SIST EN 60835-3-2:2002
(Main)Methods of measurement for equipment used in digital microwave radio transmission systems -- Part 3: Measurements on satellite earth stations -- Section 2: Antenna
Methods of measurement for equipment used in digital microwave radio transmission systems -- Part 3: Measurements on satellite earth stations -- Section 2: Antenna
Gives definitions and methods of measurement of the electrical characteristics of satellite earth-station antennas for frequencies above about 1 GHz. The methods are applicable to reflector type antennas for digital and analog signal transmission.
Meßverfahren für Geräte in digitalen Mikrowellen-Funkübertragungssystemen -- Teil 3: Messungen an Satelliten-Erdfunkstellen -- Hauptabschnitt 2: Antenne
Méthodes de mesure applicables au matériel utilisé pour les systèmes de transmission numérique en hyperfréquence -- Partie 3: Mesures applicables aux stations terriennes de télécommunications par satellite -- Section 2: Antenne
Traite des définitions et des méthodes de mesure applicables aux caractéristiques électriques des antennes des stations terriennes de liaison par satellite dans les gammes de fréquences au-dessus d'environ 1 GHz. Ces méthodes s'appliquent aux antennes de type réflecteur assurant la transmission de signaux analogues et numériques.
Methods of measurement for equipment used in digital microwave radio transmission systems - Part 3: Measurements on satellite earth stations - Section 2: Antenna (IEC 60835-3-2:1995)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-2002
Methods of measurement for equipment used in digital microwave radio
transmission systems - Part 3: Measurements on satellite earth stations - Section
2: Antenna (IEC 60835-3-2:1995)
Methods of measurement for equipment used in digital microwave radio transmission
systems -- Part 3: Measurements on satellite earth stations -- Section 2: Antenna
Meßverfahren für Geräte in digitalen Mikrowellen-Funkübertragungssystemen -- Teil 3:
Messungen an Satelliten-Erdfunkstellen -- Hauptabschnitt 2: Antenne
Méthodes de mesure applicables au matériel utilisé pour les systèmes de transmission
numérique en hyperfréquence -- Partie 3: Mesures applicables aux stations terriennes de
télécommunications par satellite -- Section 2: Antenne
Ta slovenski standard je istoveten z: EN 60835-3-2:1996
ICS:
33.060.30 Radiorelejni in fiksni satelitski Radio relay and fixed satellite
komunikacijski sistemi communications systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
NORME CEI
INTERNATIONALE IEC
60835-3-2
INTERNATIONAL
Première édition
STAN
DARD
First edition
1995-12
Méthodes de mesure applicables au matériel
utilisé pour les systèmes de transmission
numérique en hyperfréquence
Partie 3:
Mesures applicables aux stations terriennes
de télécommunications par satellite
Section 2: Antenne
Methods of measurement for equipment used in
digital microwave radio transmission systems
Part 3:
Measurements on satellite earth stations
Section 2: Antenna
© IEC 1995 Droits de reproduction réservés — Copyright - all rights reserved
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835-3-2 © IEC:1995 - 3 -
CONTENTS
Page
FOREWORD 5
Clause
1 Scope 7
2 Normative references 7
3 Definitions 9
4 Conditions of measurement 19
5 Antenna gain 21
5.1 General considerations 21
5.2 Method of measurement 21
5.3 Presentation of results 31
5.4 Details to be specified 33
6 Antenna pattern 33
6.1 General considerations 33
6.2 Terrestrial bore-sight pattern measurements 35
6.3 Measurement of antenna pattern via satellite 39
6.4 Antenna monopulse pattern 43
6.5 Measurement accuracy 45
6.6 Presentation of results 45
6.7 Details to be specified 47
7 Polarization 47
7.1 Calculation of the polarization efficiency 47
7.2 Cross-polarization discrimination (XPD) 49
7.3 Two-port discrimination of dual polarized frequency re-use antennas 57
7.4 Presentation of results 67
7.5 Details to be specified 67
8 Receive figure of merit (G/T) 67
9 Antenna noise temperature 67
9.1 General considerations 67
9.2 Method of measurement 69
9.3 Presentation of results 71
9.4 Details to be specified 71
10 Antenna return loss 71
10.1 Method of measurement 71
10.2 Presentation of results 71
10.3 Details to be specified 71
11 Transmit-receive isolation 71
11.1 Method of measurement 71
11.2 Presentation of results 73
11.3 Details to be specified 73
Figures 75
Annex A - Bibliography 105
835-3-2 ©
IEC:1995 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR EQUIPMENT USED IN
DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS -
Part 3: Measurements on satellite earth stations -
Section 2: Antenna
FOREWORD
1)
The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2)
The formal decisions or agreements of the IEC on technical matters, express as nearly as possible an
international consensus of opinion on the relevant subjects since each technical committee has
representation from all interested National Committees.
