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Keysight Technologies
Solutions for Millimeter
Wave Wireless Backhaul
Designing and Testing E-Band Backhaul
Using Effective Network Analysis, and
Signal Generation and Analysis Solutions
Application Note
Overview
The backhaul plays a critical role in the telecommunications network, comprising
the intermediate links between the core, or backbone network, and the small subnet-
works at the edge of the entire network. In microwave mobile or wireless networks,
there are three types of backhauls: macrocell, small cell and femtocell. Femtocell
backhauls normally use a broadband access technology and are not covered in this
application note. Small cell backhauls transport traffic between the outdoor small
cell site and either the node connecting to a macrocell backhaul network, or the node
connecting to the Wide Area Network (WAN)/Internet/metro network. It comprises
equipment at both ends, along with any mesh or serial equipment in between.
Today, operators have a number of different backhaul technologies to choose from,
one of which is called E-band. It presents a particularly enviable option due to its
high capacity and potential economic benefits. Available worldwide, E-band point-
to-point, line-of-sight microwave radios--also known as millimeter wave (mmWave)
radios--operate in the unlicensed 57-64 GHz frequency band at data rates up to
1 Gbps, and in the lightly licensed 71-86 GHz frequency band and 92-95 GHz
frequency band at data rates up to 10 Gbps. Such functionality makes them ideal for
dense urban environments (less than 1 km), as well as, industrial suburban environ-
ments (2-5 km). And, it's a key reason why analysts project a significant jump in the
mmWave backhaul market in coming years, driven largely by the increased use of
mmWave for Long Term Evolution (LTE) small cell backhauls.
Problem
There are a number of reasons why today's operators might want to migrate to an
E-band backhaul. Such solutions offer more bandwidth in higher frequency bands
and feature an antenna beam that is very directional and easy to control. Additionally,
the frequency bands in which E-band radios operate, namely 60 GHz and 70-90 GHz,
are now open to commercial services and products.
Despite these advantages, there are also a number of design and test challenges
that can be expected as this transition occurs. For example, the extremely narrow
beam width of E-band leaves the signal potentially vulnerable to building sway and
atmospheric interference. It also makes aligning systems very difficult. And, E-band
is very susceptible to degraded performance caused by the rain and oxygen absorp-
tion. The rain essentially interferes with the E-band's radio wave transmission, forcing
it to repeatedly transmit data to achieve a reasonable level of service. It even has the
potential to cause an interruption in service. On top of this, the cost of testing E-band
backhaul solutions is extremely high.
Solution mmWave Network measurements that can be made include
true mode, time domain, power, power
With advances in mmWave technology
Analysis Solution sweep (single frequency), power spectrum,
triggering the shift from using traditional intermodulation distortion, and noise figure,
Keysight's N5251A single sweep, 10 MHz
backhaul (e.g., optical and microwave among others. The 2- or 4-port PNA/PNA-X
to 110 GHz vector network analyzer solution
links) to E-band point-to-point links, VDI-based banded waveguide system is
employs a mmWave test controller and
having appropriate, cost-effective test and used for THz imaging and is configured
a combination of broadband frequency
measurement instruments in place is now using frequency extenders from Virginia
extenders that provide a male 1.0 mm test
more important than ever. Such solutions Diodes Incorporated (VDI) that extend the
port output connector. The N5251A is avail-
are critical to ensuring proper operation of frequency range to 950 GHz.
able as a single product solution. However,
the E-band backhaul, while also addressing it can also be configured using the PNA These banded mmWave solutions use built-
the challenges previously outlined. or PNA-X network analyzer for a lower in firmware to leverage software between
An effective mmWave test and measure- cost solution. Existing N5227A PNA and the PNA and PNA-X Series network
ment strategy must comprise both network N5247A 67 GHz PNA-X users simply need analyzers. Regardless of the frequency
analysis for mmWave component test and to add the N5261A/N5262A test controller range of the measurements being taken,
calibration, as well as, appropriate signal and broadband frequency extenders to be the instruments can be manually controlled
generation and analysis to properly test able to cover single sweep 10 MHz to 110 from the front panel. A mouse can also be
and measure communication links (e.g., GHz measurements. used to access simple pull-down menus.
