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just wondering out of curiosity the difference between intelligent reflecting surface (IRS) and more traditional antenna arrays such as phased array and reflectarray?

From the surface it looks a whole lot similar but perhaps from different angles (IRS - more system/optimization focused and antenna arrays are more studied as an independent component), but was wondering if I was missing the key concepts/ other differences behind IRS.

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Phased arrays have a number of transmitters/receivers in parallel that vary the phase in order to digitally form a lens. This lets the transmitters/receivers adjust its gain in each direction digitally. IRS are (usually) passive devices that vary how an incoming signal (possibly from a phased array, MIMO device, etc) reflects in/out of a space. They're conceptually similar, and a reflective IRS with a directional antenna pointed directly at it would effectively be a phased array.

For more information, the introduction of this paper compares IRS to MIMO and related technologies:

https://arxiv.org/pdf/1907.04789.pdf

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  • \$\begingroup\$ Thanks for the answer! I agree that IRS are more similar to reflectarrays but thought phased array would be more known, would you say that IRS and reflectarrays are essentially the same? \$\endgroup\$
    – user3602697
    Nov 19, 2020 at 15:47
  • \$\begingroup\$ Why can’t you search? \$\endgroup\$
    – Tony Stewart EE75
    Nov 19, 2020 at 15:59
  • \$\begingroup\$ Not quite. Phase arrays do not have to have a "number of transmitters in parallel". Receive only phase arrays, for example may only have a receive chain behind each individual element. And passive phase arrays only have a single transmitter and a single receiver (well, maybe more, as you need a separate receive chain for SUM, Delta AZ, and Delta EL) channels from the antenna, and possible a fourth for the guard). The best you can say is that a phase array has a number of phase shifters in parallel, one phase shifter for each element (assuming a single beam system). \$\endgroup\$
    – SteveSh
    Nov 19, 2020 at 16:12
  • \$\begingroup\$ That's what makes it a phase array - the phase shifters; not the transmitters or receivers. \$\endgroup\$
    – SteveSh
    Nov 19, 2020 at 16:14
  • \$\begingroup\$ @SteveSh Made it more general to encompass Rx, Tx. Technically a phased array doesn't even need antenna, since not all phased arrays use electromagnetic fields. \$\endgroup\$
    – user1850479
    Nov 19, 2020 at 18:27

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