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38
CHAPTER 2: System Overview
Coaxial (BNC)
signal connector
Cryogenic
coaxial cable
ZN50
Probe
Probe
arm
base
Probe arm shield
Grounded
sample holder
CONDUCTOR
Sample stage
Thermal
anchors
4 K shield stage
Radiation shield stage
Second shield stage
Vacuum chamber base
To temperature Shield
controller chassis
19-pin
connector
FIGURE 2-25 Basic configuration for DC measurements
2.4.3 Basic RF Electrical
Measurements
RF measurements can be made with similar configurations described for DC
measurements in section 2.4.2. RF measurements are typically configured with
either a BNC signal connector with ultra-miniature cryogenic coaxial cable or a
K-connector with semirigid cable as described in section 2.3.2.2. The useable
frequency range of a ZN50 configured with a BNC signal connector with ultraminiature cryogenic coaxial cable is DC to 50 MHz. While performance beyond
50 MHz is certainly possible, steps should be taken to understand the losses at the
particular frequency of interest.
The useable frequency range of the ZN50 configured with K-connectors and semirigid
cables provides continuous operation up to 100 MHz and selected band operation up
to 1 GHz. This configuration has reasonable frequency response out to 1 GHz as long
as the band between 200 MHz and 400 MHz can be avoided.
FIGURE 2-26 can add additional information; it shows the forward transmission
response of a pair of ZN50 probes configured with K-connectors and semirigid cable.
While the probes do have a response out to 1 GHz, the separation of the ground path
from the single signal tip of the ZN50 blade causes a large dip in transmission
(forward gain) at 0.3 GHz (300 MHz). Depending on the configuration of the probes
and measurement setup, this dip can vary from approximately 200 MHz to 400 MHz.
Model CPX Probe Station