Design of compact single-ended-to-balanced filtering power divider with wideband common-mode suppression

A new design of single-ended-to-balanced (SETB) filtering power divider (FPD) with wideband common-mode (CM) suppression is presented. To effectively realise high suppression of CM noise, a hybrid structure constructed by both the double-side parallel-strip line (DSPSL) and a half-mode defected ground structure (HMDGS) serving as the mid-inserted conductor plane are adopted. Besides, due to the effect of HMDGS, the rejection of second harmonics for the differential-mode (DM) transmission is also improved. Meanwhile, by employing two pairs of dual-mode resonators symmetrically coupled with a stepped-impedance input feed line and adding a DSPSL stub, wideband-filtering performance with high selectivity is achieved. For validation, a prototype of the proposed SETB-FPD centred at 5.9 GHz with a 3-dB fractional bandwidth (FBW) of 27% is designed, fabricated and measured. Results indicate that the proposed SETB FPD exhibits good performances of high selectivity, wide upper stop band, good isolation between two balanced output ports and 30-dB suppression of CM noise over the DM pass band.