PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
MILLIMETER WAVE TEST PROCEDURES
Measurement Instrumentation:
Spectrum Analyzer
External Harmonic Mixer Set, covering the necessary frequency range
High Frequency Standard Gain Horn Set, covering the necessary
frequency range
Diplexer for analyzer, if required
External L.O. Amplifier, if required
Variable Voltage Supply
Optional: Non-conductive antenna adjustment structure (mast)
Optional: High-pass and Band pass filters
Note: the calibration of equipment operating at the frequencies under
investigation may prove to be problematic. Routine calibration of
the equipment at lower frequencies may be considered sufficient by
the relevant regulatory bodies (e.g., the FCC). These regulatory
bodies, as well as the measurement equipment manufacturers and
calibration labs, should be consulted with respect to this topic.
General Information:
I. A radiated method of measurements in order to demonstrate
compliance with the various regulatory requirements has been chosen
in consideration of test equipment availability, the limitations
of many external harmonic mixers, and certain regulatory requirements.
A conducted method of measurement could be employed for certain tests
if EUT and mixer waveguides both are accessible and of the same type
(WG number) and if waveguide sections and transitions can be found.
Another potential problem is that the peak power output of devices
operating under Sections 15.253 and 15.255 may exceed the +20 dBm
input power limit of many commercially available mixers. For these
reasons a radiated method is preferred.
II. Extreme caution shall be used when measuring the field strength
of emissions from mm-wave devices. The beamwidths are extremely
narrow; thus very small adjustments to the position of the test
antennas are required in order to ensure that the measuring
instrumentation is within the maximum beam of the transmitted signal.
As a result, it is recommended that handheld field strength
measurements be made (i.e., the test antenna (horn) is held in the
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
hand). Caution shall be taken to reduce the possibility of the hand,
or body, affecting the measurement. Because horn antennas, with
large front-to-back ratios, will be used, holding them well behind
the flange will greatly reduce the possibility of adversely affecting
the measurements. When care is taken, measurements made with this
procedure have been shown to be both accurate and repeatable. Caution
shall also be taken to reduce the possible overloading of the
measuring instrumentation - it may be desirable to make use of high
pass and/or band pass filters for certain measurements.
III. In order to properly measure either the peak output power or
peak power density, the Resolution Bandwidth (RBW) of the measuring
instrumentation should be greater than the Emission Bandwidth
(EBW)(see definition below) of the signal under investigation. If
the EUT is capable of disabling the modulation, such that it transmits
an unmodulated carrier, then measurements for peak output power and
peak power density should be made in this mode. This is the preferred
method. However, if the modulation cannot be disabled, then
measurements must be made on the modulated signal. Since Spectrum
Analyzers do not typically have RBW’s of sufficient width to encompass
the EBW, this method of measurement involves either measuring
sections of the emission and totaling those sections, or measuring
the peak of the emission with a readily available RBW setting (e.g.,
1 MHz) and then mathematically calculating the total peak level over
the entire emission bandwidth by adding a correction factor derived
from 10log(EBW/RBW). Measurements must be made during the transmit
interval.
Note: because the FCC currently has reservations about the former
method, due to potentially wide variances in results based on
instrument settings, the latter method should be employed until the
issue is resolved. This correction tends to overestimate the actual
peak levels, and thus is considered acceptable by the FCC at this
time.
The emission bandwidth (EBW) is defined as the width of the signal
between two points, one below the carrier center frequency and one
above the carrier center frequency, outside of which all emissions
are attenuated at least 26 dB below the maximum level of the modulated
carrier (from 47 C.F.R. Section 15.403(c)).
IV. The peak output power of the EUT may be calculated from the
measured peak field strength, if the gain of the EUT’s radiating
element is known, using the following equation:
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P = (E × d)2
30G
where
P is the
E is the
d is the
meters
G is the
power, in Watts
measured peak field strength, in Volts/meter
distance at which the measurement was made, in
numeric gain of the radiating element
If the gain of the radiating element is not known, then either the
Effective Radiated Power (ERP) or the Effective Isotropic Radiated
Power (EIRP) may be calculated from the measured peak field strength,
by using either G = 1.64 or G = 1, respectively, in the above equation.
V.
