Feature: Communications system design


Table 7: Lengths of the middle blocks between the loops


resulting from changes in the length of the fl oating blocks. It is important to note that both the width and length of the fl oating rectangular blocks are critical factors in the fi lter’s performance, playing a more signifi cant role than other design parameters when compared with similar bandpass fi lters. Table 3 shows the eff ect of varying the gap between the loops on


bandwidth and magnitude. T is gap serves as a key distinguishing feature of our design compared to conventional open-loop resonators. It enables eff ective coupling between the resonators, enhancing overall fi lter performance. Table 4 shows the impact of altering the length of the rectangular


slots on bandwidth and magnitude. T ese slots signifi cantly infl uence the current distribution in the microstrip structure. T e four symmetrical slots (referred to as ‘gaps’ in the tables) located on the top and bottom of the resonators provide an additional degree of freedom in the analysis, off ering greater fl exibility in optimising the microstrip bandpass fi lter’s performance. Table 5 shows the eff ect of changing the width of the slots on


bandwidth and magnitude. Additionally, during the analysis it was observed that the two


small rectangles connecting the top and bottom parts of the resonators in the centre of the structure signifi cantly impact insertion loss. Table 6 shows how varying the length of the blocks between loops infl uences the bandwidth and magnitude.


Microstrip fi lter technology advances T ere have been several recent advancements in wideband microstrip fi lter technology for various frequency band applications. Zhou et al. and Golestanifar et al. demonstrated wideband bandpass fi lter designs operating between 3.15GHz and 6.05GHz, targeting the 5G NR frequency bands n77 and n79 and 5G Wi-Fi. T eir designs achieved low insertion loss, sharp roll-off rates and suppression of unwanted harmonics to 12GHz. In comparison, researchers Lin and Dong used a hybrid


multilayer half-mode substrate-integrated waveguide for enhanced selectivity, delivering a fourth-order response with improved stopband performance. More recently, a novel microstrip bandpass fi lter design


was introduced, based on an innovative open‐loop resonator confi guration. Here researchers combined optimised inductive and capacitive coupling techniques to realise a compact fi lter with a wide passband, low insertion loss and steep transition bands.


Figure 7: Measurement results for the fi lter


Figure 6: Vector Network Analyzer used for the measurements of the manufactured fi lter parameters


Figure 5: The fabricated fi lter


www.electronicsworld.co.uk December 2025/January 2026 27


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