We present a compact dual-band bandpass filter (BPF) design using λ/4 stepped impedance resonators (SIRs) embedded with spur-line for the WLAN applications. Each of the λ/4 stepped impedance resonators is shorted to the ground at its one end thru a copper via hole.  The filter covers both the operating frequencies of 2.45 GHz and 5.2-5.8 GHz. The crossly coupled mechanism is used in the filter design to provide attenuation poles by the passband edges for enhancing the signal selectivity and increasing stopband rejection levels. The spur-line is embedded in each I/O SIRs to increase the stopband bandwidth.

This document contains a compact dual-band band-pass filter (BPF) design using λ/4 stepped impedance resonators (SIRs) embedded with spur-line for the WLAN applications. The embedded spur-lines provide transmission zeros allocated in the upper stopband region for enhancing the circuit’s stopband bandwidth without affecting its passband performance. Each of the λ/4 stepped impedance resonators is shorted to the ground at its one end thru a copper via hole.  The filter covers both the operating frequencies of 2.45 GHz and 5.2-5.8 GHz. The crossly coupled mechanism is used in the filter design to provide attenuation poles by the passband edges for enhancing the signal selectivity and increasing stopband rejection levels. The tapped-line is incorporated in feed structure to save the circuit space. The spur-line is embedded in each I/O SIRs to push the upper stopband limit to a higher frequency. Effort is paid to successfully reduce the circuit size. This circuit has the circuit size of only is 10.33 × 9.7 mm2 which is considered as a very compact design. The manufacturing of this circuit is based on printed circuit board technology and can be massively produced with a very low fabrication cost. The advantages of this circuit are low cost, low profile, easy of mass production, and possibly a compact circuit size.  In conclusion, we have the following:
1.The short-circuited quarter-wavelength circuit with spur-line embedded structure effectively reduces the circuit size.
2.The planar structure and usage of printed circuit board technology of this circuit design has granted itself the advantages of low cost, low profile, and easy of mass production.
3.The introduction of implanted transmission zeros in the upper stopband region increase the stopband bandwidth.
4.This filter design is very unique which is rarely seen in the literature and has been documented by a famous international journal.

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