the transmitter, signal path and receiver). Using the firmware interface, it is easy to
The N5251A mmWave solution is the
The network analysis solution must provide switch between frequencies
only broadband solution with integrated
a single-sweep measurement capability, for measurements.
tri-axial bias tees, which provide accurate
enable full mmWave port power control control of the device bias through its force/
and support for true differential measure- sense ability. Its broad frequency enables
ments. The signal generation and analysis superb time-domain resolution and enables
solutions, on the other hand, should offer accurate leveled power to be applied to
fast measurement times and switching the device being measured, allowing users
speeds, scalability to enable the tools to be to sweep the power at the 1.0 mm port.
tailored to the users changing test needs Additionally, the N5251A features a range
and flexibility to ensure they support both of calibration choices for coax, in-fixture and
current and future formats. on-wafer devices.
One group of instruments meeting this To make S-parameter measurements up
criteria is Keysight Technologies, Inc.'s to 1.1 THz, a variety of easily configurable
mmWave product portfolio. The portfolio banded mmWave solutions configured from
features both a mmWave network the PNA and PNA-X network analyzers
analyzer solution, as well as, one for signal can be used. The 2- or 4-port OML-based
generation, signal analysis and signal path banded waveguide system features the
emulation. The network analyzer solution PNA-X and frequency extenders from OML
is ideal for mmWave device characteriza- Incorporated that cover a range of 50 GHz
tion, modeling and parameter extraction to 500 GHz. It may be configured with or
in coaxial or on-wafer, while the signal without a test set controller depending
generation/analysis solution is well suited on the measurements required and the
for testing mmWave communications links. frequency extenders being used. Specific
2
Network Analyzer RF 1 Out
RF 2 Out
IF inputs
Measurement Example R A B C D
LO
To gain a better understanding of how OUT 1 OUT 2
Pulse generators
a measurement might be taken with the
OUT 1 OUT 2
1
Source 2
2
Source 1
mmWave network analyzer solution,
3
4
R1 R3 R4 R2
consider a N5251A solution that has A C D B
been configured from a 4-port PNA
network analyzer and allows single-sweep Test Set
Interface
Test port 1
measurements from 10 MHz to 110 GHz Test port 3 IF outputs Test port 2
Test port 4
(Figure 1). The N5251A has the ability to
ALC ALC
control and use receiver leveling to set the
ALC
R A B C D
RF RF LO
Module Power
power accurately at the 1.0 mm test port.
IF Multiplexer
+
Also, it supports measurement applications -
like true differential measurements, pulsed
measurements and scalar mixer measure- R1 T1 R2 T2 R3 T3 R4 T4
M1 M2 M3 M4
M1 M2 M3 M4 M1 M2 M3 M4
ments, and has the flexibility to enable a
single touchdown for on-wafer components M1
Frequency Extender
67 GHz
Combiner
67 GHz
Combiner
Frequency Extender
M2
that completely characterizes the behavior SRC TST (A)
1.0 mm Connectors
TST (B) SRC
of the device being measured. M3
Frequency Extender
67 GHz
Combiner
67 GHz
Combiner Frequency Extender
M4
SRC TST (C)
TST (D) SRC
With the N5251A's ability to accurately
control power, gain-compression measure-
FIGURE 1. Shown here is the block diagram for the 4-port 110GHz N5251A mmWave network analyzer
ments at mmWave frequencies are much based on the N5227A PNA.
simpler. As an example, Figure 2 shows
a power sweep being used to perform a FIGURE 2. This graph illustrates
110 GHz buffer amplifier measurement, the application of a power sweep
gain compression measurement
while also doing a traditional S-parameter
at 77 GHz.
measurement.
Mixer measurements and power spectral
measurements can also be easily made
with this configuration of the N5251A.
Figure 3a shows the PNA performing a LO
power sweep of a 75 to 110 GHz down
converter mixer at a continuous wave of
75 GHz. Power spectral measurements are
made using the PNA's built-in IM spectrum
option. Figure 3b shows the measurement
of the input and output spectrum of a 110
GHz buffer amplifier measured across the
frequency range from 10 MHz to 110 GHz.
