Harmonic Suppression by Using T-shaped Spur-Line in a Compact Hairpin-Line Bandpass Filter

Abstract

This article exhibits the design of a fourth-order compact hairpin-line bandpass filter centered at 2.5 GHz and with a 3 dB fractional bandwidth of 5% along with a sharp roll-off factor and wide stopband characteristics required for Wireless Local Area Network (WLAN). Miniaturization of the conventional hairpin-line filter has been achieved by folding the open end arms twice towards the inward direction and accordingly, a size reduction of 42% has been obtained. Subsequently, T-shaped spur-lines with optimum dimensions have been incorporated at both the inner and outer edges of the coupled arms of the folded hairpin-line cell. Accordingly, two fourth-order folded fitters with outer T-shaped and double T-shaped spur-lines have been designed and verified experimentally. An extended stopband with a rejection level of 39 dB up to 3.2f 0 along with a size reduction of 46% has been achieved.

Compact High-Selectivity Wide Stopband Microstrip Cross-Coupled Bandpass Filter With Spurline

“…Moreover, the proposed filters have occupied less circuit area over [11, 12, 14, 15, 17, and 19]. The insertion loss becomes less than [13,17,19] for the same FR4 substrate and the return loss becomes greater than all the other works included in the table. It has been further noted that more number of transmission zeros have been generated for the proposed filters than [8, 10, 12 -15].…”

“…Thus, different nonuniform perturbations have been incorporated by the researchers in the coupled region between the adjacent arms of the lines. In this context, spurline is one of the most attractive microstrip defects that effectively suppress the harmonics for parallelcoupled line filter [14][15] and hairpin-line filter [17][18][19]. Hence, the next objective of the present work has been set to suppress the harmonic attenuation level below 35 dB keeping the satisfactory passband response.…”

“…In general, spurline is a microstrip defect created by etching one defected slot of L shaped in the microstrip line [16][17]. As shown in Fig.…”

“…This justifies the ability of the L-spurline for the suppression of harmonics. In the next section, the L-shaped spurline has been modified by a meander spurline [17] to provide slower wave effects for the odd-mode of EM wave and to achieve more suppression level of the harmonics along with a wider stopband.…”

“…The meander spurline is characterized by the slot width w T , slot length l T , slot gap g, periodicity p, and overall spurline length l sp . By this new slow-wave structure the overall electrical path of the odd-mode has been extended [17]. It causes more slowdown of the signal while propagating through the central wiggle.…”