comparison of performances · for the coupling loss a mobile measurement unit was used which...
Post on 19-Mar-2020
0 Views
Preview:
TRANSCRIPT
RADIO FREQUENCY SYSTEMS
R F S C o n n e c t w i t h t h e b e s t ®
COMPARISONOF
PERFORMANCESOF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
RFS kabelmetal
H.-D. Hettstedt,
B. Herbig,
G. Klauke,
R. Nagel
Reprint from the proceedings of the
ITC Conference Basel, November 1994
A4 RZ COMPARISON orange 1.FE 08.07.1999 9:46 Uhr Seite 2
R F S C o n n e c t w i t h t h e b e s t ®
Innens. A4 -Orange 1-3 08.07.1999 9:49 Uhr Seite 1
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
1. ABSTRACT
This contribution deals with the results of a measure-
ment campaign in which the influences of a tunnel on
the electrical characteristics of Leaky Feeders were
investigated. Four different types were tested, two
broadband cables working in the coupling mode from
30 to 2000 MHz, and two cables working in the
radiating mode up to 900 MHz.
2. INTRODUCTION
Leaky Feeders have already been in use for some time in
multiband systems in tunnels and other confined areas
under various conditions. Mostly they are in com-
petition with narrow banded antenna solutions under
the aspect of costs. In train and metro tunnels, cables
seem to be the only solution because of the masking
effects of the trains.
Though a long tradition of successful applications of
Leaky Feeders can be demonstrated by very positive
experiences under very different and sometimes extreme
conditions, often a very diverse opinion on confidence
in Leaky Feeders is met among system engineers. One of
the reasons may be related to the situation that
technical specifications, especially data of coupling loss,
have been gained under very different conditions, thus
the specs could not be compared directly.
In recent years, an international standardisation on
measurement procedures has been achieved, [1]. Thus
coupling loss figures, the most critical parameter, have
become reproduceable from supplier to supplier.
However, these specs are derived from measurements
on testranges in the free space, and one of the oldest
questions remains: how do these specs represent the
performance of Leaky Feeders in confined areas?
Our experiences has been that most of the complaints
have been resulted from incorrect installation or failing
to use the recommended accessories. Intensive investi-
gations on environmental tests confirmed the rule that
the greater the proportion of uncovered sections in the
outer conductor, the higher the sensitivity of the
Feeders is to humidity. Thus it was conclusively shown
that continuously slotted cables show an extremly high
sensitivity, and that RLF-type cables are virtually
unaffected. These new tests and test procedures and
longterm applications have led to a position where it is
possible to find the proper type of Feeder for the actual
purpose and to make a relatively secure prediction of
performance even under extreme conditions.
At least some of the important questions remain. The
first one is, how to qualify and quantify influences of a
tunnel on the electrical characteristics. Another question
is, are the influences on cables in the radiating mode
higher than on those in the coupling mode. This could
lead to the understanding that the newer cables in the
radiating mode lose their regular field characteristics of
the open air and of course their importance, [2]. This
paper shall help to clarify the situation, but cannot give
universal explanations, because only one type of tunnel
was investigated.
1
Text COMPARISON 08.07.1999 9:52 Uhr Seite 1
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
3. MEASUREMENTS
3.1 Tunnel
In Hanover a metro tunnel has been available for an
intensive measurement campaign. At the Waterloo
Station one line is not used, thus two closed tunnel
sections can be reached via the platform. Fig. 3.1 shows
one of two test areas at a maximum length of
approximately 130 m each in the tunnel end sections.
Fortunately no gravel and rails obstructed the measu-
rements. The tunnel has a rectangular size which differs
in height and width, presenting the opportunity to
investigate different tunnel types. Only the last part of
the sections shows a constant size. The walls are of
smooth concrete, the area dry, but very dusty.
The cables were installed using special clamps on the
outer side wall at a height of 3.3 m, which corresponds
to the window height of a train. Other cable locations,
e.g. under the ceiling, were not permitted. In Fig. 3.1
three different guide lines I,II,III are outlined. Line I was
reserved for an older ALF-type cable only, whose results
are not considered in this report. The synthesiser was
always positioned on the platform side, the load near by
the end wall.