3)
The documents produced have the form of recommendations for international use and are published in the
form of standards, technical reports or guides and they are accepted by the National Committees in that
sense.
4)
In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5)
The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6)
Attention is drawn to the possibility that some of the elements of this International Standard may be the
subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 835-3-2 has been prepared by sub-committee 12E: Radio
relay and satellite communication systems, of IEC technical committee 12: Radio-
communications.
The text of this standard is based on the following documents:
FDIS Report on voting
12E/247/FDIS
12E/262/RVD
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
Annex A is for information only.
835-3-2 © IEC:1995 - 7 -
METHODS OF MEASUREMENT FOR EQUIPMENT USED IN
DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS -
Part 3: Measurements on satellite earth stations -
Section 2: Antenna
1 Scope
This section of IEC 835-3 gives definitions and methods of measurement of the electrical
characteristics of satellite earth-station antennas for frequencies above about 1 GHz.
The methods are applicable to reflector type antennas for digital and analog signal
transmission.
The purpose of the measurements is mainly to confirm that earth-station antenna
performance complies with the requirements generally given by the satellite system provider
based on the Radio Regulations and applicable international standards such as ITU-R
Recommendation S.733-1 and the CCIR Recommendations 465-4, 580-3, 731 and 732.
The measurement procedures are often prescribed by international satellite service
organizations.
Measurements are performed under the condition that all antenna subsystem equipment is
connected unless otherwise stated.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this section of IEC 835-3. At the time of publication, the
editions indicated were valid. All normative documents are subject to revision, and parties
to agreements based on this section of IEC 835-3 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated
below. Members of IEC and ISO maintain registers of currently valid International
Standards.
IEC 50(60): 1970, International Electrotechnical Vocabulary (lEV) - Chapter 60: Radio-
communications
IEC 50(712): 1992, International Electrotechnical Vocabulary (lEV) - Chapter 712:
Antennas
IEC 835-1-2: 1992,
Methods of measurement for equipment used in digital microwave
radio transmission systems - Part 1: Measurements common to terrestrial radio-relay
systems and satellite earth stations - Section 2: Basic characteristics
IEC 835-3-4: 1993, Methods of measurement for equipment used in digital microwave
radio transmission systems - Part 3: Measurements on satellite earth stations - Section 4:
Low noise amplifier
835-3-2 © IEC:1995 - 9 -
IEC 835-3-7: 1995,
Methods of measurement for equipment used in digital microwave
radio transmission systems - Pa rt
3: Measurements on satellite earth stations - Section 7:
Figure-of-merit of receiving system
ITU-R S.465-5: 1993,
Reference earth-station radiation pattern for use in coordination and
interference assessment in the frequency range from 2 to about 30 GHz
ITU-R S.580-4: 1993,
Radiation diagrams for use as design objectives for antennas of
earth stations operating with geostationary satellites
ITU-R S.731: 1992,
Reference earth-station cross-polarized radiation pattern for use in
frequency coordination and interference assessment in the frequency range from 2 to
about 30 GHz
ITU-R S.732: 1992,
Method for statistical processing of earth-station antenna side-lobe
peaks
ITU-R S.733-1: 1993,
Determination of the G/T ratio for earth stations operating in the
fixed-satellite service
3 Definitions
For the purpose of this section of IEC 835-3, the following definitions apply.
For definitions of the general terms used in this section, reference should be made to
IEC 60 and IEC 50(712). In case of conflict, the definition given here takes precedence.
3.1 Antenna subsystem
An antenna subsystem is that pa
rt of the earth-station communication equipment
which comprises the antenna and the feed network, as shown in figure 1. The antenna
considered in this section is a reflector antenna consisting of the main reflector, secondary
reflectors, if any, and the primary radiator. The feed network usually may contain
frequency diplexers, transmit reject filters, hybrids, and a polarization diplexer (orthomode
transducer) or a polarizer, to which are connected the waveguide feeders to the transmit
and receive multiplexing and switching equipment and to the tracking receiver. The
antenna subsystem may also include provisions for pointing the antenna. The terminals of
the antenna subsystem should be specified for a given measurement.
