Abstract
We have proposed a 5 GHz microstrip-line-based bandpass filter in the applications of future wireless communication, which locates at 4.9 to 5.85 GHz of IEEE 802.11ac regulated by Federal Communications Commission (FCC). The proposed filter is composed of a folded half guided-wavelength coupled-line resonator and a pair of folded T-shaped open-end stubs, which are slightly longer and shorter than the quarter guided-wavelength. The bandpass filter possesses the sizes of 0.330 0.150, which is compact compared to a traditional hairpin-line bandpass filer, an interdigital bandpass filter, and an open-loop bandpass filter, etc., which are on the level of 0.520 0.300, 0.500 0.330 and 0.870 0.290, respectively. Note that, 0 represents the guided wavelength of the substrate at the central frequency. Next, we manipulate the lengths of the coupled line and the two open-end stubs to obtain the three transmission poles in the passband that a three-order bandpass filter can be achieved. This proposed bandpass filter can be further analyzed by the electrical circuit. The certain part of the entire structure can be corresponding to the electrical components, such as an inductance, a capacitance and an inverter. The selectivity of our bandpass filter is great because the two transmission zeroes locate outside the frequency range of the passband with the band-edge transitions equal to 113 and 48.6 dB/GHz on the lower and higher frequencies, respectively. Moreover the stopband is suppressed below -20 dB down to DC and up to 12 GHz. In addition, the performance of the insertion loss and return loss are further improved by designing an impendence-matching line, which are to 0.6 and -22 dB, respectively. Finally, the proposed filter is fabricated on the Roger board 5880 by the printed-circuit-board (PCB) fabrication process and measured by the high-frequency measurement system, a vector network analyzer Agilent N5245A. The measurement results agree with the simulated results well.