3.2 Equipment
For the coupling loss a mobile measurement unit was
used which consists basically of a computer controlled
ESVD receiver from R&S and a tracking system which
records the relationship between data and location by
40 samples per wavelength, see Fig. 3.2. The antenna
orientations for the different polarisation planes are
illustrated in Fig. 3.3. The software computes diagrams
of coupling loss including the curve of reception
probability with characteristic values of 5%, 50% and
95%. Furthermore it is possible to zoom sections of the
whole measurement run in order to consider the
different tunnel sections separately. For the
measurements of
reflection and cable
losses standard
equipment was used.
48m68m12m
4.5m
7.5m
4.9m
5.85m
I
IIIII
128m
3.3m
5.2m
Side-View
Radiating Cable
Figure 3.1:
Sketch of the
Waterloo Tunnel
in Hanover
2
Text COMPARISON 08.07.1999 9:52 Uhr Seite 2
ESVD / R&S
Computer
Dipol-Antenna Radiating Cable
3.3 m
2 m
Tracking-System
Tunnel Cross Section
λ /2-Dipole (30-to 900 MHz)
hk
d
ha
hk
d
ha
hk
d
ha
perpendicular vertical horizontal
Logarithmic Antenna (above 900 MHz)
hk
d
ha
hk
d
ha
hk
d
ha
horiz. perp. vertical horizontal
(Load-Transm.) parallel
@
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Figure 3.2:
Measurement
Equipment
for Coupling Loss
Figure 3.3:
Antenna
Orientations3
Text COMPARISON 08.07.1999 9:52 Uhr Seite 3
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
3.3 Measurement program
1. Cable-types:
Coupled mode cables: RLF 9/23 , a cable with large slot spacing
R-LFC 78, a quasi-slotted cable
Radiating mode cables: LK 37, RAY 78
2. Frequency steps : 30, 75. 145, 450, 900 MHz with λ/2-dipole 1800, 2000 MHz,
coupled mode cables only with logarithmic-periodic antenna
3. Cable losses and return losses
4. Coupling loss:
Antenna orientations: horizontal parallel, vertical, perpendicular
(dipole)
horizontal perpendicular, horizontal parallel vertical
(log.-per. antenna)
Antenna heights: 3.3 m, same as the cables, similar to free space measurements,
also 2.0 m and 4.0 m
Antenna distances: 2.0 m standard, where possible 2.0 m from opposite wall
The results were investigated for the whole cable runs and for the two different tunnel sections seperately.
5. Field distributions: at heights of 2.0 m, 3.3 m and 4.0 m
Cross section measurements of coupling loss were made in the greater tunnel section perpendicular to the
cable in all antenna orientations.
4. RESULTS
Due to the great quantity of data it is impossible to
report the results in detail in this paper. Thus only an
overview is shown in Fig. 4.1 to 4.8 which seem to be
relevant and representative diagrams.
4.1 Cable loss and return loss
The results do not differ noticeably from the catalogue
values.
4.2 Coupling loss
Fig. 4.1 to 4.4 show the comparison of the coupling loss
in free air and in the tunnel by the relevant values of
reception probability of 5%, 50% and 95%. These
considered measurements were made in the height of
the cable in order to have comparable conditions to the
standardised in free space. Only below 145 MHz greater
differences became clear. Though the tendency of
increasing coupling loss by decreasing frequencies is
normal, measurement errors have not been clarified till
now. Surprising is the fact, that the general behaviour
of each investigated cable type in free air can also be 4
Text COMPARISON 08.07.1999 9:52 Uhr Seite 4
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: horizontalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: horizontalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: verticalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: verticalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: perpendicularFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: perpendicularTunnel 0-125m
95%
5%
50%
Reception probability at discrete frequencies
Antenna height: 3.3 m, antenna distance: 2.0 m
5
Figure 4.1:
Coupling Loss of RLF 9/23 Cable
Text COMPARISON 08.07.1999 9:52 Uhr Seite 5
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
observed in the tunnel. Above 145 MHz the differences
are typical in the range of ± 5 dB which seems to be
related to the standing waves in the cross section, see
paragraph 4.3. Figs. 4.5 to 4.7 show the coupling loss
of the RLF 9/23 cable at 900 MHz where the two tunnel
sections are considered separately. The differences are
quite low and the mean values approximately 2 dB
lower, only at parallel antenna orientations the
behaviour is reversed.
