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I saw the following antenna layout in a Texas Instruments application note titled AN043, Small Size 2.4 GHz PCB Antenna. What is with the right angle the feed makes? Wouldn't that cause reflections? Or is this a special impedance tuning technique (Kind of doubt that though).

Application Note RF feed

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  • \$\begingroup\$ RF right next to the crystal, no guard ring or anything... eww. \$\endgroup\$ – rdtsc Jul 13 '16 at 19:17
  • \$\begingroup\$ @rdtsc Should not be a problem, the voltage across the signal will be a sinewave (the crystal is a high-Q resonator) so it's harmonics will be attenuated more than enough. And there is a ground line between crystal and RF. \$\endgroup\$ – Bimpelrekkie Jul 13 '16 at 20:19
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Yes of course the 90 degree angle will cause reflections. Anything that isn't a proper transmission line of the right impedance will.

Question is, how much will it reflect and maybe it is low enough. Many times a design might not be perfect but that doesn't mean it's not good enough. I guess in this case the designers wanted flexibility so they placed some pads to place components. And this happened to be the result.

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  • \$\begingroup\$ I can attest to this. I once designed a PCB with a 90-degree, non-mitred bend on a 2GHz microstrip. Worked fine, although the performance was degraded about 5%. \$\endgroup\$ – rdtsc Jul 14 '16 at 1:16

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