Four-Way Microstrip Lumped-Element Reconfigurable Dual-Mode Filtering Power Divider

In this paper, a novel four-way microstrip lumped-element reconfigurable dual-mode filtering power divider (FPD) is proposed. The two operating states are a four-way FPD with constant return loss, and a stopband filter (SBF) with high isolation, respectively. This switchless two operating states can be switched by selecting appropriate voltage without using switches. The tunable filtering response of four-way FPD based on a novel coupling scheme is realized by two pairs of varactor-tuned LC resonators. The measured four-way FPD can be tuned from0.98 to 2.08 GHz with return loss better than 18 dB. Its frequency tuning range (FTR) is 72%. The measured isolation is better than 19.5 dB from dc to 5.7 GHz. Apart from the bandpass FPD application, the proposed circuit can also be utilized as an SBF, which is different that of conventional SBF by tuning off diodes to obtain isolation. By staggering the resonant frequencies of four lumped-element resonators and decrease mutual coupling between resonators, an SBF with high isolation can be obtained between two nonadjacent ports. The measured isolation is better than 40 dB from dc to 6 GHz and better than 45 dB from 1.1 to 4.8 GHz. The proposed four-way reconfigurable dual-mode FPD exhibits wide isolation bandwidth and FTR, good return loss, high isolation level, and compact size.