Aerospace & Defense Technology - April 2021 - 24

RF & Microwave Technology

Phase

added to the extension unit. The LNAs
may also act as a pre-amp for noise figure measurements on active DUTs.

Amplitude
PA

Additional Switching
From
Beamformer

Digital Controls

To Antenna

LNA
Phase

Amplitude

Figure 4. Typical T/R module block diagram.

The ability to implement complex
signal routing by means of a single
switch and control platform is another
option. The switch and control platform base unit can be a manually operated instrument or it can be controlled
via an Ethernet interface. This interface
allows connection to a PC for automatic
and manual control via a software application.

Example Configurations

Figure 5. Generic block diagram of a T/R module.

Adding signal conditioning to the network analyzer offers yet another benefit:
measurements requiring no signal conditioning can be carried out using just the
standalone VNA, providing uncompromised network analyzer performance,
i.e. with the instrument's superior dynamic range, sensitivity, and stability.

Routing Signals
The stimulus and measured signals
from the network analyzer are fed to the
extension unit via the network analyzer's direct generator/receiver inputs.
The signals are modified via the extension unit and either output through its
ports or fed through the network analyzer ports. It includes a high-power test
set with access to the network analyzer's
generator and receiver paths.
The extension unit allows test engineers to add user-supplied components
into both the source and measurement
paths. This expands measurement capabilities by inserting amplifiers, attenua-

tors, or even other test instruments into
the measurement path. The internal hardware and switching allows this capability
to be used while keeping the DUT connected. These elements may be softwarecontrolled and switched in as required.

Signal Conditioning
In addition to the standard features,
the extension unit also offers optional
pulse modulators, combiners, output
amplifiers, and low-noise preamplifiers
(LNAs). The individual components are
activated via mechanical switches as required for a given measurement setup.
The optional amplifiers may be
switched in on the source paths. They
may be used to overcome any additional
loss in the signal path and increase the
output power at the test ports of the extension unit as well as the test ports of
the VNA. This allows output power at
the ports to be between +5 and +15
dBm, depending on installed options
and frequency. Optional LNAs may be

24

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Cov

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Figure 5 shows a generic block diagram of a T/R module, with all its functional blocks. The transmit (TX) side is
shown in the upper path and the receive (RX) side is shown in the lower
path. There are input and output
switches that control whether the module is in transmit or receive mode. The
amplitude and phase of the TX and RX
signals are adjusted by the variable
phase shifters and variable gain amplifiers on their respective paths. These adjustments are usually controlled digitally and allow the beam to be steered
across the face of the array. Typical systems have hundreds to thousands of
these T/R modules in each phased array.
The TX path uses a PA for transmitting while the RX path uses an LNA.
Typically, test engineers want to look at
the TX S-parameters from port 1 to 2, as
shown on the diagram, as well as the
RX S-parameters (port 2 to 1). The S-parameters are used to characterize all
amplitude and phase settings of the
digitally controlled components. The
LNA and PA are also characterized for
noise figure, intermodulation, 3rd
order intercept (3OIP), and compression. The input and output matches are
also important. Since T/R modules are
often used in radar systems that operate
in a pulsed mode, pulsed measurements are typically a requirement.

Single Connection Characterization
With a single connection, the network
analyzer and extension unit system can
measure and characterize both the forward (TX) and reverse (RX) directions.
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Aerospace & Defense Technology - April 2021

Table of Contents for the Digital Edition of Aerospace & Defense Technology - April 2021

Aerospace & Defense Technology - April 2021 - Intro
Aerospace & Defense Technology - April 2021 - Sponsor
Aerospace & Defense Technology - April 2021 - Cov1
Aerospace & Defense Technology - April 2021 - Cov2
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Aerospace & Defense Technology - April 2021 - Cov3
Aerospace & Defense Technology - April 2021 - Cov4
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