## 5 MTM Antenna Performance Analysis and Microwave Imaging  
The main goal of this MTM antenna design is to exploit the antenna suite for microwave imaging. For microwave imaging, the antenna should have high gain, wider bandwidth, sharp resonant frequency and higher directivity. This is essential to scan deeper tumors inside the breast with high resolution [18]. MTM (2 \(\times\) 4) structures are used in both sides of the substrate to produce a smooth radiation profile, minimize back radiation, and improve gain and efficiency compared to conventional microstrip antenna. The antenna radiation performance, directivity and front-to-back ratio are improved by using the phase reflection properties of the MTM structure. The performance characteristics of the MTM antenna have been analysed, studied and optimized using a finite integration technique (FIT)-based computer simulation technology (CST) microwave studio. The accomplishment of the parametric study provides an optimized geometric structure of the proposed antenna which is realized through an in-house PCB laser and circuit prototyping (LPKF) machine to get a physical test model. The measured results were obtained using the Agilent E8362C vector network analyzer (VNA) that covers the range from 10 MHz to 67 GHz and the Satmo near field measurement lab (UKM StarLab) using satimo passive measurement (SPM) and SatEnv software. The comparison graph of the simulated reflection coefficient of the proposed antenna is depicted in Figure 8a. The antenna without MTM has a bandwidth from 3.1 GHz to 9.00 GHz, including a band gap of 6.97 GHz to 7.67 GHz. Through the use of MTM array, the lower band is broadened by about \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Design Parameters** & **Dimension (mm)** & **Design Parameters** & **Dimension (mm)** \\ \hline L & 26 & i & 5.75 \\ W & 22 & r & 6.75 \\ f & 2 & t & 8.90 \\ h & 4 & d & 3.80 \\ s & 11.51 & u & 3.20 \\ m & 9.25 & x & 0.75 \\ g & 1.5 & H & 10.65 \\ n & 10.25 & G & 2.50 \\ p & 3 & y & 2.1 \\ v & 1.5 & z & 9.75 \\ - & - & c & 2.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Design specifications of MTM-based ultra wideband (UWB) antenna (according to Figure 7). Figure 7: Geometric layout of proposed antenna (**a**) Front side (**b**) Back side (**c**) Fabricated prototype front side (**d**) Fabricated prototype back side. 570 MHz and the upper band is broadened by about 1700 MHz without any band notch. The final bandwidth of the proposed prototype offers a bandwidth of 3.1 GHz to 10.71 GHz, which completely covers the UWB band. The impedance bandwidth of the MTM antenna with a one-sided MTM unit cell array also does not exhibit the UWB range. With front MTM, the bandwidth is from 3.36 GHz to 10.05 GHz, whereas with back MTM it is from 3.28 GHz to 10.15 GHz. The efficiency is also much better when using the MTM array. The overall efficiency is increased by 10% to 20% over the bandwidth after using the MTM array. The proposed prototype offers an average radiation efficiency of more than 70% over the operating band, which is better than the recently published UWB antennas presented in the literature. A moderate gain is found after using MTM array, a gain is an increase in lower frequency, whereas a slight diminution is found in the upper frequency. The simulated efficiency and gain of the proposed antenna is compared in Figure 8b,c. By using the MTM, the antenna bandwidth increased but no major variation was found in the resonance points. Another remarkable point is noted, namely that a large decrease in the magnitude of return loss is obtained after combining the MTM array structure on the substrate. Without MTM, it mostly decreased to about \(-\)28 dB whereas, with MTM it was about \(-\)37 dB. One major finding of this study is that there is no gap or mismatch in the entire bandwidth. The enhancement of the antenna is performance proof of the effectiveness of the negative index on the MTM structure and its suitability for MWI applications.