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I'm borrowing the RF design from the MICRF114 Development Kit.

Here's user guide- http://ww1.microchip.com/downloads/en/DeviceDoc/50002433A.pdf

The circuit I'm using is on p. 35 and the antenna layout is on p. 21.

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The issue I'm facing is that my board can only be 0.8" wide, but the antenna is 25mm (0.98") wide. I don't know enough about antenna theory to know what changes I can make to the antenna dimensions to shrink the width down, but still maintain the correct impedance.

Correct me if I'm wrong, but I think the primary consideration for resizing the antenna should be ensuring that the matching network is dimensioned properly to prevent reflections/losses in power transmission via the antenna.

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    \$\begingroup\$ Hello! Best practice is to embed the relevant figures from the datasheet into your question - it makes it quicker and easier to understand, and links are famous for breaking over time. \$\endgroup\$ – Selvek Sep 17 '18 at 18:31
  • \$\begingroup\$ Can you use a chip antenna? e.g linxtechnologies.com/wp/wp-content/uploads/ant-433-sp.pdf or johansontechnology.com/datasheets/0433AT62A0020/…. They may be good enough for what you want. \$\endgroup\$ – Big6 Sep 17 '18 at 18:38
  • \$\begingroup\$ Track sizes can be reduced with FR4 dielectric thickness. but path lengths depend on Dk and wavelength. But with equal track and gaps the overall width can be reduced after design calc. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 17 '18 at 19:47
  • \$\begingroup\$ reduction 1mm dielectric and track/gap sizes while adding some length to same as before and reduce overall width but this reduces stiffness too. Maybe if 0.75mm is doable for dielectric. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 17 '18 at 20:33
  • \$\begingroup\$ Looking at a reference design with different board geometry should be done with a grain of salt. Changing the ground plane will result in different resonances, even if you could fit the same geometry. \$\endgroup\$ – EasyOhm May 21 at 21:11
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The matching of an antenna is only one part of the design. This could still be done with a transmission line of a special length. As far as I know there is no generic way to resize your PCB antenna just by a given factor. However there will almost be certainly a different antenna design, which matches your needs and frequency. This might lead to a smaller gain, but doesn't have to. Often there are better ways which can have higher gains, despite being smaller than its predecessor.

Give us some specs. What center frequency, bandwith and antenna gain are you looking for?

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