings indicate that the amount of power absorbed by the breast phantom tissues complies with the IEEE standards, thus confirming the suitability of the recommended antenna for the early detection and localization of breast cancer. heterogeneous breast phantom; MIMO systems; reflector cavity; SAR; UWB antenna; wearable antenna +
Footnote †: journal: Applied Sciences  
Several studies have proposed different types of UWB antennas for breast cancer detection. One study developed a small, single-polarization, flexible UWB antenna array designed to resemble a bra [6]. Another study presented flexible conformal 4 \(\times\) 4 ultra-wideband antenna arrays, resembling a bra, to improve electromagnetic wave propagation [7]. A clinical prototype utilizing a microwave time domain technique, housed in a wearable bra interface, was developed for breast cancer diagnosis [8]. In another study, four 1.5 GHz meander line microstrip patch antennas were used to detect and locate tumors across the human breast [9]. A UWB microstrip patch antenna with an increased bandwidth was developed using a 100% cotton substrate for breast cancer detection [10]. Furthermore, a low-cost flexible antenna utilizing a thin film substrate was developed for MWI and early stage tumor identification [11]. A small flexible UWB monopole antenna, utilizing MEMS technology and an inhomogeneous breast phantom, was proposed for breast cancer detection [12]. In this paper, the suggested approach involves a wearable circular UWB four-element MIMO antenna array for examining a breast phantom to detect cancerous tumor tissues [13,14]. The proposed detection system is tested using both tumor and tumor-free tissues. The simulation results of the proposed detection system, obtained using 2020 CST Microwave Studio, are compared with the measurements from a vector network analyzer (VNA) and show good agreement. The presence of cancerous cells is identified by analyzing the reflection coefficient and coupling coefficient with frequency shifts. The localization stage involves examining the coupling coefficients to determine the tumor position. The proposed system is capable of the early identification and localization of 10 mm cancerous tissues within the human breast. Compared to previously reported antennas [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17], the proposed antenna has the largest fractional bandwidth among flexible antennas and maintains performance even when subjected to bending. The antenna also exhibits a high antenna gain, reaching 14.77 dBi at 11 GHz.