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Network Analyzer Calibrations
Network Analyzer Calibrations
This section explains network analyzer calibrations in detail.
What is Network Analyzer Calibration?
Network analyzer calibration greatly reduces repeatable , system-induced errors . This is
achieved by rst measuring the magnitude and phase response of one or more high-quality
standards . The standards , described below , are placed (one at a time) where the device under
test (DUT) would normally be . In other words , if the DUT would normally be placed at the end
of a certain cable , that's the exact spot you should place the standard device . This removes
errors caused by the cable and its associated connectors . This location is called the \test port."
The number of standards required depends on the calibration type .
Standards
Here are the devices that may be required during a network analyzer calibration:
Open An open is a termination that presents an open circuit to the receiver . A
natural question to ask at this point is: \Why use a special termination when
you could just remove the device under test and leave the connection open?"
The reason is that a simple open connection has unwanted capacitance that
adversely aects the calibration. A \shielded open" termination solves this
problem.
Short A short is a termination that presents a short circuit at the test port.
Load There are two types of loads , xed loads (lowband and broadband), and sliding
loads .
Fixed loads are small terminations that present a nearly perfect 50 ohm
impedance . This absorbs almost all RF energy that is produced by the RF
Source . There are two types of xed load: lowband and broadband.
A sliding load is a long device with a moving plunger . This type of load is only
used in 1-P ort calibrations . The sliding load has index marks along its length.
These marks allow you to move the plunger to dierent positions required by
the 1-P ort calibration. The device has a designed-in \mismatch" whose phase
vector changes as you move the mismatch element (the mismatch element
moves when you move the plunger). The receiver compares the vector change
at the dierent element positions , and interpolates (very accurately) the
directivity errors in the system.
Calibration Kits
The calibration standards mentioned above can be obtained by purchasing a Hewlett-P ackard
calibration kit. Cal kits can only be used with the connector type they are designed for . (F or
example , there are dierent kits for 3.5-mm and type-N connector types .)
Always use a cal kit that has the proper connector types for your test port. Do not use
adapters with a cal kit of the wrong connector type . Y our test port can have adapters on it,
provided that the adaptor will remain in place when you attach the DUT .
Data les provided with each cal kit must be loaded into the receiver . These data tell the
receiver the expected performance values of the standards . Cal kit data les are also called
\cal kit denitions" in this manual, because they dene the actual performance of the devices .
After the receiver measures the standards , it compares their apparent performance with
the information in the cal kit denition. Any dierences are due to errors in the system or
cables . The receiver produces a list of the dierences , called calibration coecients . When
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