3.2 Antenna po (antenna terminal)
rt
An antenna port may be defined at any interface of the feed network where r.f. measure-
ments are usually made. To separate antenna and feed network properties, sometimes the
feed horn waveguide flange is defined as the antenna po
rt, but in that case additional
measurements including the whole feed network may be important.
835-3-2 © IEC:1995 - 11 -
3.3 Antenna gain
The gain of a transmitting antenna is the ratio of the power flux density produced in the
far-field region, in a given direction and at a given distance from the antenna, to the power
flux density which would be produced at the same distance by a loss-free isotropic
antenna which accepts the same power from the same source as the antenna under test.
Ae
For receiving antennas, a definition of gain can be derived from that of effective area
(see 3.5) by the equation:
4It Ae
G- (3-1)
^2
where ? is the wavelength.
For the same antenna used for transmitting and receiving on the same frequency and with
the same terminals, the gains defined above for transmitting and for receiving will be
equal, because of the reciprocity of the antenna.
Theoretically, gain does not include losses arising from polarization mismatches and from
impedance mismatches at the gain-reference plane of the feed system. However, in
practical measurements these effects normally are very small and may then be neglected.
of the antenna gain (pa rtial
Nevertheless it may sometimes be necessary to give that pa rt
gain as defined in IEV 712-02-44) corresponding to a specified polarization. In this
case the reference polarization should be indicated for example by "right-hand circular
ial gain is the gain
polarization gain" or "horizontal linear polarization gain". The pa rt
multiplied with the polarization efficiency corresponding to the specified polarization.
It may be measured, for example, with a bore-sight antenna radiating with the specified
polarization towards the antenna under test. If the antenna polarization is split into two
hogonal components (which is always possible), then the antenna gain is the sum of the
ort
partial gains corresponding to the polarizations of the components.
NOTE – Unless otherwise specified, gain will be defined as the gain in bore-sight direction (maximum gain).
3.4 Antenna pattern
The antenna (radiation) pattern is an angular plot of the signal strength radiated from or
. It normally corresponds to co- or
received by the antenna with respect to a specified po rt
cross-polarization.
3.5 Effective area of an antenna
For a specified direction, the effective (active) area of an antenna is the ratio between the
power delivered to a matched load at the antenna terminals and the power flux density in
a polarization matched plane wave incident on the antenna.
NOTE – The effective area is normally determined by a gain measurement using equation (3-1).
835-3-2 © IEC:1995 - 13 -
3.6 Antenna efficiency
The antenna efficiency tt is the ratio of the maximum effective area to the projected area
A of the antenna in a plane perpendicular to the direction of maximum radiation. The
maximum effective area is related to the maximum gain G as defined in 3.3. So:
(3-2)
tl —
A = 4^c^A
where X is the wavelength.
NOTE - The reference plane for the efficiency should be the same as for the gain.
3.7 Gain-reference antenna
An antenna with precisely known gain. The gain of the antenna under test may be
compared with the gain of a reference antenna by switching between these antennas. The
reference antenna is often much smaller than the antenna under test.
3.8 Bore-sight direction
For tracking antennas, the bore-sight direction is the direction of the tracking null. For
non-tracking directive antennas, the bore-sight direction is the direction of the beam
maximum.
NOTE - Bore-sight measurements are measurements with an ancillary antenna (bore-sight antenna) usually
mounted on a tower (bore-sight tower), located at the bore-sight direction.
Antenna polarization
3.9
The antenna polarization is the polarization of the electric far-field in a specified direction
of a radiating antenna. It is also that polarization of a plane wave, incident from a given
direction and having a given power flux density, which results in maximum available power
at the antenna terminals.
NOTE - If not otherwise defined, the specified direction is the bore-sight direction. The polarization is
characterized by the polarization ellipse, or by a sum of a co- and a cross-polarized component. Therefore,
erns.
the polarization properties for all directions are also given by co- and cross-polarized antenna pa tt
3.10 Axial ratio
r is defined as the ratio of the major axis to the minor axis of
Axial ratio (or ellipticity ratio)
r= œ, circular polarization by r= 1).
the polarization ellipse (linear polarization is given by
3.11 Co-polarization (nominal polarization)
Co-polarization (of an antenna) is that polarization which the antenna is intended to
radiate (or receive).
835-3-2 © IEC:1995 -
15 -
In view of maximum power transfer under operational conditions the intended polarization
for earth-station antennas is the co-polarization of the satellite antenna in the direction of
this earth-station antenna. For linear polarization the direction of the satellite polarization
depends on the positions of the earth station and the satellite and, to a small amount, on
the polarization characteristic and direction stability of the satellite antenna.
