## 2 Materials and Methods
### Switching Mechanism  
The proposed antenna structures are separately fabricated with two different switching elements, either the PIN diode of BAR6402-V or Single Pole Double Throw (SPDT) switches of CG2415M6 as detailed in Figure 5a,b, respectively. Based on the working principle of the switching components, a different measurement setup is utilized for each approach as shown in Figure 5c,d.  
Figure 5: _Cont_.  
Understanding the equivalent circuit behavior of the PIN diode and the block diagram of the SPDT switch is critical for designing efficient and reliable frequency-reconfigurable antenna systems. This knowledge enables precise control, optimization, and adaptability of the antenna's performance, ensuring its successful integration and functionality in various communication applications. Figure 6 is detailed to allow designers to analyze  
Figure 5: The fabricated prototype antennas with (**a**) PIN diodes of BAR64-02V, and (**b**) RF switches of CG2415M6. Experimental setup for (**c**) PIN diodes and (**d**) SPDT switches.  
and predict the performance of the component within the antenna system. Understanding the equivalent circuit behavior of the PIN diode BAR64-02V is important in the design and fabrication of frequency-reconfigurable antennas. This knowledge plays a crucial role in optimizing the antenna's performance, analyzing its reconfigurability, predicting its behavior, and guiding the fabrication process. Figure 6a presents the equivalent circuit model of the BAR64-02V PIN diode. The model shows that when the PIN diode is forward-biased (positive voltage applied to the P-region and negative voltage applied to the N-region), it behaves as a series combination of a low-resistance resistor and an inductor, allowing current flow through it. This forward-biased state is known as the ON state of the PIN diode. Conversely, when the PIN diode is reverse-biased (positive voltage applied to the N-region and negative voltage applied to the P-region), it exhibits a parallel combination of a high-resistance resistor and capacitor in series with the inductor. This reverse-biased state is referred to as the OFF state of the PIN diode.  
Similarly, comprehending the block diagram and evaluation circuit of SPDT switches, such as the CG2415M6, is vital for designers to understand their functionality, control mechanisms, and performance characteristics. This knowledge aids in the design, integration, and fabrication of frequency-reconfigurable antennas. Figure 6b represents the truth table and block diagram of SPDT switches (CG2415M6 model). The SPDT switch consists of a single input or common terminal (COM) and two output terminals known as the normally open (NO) and normally closed (NC) terminals. In its resting or unactuated position, the  
Figure 6: (**a**) Equivalent circuit diagram of BAR64-02V; (**b**) block diagram, truth table, and evaluation circuit of CG2415M6 [47].  
COM terminal is connected to the NC terminal, and the NO terminal is disconnected. When the switch is actuated, the mechanical unit inside the switch changes the connection. In this new position, the COM terminal becomes connected to the NO terminal, and the connection between COM and NC is broken. The SPDT switch is commonly used to select between two different circuits or paths within a circuit. In this study, the COM terminal of the SPDT switch is connected to a digital input pin on the Arduino Uno, the NO terminal is connected to the Arduino's 3-V power supply, and the NC terminal is connected to the ground (GND) on the Arduino. Depending on the switch state, the appropriate code is written in the Arduino program to perform specific actions, control other components, or make decisions based on the connections.