A Compact Microstrip Lowpass Filter With Sharp Roll-Off Rate and Ultra-Wide Stopband Employing Coupled Polygon Patches

Abstract

Abstract-In this paper, a microstrip lowpass filter with −3 dB cutoff frequency of 1.8 GHz composed of two resonators with different polygon patches and six symmetric suppressing cells is presented. To design the proposed filter, the impact of each microstrip transmission line on the scattering parameters of the employed resonators is separately determined by extracting the equations of the insertion loss (S 21 ) and return loss (S 11 ) on the basis of their equivalent LC circuit. The designed filter is fabricated and measured, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss better than −0.35 dB and an acceptable suppression level of −22 dB from 1.87 to 19.75 GH are achieved. Furthermore, a flat insertion loss in the passband and an acceptable return loss (−19.32 dB) in this band can verify desired in-band performance. The designed lowpass filter has a high figure of merit about 36969.34.

Compact microstrip lowpass filter with ultrasharp response using a square-loaded modified T-shaped resonator

“…The group delay of presented LPF is very flat because the maximum mutability in the proposed LPF at 55% passband is only 0.04 ns. Comparisons between the designed LPF performance and similar reported structures [14][15][16][17][18][19][20][21][22][23][24][25][26][27] are shown in the Table . In this table, the sharpness of transition band is calculated as follows [13]:…”

A Design of Microstrip Lowpass Filter with Wide Rejection Band and Sharp Transition Band Utilizing Semi-Circle Resonators

“…In [14], a lowpass filter employing polygon patch resonant cells, T-shaped resonators and two different suppressing cells has been designed, although, this filter does not have a steep skirt performance. One more method to present a LPF with acceptable frequency response is cascading resonators with polygon patches [15], but it occupies a large area. In [16], employing modified hairpin resonator with long straight slots leads to designing a lowpass filter with sharp skirt performance and wide rejection band, but its return loss performance is not good enough.…”

Compact Microstrip Lowpass Filter With High and Wide Rejection in the Stopband Utilizing Flabelliform Resonators

“…In [14], a lowpass filter using polygon patch resonant cells, T-shaped resonators and two different suppressing cells is designed; however, this filter does not have a sharp transition band. Another method to design an LPF with acceptable frequency response is cascading resonators with polygon patches [15], but it has a large circuit size. In this paper, a lowpass filter (LPF) with −3 dB cutoff frequency located at 3.8 GHz is proposed.…”