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Zigbee patch antenna

Discussion in 'Wireless & RF Design' started by davidmck, Apr 14, 2009.

  1. davidmck

    Thread Starter New Member

    Apr 14, 2009
    Hi everyone!

    I'm in the process of knocking up a test board based around an Atmel AT86RF212 Zigbee Transceiver, operating at ~900 MHz.

    I've basically just followed their application note regarding the use of a balun to match transceiver output to a 50 Ω antenna... but then I started thinking about patch antennas.

    I'm just using crappy FR4 PCBs (permittivity ~4.4, height 0.062"). @ 900 MHz, a 50 Ω microstrip is about 3 mm wide (http://www.emtalk.com/mscalc.php). A basic rectangular patch design (http://www.emtalk.com/mpacalc.php) is 80 x 102 mm, input impedence 234 Ω. I can match that to my 50 Ω microstrip with a 1/4 wave transformer impedence z = (zl*z0)^0.5 = (50*234)^0.5 = 117 ohms, which is 0.45 x 48 mm (again, using the microstrip calc).

    Am I missing something obvious, or does that seem sensible? Any comments welcome :D