NOTE — The co-polarization is normally exactly circular or linear. Linear co-polarization is usually specified
with respect to the ground or the earth meridian plane belonging to the satellite position. In practice, an
antenna is also called co-polarized, even if it is only approximately co-polarized with the intended polarization
(for example, the far-field electric vector can move slightly with the frequency).
3.12 Cross-polarization
Cross-polarization (to a given co-polarization) is the polarization orthogonal to the co-
polarization (with both waves having the same direction of propagation). Two polarizations
are said to be orthogonal, if the polarization ellipses have opposite senses of rotation, the
same axial ratios and orthogonal major axes.
Two antennas are said to be cross-polarized, if their polarizations are orthogonal. Two
antennas are said to be nominally cross-polarized if their co-polarizations (nominal
polarizations) are orthogonal.
NOTE — In practice, two antennas are sometimes also called cross-polarized, if they are only approximately
orthogonal.
3.13 Cross-polarization discrimination (XPD)
For a given direction and a specified port, the cross-polarization discrimination XPD of an
antenna is the power ratio in decibels of the co-polarized and cross-polarized component
of the antenna polarization. The cross-polarization discrimination in decibels is given
by x = 10 log X. In the receive case, for example, this ratio may be measured by observing
the power ratio, when the polarization of the transmitting antenna is switched over from co-
polarization to the orthogonal cross-polarization, keeping the transmit power unchanged.
NOTE — Unless otherwise specified, the bore-sight direction is assumed. Cross-polarization is defined for
rt antenna.
each port of a multi-po
3.14 Polarization efficiency
The polarization efficiency is a factor, of unity or less, which is employed in the following
i1
equation:
• S •
Ae (0,0) (3-3)
Pr (0,8) =
where
Ae (O,9) is the effective area of a receiving antenna in a given direction (OM of
incidence;
is the power flux density of an incident plane wave from the direction (OM;
S
Pr (b,9) is the power delivered by a specified port of the receiving antenna to a
matched termination.
835-3-2 © IEC:1995 - 17 -
3.15 Dual-polarized antenna
A dual-polarized antenna is an antenna designed for simultaneously transmitting and/or
receiving signals having two o rthogonal (cross-polarized) polarizations. If it has one
receive and one transmit po rt
, then the co-polarizations related to these po rts are ortho-
gonal. If it operates with frequency re-use and therefore has four communication signal
po rt
s, the co-polarizations related to the two receive and the two transmit ports are
ort
hogonal in each case.
NOTE – If only one of the two received or transmitted operational polarizations is considered, sometimes
the ports corresponding to the same signal propagation direction are called "co-polar and "cross-polar"
ports. But the antenna polarizations related to these po
rts, despite approximating the intended co- and cross-
polarization, should then be distinguished from these polarizations.
3.16 Two-port discrimination (TPD)
The two-port discrimination (po
rt-to-port discrimination, isolation) of a dual polarized
frequency re-use earth-station antenna is defined for the two receive po rts and the two
transmit po rts.
If the satellite antenna radiates with one of the two operational polarizations, the receive
two-port discrimination of the antenna under test related to this polarization is the ratio of
the power received at the corresponding receive po
rt to the power received at the other
receive port (with both po rts terminated with matched loads).
If the antenna under test radiates with one of the two operational polarizations to the
satellite, the transmit two-po rt discrimination of the antenna under test related to this
polarization is the ratio of the power received at the corresponding port of the satellite
antenna to the power received at the same po rt when the power at the antenna under test
is switched over from one to the other transmit po rt (satellite antenna ports terminated
with matched loads).
The TPD depends on which of the two operational polarizations is transmitted or received
respectively. It will also be affected by properties of the satellite or bore-sight antenna
involved in the test and the transmission path. Therefore it is often not a sufficient
measure of quality of the antenna under test, but it may be the only measurable quality in
some practical situations.
NOTE – The two-port discrimination normally has to be distinguished from the transmit-receive isolation of a
multi-port antenna (see 3.17), as well as from the cross-polarization discrimination (see 3.13, 7.2) defined for
each of the antenna po
rts. Equal or approximately equal values for these quantities may exist only at special
frequencies or for idealized antenna properties.
3.17 Transmit-receive isolation (TRI)
The transmit-receive isolation of an antenna is the power ratio of the power transmitted at
a transmit po rt of the antenna to the power received at a receive po
rt of the antenna (by
coupling).
NOTE – The transmit-receive isolation may include the contribution of a transmit reject filter in the receive
line.
