Effective Use of Reverberation Chambers for
DO-160 and Wireless OTA Test Requirements
Yulung Tang
Outline
Short Introduction to Reverberation Chamber
Reverberation Chamber Designing
Reverberation for Wireless
Reverberation for EMC/DO-160
Summary
2
Short Introduction to Reverberation
Conventionally, anechoic chamber is where the antenna
radiated performance testing takes place for its “reflection-free”
environment.
Reflected signals cause measurement errors. Thus, the less
reflections, the better.
Although, there are always reflections to some minor degree,
which can be characterized by site validation tests.
Reflections get
absorbed.
3
Short Introduction to Reverberation
Unintuitively, an environment with a great deal of random reflections
can be used as a test environment for antenna performance testing.
In reverb chamber, we measure the signals from all the directions, No direct path.
Rely on the properties of the chamber as a cavity with multiple
reflections.
Base results on average sampled magnitude of power.
4
Chamber Transfer Function
The main concept for reverb is to characterize the
chamber transfer function / .
The chamber transfer function can be characterized
over time.
by averaging
Thus,
|
|
, assuming Rx and Tx antennas
are perfectly matched.
Chamber Transfer Function can be deduced from
either “wave perspective” or “particle perspective”[ref].
[ref] Reverberation Chambers for Wireless Applications:
http://www.ets-lindgren.com/whitepaper-safetyemc052014
Chamber Transfer Function
The chamber transfer function
/ ) can be deduced* by
using cavity power density (Sc) and antenna effective area (Ae) .
(dBm/m2)
·
(dBm)
Tx
Tx power density
Sc (mW/m2)
Rx effective area
Ae (m2)
Rx
* Aperture Excitation of Electrically Large, Lossy Cavities, David Hill, IEEE Tran. on EMC, 1994 Aug.
Cavity Power Density
Power density is a function of injected transmit power .
Given the transmit power , how much can be generated?
The injected
is not 100% converted into cavity power density
, due to cavity loss. The cavity loss is characterized by its
quality factor Q.
;
is angular frequency;
V
is the cavity energy density;
Finally, c · c is the speed of light
is stored cavity energy.
is the cavity volume.
! " ! "
.
Antenna Effective Area
$!%
&"
We know
Due to the statistical behavior of reverb chamber, the
effective area
is averaged over all incident angles.
In other words, the receive antenna can be regarded as
fully isotropic in the environment of reverb chamber.
That is, ' 1 .
Also, due to polarization mismatch, the effective area is
half in one polarization; and half for the other polarization.
Thus,
!%
)"
Chamber Transfer Function,
/
* "
*%
)"
·
* "
·
*%
)"
*+ ,"% Thus, the chamber transfer function is
*+ ,"% -.
/0
PT
PR
Chamber Transfer Function,
Thus, the chamber transfer function (
!+ ,"% /
) is a
repeatable quantity.
The deduction is based on the ideal case that the cavity
stores the energy uniformly for the given volume.
V implies the cavity is perfectly stirred
statistician uniformity.
It is very important to notice that the ideal chamber
transfer function is independent of the distance between
the two antennas.
The designing of the reverberation chamber is aimed to
achieve the ideal chamber transfer function as much as
possible.
From Particle Perspective
The injected power will not be 100% stored inside the
cavity due to its cavity loss, which is also characterized by
qualify factor Q .
(1)
Also, due to the statistic behavior, the stored energy is
carried out throughout all existing particles.
Thus,
· 1 · (2)
is cavity volume, 1 is spectral mode density,
power.
Combining (1) and (2), we can obtain
is receive
23 .
Spectral Mode Density, 1
Given a cavity of volume V, with three edges of L1, L2 and
L3 , we calculate its spectral mode density.
%
45
7
65
8
4%
7
6%
8
4+
7
6+
λ
2 orthogonal polarizations
The total number of modes is
&
6
6
6
: 5 % + · 9
)
λ λ λ
6 6 6
)"
)
: 5 %+ + +
9
λ
9λ
K
J
;<=;>?@<? · 2 ?B;C;D@EFG@?F;<H7
Thus, the mode density is
1
)"
+
9λ
And the spectral mode density is 1
) + "
9 +
) % "
+
.
