Broadband microstrip impedance transformer

A broadband impedance transformer is proposed for microstrip realization and to release the tight gap size (30 pm) required for coupled-stripline. Design curves of the transformer are obtained by solving the analytical equations derived from the transmission line theory. Two transformers are fabricated and measured. One is designed for a 1:2 ratio and return loss better than 30 dB over a fractional bandwidth Δ = 68%, and the other is a 1:2.8 transformer with |S11| <; -25 dB over a bandwidth of Δ = 71%. In realization, the metal traces are folded so that the circuit sizes are less than λ/8×λ/8. Good agreement between measured and simulation is obtained.