835-3-2 ©
IEC:1995 - 19 -
3.18 Far-field (far-zone,
Fraunhofer zone)
The far-field of an antenna begins at that distance L from the antenna, where the antenna
pattern is approximately independent of the distance where it is measured. The far-field
distance L is normally defined by the equation:
L - 2 D2
(3-4)
X
where
D is the maximum aperture dimension of the antenna;
X is the wavelength.
For far-field measurements the measurement distance will be greater than the maximum
far-field distance resulting from the minimum operational wavelength.
NOTES
1 When the maximum aperture dimension
d of the opposite antenna is larger than approximately 0,64 D,
the following minimum distance may be required for measurement:
Dd
L
(3-5)
0,32 X.
If O <
0,64 d, then equation (3-4) should be used with d instead of D.
2 For low sidelobe antennas, measurement distances longer than that of equation (3-4) may be required.
3.19
Noise temperature of an antenna
The noise temperature of an antenna is the temperature of a resistor having an available
power per unit bandwidth equal to that at the antenna output at a specified frequency.
NOTE — The noise temperature of an antenna depends on its coupling to all noise sources in its environ-
ment as well as noise generated within the antenna (for example, by ohmic losses).
4 Conditions of measurement
The measurements described in this standard shall be made as far as possible under
realistic operational conditions. They shall be carried out within all the frequency bands
given in the detailed equipment specification. The measurements may be made under
different environmental conditions within the limits agreed between the pa
rties concerned,
for example:
- wind velocity;
-
hail;
ice;
- rain;
snow;
-
- solar radiation;
- temperature range.
It should be recognized that mechanical deformations of the antenna geometry, due to
the influence of gravity, wind and antenna pointing angle, can affect the results of the
measurements, particularly those of gain, sidelobes, cross-polarization and two-po
rt
discrimination.
835-3-2 © IEC:1995 - 21 -
5 Antenna gain
5.1 General considerations
The antenna gain of a
satellite earth station may be measured by one of the following four
methods:
a) comparison with a gain-reference antenna;
b)
satellite substitution method (receive band);
c) satellite link power method (transmit band);
d) radio star method.
The comparison with a gain-reference antenna (standard gain-horn method) is applicable
if a terrestrial bore-sight range is available. The range shall have sufficient length and
sufficiently low ground reflection for the measurement. This method may be carried out
when the length of the range is greater than the far-field distance (see 3.18).
The satellite substitution method and satellite link power method are practical and
convenient methods for antennas of all sizes, but are in general not very accurate. These
methods are applicable when the bore-sight range is not available and when the antenna
under test is not large enough for the radio star method.
The radio star method is feasible for large antennas. Practicality of the method depends
on the radio star flux density, the antenna gain, system noise temperature and visibility of
the radio star. This method is applicable when the Y-factor (the ratio of the received power
from the radio star to the sky noise power) is greater than 2 dB (see IEC 835-3-7). The
measurement is performed by the simultaneous measurement of G/T and the system noise
temperature.
There are some small antennas whose feed includes a non-detachable low noise amplifier
or transmit power amplifier. For these antennas, an equivalent alternative feed subsystem
can be used for the measurement. The appropriate method is the standard gain-horn
method using a terrestrial bore-sight range.
The reference points in the antenna subsystem at which the transmit and receive gains
are to be measured or referred shall be specified. Also, the extent of filters, couplers,
switches and other components in the transmission line, whose losses are to be included
in the gain computation and measurement, should be specified.
5.2 Methods of measurement
5.2.1 Comparison with a gain-reference antenna
5.2.1.1
General considerations
Gain measurement by comparison with a gain-reference antenna involves the comparison
of the signal level received by a gain-reference antenna and that received by the antenna
under test from the same distant radiating source (bore-sight antenna).
It is preferable that the type of polarization (for example, linear or circular) of the source
antenna and the gain-reference antenna is the same as that of the antenna under test.
However, it is possible to use a linear polarized source antenna and/or gain-reference
antenna for the measurement of a circular polarized antenna with correction (see 5.2.1.3).
NOTE – Generally, the physical dimensions, and hence gain, of the antenna under test are greater than
those of the gain-reference antenna.
835-3-2 ©
IEC:1995 -
23 -
5.2.1.2 Method of measurement
Figure 2 shows the block diagrams of two similar arrangements commonly used for the
measurement of the antenna gain-by-gain comparison.
The r.f. receiver is successively connected to the antenna under test and to the gain-
reference antenna, using either a flexible coaxial cable terminated by a coaxial-
to-waveguide transition and an isolator or by a waveguide switch associated with two
waveguide runs with known losses.
