A tunable and reduced size power divider using ferroelectric thin-film varactors

A new concept for a reduced size and tunable power divider is presented based on barium-strontium-titanate (BST) varactors. The proposed topology operates like a conventional Wilkinson power divider while achieving size reduction and a frequency agile behavior in the frequency range of 1.7 GHz to 2.1 GHz. Tuning the operating frequency is achieved by substituting the quarter-wavelength transmission line segments with equivalent lowpass structures and using ferroelectric varactors as tuning elements. A prototype circuit was implemented and characterized showing good agreement between simulation results and measurements. The additional insertion loss in both output branches varied from 1.2 dB to 0.6 dB while maintaining a worst case amplitude- and phase difference of 0.5 dB and 9 degrees respectively for all operating cases. The isolation between the two output ports exceeded 25 dB over the whole tuning range.