Anritsu 37 D Series, Maintenance Manual

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In 20 GHz models, RF from the Source Module is routed to the Trans-
fer Switch.
In 40 GHz models, RF from the Source Module is routed into the
Source Doubler Module (SDM) and, if the instrument sweep is set to
any frequency above 20.0 GHz, the frequency is doubled. While the fre-
quency of the instrument operation is below 20.0 GHz, the SDM is in a
pass-through mode and no doubling occurs. The RF from the SDM out-
put is then routed to the Transfer Switch.
RF Output from the transfer switch is simultaneously routed through
two outputs in normal S Parameter operation. In this operation mode,
one Reference Signal and one Test Signal is generated. The Reference
Signal is critical for the phase locking of the RF Source and is used in
the measurement of phase angles. The Test Signal is eventually routed
to the Device Under Test and is not related to phase locking of the RF
Source.
S Parameter measurements are defined as ratios of the Test to the
Reference Signals and are defined as:
q S11 = Test A/Ref A = b1/a1
q S21 = Test B/Ref A = b2/a1
q S12 = Test A/Ref B = b1/a2
q S22 = Test B/Ref B = b2/a2
The full RF path of the Reference Signals is shown in Figure 3-3,
Source Lock Signal Paths. The full RF path of the Test Signals in a
transmission measurement (S21 or S12) is shown in Figure 3-2. In a
reflection measurement (S11 or S22), Test Signals originate from the
Transfer Switch opposite from what is shown in Figure 3-2. (In other
words, Test A routes through the RF components on its way to Test
Port 1 and Test B routes through the RF components on its way to
Test Port 2).
Leveling of the RF is accomplished by detectors in the Transfer Switch
that sense the levels of the Reference Signal. This detected signal is
sent to the A21A2 PCB in the Source Module.
Test Signals that are routed to the DUT for test have passed through
the non-coupled arm of the coupler. Signals that have passed through
the DUT (or have reflected back from the DUT) are passed through
the coupled arm of the couplers at the test ports. The signal received
from the DUT is returned to the Sampler/Down Conversion Module
(via the step attenuator for 300 series instruments).
ANALOG SUBSYSTEM ASSEMBLIES THEORY OF OPERATION
3-12 37XXXD MM