Evaluation of Coaxial Slotted-Line Impedance Measurements

Most ultra-high-frequency impedance measurements are made by detecting the voltage-standing-wave ratio and nodal position in a slotted section of coaxial transmission line. Sources of error in these measurements are discussed and methods of eliminating or evaluating them are presented. It is shown that the maximum error due to structural defects in determining the relative voltage can be predicted experimentally for most standing-wave machines and that the resulting maximum error in the voltage-standing-wave ratio is twice the maximum error in determining the relative voltage. The resulting maximum error in the nodal position and, also, the fractional errors in the load resistance and reactance due to the errors in the voltage-standing-wave ratio and nodal, position are calculated and presented in graphical form.