1 I .
Chamber Transfer Function,
23 The chamber transfer function is
) % "
The spectral mode density is 1
And
Thus,
/
+
.
.
2:
23 "
L3% M
· + ·
+
,"% +
!+
,"%
Same as the deduction from wave perspective.
From the particle perspective, we can see how
the mode density or particle density can effect the
transfer function.
Outline
Short Introduction to Reverberation
Overview of AMS7000 System
SISO Testing with AMS7000
MIMO Testing with AMS7000
Summary
14
Outline
Short Introduction to Reverberation Chamber
Reverberation Chamber Designing
Reverberation for Wireless
Reverberation for EMC/DO-160
Summary
15
AMS-7000
Wireless Reverb
OTA Chamber
700 MHz – 6 GHz
Portable Platform
External: 2.0m x 1.5m x 1.2m
Working Volume: 0.9m x 0.9m x 0.6m
Support for mobile, tablet, laptop and
phantom
SISO TRP, TIS and Throughput
Measurements
MIMO Throughput Measurements
Direct Correlation to CATL Lab
Results
Faster Test Times
Operates with EMQuest™ Software
Convenient for large DUTs and
complex DUT cable management
Fast System Calibration
Reverberation SISO OTA Testing
method has been accepted by
China standard YD/T 1484.1
What’s in the AMS-7000 Chamber
Tuners - Two tuners placed
vertically and horizontally to
maximize stirred volume.
Turntable - To improve sampling
diversity by adding spatial
(platform) stirring
Rotating Ortho-antenna –
Provides measurement of
multiple polarities at multiple
orientations
Decoupling Partition – Reduces
the direct measurement path
DUT Support - Repeatable DUT
placement to improve accuracy.
Variable Load - RF absorber to
vary the chamber loading and
time domain response.
Reverberation Stirring - Tuners
Two tuners provide the changes in the resonant length
of the chamber in all three dimensions.
These changes in the resonant length introduces the
variety of additional modes.
Tuners can be stepped or stirred continuously at
different speeds independently.
Tuner
Stirring
Reverberation Stirring - Turntable
A turntable is used to support the measurement antenna
and DUT. The speed of the turntable can be varied
independently of the tuners.
This adds stirring and although can provide changes in the
mode structure the main benefit is in position stirring.
The measurement antenna rotates with the tuner with
different speed is another degree of position stirring.
Position
Stirring
Decoupling – Isolation Partition
In reverb, the energy from the Tx antenna ideally couples to
the Rx antenna via the path of multiple reflections.
In reality, there is still certain energy coupled directly from
one to the other.
Adding the partition is to provide additional isolation between
the transmit and receive antennas.
Decoupling
Chamber Loading
We load the chamber with different quantiles of absorbers,
which will in turn adjust the overall fading time constant.
The more loading, the less the time constant, meaning
signals die out faster.
Outline
Short Introduction to Reverberation Chamber
Reverberation Chamber Designing
Reverberation for Wireless
Reverberation for EMC/DO-160
Summary
22
Calibration Setup
Calibration is performed to characterize the
chamber transfer function (fx) by averaging
NO
| | over sufficient samples
|-QR |Q
N
P
fx
|-QR |Q
23
Calibration
Same as range loss, we apply chamber transfer
function as the correction for TRP and TIS.
K Factor
24
Calibration
S11, S22, S12 and S21 were used to calculate G.
With corrections for the mismatch of the transmit and receive the
expanded transfer function becomes :
(<|S21| 2S)
<S|21| 2 >corr = ( − |TS11 >|2)( − |TS22 >|2)
Where the term <|S21| 2 >corr represents both the stirred and unstirred
energy in the chamber.
<|S11| 2 > and <|S22| 2 > represents the reflection coefficients of the
transmit and receive horn antennas in the chamber.
Compare to
*+
UV WV
,"% (=XY , =[Y are efficiencies for RX and TX antennas)
Coupling in the Reverb
The complex S parameters can be used to
measure the existence of bias.
