The gap between the two microstrip lines is inversely proportional to the bandwidth (BW). This characteristic of resonator can be used with minimum cost to design ultra-narrowband filters. However, the quality factor of dielectric cavity resonator is high but there has been developing in planar structures in order to decrease size of those filters. The disadvantage of high conductor loss of the planar filters using conventional thin film conductor can be overcome by replacing them with high-temperature superconductor (HTS) thin films 7. However, this will be expensive to design the filters. The GENESYS programming has been used to simulate the resonator. And then the design was fabricated. the complete parallel-coupled resonator shows in Figure 3.1. For the measuring the vector network analyzer (VNA) was used. The circuit then was measured using vector network analyzer (VNA).
Figure 3.1: The microstrip parallel-coupled resonator Fabricated circuit.
The correct measurements of the gap between the two coupled conductors were 0.56 mm and 2.63 mm. While the gap between the two coupled conductors was increased, also the attenuation at the center frequency will increase, but the bandwidth will decrease. Such the result was got experimentally from the simulation.
Figure 3.2: The insertion loss in Simulation and measurement.
The insertion loss of the microstrip resonator demonstrates in Figure 3.2 from the results of simulation and measurement. The simulation result of The center frequency was at 1.707 GHz with insertion loss of –2.807 dB . However, the result was at 1.675 GHz for the measurement result and–6.593 dB insertion loss. In general, there are an agreement between the results that demonstrates in measurement result. Because of the imperfection of manual fabrication and dielectric process, the loss has been shown in the differences between the measurement and simulation results. Tables (1, 2) indicate different results at various frequencies for examination. The focus was to the insertion loss. From the tables, we can demonstrate that the response was resonated at every ± 1.8 GHz.
Table 1: Simulation of the Insertion loss
Table 2: The insertion loss of the fabricated circuit
the second resonant frequency from the measurement result was at 3.34 GHz from the table 2 with insertion loss of -5.386 dB.
Figure 4.3: The result of SWR with simulation
The simulation result of standing wave ratio, SWR demonstrates in figure 4.3.The SWR is a circuit matching measurement. The value of SWR at 1.707GHz was 1.823 from the simulation; while the measurement demonstrates in Figure 4.3 at 1.675GHz were 3.728.
Figure 4.4: The result of SWR from Measurement.
Table 3, 4 demonstrates the results of various resonant frequencies for the measurement and simulation respectively.
Table 3: The result of SWR from measurement
Table 4: The result of SWR from simulation
The SWR at 3.457 GH was 1.933dB as in table 4 demonstrates, while in Table 3, the SWR at 3.34 GHz was 1.261dB. We get the minimum SWR at the second resonant frequency of measurement.
The result shows that the simulation was small in both critical points. However the lowest value was come from the measurement. The small value of SWR is considered a good matching level while the high SWR means the port was not properly matched 15, 16