# A Modified Compact Flexible Vivaldi Antenna Array Design for Microwave Breast Cancer Detection
###### Abstract
Similar experimental results with 330 samples were also reported in [10]. This reported contrast allows for smaller breast tumors detection with higher accuracy than traditional methods [11; 12]. In microwave imaging, there are two approaches: tomography- and radar-based. In microwave tomography, the dielectric properties of the breast are calculated by transmitting narrowband microwave signals through the breast. The backscattered signals are collected through multiple receiving antennas. However, this method requires many transmitting and receiving antennas. Additionally, it requires solving a non-linear inverse scattering problem which requires a computationally intensive reconstruction algorithm. In radar-based imaging, antennas are used to transmit and receive the backscattered signals using the transmitting antenna (monostatic) or additional antennas (multistatic). The monostatic arrangement can be used multiple times from multiple locations to provide a sufficient number of channels for imaging. Alternatively, the multistatic antenna array method uses multiple antennas at a fixed location to collect the backscattered signals. This method avoids the mechanical issues of monostatic imaging systems. Successful imaging systems based on this idea have been developed in [13; 14; 15]. In MWL, antennas play a vital role in the imaging process. They act as transceivers where a transmitting antenna becomes a receiving antenna (sensor) in the next iteration. Thus, careful antenna design is required to meet system requirements. Recent studies have shown that antennas used for MWI should have the following properties: small size, high gain, directive power radiation, and wide bandwidth. The operational frequency band is also important: lower frequency bands provide greater penetration, and higher bands offer better range resolution. However, lower frequency requires a larger antenna footprint, and higher frequency causes higher power losses [16; 17]. UWB antennas have attracted researchers for their unique features: high data rate, small size, low cost, and power spectrum density. They can also be designed to operate in both low and high-frequency ranges. Moreover, they are environmentally friendly, biocompatible, and biologically friendly [18]. Several types of UWB antenna for MWI have been proposed, including omnidirectional vs. directional radiation pattern [19]; wide range vs. narrowband [20]; high vs. low frequency [21]; etc. However, in all cases, the system requires high efficiency, high gain, and compatibility to penetrate the human body [3]. To date, many UWB antennas for MWI breast imaging have been reported: compact planar UWB antenna [22], modified antipodal Vivaldi antenna [3], hemispherical antenna [17], reflectarray antenna [23], flexible monopole antenna [7], circular polarized radial line slot array antenna [24], and many more. The human breast, on the other hand, has an inhomogeneous and complex structure of skin, fat, gland, and muscle. Each of these substances has different dielectric properties, namely relative permittivity and conductivity. This inhomogeneous environment can be modeled by stacking several homogeneous layers that represent the properties of skin, fat, gland, and muscle. The proposed structure is not a representation of the real breast. However, the model is widely used in laboratory environments for prototype breast imaging systems [5; 7; 25; 26]. Successful imaging systems require preprocessing for backscattered signals to remove artefacts and reflections. Several artefact removal algorithms have been reported in the literature. The Average Subtraction method subtracts the response of each channel from a reference waveform. The reference waveform is the average response of all imaging channels [27]. This method assumes that the artefact is similar in each channel. Adaptive filtering extends this idea to compensate for channel-to-channel variation in the artefact [28]. The rotational subtraction method has been reported in [29].