© The Institution of Engineering and Technology
A miniaturised balun filter with tunable power division ratio (PDR) and centre frequency is presented. Compared with the conventional balun filter, the proposed one with a varactor diode and a slide rheostat loaded onto transmission line (TL) reduces the electrical length of TL from 180° to 108°. Meanwhile, the varactor diode and slide rheostat are also utilised to control the PDR at two output ports. Moreover, passband frequency can be tuned by controlling the varactor diodes loaded onto the dual-mode resonators. The proposed balun filter achieves a tunable power division from 1:1 to 3:1 and 28.6% wide frequency turning with better than 12 dB return loss. The total electrical size of fabricated circuit is 0.23 × 0.12λg .
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content/journals/10.1049/el.2017.0866
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Design of miniaturised balun filter with tunable power division ratio and centre frequency