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I'd like to design an RFID reader with 4 output antenna ports. My RFID reader's module maximum output power is 30 dBm.

My target is for the maximum output power in the antenna ports to be 30 dBm.

If I use an RF switch to configure the antennas, I will have power losses and the power of ports will be less than 30 dBm.

Can you recommend a way to switch between antennas that won't cause losses?

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  • \$\begingroup\$ Why not simply use an RFID reader chip with each antenna. Getting the switching between the reader chip and the antennas might not be that easy to get working. You should also mention the frequency at which your RFID works. Power losses are not an issue until too much power is lost. Quantify the losses you can accept. 0.1 dB, 1 dB or 6 dB ??? \$\endgroup\$ Nov 20, 2017 at 13:52
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    \$\begingroup\$ Why 0.1 dB? Where did you get that number from? How much drop in range will 0.1 dB cause? My guess: almost nothing. Even if you would accept 1 dB loss then you'd hardly notice. Do you always place the RFID near the reader with 0.1 dB accuracy? My point is: you cannot just say that you need max 0.1 dB loss without proving why. I can already tell you now that achieving 0.1 dB or less loss at 868 MHz will be impossible. \$\endgroup\$ Nov 20, 2017 at 14:05
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    \$\begingroup\$ If you implemented an RF switch with a loss of less than 1 dB at 868 MHz in a product then any experienced RF engineer will say that you did a good job especially if you have no experience at RF. If you'd say: "But I want 0.1 dB loss." then they'd laugh and say that that would be quite a challenge even for them. \$\endgroup\$ Nov 20, 2017 at 14:11
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    \$\begingroup\$ 30 dBm? You need to cook food with your RFID transmitter? That's one full Watt. I don't know whether that's normal for RFID systems, but as a digital comms engineer: that is a farking lot of power. \$\endgroup\$ Nov 20, 2017 at 16:02
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    \$\begingroup\$ For a multi-antenna reader, you don't need much isolation, 10 or 15 dB is fine. Most switches aim for 40 dB so have greater losses. At a single frequency you can use transmission line tricks and PIN diodes. Scratch on the net for amateur radio solid state T/R switches for QSK EME. I remember seeing one for hundreds of watts at hundreds of MHz, so losses might be quite low. Not 0.1 dB though! Watch out for harmonics generated by the switch - the rules are very strict because 2x868 is in the cellular band. P.S. Ignore the combative comments above, but refine your question as you learn more. \$\endgroup\$
    – tomnexus
    Nov 20, 2017 at 17:49

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You can check out the Skyworks SKY13414-485LF chip, if you want to design something yourself. It's an SP4T antenna switch that could work in your application. Insertion loss is 0.5dB maximum, so if you absolutely want +30dBm output power, you need a reader with an output power of at least +30.5dBm. In reality you probably need more like +33dBm, because there are additional losses for filters and transmission lines. Maximum power the chip can handle is +37dBm.

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