The peak power density of an emission may be calculated from
its measured peak field strength using the
following equation:
Pd = P t
(4πd2)
where
Pd is the power density, in Watt/Meters2
Pt is the EIRP, in Watts
d is the measurement distance, in meters
Conversely, the power density limits specified in the FCC Rules may
be converted mathematically to equivalent field strength values,
against which the measured field strength of the EUT’s emissions
may be directly compared, using the following equation:
Pd = E2
377
where
Pd is the power density limit at a specific distance, in
Watt/Meters2
E is the equivalent field strength at that specific
distance, in Volts/meter
377 is free space impedance, in Ohms
Solving for the equivalent field strength limit:
E = (377 × Pd)½
VI. The average output power levels and the average power density
levels may be mathematically derived from the measured peak levels,
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
in the case of a pulsed emission, based on the application of a duty
cycle correction factor, derived from:
20log(ton/T)
where
ton is the total “on” time during a transmission burst,
in seconds
T is the period between transmission bursts, in seconds
If the emission under investigation is not pulsed, then the average
levels may be measured by using a video filtering technique (i.e.,
VBW << RBW).
VII. Care should be taken to ensure that measurements are made,
whenever possible, in the far field, so that a linear distance
attenuation factor (20 dB/decade) may be applied. At the frequencies
under investigation, the distance from the radiating element of the
EUT to the edge of the far field may be calculated from the following
equation:
r = 2 × ℓ2
λ
where
r is the distance from the radiating element of the EUT
to the edge of the far field, in meters
ℓ is the largest dimension of both the radiating element
and the test antenna (horn), in meters
λ is the wavelength of the emission under investigation
(300/f(MHz)), in meters
If measurement practicalities or system sensitivity limitations
require that the measurement be made in the near field, then an inverse
squared distance attenuation factor (40 dB/decade) shall be applied
from the point of measurement to the distance calculated as the edge
of the far field (if it is less than the distance at which the specific
limit (to which compliance is being tested) is specified), after
which a linear distance attenuation factor shall be applied out to
the distance at which the specific limit (to which compliance is
being tested) is specified (e.g., 3 meters).
VIII. An external mixer may generate false images. Care should
be taken to ensure that any emission measured by the Spectrum Analyzer
does indeed originate in the EUT. Most Spectrum Analyzers have a
Signal Identification feature that should be utilized if there is
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
any question as to the source of the emission under investigation
(i.e., it is not the fundamental emission, or a harmonic falling
precisely at the correct frequency). In addition, if the fundamental
emission overloads the front end of the Spectrum Analyzer, it is
likely to result in harmonic distortion. In such a case, a band
pass or high pass filter should be used to prevent the measurement
of false harmonic levels.
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
General Emission Bandwidth Measurement Procedures
Test Set-Up
Figure 1
Arrange the EUT and test equipment as shown in Figure 1.
I.
Use the following Spectrum Analyzer settings:
Span = approximately 2 to 3 times the EBW, centered on the carrier
frequency
RBW ≈ 1% of the EBW (if possible - if the EBW is greater than 100
times the largest available RBW, then use that setting)
VBW ≥ RBW
Sweep = auto
Detector function = peak
Trace = max hold
II. The EUT should be transmitting at its maximum data rate. Allow
the trace to stabilize.
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
III. Use the marker-to-peak function to set the marker to the peak
of the emission. Use the marker-delta function to measure 26 dB
down one side of the emission.
IV. Reset the marker-delta function, and move the marker to the
other side of the emission, until it is (as close as possible to)
even with the reference marker level. The marker-delta reading at
this point is the 26 dB bandwidth of the emission.
V. If this value varies with different modes of operation (e.g.,
data rate, modulation format, etc.), repeat this test for each
variation.
General Field Strength Measurement Procedures
Arrange the EUT and test equipment as shown in Figure 1. The distance
at which various limits are specified in the FCC Rules is 3 meters,
however, it is strongly recommended that closer measurement distances
be utilized, as permitted by Section 15.31(f)(1) (see General
Information VII, above).
I. Set Spectrum Analyzer RBW, VBW, span, etc., to the proper values.
Note these values. Enable 2 traces, one set to “clear write”, the
second set to “max hold”.
II. Begin handheld measurements with the test antenna (horn) at
a distance of 1 meter from the EUT (see General Information VII,
above), in a horizontally polarized position. Slowly adjust its
position, entirely covering the plane 1 meter from the EUT.
Observation of the 2 active traces on the Spectrum Analyzer will
allow refined horn positioning at the point(s) of maximum field
intensity.
III. Repeat (II) with the horn in a vertically polarized position.
IV. If the emission cannot be detected at 1 meter, reduce the RBW
in order to increase system sensitivity. Note the value. If the
emission still cannot be detected, move the horn closer to the EUT,
noting the distance at which a measurement is made.
