Plug In and Measure with High Accuracy through
SMART SENSOR TECHNOLOGY
The accuracy of microwave power
measurements depends on the sensor characteristics, and is impacted
by signal level, temperature and frequency. For the NRP, Rohde &
Schwarz is using an approach it introduced years ago: all
calibration data is stored directly in the sensor, which ensures
high-precision measurements and minimizes operating errors. This
eliminates the need for calibration before the measurement. After
plugging in the sensor the measurement can be started immediately.
The sensors can perform reliable measurements for an extended period
of time and the recommended calibration interval is 2 years.
In the past, microwave power meters required different sensors to
cover all applications: thermal, diode as well as peak power
sensors. The sensors from the NRP family now make life much easier –
in many cases, a single sensor can perform all necessary
measurements: average power, burst power and time gating also on
signals with high bandwidth and wide dynamic range. This capability
is achieved with the innovative SMART SENSOR TECHNOLOGY™, a fused
- 3 signal paths, each fitted with triple diodes
- 6 dB wide overlap ranges, smooth transitions from one path to
- Parallel signal processing in the three paths with
simultaneous scanning and analysis
- Chopper stabilization of signal paths for recurring signals
S-Parameter and G Corrections – Accounting for the
Errors in power measurements on RF and
microwave signals are often caused by a mismatch of source and
sensor. To reduce the mismatch, the complex reflection coefficient G
of the source is transmitted to the sensor via the USB data
interface. The sensor then corrects the matching error by means of G
correction, taking into consideration its own low impedance
mismatch. This approach yields measurement results of significantly
A similar mismatch problem is encountered where the sensor is
connected to the source via a cable or an attenuator for level
matching. This applies especially in production facilities. For the
NRP, a PC software tool allows the transmission of the complete
s-parameter data set of the additional component into the sensor's
memory via the USB data interface. This yields a perfectly correct
reading and the sensor practically behaves as if it was connected
directly to the source.
High Measurement Throughput for
The NRP is equipped with several new features
that help increase measurement throughput over conventional
approaches. These include an enhanced auto-filter function, a user
definable measurement window, and a high sample rate.
To obtain a noise-reduced display, the measurement signal is
filtered via averaging which increases the measurement time. The
classic auto-filter function must compromise between measurement
time and display noise, but this can lead to an unacceptable noise
level. The enhanced auto-filter function now offers a Fixed Noise
mode in which the sensor keeps the S/N ratio below a user defined
level, as long as the user-defined measurement time is not exceeded.
This results in stable measurement results matched to the user’s
Very low-frequency-modulated signals are typically measured using
large averaging factors to keep the display stable. In order to
shorten the measurement time the NRP uses windowing. In this mode,
the measurement time interval is adapted to the signal period.
Adjusting the window to the modulation period yields a perfectly
stabilized measurement result. If the size of the measurement window
is not critical and filtering is not necessary, the NRP excels with
1500 measurements per second (buffered mode, measurement interval 2
x 100 µs).
Power Sensors NRP-Z11, -Z21 can measure the average power not only
continuously over the signal, but also synchronized with the signal
over definable periods of time. This is useful for measurements on
signal bursts and individual timeslots of time division systems as
well as power vs. time measurements.
To support signal-synchronized measurements the NRP offers
extensive trigger capabilities. The trigger can be derived from the
test signal (internal triggering) or from an external signal. The
internal trigger is particularly useful for burst measurements.
Unwanted power components at the beginning or end of the burst can
be excluded from the displayed result with the commands EXCLUDE
START and EXCLUDE END.
With an external trigger signal, the NRP can carry out
measurements on signals with up to 128 timeslots (26 when controlled
by the basic unit). This allows entire frames of GSM/EDGE signals to
be analyzed. The number and timing of the timeslots relative to the
trigger event is user selectable. On the NRP base unit the trigger
input is situated on the rear panel. If the sensor is operated from
a PC, triggering via the USB Adapter NRP-Z3 is possible.
For more in-depth signal analysis the PC software toolkit offers
the display of a power vs. time template for recurring and
non-recurring waveforms. This function relies on internal or
external trigger, and requires that the power sensors be connected
directly to a PC via USB interface. The number of test intervals
(points) can be increased to 1024, and signal details down to a
duration of about 10 µs can be resolved.
Power Sensor with USB Interface -
Connect Directly to a PC
The sensors of the NRP-Z series are
complete miniature power meters, and can be used alone without the
NRP display unit. The sensors contain a CPU that controls the
sensor, processes the measurement results and operates the
interface. All measurement data and settings can be transmitted via
an optional USB interface. This concept is being used for the first
time in classic microwave power measurement.
Connecting the sensors directly to a PC is the most
cost-effective method for high-precision power measurements,
especially if a PC is used already for data acquisition and
evaluation. This is commonly the case in production environments
that include a process controller. Omitting the NRP display unit
saves space in the rack and reduces costs. Service technicians will
also appreciate this option since the power sensor is only 1.9 x 1.2
x 6.7 inches and can easily be operated from a laptop.
A software toolkit is required to control the NRP power sensors
via a PC. This toolkit is supplied as standard with every NRP
sensor. It includes a DLL (dynamic link library) for individualized
use of the entire sensor functionality under Windows, and the Power
Viewer, a virtual power meter with basic measurement functions for
the PC workstation. The Power Viewer includes a subset of the
functionality of the NRP base unit. The passive USB Adapter
NRP-Z4 provides all basic functions. It handles the
transmission of settings and measurement data as well as the power
supply of the sensor. The active USB Adapter NRP-Z3 for
applications requiring external triggering of the power sensor. It
also offers a separate power supply.
For applications requiring a basic unit, the NRP offers
key advantages. It has a small size, and is lightweight and rugged.
It can be fitted with one, two or four measurement inputs (Options
NRP-B2 and NRP-B5). GPIB is standard as are trigger input and analog
The user interface of the NRP power meter is controlled similarly
to a PC via menu bars, menus and dialog boxes. All functions are
grouped into only three menu levels, and the operating concept is
self-explanatory. The high-resolution graphical display can show as
many as four measurement results at the same time. The user can
choose whether to display data from up to four different sensors, or
from different timeslots of a TDMA signal measured by one sensor.
Values obtained by calculation, such as SWR or return loss, can also
NRP Display Unit Options:
NRP-B1: Sensor Check Source - The test generator is
provided to check the function of the sensor, eg. after
overloading or excessive mechanical stress. It generates a
low-distortion, highly accurate 50 MHz signal of 1 mW power (0
NRP-B2: Second Sensor Input (B) - Provides the 2nd
sensor input, located on the front panel of the NRP.
NRP-B5: 3rd and 4 th Sensor Input (C, D) - The NRP unit
can be equipped with 4 measurement inputs to handle 4 sensors
simultaneously. To make the results from all 4 sensors visible 4
different display windows can be opened on the NRP unit. All the
results from the four different sensors can be transmitted via the
remote interface to a PC in parallel.
NRP-B6: Rear-panel Sensor Input A & B -
NRP in a test rack, it is useful to change the 1st and 2nd sensor
input from the front side to the rear panel. (not to be fitted
with option R&S NRP-B5).