Wideband tunable in-phase power divider using three-line coupled structure

An in-phase power divider (PD) with a wide tuning range for the power division ratio across one octave bandwidth is presented. The device uses a quarter-wavelength three-line coupled structure with controllable coupling factors using two centrally connected varactors. One terminal of the central coupled line is connected to the input port, whereas its other terminal is grounded. The two coupled side lines are connected to the output ports, whereas an isolation resistor connects their other ends. The mode theory is used to analyze the performance and predict the initial dimensions. To validate the design, a prototype of dimensions 30 × 20 is built on Rogers RO6010 substrate and tested. The results indicate a tunable power division ratio from 1:1 to 1:2.4 with less than 0.5 dB additional insertion loss across the frequency band 0.7-1.4 GHz. The device has more than 10 dB return loss at all the ports and more than 15 dB isolation between the output ports. The two output signals are in-phase across the whole band with less than 8° differential phase imbalance