Synthesis of Low-Pass Real-to-Real Impedance Transformer With Coupled-Inductors

A network-synthesis procedure for a new low-pass real-to-real (resistance-to-resistance) impedance transformer is presented. Conventionally, the well-known impedance transformer had an all-pole transmission function, and suffered from a theoretical limit on its operating bandwidth, reflection coefficient (mismatch), and impedance ratio (BRR). In this brief, the limit has been surpassed by an introduction of another transmission function having transmission zeros. The resulting impedance transformer involves negative-coupled inductors, with its coupled coefficient -1 <; k
_ind
<; 0 depending on the BRR, and can realize arbitrary BRR without increasing the number of elements N of the network. Especially, when k
_ind
≈ -1 is assumed to be realizable, N = 4 can realize any BRR.