Analysis of Image Recovery Down Converter

Abstract

This paper presents the image recovery theory of a down converter.
The analysis has been performed regarding the properties of the schottky-barrier diode mixer consisting of a nonlinear conductance g, a junction capacitance C_j and an ohmic spreading resistance R_s, and having an arbitrary load impedance at the image port.
By treating g and C_j separately, the formulas for the input and output matching admittances, the converter loss and the noise figure of the down converter are derived, and it is shown how C_j affects the total noise figure for various arbitrary image impedances.
The effect of mismatching between the converter and the IF amplifier is also studied and the experimental results of a down converter satisfying the conditions of shorted image impedance (conversion loss : 2.6-2.9 dB, noise figure : 3.6-3.9 dB) are discussed.