| Summary: | 碩士 === 國立中央大學 === 電機工程研究所 === 94 === Wideband bandpass filters are essential to modern broadband wireless communication systems. In the past, microstrip bandpass filter have been studied extensively. In contrast, there is little work on coplanar-waveguide (CPW) bandpass filters. The traditional design of wideband bandpass filter is realized via the enhancement of the electromagnetic coupling in structures. However, the limitation on fabrication processes renders the bandwidth somewhat limited. An ultra-broadband (2GHz-8GHz) CPW bandpass filter is proposed in this thesis. The CPW bandpass filter is designed via cascading CPW lowpass and highpass filters. The cascaded CPW bandpass filter is of greater than 120% 3-dB fractional bandwidth. Indeed, the cutoff frequencies of the passband are realized via separately adjusting the ones of the CPW lowpass and highpass filters. This approach offers more design freedoms than the traditional bandpass filter design. On the other hand, the proposed filter shows sharp skirt selectivity at both the passband edges and high stopband rejection. The proposed filter is fabricated for experimental verification. The measurement and simulation results are in good agreement. Also, the corresponding lumped equivalent circuits are demonstrated. Finally, the proposed filter is in conjunction with a broadband exponentially tapered slot antenna through a CPW to slotline transition for application demonstration.
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