Power Meter R&S NRP
in
◆ Innovative multipath sensor
technology
◆ 90 dB dynamic range
◆ High measurement speed
◆ Intelligent sensors – simply plug in
and measure
◆ Accurate measurement of average
power regardless of bandwidth and
modulation
◆ Multislot measurements for
common time division systems
(e.g. GSM/EDGE, DECT)
◆ Handling of external components
through Γ and s-parameter correction
◆ Simultaneous operation of up to
4 sensors on basic unit
◆ Operation of sensor directly from PC
via USB interface
◆ 2-year calibration cycle
Ready for a wide variety of applications
The RF and microwave Power Meter
Designed for R&D
R&S NRP is always the right choice:
It is ideal for daily use in research and
development, production or mobile
service, not to mention when analyzing
broadband modulation signals of thirdgeneration mobile radio. The versatility
of the novel R&S NRP power meter
series is primarily due to the newly
developed sensors in
. These sensors are intelligent standalone instruments that communicate with the
basic unit or a PC via a digital interface.
The , now
implemented for the first time, sets
Top measurement accuracy plus a
dynamic range of 90 dB for broadband
signals of any modulation are the most
requested characteristics of a modern
power meter. The versatile R&S NRP
sensors in
feature exactly these characteristics and
are a priceless investment if you wish to
meet future requirements such as the
broadband modulation types of thirdgeneration mobile radio. In addition, they
are also capable of handling the RF bandwidths beyond 100 MHz that are already
under discussion for wireless LAN.
new standards in terms of universality
and accuracy. The R&S NRP basic unit
offers exactly what you expect for
today’s needs: compact size, intuitive
user interface and multichannel capability.
A power meter must of course be easy to
operate: The numerous sensor functions
can be activated via an intuitive user
interface, and the high-resolution display
indicates up to 4 measurement results at
a time. As with other power meters from
Rohde&Schwarz, all calibration data is
stored in the sensor, which ensures highprecision measurements by minimizing
operating errors.
Sensor connectors on front
panel, channel B: option
R&S NRP-B2
Built-in test generator
(option R&S NRP-B1)
Display of up to
4 measurement
results
Softkeys and window-oriented
menu technique
Power sensor in
with 90 dB dynamic range
Function keys for fast access to
important functions
2 Power Meter R&S NRP
Ideal for production
S
n
Mobile use
For any type of test signal:
If you have ever dealt with microwave
power measurements, you know that the
necessary filtering of results due to the
noise characteristics of the sensor as well
as delays in measurement range selection and command/result processing can
have negative effects on throughput in
production. And this is where the R&S
NRP with its innovative features offers
straightforward solutions:
◆ Autofilter
◆ Parallel processing
◆ Speed
It goes without saying that the basic unit,
which can accommodate up to 4 sensors
at the same time, can be fully remotecontrolled. In addition, the sensors can
directly be connected to a PC. It is good to
know that the sensors can perform reliable measurements for an extended
period of time owing to the long calibration interval of 2 years.
The handy, lightweight and sturdy instrument, which can also be powered from
the optional battery for several hours,
makes mobile use a pleasure. With an
operating temperature range from 0°C to
50°C, the Power Meter R&S NRP can be
used under almost any conditions.
allows every
R&S NRP sensor to be operated directly
from a PC, making it the smallest and
most lightweight microwave measuring
instrument available.
Microwave power meters have historically required a multitude of different
sensors to cover all applications. Thermal
sensors, diode sensors as well as peak
power sensors were used to handle the
various measurement tasks. The sensors
of the R&S NRP family now make life
much easier – in many cases, a single
sensor can perform all necessary measurements (see table 1).
Table 1: Sensor technologies and their applications
Application ↓ Sensor → Thermoelectric sensor Diode sensor (CW) Peak p ower sensor Sensor in
Average power
Burst power –– ––
Time gating –– ––
Signal with extremely high bandwidth ––
Measurement over wide dynamic range ––
optimal possible –– not possible
Summary
◆ One power sensor
◆ 90 dB dynamic range
◆ CW and broadband-modulated signals
◆ Time-gating applications
◆ High measurement accuracy and speed
ensor i
Power Meter R&S NRP 3
High system accuracy through
Plug in and measure
The accuracy of microwave power measurements essentially depends on the
characteristics of the sensor, but it is
impossible to eliminate level, temperature and frequency influences by traditional means. Rohde&Schwarz solved
this problem years ago by introducing a
novel approach: Measure the deviations
of each manufactured sensor from the
ideal characteristics and then store the
values in the sensor as a data record. This
means that you do not have to bother
with calibration data. Instead, you simply
plug in the sensor and start the measurement, which is a significant advantage in
day-to-day work.
Precise calibration
High measurement accuracy –
even with modulated signals
Benefitting from all the factors described
above, Rohde& Schwarz broadband
power meters have a very low measurement uncertainty, which is still the decisive argument in their favour. In the past,
however, the data sheet specifications of
about 2% (0.09 dB) could seldom be
achieved in practice. This was due to error
sources associated with the test signal or
external circuitry: harmonics and nonharmonics, modulation, mismatch of the
source, and the influence of attenuators
and directional couplers connected
ahead of the sensor for level matching.
The R&S NRP sensors represent a big step
forward in solving these problems. The
concept of
(see page 5) comprises an entire series of
measures intended to make the sensors
similar to thermal sensors in behaviour.