Ideal: expected normally distributed S21
Reality: offset Cluster B
Im
Direct Component ≈ c
Offset
c
A
Cluster
B
Re
Coupling in the Reverb
The unstirred power is represented |<S21> |2
The K Factor = Ratio of Unstirred to Stirred energy
K = Unstirred/Stirred
2
|<S
>
|
21
K = T|S21 \TS21 >|>2
Note that we take the average of S21 to evaluate unstirred
power, but the average of |S21| 2 to evaluate overall chamber
transfer function.
EUT Test Setup – TRP
Both TRP and TIS can be performed with one
single communication tester box.
TRP = fx + cable loss + <Measured Power>
fx
28
EUT Test Setup – TIS
TIS = fx + cable loss + <Measured Sensitivity> normalized
to <RSS>
To speed up the test, only a few sensitivity measurements
are taken, then normalized to the <RSS> curve.
fx
29
Comparison btw Anechoic & Reverb
GSM850
GSM900
GSM1800
GSM1900
WCDMA Band1
WCDMA Band8
CDMA2K BC0
Anechoic
AMS7000
Delta
Anechoic
AMS7000
Delta
25.60
27.51
28.72
28.81
28.57
28.67
26.80
26.66
26.57
27.37
27.82
27.48
21.24
21.00
20.86
20.27
20.25
19.79
19.90
19.94
21.31
25.57
27.45
30.34
29.09
29.95
28.73
26.89
26.81
26.28
28.05
28.67
28.88
21.66
21.22
20.20
21.39
21.53
18.60
20.76
20.90
21.69
0.03
0.07
-1.62
-0.28
-1.38
-0.05
-0.09
-0.15
0.30
-0.69
-0.86
-1.41
-0.42
-0.22
0.66
-1.12
-1.28
1.19
-0.86
-0.96
-0.38
-105.99
-105.27
-104.81
-105.64
-105.64
-105.40
-103.52
-106.31
-104.92
-107.61
-107.27
-106.99
-104.85
-106.47
-105.03
-107.00
-108.02
-107.12
-106.97
-106.71
-105.23
-0.35
0.37
0.59
-107.07
1.02
-105.61
-107.47
-107.32
-107.39
-105.66
-106.05
0.69
-0.20
-0.85
0.63
1.05
30
MIMO Testing with Reverberation
There are ways to test MIMO devices in
reverberation chambers.
We can simply look at two main setups.
Reverberation system without channel emulation.
Reverberation system with channel emulation.
Either methods are intended to create fading
environments.
MIMO without CE
The Reverb is a simple uniform cavity with limited spatial differentiation.
Time response is based on cavity losses.
Replicating a real world profile is approximate.
Temporal differentiation can be improved by adding the channel emulator
into the test system.
MIMO w/o CE – WiFi Throughput
AP as the comm tester.
Vaunix digital attenuators.
Iperf to measure thruput.
WiFi
AP IPERF setup
Coax
Coax
Coax
M4
M4
Ethernet
Coax
USB
AMS-7000
33
MIMO w/o CE – LTE CA Throughput
Four inputs = 2x2 MIMO for 2 carriers
PCC and SCC are measured
Separately.
34
MIMO with CE – PDP
RC + CE SCME Uma
Ref: CTIA Certification Program Working Group Contribution, MOSG150104
35
MIMO with CE – Rayleigh Fading
RC + CE SCME Uma
Measured Rayleigh P robability Density (probability = 10^y)
Rayleigh Probability Density Function
Rayleigh CDF Function Rayleigh CDF Theory
0
-0.5
-1
-1.5
-2
-2.5
-3
-30
-25
-20
-15
-10
Power (dB)
-5
0
5
Ref: CTIA Certification Program Working Group Contribution, MOSG150104
10
36
Outline
Short Introduction to Reverberation Chamber
Reverberation Chamber Designing
Reverberation for Wireless
Reverberation for EMC/DO-160
Summary
37
Copyright 2006-2013, ETS-Lindgren, Inc.
About DO-160
DO-160, Environmental Conditions and Test Procedures for
Airborne Equipment, prepared by RTCA SC135
Current ver. DO-160G (Dec. 2010), superseding F ver. (2007)
5 years before migrating to the next H version.
Tests specified in DO-160G are typically performed to meet
FAA (Federal Aviation Administration) regulations, covering
electronic or electrical equipment installed on commercial
aircraft.
