# Testing and Analysis of MOSFET-Based Absorber Integrated Antenna for 5G/WiMAX/WLAN Applications
## 3 Design Analysis of SRD Pulse Generator and Diode-Based Quasi-Circulator
### Transient 3D Electromagnetic Circuit Simulation of SRD Pulse Generator  
At the prototype design level, there are several techniques for producing wide band pulses [39; 40]. Avalanche transistors, tunnel diodes, non-linear transmission lines (NLTLs), photoconductive switches, bipolar transistors, field-effect transistors (FETs), and step recovery diodes (SRDs) are some examples [41]. The pulse generator used in place of the low noise amplifier is made up of a coplanar waveguide layout that includes a helical coil, two lumped capacitors, and a step-recovery diode (SRD). A sinusoidal signal has been used to exit the pulse generator through port-1, thus passing through a low-pass filter (capacitor C\({}_{2}\) and helical coil) and reaching an SRD connected in parallel with capacitor C\({}_{3}\). The SRD's strong nonlinearity produces a very sharp peak, further filtered at the output by a DC blocking capacitor (C\({}_{1}\)), thus producing a signal output at port-2. In Figure 7, the values of capacitors C\({}_{1}\), C\({}_{2}\), and C\({}_{3}\) and inductors L\({}_{1}\) and L\({}_{2}\) are 15 pF, 68 pF, 0.35 pF, 0.6 nH, and 0.6 nH, respectively. A maximum frequency of 6 GHz has been defined in both the 3D project and the schematic's transient tasks to resolve the expected high-frequency material properly. Probes P1 and P2 have been used to record the input and output voltage and current signals at the desired frequency. From Figure 8, the input the peak voltage and current at port-1 or Probe P1 are 2.5 V and 0. 269 A, respectively, signifying a total input power of 0.66 Watts, and values are shown in Table 2.  
Figure 5: Gain vs frequency plot at both resonance frequencies. Figure 6: DMS cylindrical patch antenna. The 3D Electromagnetic Circuit Simulation of 3-Port Diode-Based Quasi-Circulator Using Directional Couplers  
A simplified form of a circulator, a quasi-circulator carries a signal from port-1 to port-2, from port-2 to port-3, and from port-3 to port-1. During this process, one of the ports is isolated; thus, no signal is transmitted to the isolated port. The quasi-circulator has been widely employed as a duplexer in various front-end modules of communication and radar systems, allowing the isolation of different sections within the front-end communication systems [42; 43; 44; 45]. The novel diode-based quasi-circulator model used in the proposed MOSFET-based absorber active integrated antenna was designed with directional couplers, high-frequency Schottky diodes, and resistors. In Figure 9, a schematic depiction of a \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Voltage** & **Current** & **Power** \\ \hline P1 & 2500 mV & 263 mA & 660 mW \\ \hline P2 & 2500 mV & 26.9 mA & 67 mW \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Equivalent voltage, current, and power at the input and output terminal of the pulse generator. Figure 8: SRD pulse generator time-domain input and output. (a) Voltage; (b) current. Figure 7: SRD pulse generator used to provide the equivalent incident power for proposed active antenna integrated design testing. three-port active diode-based quasi-circulator is shown and detailed using unilateral power divider/combiner and diode characteristics. Considering the three-port quasi-circulator presented in Figure 8, signals incident on port-1(1) of directional coupler DC1 (port-1 of circulator) are coupled almost in equal shares to the two opposite ports 2(1) and 2(2). At this stage, diode 1 (DIODE 1) is ON while diode 2 (DIODE 2) is OFF. Since DIODE 2 is OFF, signals incident on port-1(1) of directional coupler DC1 will be allowed exit port-2(1), flowing through DIODE 1 to port-1(1) of directional coupler DC2. When the signals reach port-1(1) of directional coupler DC2, the signals are also coupled in almost equal shares to the two opposite ports, ports 2(1) and 2(2). In port-2(2), the signal is matched to a 50 \(\Omega\) resistor R\({}_{1}\), thus allowing the signal to flow through port-2(1) of directional coupler DC2 (port-2 of the circulator).