Model XC0900A-20
Rev F
20dB -- 30dB
DIRECTIONAL
COUPLER
OUTPUT
DELAY
MAIN
AMPLIFIER
INPUT
10dB
DIRECTIONAL
COUPLER
3dB
HYBRID
COUPLER
TERMINATIONS
** (see table below)
50 Ohm
DELAY
ERROR
AMPLIFIER
** RECOMMENDED TERMINATIONS
CARRIER
CANCELLATION
Power (Watts)
MODEL
8
15
RFP-060120A15Z50
RFP-250375A4Z50
RFP-375375A6Z50
RFP-500500A6Z50
50
100
Figure ap.n.2-1. Generic Feed Forward Circuit Schematic
Both directional couplers in the Figure ap.n.2-1 have one port terminated with a 50Ω resistor. In order to achieve
optimum performance, the termination must be chosen carefully. It is important to remember that a good termination
will not only produce a good match at the input of the coupler, but will also maximize the isolation between the input port
and isolated port. Furthermore, since the termination can potentially absorb high levels of power, its maximum power
rating should be chosen accordingly. A list of recommended terminations is shown in Figure ap.n.2-1. For an ideal
lossless directional coupler, the power at the coupled and direct ports can be written as:
P
input
Pcoupled
=
Watts
Eq. ap.n.2-1
Coupling(dB)
10
10
P
input
Pdirect = P −
Watts
Eq. ap.n.2-2
input
Coupling(dB)
10
10
where Pinput is the input power in Watts, and Coupling(dB) is the coupling value in dB.
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