FIGURE 3b.
Shown here is
input/output of an
amplifier at 77 GHz.
With the PNA's IM
spectrum option, FIGURE 3a. This S21 plot results while sweeping the LO from
all spectral power -20 to +11 dBm at a mmWave frequency of 75 GHz.
components can be
measured across the
10MHz to 110 GHz
frequency range.
3
mmWave Signal Controlling PC M8190A wideband AWG
Generator and (Could be desktop, laptop or embedded)
MATLAB
Waveform
Analysis Solution Differential IQ AWG to PSG
PSG: E8267D-520-016 (I/Q modulation)
mmWave signal generation and analysis, IF-RF up-converter
Differential IQ
as well as, signal path emulation, is pos- AWG to Scope
Up-converter
MXG1: N5183B -520 (Tx LO)
sible using Keysight's M8190A wideband
arbitrary waveform generator (AWG), DUT
PSG signal generators, PXA/EXA spectrum
Demod
89601B VSA SW
MXG2: N5183B-520 (Rx LO)
analyzers, and high-performance Infiniium Down-converter
Series oscilloscope with the 86901B RF-IF down-converter
vector signal analysis software (Figure 4). Acq'd signal
WARNING : Exi t 89 600 V SA So ftwar e bef ore chang ing i nstru ment setu p
Consider, for example, the evaluation DSA91304A Infiniium oscilloscope
of a transceiver. Testing the transceiver
requires a simulated transmitter and/or
FIGURE 4. This block diagram depicts the overall modulated signal generation and analysis solution
a simulated receiver. Ideally, both should
that can be used for mmWave backhaul measurements and analysis.
be flexible enough to generate real world
distortions on the source side and com-
pensate for them on the sink side. With
the M8190A high-performance arbitrary
waveform generator working at 12 bit and
12 GSa/s or at 14 bit and 8 GSa/s, users
have the ability to create these types of
waveforms to use as a test source. The
vector PSG signal generator acts as an
external I/Q modulator. On the analyzer
side, an Infiniium oscilloscope is used with
its support for up to 63 GHz of real-time
frequency bandwidth. The PXA and/or
EXA with 160-MHz RF analysis bandwidth, FIGURE 5. Analysis of the transceiver produces a 64-QAM constellation with 3 GSymbols/s and a
Q-eye and I-eye diagram on a 86 GHz communication link.
together with a Keysight smart mixer could
also be another choice--depending on
the signal bandwidth and frequency. The
Summary of Results The Power to
test solution also includes software con-
Ongoing advances in mmWave technol-
Accelerate Wireless
sisting of MATLAB support for customized Design and Test
ogy are helping to shift backhauls away
signal creation, Signal Studio support for
from traditional technology and toward
specific signal formats such as LTE, and the Keysight is a leader in wireless test,
more economical, high-capacity E-band
89601B software for signal analysis. focused on the highest-performance
point-to-point links. Unfortunately, the
challenges associated with these links design and test of wireless devices and
During actual measurement of the trans- networks, with application-focused
further complicate an already difficult
ceiver, a signal would first be generated by platforms optimized for existing and
design and test process. Fortunately, the
the M8190A AWG or Signal Studio, emerging standards. Adding to this
N5251A mmWave network analysis solu-
up-converted with a Keysight E8267D optimal R&D and field support, Keysight
tion for component test and the mmWave
vector signal generator and/or external allows engineers to better understand the
signal generation and analysis solution
third-party upconverter, and then transmit- intricacies of the continuously evolving
for testing communication links, are
ted to the Device Under Test (DUT), in this wireless industry so you can accelerate
helping to make these challenges much
case, an 86 GHz link. Next, it would be your development of products.
less formidable. As a result, they are now
down-converted by an external device,
providing today's engineers with a critical
such as a Keysight smart mixer or third-
tool for ensuring the proper operation of
party downconverter, and analyzed by the To learn more about Keysight's
E-band backhaul, and in turn, helping the
Infiniium oscilloscope, or PXA/EXA using suite of test and measurement
technology's continued proliferation.
89601B vector signal analyzer software products please visit:
(Figure 5). www.keysight.com/find/powerofwireless
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