Design a Quasi-Elliptic Bandpass Filter working at 2.5 GHz using K and J inverter

Abstract

Micro-strip line bandpass filters are becoming increasingly important in modern wireless communication. BPFs can select desired microwave signals to improve the bandwidth efficiency. Secondly, BPFs can be cooperated into some devices such as power amplifiers, oscillators to improve the performance or modify the characteristics of these devices. Generally, we require that the BPFs has the features of high selectivity, sharper roll-off, wider rejection band and good fabrication tolerance. This report will focus on the design of a quasi-elliptic response bandpass filter which satisfies the requirements above. This kind of BPF achieves high selectivity by introducing two transmission zeros aside passband so that the frequency response has a sharp roll-off at cut-off frequencies. To generating transmission zeros, gap couplings can be utilized between non-adjacent resonators. Additionally, via coupling is utilized for main-coupling between quarter-wavelength resonators to build a bandpass filter. The reason to consider via coupling is that it has more compact size, which is important for the filter miniaturization. The filter is designed and simulated using HFSS. The filter is implemented by normal PCB process and measured using Agilent 8753ES Vector Network Analyzer. To summarize, quasi-elliptic response bandpass filter has a high selectivity and tunable center frequency, also a wider rejection band. Moreover, the second suppress response is far from the center frequency. Hence, quasi-elliptic response bandpass filter is a good candidate for wireless communication for its advantages mentioned above.