###### Abstract  
A substrate-integrated waveguide (SIW) bandpass filter (BPF) with extraordinary selectivity and an adequate upper stopband for C-band Satellite Communication (SATCOM) applications is proposed in this paper. The design comprises comb-shaped slots engraved on a half-mode SIW (HMSIW) that constitute a multimode resonator (MMR). Its performance is further ameliorated by applying the first and second iterations of the Minkowski fractal curve in the ground plane as a defected ground structure (DGS). The Minkowski fractal has advantages in terms of better bandwidth and miniaturization. The filter is first simulated using the commercial full-wave electromagnetic simulator HFSS v19 and then fabricated on a 0.062\({}^{\prime\prime}\) (1.6 mm) FR4 with dielectric constant \(\varepsilon_{\mathrm{r}}\) = 4.4. The measured results are comparable with the simulated ones and demonstrate that the BPF has a resonant frequency (f\({}_{0}\)) of 4.75 GHz, a 3 dB bandwidth of 770 MHz (fractional bandwidth of 21.4%), an insertion loss of 1.05 dB, and an out-of-band rejection (in the stopband) of more than 28 dB up to 8 GHz, demonstrating a wide and deep stopband. Using the multimode resonator (MMR) technique, a wide bandwidth has been achieved, and by virtue of using half-mode SIW (HMSIW), the proposed BPF is compact in size. Also, the fractal DGS aids in better stopband performance. in [6]. Further, a modified novel BC-CSRR pair was proposed in order to increase the rejection bandwidth. A compact HMSIW C-bandpass filter having a center frequency of 6.5 GHz was proposed and designed by [7]. The design consisted of C-shaped slots acting as a multimode resonator and two dumbbell-shaped DGSs on the ground plane to enhance the filter performance. A fourth-order cross-coupled bandpass filter was proposed and realized by [8] with QMSIW cavities and an S-shaped slot-coupling structure having a center frequency of 5.47 GHz. A selective BPF for Ku/K bands was proposed and designed by [9] using folded SIW (FSIW) technology integrating an E-shaped slot in the central septum. In recent times, higher-order BPFs for satellite applications were proposed by [10] using multiple single-mode resonators and combine resonators. A compact and selective composite microstrip BPF embedded with a pair of quarter-wavelength open-circuited stubs and a spurline was proposed by [11]. Most recently, a dual-band SIW BPF multimode resonator with overlapping modes was proposed by [12]. To control the overlapping modes, two types of slotlines and a pair of via perturbations were introduced. An SIW BPF with an adaptable passband using assembled multimode resonant printed circuit boards (PCBs) was proposed by [13]. To achieve the requisite filtering response with a different number of passbands, three distinct PCBs with perturbed modes were used. This work realizes a miniaturized selective three-pole bandpass filter by integrating a Minkowski fractal geometry (as a defected ground structure) with a comb-shaped slotted half-mode SIW. The idea of the half-mode SIW BPF was introduced by [14], which diminishes the size of the original SIW structure by practically half. Fractal geometry [15] has been extensively used in electromagnetics to improve performance and miniaturize systems by leveraging fractals' space-filling characteristics in passive microwave circuits and antenna design. The designs are simulated using the EM simulator HFSS v.19 software. Hence, this design is completely novel as it combines features of a multimode resonator, half-mode SIW, and fractal DGS for C-band applications. Such a design is proposed and validated for the first time. A brief outline of the proposed filter design process is as follows: For the proposed BPF design, first an HMSIW for the desired cutoff frequency is designed. Thereafter, a comb-shaped MMR structure is introduced on the upper metallic plane and analyzed. Further, to enhance the stopband performance, the first and second iterations of the Minkowski fractal DGS are introduced in the ground plane.