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In order to maximize power transfer, and minimize signal reflection, one would impedance match between a output load and an antenna and between an input load and an antenna.

However, is there any impedance matching between the two antennas that is required to maximize power transfer? For example, if one has a 50ohm matched TX and a choice between a 75ohm or 50ohm matched RX, which would provide higher power transfer and why?

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    \$\begingroup\$ Is this a homework or class-related question? \$\endgroup\$
    – mkeith
    May 24, 2021 at 22:57
  • \$\begingroup\$ No, research related. I'm attempting to optimize an rf channel. The 50 and 75ohm examples are just co-ax options that we commonly use in our lab. \$\endgroup\$
    – Leo
    May 25, 2021 at 23:10

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The antennas act as transformers between their terminals on and the free space propagating wave. The impedance at the terminals of the antenna depends on the antenna shape and the characteristics of the space that the waves are traveling in. Maximum power is transferred when the antennas are driven and loaded with their terminal impedance. If both antennas are fifty ohm ones, maximum power will be transferred with 50 ohms on both. However, it would be possible to get the same power transfer with one antenna that is 50 ohms and another that is 75. Both antennas do not need to be the same impedance to have the best power transfer.

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Yes. The antennas should be matched. The TX is the load antenna. The RX is the source. The 50 ohm source will deliver maximum power to a 50 ohm load but not to any other impedance. It may be more power efficient to simply use a passive reflector, rather than a TX and RX antenna connected by coax. A flat plate reflector, angled just right, works surprisingly well.

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