Open AccessSharp roll‐off planar lowpass filter with ultra‐wide stopband up to 40 GHz
Author(s) -
Jiang Shu,
Xu Jinping
Publication year - 2017
Publication title -
electronics letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.375
H-Index - 146
eISSN - 1350-911X
pISSN - 0013-5194
DOI - 10.1049/el.2017.1238
Subject(s) - stopband , microstrip , transition band , low pass filter , materials science , resonator , planar , bandwidth (computing) , electrical impedance , elliptic filter , optics , cutoff frequency , physics , optoelectronics , band stop filter , electrical engineering , telecommunications , prototype filter , engineering , computer science , computer graphics (images)
A microstrip planar lowpass filter (LPF) with sharp roll‐off and ultra‐wide stopband up to 40 GHz is presented. The central part of the LPF consists of three basic circular sectors, two smaller quadrants and a number of high‐impedance lines that are cross‐coupled to form a high cut‐off rate and a moderate stop band from 2.3 to 10 GHz. Then, four types of resonator cells, three of which are high‐impedance lines loaded with semi‐circulars and one of which comprises folded step‐impedance lines, are added to the central part to generate additional transmission zeroes up into Ka band. As a result, an ultra‐wide stopband with 18th‐harmonic suppression has been attained. A demonstration filter with 3 dB cut‐off frequency of 1.96 GHz has been designed and fabricated. The measured results show that the relative stopband bandwidth of the LPF is 180% with suppression level >25 dB, and the roll‐off rate is 104 dB/GHz. The functional area size of the LPF is 18.4 × 11.6 mm, which corresponds to 0.189 × 0.121 λ g ( λ g is the guided wavelength at f c ).