Tests and test levels/limits in DO-160G are applicable virtually
to most types of aircraft, such as business jets, helicopters, as
well as the newest airliners from Boeing and Airbus.
The revision of DO-160G is coordinated with EU sister org to
RTCA, EUROCAE. As a result, European version of DO160G, ED-14G is identical to DO-160G.
Copyright 2006-2013, ETS-Lindgren, Inc.
About DO-160
There are 26 sections in DO-160G.
The first three sections covering basic purpose and definitions are
referenced in all the other sections.
Section 1: Purpose and Applicability
Section 2: Definition of Terms
Section 3: Condition of Tests
Section 15 to 23 and Section 25 cover EMC tests.
Section 15: Magnetic Effect
Section 16: Power Input
Section 17: Voltage Spike
Section 18: Audio Frequency Conducted Susceptibility – Power Inputs
Section 19: Induced Signal Susceptibility
Section 20: Radio Frequency Susceptibility (Radiated and Conducted)
Section 21: Emission of Radio Frequency
Section 22: Lighting Induced Transient Susceptibility
Section 23: Lighting Direct Effects
Section 25: Electrostatic Discharge (ESD)
Copyright 2006-2013, ETS-Lindgren, Inc.
Section 20: Radio Freq RS and CS
Test Purpose/Requirements:
Susceptibility tests to determine whether the EUT can operate as
required when the EUT and its interconnecting cables are exposed to
Radio Frequency interferences.
Signals of Continuous Wave (CW), Square Wave AM (SW) and Pulse
Modulated (PM), are required.
Interconnecting cables are at least 3.3m in length, while power leads
are no more than 1m.
CS from 10kHZ to 400MHz, and RS from 100MHz to 18GHz.
RS can be done either in anechoic chamber or reverberation chamber.
Conducted Susceptibility is similar to MIL-STD-461F CS114.
Radiated Susceptibility is similar to MIL-STD-461F RS103.
Applicable Equipment Categories:
7 CS categories and 10 RS categories. Category S is the least severe
at 1 V/m while Category L is the most severe at levels up to 7200 V/m.
Intent of RTCA DO-160, Section 20,
Reverberation Testing
The purpose of the RTCA-D-160, Section 20 is to verify
the equipment under test (EUT) ability to withstand an
electromagnetic environment.
Uniformity requirement: Isotropic Field Conditions
Frequency Point Test Criterion: Table 20-4
Nine Tuner Positions for the Unloaded Chamber Calibration
The reverberation method is an alternative method to take
advantage of the properties of a resonant cavity enabling
the desired field severity with cost effective RF amplifiers
(lower rated amplifiers to achieve the equivalent field
levels as compared to anechoic or semi-anechoic method.
41
RTCA DO-160, Section 20, Reverberation Testing Isotropicity
DO-160 defines the
isotropic field as
the field probes: X,
Y, Z and Composite
axis standard
deviation to comply
with the Figure 2011.
42
RTCA DO-160, Section 20, Reverberation Testing –
Frequency Points
DO-160 Test Criterion – Table 20-4
43
RTCA DO-160, Section 20, Reverberation Testing –
Probe Positions
DO-160 Calibration
Setup
Notes were not included
with the figure
44
Measured Results
Test frequency starting from 300MHz
3.4m x 2.7m x 2.44m, and 6dB loading
45
Estimation of Required Power
The Ē field versus input power can be estimated from:
A. Field converted to required power
( Used in the standard, IEC 61000-4-21 )
B. Quality Factor
1
1
=
QT Qw + Qa
C. And once again, the chamber transfer function.
PAv Re c
Q.Pin .η 2 λ3
=
16.π 2V
Summary
Reverb Method is an alternative method of performing
OTA TIS, TRP, MIMO TP, and DO-160 RS
measurements.
The theoretical background has been quickly introduced.
The main concept of the reverberation chamber
designing is the realization of the ideal chamber transfer
function.
For wireless, the reverberation methodology has gained
great intension recently in MIMO OTA testing.
For EMC, its nature of using less power for generating
high field makes the reverberation chamber the ideal
solution for high field test requirement, such as DO160
cat L.
47
Thank You