Dual-Band Filtering Power Dividers With Multiple Out-of-Band Transmission Zeros and DC-Blocking

In this letter, a novel topology of <tex-math notation="LaTeX">N</tex-math> -section dual-band filtering power divider (DBFPD) with multiple out-of-band transmission zeros (TZs) is proposed. The proposed design can not only realize the <tex-math notation="LaTeX">n</tex-math> th-order filtering function but also (2 <tex-math notation="LaTeX">N</tex-math> <tex-math notation="LaTeX">$+$</tex-math> 1) TZs between the two passbands by different values of <tex-math notation="LaTeX">N</tex-math> . It mainly consists of 2( <tex-math notation="LaTeX">N</tex-math> <tex-math notation="LaTeX">$+$</tex-math> 1) coupled lines and 2( <tex-math notation="LaTeX">N</tex-math> <tex-math notation="LaTeX">$-$</tex-math> 1) shunted coupled stubs. A resistor-loaded three-line parallel coupled line is used to realize the expected power dividing ratio and good in-band isolation simultaneously. In addition, two stepped impedance stubs are introduced at output ports to improve frequency selectivity. Through mathematical analysis of its <tex-math notation="LaTeX">S</tex-math> -parameters, a set of simultaneous equations can be derived to obtain all the electrical dimensions according to the design specifications. To verify the correctness of the proposed technique, a dual-band FPD ( <tex-math notation="LaTeX">N</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 1) prototype operating at 1.1 and 2.9 GHz with the fractional bandwidths of 18.2% and 6.67% is designed and fabricated. Good agreement between simulated and measured results evidently reveals that the proposed design holds its attractive advantages of multiple out-of-band TZs, good full-frequency isolation, high band-to-band and out-of-band rejections, inherent dc-blocking, and compact size compared with reported works.