At the beginning of the measurement, both antennas, the gain-reference antenna and the
antenna under test, shall be slightly de-pointed by a fraction of a beamwidth alternately
in azimuth and elevation. The antennas are then panned or rotated in azimuth and/or
elevation, through the point of maximum signal strength and then reset to that point in
order to establish the bore-sight direction in azimuth and elevation for each antenna in
turn for maximum received power. The azimuth and elevation settings of both the gain-
reference antenna and the antenna under test are then maintained for the duration of the
measurements. In addition, the exact polarization of the antennas should be checked and,
if necessary, adjusted for maximum receive level.
Step 1:
Connect the receiving equipment to the gain-reference antenna and note or
record the indicated received power, Pr.
Step 2:
Connect the receiving equipment to the antenna under test, increase the
attenuation of the variable attenuator in order to receive the same order of magnitude
of indicated received power, and note or record the received power, Pa, and the
difference in the variable attenuator readings recorded in steps 1 and
2.
Step 3:
Repeat steps 1 and 2 until an acceptable repeatability is achieved in
the measurement of Pr and Pa
. Lack of repeatability may be due to instability in the
transmitting source, or in the receiving equipment, or in the test-range propagation path
conditions.
The gain of the antenna under test can then be calculated by the following general expression:
Pa
)+ L+ Gr (5-1)
where
Ga
is the calculated gain of the antenna under test at the gain-reference point;
Gr is the gain of the gain-reference antenna;
Leg
is the difference between the attenuator reading in step 2 and the reading in step 1
(generally, Leg > 0 dB).
NOTES
1 To eliminate the influence of ground reflections, the power received by the gain-reference antenna
should be recorded for different heights of the gain-reference antenna above ground. Interference of
the ground reflections with the directly received wave cause a nearly periodic level variation with height.
The amount of the variation of the gain-reference antenna height should be large enough to record one
or more of these oscillations. (A separate construction for accurate moving of the gain-reference antenna
is recommended.) The average level received by the gain reference antenna should be determined and
used for the gain calculation. For a good test range, the peak-to-peak level variation with height may be less
than 0,4 dB.
2 Most often, a swept-frequency measurement is used to measure
Pr and Pa as a function of frequency.
However, in the case of a fixed frequency measurement there will be less difficulty in adjusting
Pa to exactly
the same value as
Pr which will then simplify the above equation and hence calculation of
Ga.
IEC:1995
835-3-2 © - 25 -
5.2.1.3 Correction for a circularly polarized antenna measured by using a linearly
polarized source and/or gain-reference antenna
Case 1:
For an antenna under test with a good axial ratio
When the axial ratio of the antenna under test is less than about 2 dB, simple corrections
described below can be applied:
a)
a linearly polarized source antenna and a linearly polarized gain-reference antenna.
The measured gain of the antenna under test is 3 dB lower than the actual gain. There-
fore, 3 dB shall be added to the measured gain.
b) a circularly polarized source antenna and a linearly polarized gain-reference antenna.
The received level by the gain-reference antenna is 3 dB lower than by a circularly polarized
antenna of the same gain. Therefore, 3 dB shall be subtracted from the measured gain.
NOTE — When a circularly polarized gain-reference antenna is used, no correction is necessary.
Case 2: For an antenna under test with a poor axial ratio using a linearly polarized
source antenna
Firstly measure the antenna gain, Go (dB), with an appropriate polarization angle of
the source antenna. Then rotate the polarization angle of the source antenna by 900
and measure the antenna gain, G90 (dB), again. Apply the same correction as for
case 1 a) if a linear polarized gain-reference antenna is used. Then the antenna gain,
G,
can be derived as:
l
G= 10 log 10 ( G0 ) + 10 G0 ) (dB) (5-2)
NOTE — When a circularly polarized source antenna is used, no correction is necessary other than the same
correction as for case 1 b) above.
5.2.1.4
Gain measurement accuracy
As this method involves only a comparison between two antennas, the absolute accuracy
of the power-meter used is not important.
To minimize the errors associated with gain differences between the receiving equipment
and other active electronic equipment, for example recorders, involved in the measure-
ments, a single common set of receiving electronic equipment, recorders, etc. is normally
used for both measurements with the gain-reference antenna and with the antenna under
test. Care shall also be taken to minimize errors associated with gain drift in the receiving
electronic equipment, recorders etc., as well as changes of power output and frequency of
the transmitting source. The time between measurements shall be as sho
rt as possible to
avoid the effects of such variation.
