A Horst-Type Power Divider With Wide Frequency Tuning Range Using Varactors

This paper presents a novel power divider with a wide frequency tuning range. In our previous work, a pair of capacitors were connected in parallel with the front transmission lines of a Trantanella-type power divider introducing an additional reflection minimum, together with the original reflection zero to broaden the bandwidth. In this design, the latter transmission lines are removed. The added capacitors generate a reflection minimum, which can be easily controlled by varactors. Thus, the frequency band of the power divider can be flexibly tuned by altering the varactors. Design parameters are carefully chosen to eliminate the effect of the original reflection zero. By doing so, the power divider will have a tunable center frequency instead of a tunable bandwidth. Theoretical formulas for the characteristic impedances and electrical lengths of the transmission lines of the power divider are derived and analyzed. A power divider has been designed and fabricated to demonstrate the validity of the proposed design. The measured results indicate that the power divider can achieve a frequency tuning range of 0.9–4.2 GHz (
${f}_{H}/{f}_{L}= 4.67$
:1), with in-band input and output return losses, both better than 22 dB, and an insertion loss of 3.2–4 dB. The measured in-band isolation is better than 15 dB. The power divider has a simple layout and a compact size of
$0.2\,\,\lambda _{g} \times 0.16\,\,\lambda _{g}$
, which demonstrates the excellent potential of the proposed power divider for modern communication systems.