Abstract
A multilayer bandpass filter with high selectivity is proposed in this letter. Discriminating coupling formed by slot-coupled quarter-wavelength and half-wavelength resonators introduces a zero at 3f0 (f0 is the center frequency) and the second harmonic is also suppressed due to the quarter-wavelength resonators. Owing to multilayer structure, source-load coupling is introduced to improve selectivity. Then an extra coupled line path is added with the same amplitude as the discriminating coupling path while they are out of phase. Thus signal cancellation produces three extra transmission zeros, with the selectivity and suppression performance further improved. To validate the design, a prototype bandpass filter centered at 2.49 GHz with 3 dB fractional bandwidth of 8.1% is fabricated. Both simulated and measured results are in good agreement and show good performance of the proposed bandpass filter.
Highlights
Bandpass filter (BPF) is an essential component in transmitters and receivers
While quasi-elliptic function response can realize the same selectivity with fewer orders and quasi-elliptic filter has lower insertion loss with high selectivity [1]
A multilayer bandpass filter with high selectivity and wide stopband is proposed in this letter
Summary
Bandpass filter (BPF) is an essential component in transmitters and receivers. For anti-interference, high performance BPF with sharp selectivity as well as wide stopband is important and necessary. In [11], a high selectivity bandpass filter with 5 zeros and 6 poles is obtained by six pairs of coupled lines. Another way to realize prescribed TZs is synthesis of the coupling matrix to generate the transfer and reflection polynomials for specific class of filter[12,13], and to simplify the computational complexity and eliminate redundancy, synthesis algorithms are invented to extract coupling matrix from zeros and poles[14,15]. Transmission zeros are produced to improve the selectivity and broaden the stopband performance of the proposed BPF. Theoretical analysis of the proposed BPF is demonstrated in detail and a prototype is fabricated to validate the design. Both simulated and measured results are in good agreement, showing the good performance of the proposed BPF
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