Broadside-coupled multi-octave impedance transformer

This paper presents a novel structure for ultra broadband 4:1 broadside-coupled PCB impedance transformer. Analysis, simulations and measurements of the developed transformer are introduced and discussed. Three prototypes of the proposed structure are implemented at center frequencies 5.65 GHz, 4.35 GHz and 3.65 GHz, respectively with fractional bandwidth of greater than 180 %. The implemented transformers show an ultra broadband performance with a transmission loss less than 1 dB and return loss at least 10 dB across the desired bandwidth. During comparison, simulations and measurements are found very close to each other. To the author's best knowledge the achieved performance of the designed transformer is better than so far published state of the art results.