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2.3.3.2 Microwave-Compatible Cables and Connectors
A microwave probe cable consists of a microwave semirigid coaxial cable with
connectors permanently mounted on each end. There are two frequency
configurations for the probe cables, determined by the connector used. The hermetic
bulkhead feedthrough has matched connectors to the chosen frequency range. The
outer conductor of the semirigid coaxial cable is grounded by the hermetic
feedthrough. The microwave probe must be specified with the same frequency and
connector type as the probe cable.
Thought should be given to the measurement equipment that will be used with the
microwave probes, as the connections on existing measurement equipment may
dictate the connectors on the microwave probe arms.
1.
K-connector (2.92 mm) with semirigid cable:
this is the general purpose microwave
connection rated for continuous mode free operation from DC to 40 GHz.
K-connectors mate to SMA connectors, making this a configuration that allows
easy exchange between the microwave probes configured with K-connectors and
ZN50 probes that have SMA connectors. This configuration can also be used with
external measurement cables with either K-connectors or SMA connectors. The
semirigid microwave cable is limited to operation below 350 K.
2.
V-connector (1.85 mm) with semirigid cable:
this is a precision microwave connection
rated for continuous mode free operation from DC to 67 GHz. V-connectors mate
to 2.4 mm connectors. This configuration can be used with external
measurement cables with either 2.4 mm or V-connectors. The semirigid
microwave cable is limited to operation below 350 K.
2.3.3.3 Microwave Calibration Substrate
For the most accurate microwave measurements, especially when performing wide
band frequency measurements, the frequency dependent losses in the probes and
cables should be removed using a calibration substrate. A calibration substrate is
used in conjunction with a vector network analyzer (VNA) to characterize the
measurement setup out to the tips of the GSG probe. Lake Shore offers two calibration
substrates, CS-5 for 75 µm to 250 µm probe pitch and CS-15 for 50 µm to 150 µm
probe pitch. Each substrate is capable of calibrating SOLT (short-open-load-through),
LRL (line-reflective-line), and LRM (line-reflective-match). See section 2.5 for more
information on microwave calibrations.
FIGURE 2-15
Microwave cable with hermetic feedthrough
FIGURE 2-16
CS-5 calibration
substrate