## 5 Fabrication and Results  
To corroborate the outcome, the proposed filter was fabricated with FR4 substrate material, which had a depth of 1.6 mm, a relative dielectric constant of 4.4, and a tan \(\delta\) = 0.02. FR4 substrate is readily available and economical. The filter was fabricated using Accurate's CNC PCB prototyping machine, IN, USA and tested using a vector network analyzer in the JIIT Microwave Research Laboratory. Figure 18a,b portray the image of the upper and lowermost sheet of the BPF with complete dimensions of 19.5 mm (length) \(\times\) 6.5 mm (width). A one INR Indian coin (INR) is used for size reference.  
The Anritsu S 820E vector network analyzer (CA, USA) available in our microwave research laboratory was utilized to measure the scattering properties of the manufactured filter. A two-port SOLT (short open load and thru) calibration was carried out to take into consideration the losses brought on by the cable joining the V  
Figure 16: Mode chart of a comb-slotted MMR filter with a DGS for various values of L.  
Figure 17: Current distribution in the (**a**) passband and (**b**) stopband.  
Figure 18: (**a**) Upper and (**b**) bottom views of the fabricated bandpass filter.  
compares and illustrates the outcomes of the HFSS simulation with the measured data. With a center frequency of 4.7 GHz, it displays the observed passband of the filter, which ranges from 4.1 to 4.87 GHz with a 3 dB bandwidth of 0.77 GHz and a 3 dB fractional bandwidth (FBW) of 21.4%. In the passband, the insertion loss is 1.15 dB, while the maximum observed measured return loss is 18.8 dB. The measured result shows that it attains good attenuation in the upper stopband. The measured roll-off rates at the passband's upper and lower edges are 62 dB/GHz and 68.5 dB/GHz, respectively. Also, three transmission zeros are produced at frequencies of 2.65 GHz, 6.12 GHz, and 6.87 GHz, which augments the selectivity of the response. As shown in Figure 18, the out-of-band rejection in the stopband is >28 dB till 8 GHz. Figure 19 shows that there is worthy conformity amid the simulated and measured result, except for a petite swing in measured return loss and roll-off rate, which may be affected by the tolerance in the fabrication. There is a slight deviation between simulated and measured results. This error may be attributed to fabrication error and/or during measurement due to bending of the cable, connector loss, etc. It may be due to imprecise permittivity in the simulation.  
Figure 20 depicts a comparison of the simulated and measured group delay responses, which elucidates a nearly flat response across the desired frequency band.  
A performance investigation including the Q factor [29] of some recently reported SIW bandpass filters for C-band applications is encapsulated and compared in Table 1.  
Figure 19: Comparison of the simulated and measured S parameter results.  
Figure 20: Comparison of the simulated and measured group delays.  
From the above table, it can be established that in [4], an HMSIW filter is made using D-shaped resonators. It has reasonably good stopband performance but suffers from low selectivity. The BPF proposed in [5] is designed using the HMSIW methodology consisting of transverse slots. Although the design is simple, it suffers from a large size and poor selectivity. The filter proposed in [6] using the broadside coupled CSRR technique has a smaller size but has the disadvantage of very high insertion loss. The filter proposed in [7] is made using HMSIW with DGS technology. It has the disadvantage of a larger size and poor stopband performance. The filter proposed in [8] is designed using quarter mode SIW techniques with S-shaped slot tech, but it suffers from a very large size. Consequently, the proposed filter with a small size, low loss, and better frequency response can be useful for various C-band applications.