V. Note the maximum level indicated on the Spectrum Analyzer. Adjust
this level, if necessary, by the conversion loss of the external
mixer used, at the frequency under investigation (cable loss should
also be measured, but will probably prove to be negligible, as the
external mixer has mixed down the signal to a (relatively) low
frequency before it is conducted down the cable to the Spectrum
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
Analyzer). Calculate the field strength of the emission at the
measurement distance from the following equation (FCC OST 40):
E = 2π
λ
where
(120 P/G)
½
E is the field strength of the emission at the measurement
distance, in Volts/meter
P is the maximum, adjusted level indicated on the Spectrum
Analyzer, in Watts
λ is the wavelength of the emission under investigation
(300/f(MHz)), in meters
G is the numeric gain of the test antenna (horn)
VI. Based on the distance at which the measurement was made and
the calculated distance to the edge of the far field, determine the
appropriate distance attenuation factor (see General Information
VII, above). Apply this factor to the calculated field strength
in order to determine the equivalent field strength at the distance
at which the regulatory limit is specified. Based on the RBW used
to make the measurement, the measured EBW of the emission under
investigation, and the gain of the transmitting element, calculate
the power density and peak output power of the emission/EUT (see
General Information III and IV, above), and, possibly, the average
power density and average output power (see General Information VI,
above). Compare to the appropriate limit(s)(see General Information
V, above). If it is a pulsed emission, apply the calculated duty
cycle correction factor to these levels to determine the average
power density and average output power (see General Information VI,
above).
VII. Repeat (I) - (V) for every emission that must be measured,
up through the required frequency range of investigation (as
specified by the regulatory requirements to which compliance is being
tested), in all operating configurations of which the EUT is capable
(e.g., forward-looking vehicle radar systems at rest and in motion
(Sections 15.253(b) and (c))).
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
General Frequency Stability Measurement Procedures
Test Set-Up
temperature chamber
10 - 100 cm mixer w/horn
EUT
LO pre-amp
diplexer
variable voltage supply
spectrum analyzer
V
FIGURE 2
I. Arrange EUT and test equipment as shown in Figure 2. The external
mixer may be placed inside the temperature chamber only if its
frequency drift characteristics v temperature are known and can be
factored in, otherwise, the mixer should be placed outside the chamber
in front of the temperature chamber door, and the chamber door opened
for each reading.
II. With the EUT at ambient temperature (approximately 25 °C) and
voltage source set to the EUT’s nominal operating voltage (100%),
record the spectrum mask of the EUT emission on the Spectrum Analyzer.
III. Vary EUT power supply between 85% - 115% of nominal, and record
the frequency excursion of the EUT emission mask.
IV. Set the power supply to 100% nominal setting, raise EUT operating
temperature to 50 °C. Record the frequency excursion of the EUT
emission mask.
V.
Repeat step 4 above at each 10 °C step down to -20 °C.
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
The EUT frequency excursion must remain within the frequency ranges
called out in the appropriate regulatory standards.
Note: The test distance is chosen to insure that input to the mixer
is less than the rated maximum, using the relationship between
transmit power, received power, transmit antenna gain, receive
antenna gain, and path loss:
Pr, dBm = Pt, dBm +Gt, dBi + Gr, dBi – Lp, dB
where
Lp = -27.6dB
*** Included below, for reference, are checksheets provided by the
FCC during TCB training classes intended for use during the review
of mmWave devices seeking authorization under Sections 15.253 or
15.255.
Vehicle Radar Systems (47 C.F.R. Section 15.253)
_
Because mm wave devices are not categorically excluded from RF
exposure requirements, they will not be designated under this
scope of accreditation at this time.
15.253(a):
___ Does the EUT meet the definition of a vehicle-mounted field
disturbance sensor, as its primary mode of operation, based on the
technical description?
15.253(b):
___ Were acceptable test procedures and instrument settings used
to measure the radiated power density of the fundamental emission?
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
___ Does the measured power density comply with the appropriate
limit, as determined by the frequency band of operation, the position
of the EUT with respect to the vehicle, and whether or not the vehicle
is in motion?
15.253(c):
___ Do all out-of-band emissions meet the definition of spurious
emissions?
15.253(c)(1):
___ Were acceptable test procedures and instrument settings used
to measure unwanted radiated emission levels below 1 GHz?
___ Do the measured unwanted radiated emission levels comply with
the Section 15.209 field strength limit?
15.253(c)(2):
___ Were acceptable test procedures and instrument settings used
to measure the radiated power density of spurious emissions?
___
Was the correct frequency range investigated?
___ Do the measured spurious power densities comply with the
appropriate limit, as determined by the frequency band of operation,
the frequency of the spurious emission, and the position of the EUT
with respect to the vehicle?
15.253(d):
___ Were acceptable test procedures and instrument settings used
to determine the peak levels of the measured radiated power densities
of all emissions?
