Design of High Performance Microstrip LPF with Analytical Transfer Function

Abstract

By exploiting butterfly and T-shaped resonators, a new design of microstrip lowpass filter (LPF) is proposed and analyzed. The LPF is investigated in four sections. Analyzing initial resonator and its equation in detail, providing a sharp skirt by using series configuration, suppressing in middle frequencies and suppressing in high frequencies are focused in each section, respectively. To present a theoretical design, LC equivalent circuit and transfer function are precisely calculated. The measured insertion loss of the LPF is less that 0.4 dB in frequency range from DC up to 1.25 GHz, and the return loss is better than 16 dB. A narrow transition band of 217 MHz and a roll-off rate of 170.5 dB /GHz are indicative of a sharp skirt. By utilizing T-shaped and modified T-shaped resonators in the third and fourth sections, respectively, a relative stopband bandwidth (RSB) of 166 % is obtained. Furthermore, the proposed LPF occupies a small circuit of

New design of an adjustable compact microstrip lowpass filter using Z‐shaped resonators with low VSWR

“…From Table 6, it can be clearly observed that the suggested LPF is superior to the previously published LPFs. The parameters in Table 6 are comprehensively explained and mentioned in References 12 and 24…”

“…LPFs play a key role in wireless communication systems owing to their tasks in eliminating unwanted harmonics and noise 3 . Growing demands for these elements motivate scientists to design LPFs with diverse structures and specifications 4‐19 . C‐shaped structures along with complementary split‐ring resonators were used to design an LPF 4 .…”

“…Despite reaching an extended stopband in Reference 11, its high return loss can be mentioned as a serious drawback. In another paper, butterfly and T‐shaped resonators were properly combined to reach an LPF with negligible return loss, 12 yet the proposed structure is too complicated. To obviate this problem, a simple structure using open stubs was suggested, 13 but this LPF suffers from a low roll‐off rate and a large circuit size as well.…”

High performance LPF with negligible group delay using circular resonator and transfer function analysis

“…Compact size, negligible losses (insertion and return loss), high roll‐off rate and wide stopband are considered as the most efficient factors in LPFs designing. Numerous structures of LPFs have been proposed and analyzed in order to enhance these features . Using hairpin resonators and rhombic stubs, two LPFs were suggested in Refs., respectively, but both of them suffer from gradual transition bands.…”

“…In order to achieve a narrower transition band, butterfly resonators were employed in Ref. . Despite reaching high selectivity, the stopband bandwidth of the designed LPF in Ref.…”