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Incident power and unmatched loads

  1. Nov 9, 2013 #1

    I've been working with a bolometer and a directional coupler for calculating the module of the reflection coefficient of a load.

    I used several loads (matched and unmatched) and found out that the incident power (I measured a sample at the coupled port) was the same each case.

    Why? I thought the load would only receive maximum power (all available power) when it was matched. Does the incident power not depend on the load?

  2. jcsd
  3. Nov 10, 2013 #2


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    Science Advisor

    The incident energy to the load interface depends only on the transmitter energy and line loss.
    The reflected energy is the product of the incident energy and a function of the load impedance match.
    The difference is the energy transferred to the load.
    The transmitted energy can not “know” what impedance is ahead.
    The transmitted energy cannot “see” any reflected energy travelling in the opposite direction.
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