___ Do the peak levels of the measured power densities comply with
the limit of Section 15.35(b)?
15.253(e):
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
___ Was an acceptable test procedure was used to measure frequency
stability?
___ Does the measured frequency stability data indicate that the
fundamental emission will be maintained within the band of operation
under all conditions of normal operation, as specified in the user’s
manual?
15.203 and 15.204:
___
Does the EUT comply with these Sections?
_
Test procedures for mm wave devices are, as of yet, undocumented.
When a “recommended” test procedure is released by the OET Lab,
or by some industry group, guidance will be provided as to what
is considered “acceptable test procedures”.
_
Convert power density limits to EIRP levels, then to equivalent
field strengths at the measurement distance. Measured field
strengths may then be compared to these values.
_
Determine whether measurements are made in the far field or not,
so that a proper distance correction factor may be applied.
_
In re 15.253(d)- a test or a calculation may be used to determine
the peak level of the emission, as determined by the emission
characteristics.
_
In re 15.253(e)- a plot of the emission at the bandedge, with
the EUT tuned to a bandedge channel, may be required for devices
that do not utilize a standard carrier which may be measured.
mm-Wave Systems - Section 15.255
_
Because mm wave devices are not categorically excluded from RF
exposure requirements, they will not be designated under this
scope of accreditation at this time.
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
15.255(a):
___ Does the EUT operate in a manner which is not excluded by this
Section, based on the technical description, user’s manual, or any
advertising literature which has been submitted?
15.255(b)(1) and (2):
___ Were acceptable test procedures and instrument settings used
to measure the peak radiated power density and the occupied bandwidth
of the fundamental emission?
___ Were acceptable methods used to calculate the average radiated
power density of the fundamental emission?
___ Does the measured peak power density comply with the appropriate
limit, as determined by the type of operation, the occupied bandwidth,
and the frequency of the emission?
___ Does the calculated average power density comply with the
appropriate limit, as determined by the type of operation, the
occupied bandwidth, and the frequency of the emission?
15.255(b)(3):
___ Were acceptable test procedures and instrument settings used
to measure the peak output power and the peak radiated power density
of the fundamental emission?
___ Do the measured peak output power and peak radiated power density
comply with the appropriate limit?
15.255(c)(1):
___ Do all out-of-band emissions meet the definition of spurious
emissions?
15.255(c)(2):
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
___ Were acceptable test procedures and instrument settings used
to measure unwanted radiated emission levels below 1 GHz?
___ Do the measured unwanted radiated emission levels comply with
the Section 15.209 field strength limit?
15.255(c)(3):
___ Were acceptable test procedures and instrument settings used
to measure the radiated power density of spurious emissions?
___
Was the correct frequency range investigated?
___ Do the measured spurious power densities comply with the 90
pW/cm2 limit?
15.255(c)(4):
___
Does the EUT comply with Section 15.215(b)?
15.253(d):
___ Are all emissions in the 59.0-59.05 GHz band either spurious,
or related to a publicly accessible coordination channel?
15.253(e):
___ Were acceptable test procedures and instrument settings used
to measure the peak output power and emission bandwidth?
___ Does the measured peak output power comply with the appropriate
limit, as determined by the emission bandwidth?
15.255(f):
___ Was an acceptable test procedure was used to measure frequency
stability?
___ Does the measured frequency stability data indicate that the
fundamental emission will be maintained within the band of operation
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
under all conditions of normal operation, as specified in the user’s
manual?
15.255(h):
___ Does the applicant state that the EUT will not be equipped with
external phase-locking inputs that permit beam-forming arrays to
be realized?
15.255(i):
___ If applicable, does the applicant state that the EUT transmits
the required identification feature?
___ Does the required identification feature contain all of the
necessary information?
___ Is a method specified whereby interested parties can obtain
sufficient information, at no cost, to enable them to fully detect
and decode this transmitter identification information?
15.203, 15.204, and 15.207:
___
Does the EUT comply with these Sections?
_
Test procedures for mm wave devices are, as of yet, undocumented.
When a “recommended” test procedure is released by the OET Lab,
or by some industry group, guidance will be provided as to what
is considered “acceptable test procedures”.
_
Convert power density limits to EIRP levels, then to equivalent
field strengths at the measurement distance. Measured field
strengths may then be compared to these values.
_
Determine whether measurements are made in the far field or not,
so that a proper distance correction factor may be applied.
_
In re 15.255(f)- a plot of the emission at the bandedge, with
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PROCEDURE FROM TCB COUNCIL MEMBERS – ACCEPTED BY FCC LAB
the EUT tuned to a bandedge channel, may be required for devices
that do not utilize a standard carrier which may be measured.
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