Technical Notes; Measuring Principle - Deepace KC901M User Manual

Chapter Six Technical Specification
6.1 Measurement Theory
KC901M's circuit is comprised of one signal source and two receivers.
The signal source is divided into two frequency bands: the signal lower than 60MHz
(except audio frequency source) is produced by DDS directly; the one higher than
60MHz is produced by PLL. The signal sources of two frequency bands are gated by a
RF switch and converged into one RF signal to output.
Both receivers are digital-IF synchronous receivers. S21 function is so-called
"simplified vector" in that in this mode, the instrument's receivers can only detect the
forward signal but not the reverse signal. So it can only run the simplified calibration
model. It only erases the errors of the frequency response.
Check Chart 6-1 for KC901M's schematic diagram.
KC901M's signal source generates a RF CW signal and output at port 1 when
measuring S11 parameter. Use the Forward divider to get the forward signal and then
use a Directional Coupler after the divider to get the reverse signal. The forward
signal and the reverse signal are sent to two receivers respectively. After double
-conversion and ADC sampling, these two signal become a digital string and then are
sent to a FPGA for further processing. KC901M use the inner product of vector
method to measurement the phase and use the Rms detection to measurement the
amplitude. All the data of RF measurement are derived from calculating the
forward/reserve signal and the phase difference.
Chart 6-1: KC901M's Schematic Diagram
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