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LRL/LRM Calibration
(Coaxial)
An LRL cal kit is necessary to perform the coaxial calibration. Calibra
-
tion kits for GPC-7 are available from Maury Microwave and Agilent.
Two line lengths are used as the impedance standard. The calibration
frequency range is limited by the difference in the lengths of the two
lines. Their length must be different by approximately 90 degrees at
the mid-band frequency. A good calibration can be achieved over the
range of 18 degrees to 162 degrees making it possible to calibrate LRL
over a 9:1 frequency range.
LRL calibration is very sensitive to uncalibrated source match. If some
padding is placed at the test ports, the directivity and source match
will be improved. If the goal is high level measurements, then padding
should be included. If low level measurements are being performed,
then the padding must be left out.
Step 1. Same as Steps 1 through 6 in the Microstrip proce
-
dure, except choose COAXIAL in menu C11A.
Step 2. When menu C3E (left) appears, if you want to
change line impedance, place cursor on REFER-
ENCE IMPEDANCE and press the Enter key.
Step 3.
When menu C17 (left) appears, move cursor to REF-
ERENCE IMPEDANCE, key in the value, then
press the Enter key.
Step 4. Same as Steps 9 through 16 in the microstrip proce-
dure.
In the coaxial, three-line calibration there are fac
-
tors you need to be aware of. Note that it is the line
length differences that are important to the LRL cal
-
ibration, namely (L2–L1) and (L3–L1) where L1 is
the length of line 1, L2 is the length of line 2, and L3
is the length of line 3.
Longer length differences are used for longer wave
-
lengths (lower frequencies). For frequencies up to
and including the breakpoint frequency, the larger
absolute value of the (L2–L1) and (L3–L1) differ
-
ences is used. At frequencies above the breakpoint,
the smaller absolute value of the (L2–L1) and
(L3–L1) differences is used.
LRL/LRM CALIBRATION MEASUREMENT CALIBRATION
7-44 37xxxE OM
MENU C3E
CONFIRM
CALIBRATION
PARAMETERS
LRL/LRM
PARAMETERS
REFERENCE
IMPEDANCE
TEST SIGNALS
START CAL
PRESS <ENTER>
TO SELECT
OR CHANGE
MENU C17
ENTER
REFERENCE
IMPEDANCE
REFERENCE
IMPEDANCE
50.000 W
PRESS <ENTER>
WHEN COMPLETE