Low-Cost Impedance Tuner Utilizing Quadrature Coupled-Line Coupler for Load and Source Pull Transistor Measurement Applications

A low-cost impedance tuner, well suitable for load and source pull transistor measurements is presented. The proposed circuit consists of 3-dB quadrature coupled-line directional coupler with tuning components realized as shorted microstrip line sections with appropriate sliding shorting elements, which allow to provide any desired impedance. The theoretical analysis of the proposed circuit has been performed and the principle of circuit's behavior has been explained. An exemplary impedance tuner has been designed, manufactured and measured. The obtained measurement results prove the usefulness and demonstrate the advantages of the presented approach.