Wide-band ratiometric radio frequency bridge

An rf bridge, comprising four sides positioned symmetrically around a vertical diagonal and a horizontal diagonal;

• said diagonals being mutually bisecting and forming reference positions only for said sides of said rf bridge, said sides which are adjacent being connected;
• a means for series connecting an unknown impedance value, ZX, in a one of said sides between a right end of said horizontal diagonal and a bottom end of said vertical diagonal;
• a set of three general and known impedance values with one each of said general and known impedance values series connected in three of said sides not containing said unknown impedance value, ZX;
• a ground connected to said rf bridge at said right end of said horizontal diagonal;
• an a.c. voltage source having a variable frequency, and arbitrary internal impedance, connected to said rf bridge between a top end and said bottom end of said vertical diagonal;
• a measuring means comprising two logarithmic amplifiers with inputs connected, one each, to said rf bridge at a left end of said diagonal and said top end of said vertical diagonal, a difference amplifier with inputs connected, one each, to video outputs of said logarithmic amplifiers, and a phase detector with inputs connected, one each, to rf outputs of said logarithmic amplifiers.