This includes very accurate measurement
of average power, regardless of modulation (FIG 1), as well as high immunity to
incorrect weighting of harmonics, spurious and other interference signals. The
maximum speed of 1500 measurements
per second (in buffered mode, measurement interval 2 x 100 µs) nevertheless
equals that of diode sensors.
A power sensor can only be as good as
the measuring instruments used to calibrate it. This is why the standards
employed by Rohde& Schwarz are directly
traceable to the power standards of the
German Standards Laboratory (PTB).
0.2
0.15
0.1
0.05
Error in dB
0
–0.05
–0.1
–0.15
–0.2
–60 –30 0–10–50 –20–40 2010
Power level in dBm
FIG 1: Modulation-related errors of an R&S NRP-Z11 or R&S NRP-Z21 power sensor for a 3GPP test
signal (test model 1-64) compared to a CW signal of the same magnitude.
Red: default setting; yellow: transition area between measurement paths shifted by –6 dB;
light blue: uncertainty caused by noise (modulation effect below –30 dBm negligible).
4 Power Meter R&S NRP
The Power Sensors R&S NRP-Z11 and R&S NRP-Z21 fuse
multiple-path architecture, multiple-diode technology and a
simultaneously scanning multichannel measurement system
into a unique high-performance concept.
Multiple-path architecture is the combination of two or three
diode detectors to obtain a large dynamic range for modulated signals. This is achieved by operating each detector
exclusively in the square-law region and by using only the
optimally driven detectors for the measurement.
Multiple diodes comprise several zero-bias Schottky diodes
connected in series and integrated on one chip. When used
in an RF detector, they expand its square-law region, because
the measurement voltage is split among several diodes – so
that each one is driven less – while at the same time the
detected voltages of the individual diodes are added together.
Rohde&Schwarz's multiple-path architecture (patent
pending) is characterized by the following features (FIG 2):
◆ 3 signal paths, each fitted with triple diodes
◆ 6 dB wide overlap ranges, smooth transitions
◆ Simultaneous scanning and analysis
◆ Chopper stabilization of signal paths for recurring signals
The advantages over conventional technology are obvious:
high signal/noise ratio throughout, low modulation effect,
negligible delays and discontinuities when switching signal
paths, as well as the ability to perform a time-domain analysis of the test signal within the available video bandwidth.
As a consequence, these sensors not only compete with peak
power meters – they are indeed superior in two respects:
◆ No restrictions on the RF bandwidth of the test signal
◆ Wider dynamic range
As a result, it is already possible today to analyze extremely
broadband signals, such as are planned for wireless LAN or
will be created by combining several carriers in accordance
with 3GPP.
A
14 dB
–19 dBm to +7 dBm
P
i
–67 dBm to –13 dBm
34 dB
+1 dBm to +23 dBm
Chopper
FIG 2: Sensor architecture in R&S NRP-Z11 and R&S NRP-Z21.
D
A
D
A
D
Error
correction
Weighting
External trigger
Power Meter R&S NRP 5
Power Meter R&S NRP 5
+
P
m
Power measurement without external influences
Γ correction – accounting for
the source mismatch
The most important source of error in
power measurements on RF and microwave signals is the mismatch of source
and sensor. Due to reflections that cannot
be eliminated, it is not the nominal power
of the source that is transmitted to
P
GZ0
the power sensor, but the power P
that deviates to a certain extent from the
nominal value. To minimize the influence
of mismatched sources, the standing
wave ratio (SWR) at the sensor end was
reduced to the extent technically feasible
(1.11). However, a signal source with an
SWR of 2, for example, still leads to an
additional uncertainty of the measurement result of ±3.5% (0.15 dB). Although
this error normally is decisive for total
measurement uncertainty, it was frequently not taken into account because it
could not be specified for the sensor
alone.
Here the R&S NRP sensors boast another
innovation: To reduce the mismatch, the
complex reflection coefficient of the
source is transmitted to the sensor via the
USB data interface, and the sensor corrects the matching error by means of
Γ correction, taking into consideration its
own low impedance mismatch. This
approach yields a measurement result of
significantly higher precision.
(FIG 3)
i
P
GZ0
G
≠ 0 Γ
Γ
L
Source
FIG 3: Γ correction function: By taking into account the complex reflection coefficient ΓG of the source,
the measurement result (P
displayed.
) is corrected in such a way that the nominal power of the source P
i
≠ 0
G
P
i
Power Sensor
R&S NRP-Z11/-Z21
is
GZ0
S-parameter correction –
accounting for additional
components
A similar mismatch problem is encountered in test setups where the sensor
cannot be connected directly to the
source to be measured. Especially in production facilities, it is often necessary to
connect a cable or an attenuator for level
matching. In this case, the interactions
between three components must be
taken into account – a non-trivial bit of
mathematics involving complex numbers.
Here, too, the R&S NRP offers a straightforward, standardized solution to the
user. With the help of a small software
tool that runs on any PC, the complete
s-parameter data set of the twoport connected ahead can be loaded into the sensor's memory via the USB data interface.
The data format required (s2p/Touchstone) is provided by any vector network
analyzer.
After the source's complex reflection
coefficient has been transmitted (optionally), a perfectly corrected reading is
obtained; the sensor practically behaves
as if it were connected directly to the
source (FIG 4).
6 Power Meter R&S NRP
P
GZ0
G
Source
FIG 4: Shifting the measurement plane from 1 to 2 by means of s-parameter correction. The influence
of the additional component is compensated for, so that the nominal power P
sured.
Plane 2 Plane 1
Attenuator
Measured
s-parameters
P
i
Power Sensor
R&S NRP-Z21
of the source is mea-
GZ0
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