Specifications

While the RF I-V measurement method is based on the same
principle as the I-V method, it is configured in a different
way by using an impedance-matched measurement circuit
(50 Ω) and a precision coaxial test port for operation at
higher frequencies. There are two types of the voltmeter and
current meter arrangements that are suited to low imped-
ance and high impedance measurements.
Impedance of DUT is derived from measured voltage and
current values, as illustrated. The current that flows through
the DUT is calculated from the voltage measurement across
a known R. In practice, a low loss transformer is used in
place of the R. The transformer limits the low end of the
applicable frequency range.
The unknown impedance (Zx) can be calculated from measured
voltage and current values. Current is calculated using the voltage
measurement across an accurately known low value resistor (R.) In
practice a low loss transformer is used in place of R to prevent the
effects caused by placing a low value resistor in the circuit. The
transformer, however, limits the low end of the applicable frequency
range.
The reflection coefficient is obtained by measuring the ratio
of an incident signal to the reflected signal. A directional
coupler or bridge is used to detect the reflected signal and a
network analyzer is used to supply and measure the signals.
Since this method measures reflection at the DUT, it is
usable in the higher frequency range.
I-V method
RF I-V method
Network analysis method
Figure 2-1. Impedance measurement method (2 of 3)
2-2