To minimize the non-linearity errors associated with the signal detectors, electronic
receiving equipment, recorders, etc. which are used to receive and record signals at
widely different levels, it is desirable to reduce the received signal level of the generally
larger antenna under test to the same level as that received by the smaller gain-reference
antenna by using a calibrated attenuator.
835-3-2 © IEC:1995 -
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It is essential to establish the linearity of the receiver over the whole range of signal levels
likely to be received during the measurements.
To minimize any errors associated with non-uniformities in the illuminating field, the
gain-reference antenna and the antenna under test shall be located as close to each other
as possible.
Care shall be taken to ensure that the effect of the structure associated with the antenna
under test, which may be large, does not significantly alter the characteristics of the gain-
reference antenna.
In cases where the incident field illuminating the aperture of the antenna under test
departs significantly from a plane wave front having uniform amplitude and phase, a power
transfer correction factor for each antenna is also required in order to accurately establish
the gain of the antenna under test.
Other causes of error are as follows:
-
the inaccuracy of calibration of the gain-reference antenna and of the variable
attenuator;
-
an increase or decrease of the test-range path loss, due to propagation effects,
including environmental influences;
an insufficient signal-to-noise ratio;
-
measurement observation errors;
ground and/or other reflections.
5.2.2
Satellite substitution method (receive band)
The principle of this measurement technique is to compare the signal level received by
the low noise amplifier (LNA) from the satellite with that of a known source injected at the
input of the same LNA (see figure 3).
In the first step, an unmodulated carrier is transmitted to the satellite from the satellite
system monitoring station (SSM) (or from the antenna under test in coordination with
the SSM). The downlink EIRP of the signal from the satellite is measured by the SSM. In
the direction of the antenna under test, the downlink power relationship is:
EIRP - L - a + G = P (5-3).
where
EIRP is the effective isotropically radiated power of the satellite antenna (dBW) into
the direction of the maximum of the satellite illumination pattern;
L is the downlink path loss from the satellite to the antenna under test (dB) (includ-
ing atmospheric absorption loss, if necessary);
a is the difference between the maximum of the satellite illumination pattern or
"footprint" on the earth and the actual illumination into the direction of the earth
station (dB);
G is the gain of the antenna under test (dB);
P
is the power level at the gain-reference point of the antenna (dBW) (that is input
to the LNA).
835-3-2 © IEC:1995 - 29 -
The power level P0
at the LNA output is displayed on a spectrum analyzer and recorded.
Then the transmission from the satellite is stopped, and an unmodulated carrier from a
signal generator is injected by means of a cross-guide coupler at the input to the LNA. The
signal level is adjusted so that the power level at the output of the LNA is equal to Po.
The output power of the signal generator is recorded.
Now:
— a= P (5-4)
Pgen
where
Pgen
is the output power of the signal generator adjusted by a precision attenuator
(dBW);
a is the cross-guide coupling factor referenced to the antenna gain-reference
point (dB);
P is the equivalent power level at the antenna gain-reference point equal to that
measured while looking at the satellite signal (dBW).
Then, by substitution, the gain of the antenna under test is calculated from the following formula:
G = (Pgen - a) - (EIRP - L - a) (5-5)
where
Pgen
and EIRP are measured values and the values of the other parameters are known
from previous measurements or calculation.
The measurement accuracy depends mainly on that of the satellite EIRP, which is
measured at the SSM. The total error may be typically of the order of 1 dB to 2 dB.
In this measurement, the polarization of the satellite antenna and that of the antenna un-
der test shall be aligned in case of linear polarization. The error due to a misalignment of
the polarization angle of 8°, for example, is approximately 0,08 dB.
5.2.3 Satellite link power method (transmit band)
The measurement of transmit band antenna gain (see figure 4) relies on a knowledge of
the antenna gain of the reference satellite system monitoring station (SSM).
In the first step of the measurement, the SSM transmits an unmodulated carrier with EIRP
which is below the saturation of the operating satellite transponder. The uplink power
relationship is:
m Lm
Gm + P - - am Sm (5-6)
=
where
Gm is the antenna gain (dB);
Pm
is the uplink power measured at the gain-reference point of the antenna (dBW);
Lm
is the uplink path loss from the earth station to the satellite (dB) (including atmos-
pheric absorption loss, if necessary);
am is the difference between the maximum of the satellite illumination pattern or "foot-
print" on the earth and the actual illumination in the direction of the earth station;
Sm is the power of the signal arriving at the satellite (dBW).
835-3-2 © IEC:1995 - 31 -
Subscript "m" refers to the SSM. The SSM records the transmit power, Pm.
