## 1 Introduction  
Bandpass filters are the main elements used in communication systems for signal receiving and processing. Bandpass filters were initially designed using a common operating mechanism, involving cascading HP or LP filters using MMRs with central frequencies equal to quarter or full wavelengths. However, with these techniques, the design topology becomes pricey and complex. The construction of a planar microstrip transmission line may be able to circumvent the aforementioned mechanisms because of its simple design, low cost, and easy fabrication process. Wide pass-band filters are becoming increasingly recommended due to their compatibility with integration into various circuits and antennas, which helps to enhance the performance of radio systems [1; 2; 3]. Over the past few decades, microwave researchers have adopted a few approaches for designing wideband filters [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. Furnel-type ASIRs and DGSs (defected ground structures) were used to design wideband bandpass filters (BIFs) with upper wide stopband responses [4; 5; 6; 7]. In [8], a filter based on a circular quadruple/ quintuple-mode resonator with fractional bandwidths (FBWs) of 60% and 62% was created using parallel-coupled microstrip lines. These topologies, however, showed a high IL. By employing interdigital strip lines and grating arrays to attain a respectable FBW of roughly 177%, a wideband filter with a frequency range of 0.29 GHz to 4.82 GHz was designed by the authors of [9]. While this design offered a wide bandwidth, it had a complex geometry, which may introduce challenges in practical implementation. The authors of [10] use interdigital lines and DGSs to develop and construct a wideband BPF on the back of the Rogers RO-4350 substrate that operates between 2.2 GHz and 7.6 GHz, with improved upper-frequency band suppression. The filter's upper stopband suppression was greatly improved up to 32 GHz by achieving four transmission zeros (TZs) in its passband. The given filter, however, makes use of an intricate design that can lead to manufacturing measurements being costly. In [11], the authors constructed a filter with a fractional bandwidth of 62.3% using a staircase resonator. In a recent study [12], a new H-type sandwich topology was utilized to achieve a broad bandwidth filter response with a fractional bandwidth (FBW) of approximately 132%. The addition of source-to-load coupling improved the filter's selectivity, but it also increased the insertion loss (IL) in the passband. The overall footprint of the structure covered an area of around 32 \(\times\) 15 mm. Another research work [13] implemented a high-selectivity UWB filter based on a tapered transmission line resonator (TTR). The design employed a sophisticated geometry to achieve IL \(<\) 1 dB and RL \(>\) 17 dB. Despite reducing the circuit size and achieving good control over the bandwidth, there is still potential for improvement in the passband performance of the TTR-based UWB filter. In [14], a filter with a good passband was created by combining a low- and high-pass filter. The topology developed an acceptable return loss and a good insertion loss of 0.4 dB. The FBW, however, was only 107%, which was not particularly high. One of the advantages of this prototype is to block unwanted signals up to 20 GHz. Now, to ensure compliance with FCC UWB range regulations and mitigate interference from other frequency bands, the authors of the references [15; 16; 17; 18; 19; 20; 21] have proposed various methods to achieve UWB filters with stopband characteristics such as SIRs, ASIRs, and DGSs, respectively. It is interesting to note that several studies have also been conducted to realize UWB filters with low insertion loss and stopband characteristics. For example, in [22; 23; 24], UWB filters with low insertion loss were achieved by cascading low-pass and high-pass filter sections. This approach allows for effective filtering across a wide frequency range.