APPENDIX A
Antenna System
The antenna system is vital to the success of any RF
repeater. It was only when high performance microwave
antennas became available that high capacity RF repeater
became practical. The antennas must have high gain (25-50
dB), clean pattern, low sidelobes and good Front-to-Back
ratio. It is the sidelobes and Front-to-Back ratio that control
much of the echo that results from antenna to antenna
coupling. Foreground obstructions also produce an echo
component which is site specific.
The objective for permissible echo varies with the type of
transmission and its bandwidth. High capacity analog radios
require 50-55 dB C/I while low capacity analog and digital
radios require 24-30 dB C/I. The actual amount of echo
permitted must be calculated based on the radio manufactur-
er’s specifications and end system design requirements. Table
A-1 shows the required RF repeater C/I with different types
of radios.
For example, a 16 QAM digital system requires 33 dB
RF-2000E/EW Repeater
RF-2000E/EW Repeater
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C/I at the repeater. The 2.5 GHz RF repeater gain is 50 dB.
antenna-to-antenna decoupling required is 33+50=83 dB.
This can be obtained from two 41 dB gain standard anten-
nas with 48 dB Front-to-Back ratio (F/B). Cross polarization
of the antenna is recommended. An antenna Cross Polarization
(XPD) of 20 dB is easily obtained. Antenna separation loss of
49 dB is assumed by taking 75% of free space loss between
the feeds of the two antennas. The decoupling is now:
+48
dB
F/B of Antenna #1 (standard)
-41
dB
Gain of Antenna #1 (8 foot)
+48
dB
F/B of Antenna #2 (standard)
-41
dB
Gain of Antenna #2 (8 foot)
+20
dB
Antenna XPD
+49
dB
Antenna separation loss (25 feet)
83
dB
Total decoupling loss
-50
dB
Repeater Gain
33
dB
C/I
In this situation, two standard antennas are adequate. If
the repeater antennas could not be cross polarized, one or
even two of the high performance antennas should be used.
31
Table A-1
C/I Requirements For Digital Radios
For -1 dB system gain at 10 BER or BER<10 at normal RSL, use following table:
MODULATION TYPE
MINIMUM C/I
4 PSK
24
8 PSK
28
16 QAM
33
64 QAM
40
MSK/FSK
30
9 QPRS/QPR 3
31
25 QPRS/QPR 5
32
49 QPRS/QPR 7
33
81 QPRS/QPR 9
35
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