I am designing a layout for this Chip antenna "https://www.johansontechnology.com/datasheets/antennas/2450AT18B100.pdf". In the datasheet they have Test Board as an example layout. I have a couple of questions on their test board. As shown in the below layout: enter image description here

  1. I am not sure what no ground means here?

  2. I know that the antenna pin with the brown mark is connected to the inductor, but what is the other antenna pin connected to?

  3. Should the ground plane be exactly 46mm? What if I need it to be smaller?

  4. The feed line should be 50ohm, can I change the line width, and decrease the 19mm length and keep the impedance the same?

Thanks in advance.

  • 2
    \$\begingroup\$ If you read the pdf you've linked to, you'll see the pin connections spelt out in the 'Terminal Configuration' table, NC means no connection. So it's important to use the size of pad they've used on the footprint. \$\endgroup\$
    – Neil_UK
    Jul 11, 2017 at 7:38

1 Answer 1

  1. No ground plane. Remove all copper from that area to the limits given in the datasheet. This is to allow the antenna to radiate properly.

  2. Second antenna pin is connected to ... Nothing. It there just to hold the antenna in place.

  3. You don't have to have a board the same size, but it is probably better to be larger than smaller - and keep other (large) components away from the antenna.

  4. You can change the line width, but you need to use a line impedance calculator to make sure you get back to 50 Ohms impedance. The length nothing to do with the impedance. You probably do need to stay 19mm away from the antenna with the RF connector. It will interfere with the radiation pattern if you get it too close.

  • \$\begingroup\$ How can I route RF input (Yellow circle at the end of the Feed line)? do I have to use a different layer, until I get out of the ground plane? \$\endgroup\$ Jul 11, 2017 at 19:19
  • \$\begingroup\$ If you aren't using an RF connector, you would route the signal from your source to the antenna using an impedance matched line like in the picture. \$\endgroup\$
    – JRE
    Jul 11, 2017 at 19:31
  • \$\begingroup\$ Yes that is exactly what I am going to do, no RF connectors. My question is, can I route the impedance matched line to my source through the ground plane, or should I use a different metal layer? \$\endgroup\$ Jul 11, 2017 at 19:36
  • 1
    \$\begingroup\$ For a an impedance matched line, you need a ground plane. Take a look a striplines. They depend on having a ground plane. If you have to route your signal through the ground plane, you will have to have a grounded area on the layer opposite the trace. \$\endgroup\$
    – JRE
    Jul 11, 2017 at 19:41

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