# Spiral-Resonator-Based Frequency Reconfigurable Antenna Design for Sub-6 GHz Applications
## 3 Results and Discussions
### Measurement Results  
The experimental setups are utilized for the proposed antenna with PIN diodes and SPDT switches as given in Figure 10. The main goal of the experimental process is to ensure that the physical realization of the antenna aligns with the intended design specifications. The measurement results of the fabricated antenna for different states are obtained in terms of reflection coefficients in Figure 11a-d to compare the numerically calculated and measured results. Figure 11a outlines the measured and simulated reflection coefficient of the OFF-OFF configuration. As seen in Figure 11a, the resonance frequency is almost identical for the simulation and measurement results. It is also clear from Figure 11a that there is a discrepancy between the simulated and measured reflection coefficient of the proposed antenna with PIN diodes. As seen from the ON-ON state given in Figure 11b, the simulation and measurement results of the proposed antenna with SPDT switches are in good agreement whereas the measurement results with PIN diodes are not compatible with the simulation result. Then, Figure 11c illustrates the comparison of the simulation and measurement results for the proposed antenna with an ON-OFF configuration. It is deduced from Figure 11c that the simulation result is compatible with the measurement result of the proposed antenna with the SPDT switch. Figure 11d depicts that the proposed antenna configuration does not radiate in the sub-6 GHz frequency range due to the effect of the spiral resonator because the spiral resonator introduces impedance variations at its resonant frequencies. This restriction causes an impedance mismatch between the spiral resonator and the feeding network. On the other hand, the addition of the spiral resonator results in additional resonator modes, which originate the undesired frequency shifts and distortions. Figure 9: _Cont._Figure 9: Radiation pattern characteristics for PIN diode states at their resonance frequencies: (**a**) state \(-1\), (**b**) state \(-2\), and (**c**) state \(-3\). Figure 10: The measurement setup of the proposed antenna with (**a**) PIN diodes, (**b**) SPDT switches. Figure 11: _Cont._  
The measurement results of the proposed antenna with PIN diodes and SPDT switches can differ from each other due to several factors. First of all, PIN diodes and SPDT switches have different characteristics and switching mechanisms. PIN diodes typically have a slower switching speed compared to solid-state switches like SPDT switches. This difference in switching speed can affect the antenna's performance, especially in dynamic or fast-changing scenarios. SPDT switches are used to provide faster and more reliable switching, resulting in better overall antenna performance. Secondly, the insertion loss of the switching components varies between PIN diodes and SPDT switches. Insertion loss refers to the loss of signal power when it passes through the switching element. PIN diodes may introduce higher insertion loss compared to SPDT switches, which can impact the antenna's overall efficiency and gain. PIN diodes and SPDT switches also have different RF impedance characteristics. These impedance differences affect the matching network and impedance matching of the antenna. That is why the impedance is not properly matched; it leads to signal reflections, reduced power transfer, and degraded antenna performance. The control circuitry for PIN diodes and SPDT switches may differ in terms of complexity, biasing, and control voltages. If the control circuitry is not properly designed or implemented, the measured result introduces additional losses or mismatches, impacting the antenna's performance differently for PIN diodes and SPDT switches. Each switching component introduces parasitic effects that can affect the antenna's behavior. These parasitic effects include capacitance, inductance, and resistance associated with the switches themselves or their control circuitry.