# Testing and Analysis of MOSFET-Based Absorber Integrated Antenna for 5G/WiMAX/WLAN Applications
## 2 Double Material Substrate (DMS) Cylindrical Surrounding Patch Antenna (CSPA) Design and Analysis  
The DMS CSPA was designed using a combination of polyimide substrate and FR-4 substrate with dielectric constants of 3.5 and 4.3, respectively, as in previous work [34]. In continuation of this proposed co-design, the dimensions of the cylindrical patch antenna were altered on purpose by reducing the thickness of the polyimide substrate from 2 mm to 0.5 mm, thus reducing the overall dimension and increasing the bandwidth of the antenna. The revised dimension of the antenna used in the proposed MOSFET-based absorber antenna design is shown in Figure 1 and its parameters are given in Table 1. The adopted modeling, algorithm, and 2D radiation pattern for the cylindrical surrounding patch antenna used in the proposed integrated design have been explained in our previous works [34; 35; 36]. As shown in Figure 2, the thinner polyimide substrate caused the lower and upper bands of the WiLAN and WiMax frequency bands to move their backward resonance frequencies from 2.68 GHz to 2.37 GHz and from 5.55 GHz to 5.3 GHz, respectively. In addition, there is an increasing change in return loss from \(-\)26 dB to \(-\)19.5 dB and from \(-\)16 dB to \(-\)14.5 dB in the lower and upper bands, respectively. These values may not be practical for the physical implementation of the proposed design, but an increase in return loss values at both resonance frequencies has been observed to be advantageous in terms of providing the needed reflected power for the MOSFET-based absorber in the proposed circuitry. Figure 1: Proposed MOSFET-based absorber active integrated antenna block diagram. Before the dimensions of the antenna used for the proposed MOSFET-based absorber active integrated antenna design were altered, a bandwidth of 0.7 GHz (2.28 GHz to 3 GHz) and 1.1 GHz (4.9 GHz to 6.1 GHz) was observed for the lower and upper bands, respectively. Now, using a polyimide value of thickness 0.5 mm resulted in an increased bandwidth of 1 GHz (2 GHz to 3 GHz) and 1.5 GHz (4.6 GHz to 6.1 GHz) for the lower and upper bands, respectively. Considering the directivity and gain values presented in Figures 3 and 4, the antenna efficiency factor K and radiation efficiency of the DMS antenna are computed as:  
\[G=KD \tag{1}\]  
\[Radiation\ efficiency=\frac{G}{D}\times 100 \tag{2}\] \begin{table}
\begin{tabular}{c c c} \hline
**Description** & **Parameter** & **Value (in mm)** \\ \hline The outer radius of ground & \(R_{go}\) & 12.12 \\ \hline Inner radius of ground & \(R_{gi}\) & 11.32 \\ \hline Outer radius of the polyimide substrate & \(R_{so,pl}\) & 12.62 \\ \hline Outer radius of FR-4 substrate & \(R_{so,f-4}\) & 15.42 \\ \hline Length of ground & \(L_{S}\) & 22.87 \\ \hline Length of substrate & \(L_{s}\) & 39.84 \\ \hline Substrate and patch top difference & \(\Delta L\) & 2.070 \\ \hline Inset feed length & \(Y_{0}\) & 3.11 \\ \hline Width of feed & \(W_{f}\) & 5.70 \\ \hline Height of patch & \(H_{p}\) & 0.8 \\ \hline Length of patch & \(L_{p}\) & 11.04 \\ \hline Width of patch & \(W_{p}\) & 17.26 \\ \hline Assumed width of the ground & \(W_{S}\) & 46.06 \\ \hline Thickness of ground & \(H_{g}\) & 0.8 \\ \hline Thickness of polyimide substrate & \(H_{s,pl}\) & 2.0 \\ \hline Thickness of FR-4 substrate & \(H_{s,f-4}\) & 2.8 \\ \hline Effective length & \(L_{eff}\) & 15.27 \\ \hline \end{tabular}
\end{table} 
Table 1: Parameters used for CSPA modeling. Figure 2: Return loss and equivalent bandwidth at both resonance frequencies using polyimide substrate of thickness 0.5 mm and 2 mm. The dimensionless antenna efficiency factor K must meet the maximum performance requirement of \(0\leq\text{K}\leq 1\), where G and D stand for gain and directivity, respectively [37; 38]. A lossless antenna is represented by a value of K = 1. In addition, as shown in Figures 3 and 4, the benefit is never greater than the directivity (D) in practice.