XC3500M-20S Datasheet, PDF (19/21 Pages) Anaren Microwave – 20dB Directional Coupler

INPUT
1
4
FORWARD
MEASUREMENT
Model XC3500M-20S
Rev A
ISOLATOR
2
3
**TERMINATION
LOAD
Reflected
Wave
REVERSE
MEASUREMENT
** RECOMMENDED TERMINATIONS
Power (Watts)
8
15
50
150
MODEL
RFP-060120A15Z50
RFP-250375A4Z50
RFP-375375A6Z50
RFP-500500A6Z50
Figure ap.n.1-2. Forward and Reverse Sampling
The isolator in Figure ap.n.1-2 prevents the reflected wave from exciting the directional coupler. A list of recommended
terminations is shown in the figure.
Directional Couplers in Feed-Forward Amplifier Applications
Feed-forward amplifiers are widely used to reduce distortion due to nonlinearities in power amplifiers. Although the
level and complexity of feed-forward amplifiers varies from one manufacturer to another, the basic building block for this
linearization scheme remains the same. A basic feed-forward schematic is shown in Figure ap.n.2-1. The input signal
is split in two using a hybrid coupler or power divider. The output of the main amplifier is sampled with a 20dB-30dB
directional coupler. The XC3500M-20S is an excellent candidate for this sampling since it provides great return loss
and directivity. The sampled signal, which consists of a sample of the original input signal plus some distortion, is
inverted and then combined with the output of the first delay line. This procedure subtracts (through destructive
interference) the sample of the original input signal, leaving only the distortion or error component. The error
component is then amplified and combined with the output of the second delay line using another directional coupler. In
many cases, a 10dB coupler is used to combine the two signals. The XC3500M-20S is a perfect choice for this
injection because it has tight coupling, superior directivity, and excellent match.
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