A Wideband Microstrip to Bilateral Slotline Transition Using Constant Impedance Bilateral Slotline and Heart-Shaped Irregular Cavity

A microstrip to bilateral slotline (BS) transition is proposed in this letter, which contains a 50-Ω constant impedance BS and a heart-shaped slotline cavity. Unlike traditional slotline transitions, the proposed transition does not suffer from matching issues when losses are incurred by multi-section impedance transformers and this transition has a potential to operate from 530 MHz to over 20 GHz if a K-connector is used. This letter will illustrate the discovery of BS with constant impedance first and then its application in design of the 50-Ω BS. The heart-shaped slotline cavity is proposed for bandwidth improvement. And the transition size is also reduced due to the absence of multi-section impedance transformers. A prototype is fabricated and measured to demonstrate this concept of the design, and it has a practical operating bandwidth from 0.53 to 12.23 GHz (about 23:1) with return loss better than 10 dB and insertion loss less than 3 dB.