Tunable impedance network

A method of tuning the impedance of a tunable impedance network to a reference impedance having a real and imaginary part, the tunable impedance network comprising a plurality of transformers connected in series, each transformer having a primary winding and a secondary winding, the transformers having a voltage transformation ratio of N:1 with N>1, with connected at the secondary winding of each transformer an impedance structure acting as a resonant circuit together with the inductance of the secondary winding, the impedance structure being a tunable passive network comprising at least one tunable resistor circuit and at least one tunable capacitor circuit, wherein each of the tunable resistor circuit and the tunable capacitor circuit comprise at least one transistor circuit, the method comprising:

• tuning the imaginary part of at least one of the impedance structures so as to change its resonance frequency to mimic the reference impedance;
• and
• tuning the real part of at least one of the impedance structures so as to change its Q-factor to mimic the reference impedance.