These considered characteristics are typical in this type
of tunnel. Results from other locations do not differ
significantly. On the whole, the field characteristics can
be explained as a superposition of free air characteristics
and influences from the standing waves.
4.3 Cross section measurements
Fig. 4.8 shows the coupling loss in the cross section of
the large part of the tunnel. It was measured at an
antenna height of 3.3 m at 900 MHz at all antenna
orientations. Evidently the RLF-type cable excites an
electrical field of a standing wave. At greater distances
than 2.0 m a field distribution with a regular periodicity
of one wavelength can be observed of which the mean
value is quite similar to that of measurements along the
cable at equivalent antenna positions, compare Fig. 4.1.
The deep and sharp minima should be noted. These
field characteristics are typical for other antenna heights
and frequencies as well. They demonstrate that small
deviations in distance from the cable can lead to large
changes in field strength.
6
5. CONCLUSIONS
This particular rectangular metro tunnel influences the
field characteristics of the investigated cables installed
on a side wall. The relevant values of reception pro-
bability are comparable with those measured in the free
space. The maximum differences are in a typical range
of ± 5 dB above 145 MHz. The influences on cables in
the radiating mode are not greater than on cables in the
coupled mode. The coupling loss measured in the
tunnel section of smaller size is approximately 2 dB
lower. A field of a standing wave in the cross section
leads to a constant mean level which is similar to that
measured at 2.0 m distance along the cable. The
deviations are periodic with the wavelength.
6. ACKNOWLEDGEMENTS
The authors would like to extend their thanks to the
UESTRA AG, Hanover, for their kind permission to use
the tunnel and to Mr. Witwer for his good collabora-
tion. Furthermore, they wish to thank Mr. Mahlandt
from the Cable Development Department for his helpful
advice and for his supply of software. Mr. H. Cyriacks is
also thanked for preparing the large quantity of data.
7. REFERENCES
[1] IEC: Recommendations of Subcommittee 46 A., 1993
[2] H.-D. Hettstedt: Development and Applications of
Leaky Feeders,
International Seminar on Communications Systems
For Tunnels, London, 1993
Text COMPARISON 08.07.1999 9:52 Uhr Seite 6
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: horizontalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: horizontalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: verticalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: verticalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: perpendicularFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 500 1000 1500 2000
Frequency / MHz
Antenna Orientation: perpendicularTunnel 0-125m
95%
5%
50%
Reception probability at discrete frequencies
Antenna height: 3.3 m, antenna distance: 2.0 m
7
Figure 4.2:
Coupling Loss of R-LCF 78 Cable
Text COMPARISON 08.07.1999 9:52 Uhr Seite 7
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: horizontalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: horizontalTunnel 20-120m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: verticalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: verticalTunnel 20-120m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: perpendicularFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: perpendicularTunnel 20-120m
95%
5%
50%
Reception probability at discrete frequencies
Antenna height: 3.3 m
Antenna distance: 2.0 m, λ/2-dipole
Figure 4.3:
Coupling Loss of LK 37 Cable
8
Text COMPARISON 08.07.1999 9:52 Uhr Seite 8
