Compact Tunable Left Handed Ferrite Transformer

Abstract

In this paper, a novel compact and tunable impedance transmission line transformer is presented for the first time. The transformer is designed using a left handed coplanar waveguide transmission line on a ferrite substrate. Based on the dispersive properties of the ferrite medium, the theoretical study of the transformer has been carried out using its equivalent circuit analysis and the composite right / left handed transmission line theory. The theoretical study was verified through full wave electromagnetic numerical simulations. The results show that the transformer matches a 25 Ω load to a 50 Ω line with tunability from 2.55 GHz to 3.2 GHz. The return loss at center frequency is better than 20 dB with insertion loss better than -1 dB. The transformer has a very compact size with dimensions of 4.25 × 21 mm2, showing approximately 64% reduction in size in comparison with a conventional right-handed transformer within the same operating frequency band. Moreover, the proposed coplanar waveguide transformer configuration has smaller demagnetization factor and hence it requires smaller DC magnetic bias values compared to microstrip configuration.