Under these conditions, the satellite will generate a certain EIRP. The SSM measures the
downlink power level, PssM ,
of the loop-back of its own uplink signal. The antenna under
test then transmits an unmodulated carrier with an EIRP for which the SSM measures the
same value of P as before. For this, the uplink power relationship is:
ssM
Gt +Pt - Lt - at =St =Sm
(5-7)
where
subscript 1" refers to the antenna under test. The transmit power from the antenna
under test, Pt, is recorded.
From the above, the gain of the antenna under test can be calculated as:
Gt = (Gm + Pm) + (Lt - Lm) + (at - am) - P
t (5-8)
where
Pm and Pt are measured values and the values of the other parameters are known
(from previous measurements or calculation).
The measurement accuracy mainly depends on that of the antenna gain of the SSM and
the measurement accuracy of the transmit power from the SSM antenna and the antenna
under test. The error is typically of the order of 1 dB to 2 dB.
In this measurement, the polarization of the satellite antenna and that of the antenna
under test shall be aligned in case of linear polarization. The error due to a misalignment
of the polarization angle of 8°, for example, is approximately 0,08 dB.
5.2.4 Radio star method
The gain measurement using a radio star is performed by a measurement of G/T and the
system noise temperature at the same reference point of the antenna. The antenna gain is
calculated by the following equation:
G = (G/T) + 10 log TS
(5-9)
where
G is the gain of the antenna under test (dB);
G/T is the receive figure of merit measured by the radio star method (dB/K);
TS
is the measured system noise temperature (K).
The measurements of the system noise temperature and G/T are described in clauses 8
and 9, respectively.
5.3 Presentation of results
The antenna gain at the gain-reference point shall be expressed in decibels relative to an
isotropic source for the specified frequencies and polarizations. It is preferable to perform
the measurements at least at three frequencies within the specified frequency band and to
represent the frequency dependence of the gain graphically.
835-3-2 © IEC:1995 -
33 -
5.4 Details to be specified
The following items shall be included, as required, in the detailed equipment speci-
fications:
a) method of measurement;
b) measuring frequency;
c) polarization;
d) the inte rface point in the antenna system at which the gain is to be measured;.
e) weather conditions;
f)
minimum required antenna gain;
g) radio star to be used (in case of radio star method).
6 Antenna pattern
6.1 General considerations
If the antenna has separated po rt
s (for different frequency bands, polarizations or tracking
signals), patterns shall be measured at each of the po rts. Patterns may also be measured
for each operational polarization. For a given po rt
and frequency, transmit and receive
patterns are the same. The signal level, measured at a specified antenna po
rt, is typically
expressed in decibels relative to the co-polarized beam peak or in decibels relative to an
isotropic radiator.
Antenna patterns shall normally be measured under far-field conditions. This may be
achieved by a remote terrestrial bore-sight antenna positioned in the far-field or by a
satellite antenna as the second antenna. The antenna under test may be used as transmit
or receive antenna. Co- and cross-polarization antenna patterns of both principal axes
shall be measured. If intolerable high sidelobes could occur in the ±45° cuts, pattern
measurements in these planes may be useful too.
Smaller antennas are sometimes mounted on an hour-declination-angle positioner (polar
mount). In this case, making satellite measurements, orbit plane patterns (constant
declination) instead of azimuth patterns (constant elevation) shall be measured. Alterna-
tively bore-sight measurements may be performed putting the antenna-positioner-unit on a
separate elevation over azimuth positioner.
If only an azimuth positioner can be used, elevation patterns may also be measured,
provided it is possible to rotate the antenna under test 90° around the main beam axis. (If
the antenna is symmetric the feed alone may be rotated.)
Because of the limited resolution accuracy, patterns of highly directive antennas normally
shall not only be measured in a wide angle range, but also in an extended near-in angle
range around the main beam, including some of the first sidelobes. The cross-polarized
835-3-2 © IEC:1995 -
35 -
pattern is normally measured only in the near angle range. The wide angle cross-
polarization level may be of interest if it lies above the co-polarization level. Notice that
the wide-range cross-polarization pattern depends on the possible antenna orientations
due to the antenna mounting system and the angle position of the source antenna.
The cross-polarization maximum is usually found within the null-width of the antenna
beam. With linear vertical or horizontal co-polarization, this maximum is often determined
by the feed horn and then normally occurs in the ±45° planes.
NOTES
1 Antenna sidelobes cause interference only in the direction of other communication satellites (for
geostationary satellites these are directions nearly parallel to the equatorial plane) or in horizontal directions
(to terrestri
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