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: horizontalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: horizontalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: verticalFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: verticalTunnel 0-125m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: perpendicularFree Air 100m
95%
5%
50%
50
60
70
80
90
100
Co
up
lin
g L
oss
/ d
B
0 200 400 600 800 1000
Frequency / MHz
Antenna Orientation: perpendicularTunnel 0-125m
95%
5%
50%
Reception probability at discrete frequencies
Antenna height: 3.3 m
Antenna distance: 2.0 m, λ/2-dipole
9
Figure 4.4:
Coupling Loss of RAY 78 Cable
Text COMPARISON 08.07.1999 9:52 Uhr Seite 9
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Antenna: 3.3 m height, 2.0 m distance,
horizontal orientation
Figure 4.5:
Coupling Loss of RLF 9/23 Cable
at the two Tunnel Sections
from 20 to 80 m and 80 to 125 m
10
Text COMPARISON 08.07.1999 9:52 Uhr Seite 10
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Antenna: 3.3 m height, 2.0 m distance, vertical orientation
Antenna: 3.3 m height, 2.0 m distance,
vertical orientation
Figure 4.6:
Coupling Loss of RLF 9/23 Cable
at the two Tunnel Sections
from 20 to 80 m and 80 to 125 m
11
Text COMPARISON 08.07.1999 9:52 Uhr Seite 11
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Antenna: 3.3 m height, 2.0 m distance,
perpendicular orientation
Figure 4.7:
Coupling Loss of RLF 9/23 Cable
at the two Tunnel Sections
from 20 to 80 m and 80 to 125 m
12
Text COMPARISON 08.07.1999 9:52 Uhr Seite 12
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Figure 4.8:
Cross Section
Measurements
at 900 MHz,
Antenna Height: 3.3 m13
Text COMPARISON 08.07.1999 9:52 Uhr Seite 13
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
Distance
between
leakages
d → 0
d << λ
d in order of λ
d >> λ
Geometrical
characteristics
Continuously
slotted
Quasislotted
Special slot
arrangements
Large distance
between slots
Electrical
field
Noncoherent
interferences
Noncoherent
interferences
Coherent
interferences of
spherical waves
predominate
Noncoherent
interferences
Electrical
mode
Coupled mode
Coupled mode
Radiating mode
Coupled mode
Field
characteristics
Very irregular
electrical field
Very irregular
electrical field
Transverse
electrical wave.
Function of
linear array
Very irregular
electrical field
Table 3.1:
Overview of modes
14
Text COMPARISON 08.07.1999 9:52 Uhr Seite 14
COMPARISON OF PERFORMANCES
OF DIFFERENT LEAKY FEEDERS IN A METRO TUNNEL
15
Text COMPARISON 08.07.1999 9:52 Uhr Seite 15
R F S C o n n
R F S G R O U P M E M B E R SR F S G R O U P M E M B E R S
S A L E S O F F I C E S
2299.050.PM 171 001 55 - 01
Please visit us on the internet at http: //www.rfs-group.com
FRANCE: RFS FranceTel: +33-1 3423 6200Fax: +33-1 3423 6324
BRAZIL: RFS Brasil - kmPTel: +55-11 7961 2433Fax: +55-11 494 2937
USA: RFS CablewaveTel: +1-203 630 3311Fax: +1-203 821 3852
AUSTRALIA: RFS AustraliaTel: +61-3 9761 5700Fax: +61-3 9761 5711
GERMANY: RFS kabelmetalTel: +49-511 676 2520Fax: +49-511 676 2521
INDONESIA: RFS IndonesiaTel: +62-21 797 60 76Fax: +62-21 797 60 77
THAILAND: RFS ThailandTel: +66-2 273 8051-2Fax: +66-2 273 8053
CHINA: RFS BeijingTel: +86-10 659 00370Fax: +86-10 659 06932USA: RFS Cablewave
Western RegionTel: +1-510 661 9620Fax: +1-510 661 9630
USA: RFS CablewaveEastern RegionTel: +1-203 630 3311Fax: +1-203 821 3852
USA: RFS CablewaveSoutheast RegionTel: +1-770 649 9929Fax: +1-770 649 8884
USA: RFS CablewaveMidwest RegionTel: +1-630 516 0106Fax: +1-630 516 0207 UK: RFS UK
Tel: +44-1494 447 110Fax: +44-1494 442 742
HONG KONG: RFS Hong KongTel: +852-2861 4438Fax: +852-2861 4488
RUSSIA: RFS MoscowTel: +7-095 258 0632Fax: +7-095 258 0633
CHINA: RFS ShanghaiTel: +86-21 5836 8417Fax: +86-21 5836 8291
ITALY: RFS ItaliaTel: +39-039 2 14 85 69Fax: +39-039 2 14 85 53
SINGAPORE: RFS SingaporeTel: +65-272 9233Fax: +65-272 9266
A4 RZ COMPARISON orange 1.FE 08.07.1999 9:46 Uhr Seite 1
top related