Design of an Ultra-wideband Transition from Double-sided Microstrip to Parallel-strip line for Balanced-type Antenna

Background: This paper presents the design and implementation of an ultra-wideband transition from double-sided micro-strip to parallel-strip line which is usually used as balanced antenna feed. Methods: This transmission is composed of a near-optimum taper of metal on top layer and exponential taper of ground on bottom layer. The transmissions were simulated and optimized by CST Microwave Studio and then they are fabricated. Finally, the results of simulations and measurements are compared. Results: The measured results show that the performance of two back-to-back near-optimum taper transmission possesses a return loss of better than 10 dB and insert loss of one transition less than 1 dB over a bandwidth from 1.20 to 5.75 GHz (1:4.8). For a wider bandwidth, an insert loss of one transition less than 3 dB and return loss better than 10 dB can be achieved from 1.20 to 9.68 GHz (1:8.1). With 100 ohm resistor loading, the return loss of near-optimum taper transmission better than 10 dB can be received from 0.86 to 11 GHz (1:12.8).