Miniaturized Single-Ended-to-Balanced Filtering Power Divider With High Selectivity Based on Tri-Mode Resonator

In this brief, a filtering power divider (FPD) based on a novel tri-mode resonator (TMR) is proposed firstly. Characteristic mode analysis (CMA) method is utilized to analyze the three modes of TMR in detail. Meanwhile, two transmission zeros (TZs) are generated due to TMR, which can improve the passband selectivity greatly. Then for the purpose of meeting the connecting requirement between single-ended and balanced components, a single-ended-to-balanced (SETB) FPD is realized on the basis of the FPD. In order to realize the miniaturization, a multilayer microstrip-slotline (M-S) transition structure is applied. As a result, the additional half-wavelength transmission slotline is not required. To validate the design method, the prototype has been manufactured and measured. The overall size is about $0.38\,\,\lambda _{\mathrm{ g}} \times 1.04\,\,\lambda _{\mathrm{ g}}$ and the common-mode (CM) suppression level is better than 28.5 dB at all frequencies (the fractional bandwidth is 200%). Furthermore, the in-band insertion loss is lower than 1.2 dB and the isolation is higher than 17.6 dB in the passband.