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I have a single-side ifa antenna design to which I wish to solder a coaxial feed. Now, I only have this female SMA connector with 5 pins on the otherside that I wish to solder to my PCB.

This may seem like an odd question but: will it function if two of the 5 pins are on the dielectric plate and the bottom two are on a conductive plate (copper)?

Fifth one is on the middle and on the feed point. I did consider moving the feed point a tad lower but making the feed point longer would require me to change all the other parameters to compensate it, which I couldn't find a way to do.

The antenna is designed to work at 2.4GHz frequency.

Antenna design

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  • \$\begingroup\$ What frequency is this? At 100 MHz, one pin is enough. At 2.5 GHz you'll need all four, and some care about the shape of the hole in the groundplane... \$\endgroup\$
    – tomnexus
    Feb 25, 2020 at 13:29
  • \$\begingroup\$ @tomnexus 2.4GHz frequency is the plan. How do you mean shape of the hole? \$\endgroup\$
    – Jaacob
    Feb 25, 2020 at 14:08
  • \$\begingroup\$ Everything matters at GHz. The 5 pin connector will work for that frequency, but you need to a) surround it with ground b) choose an appropriate size hole in the ground for the RF pad. c) choose a pad size. d) run a 50 Ohm track away from the connector to the antenna. e) no thermals on the ground pins! Also - you don't want the bulk of the connector and cable anywhere near the antenna. I assume this is a prototype antenna for a board-mounted radio... \$\endgroup\$
    – tomnexus
    Feb 25, 2020 at 14:12
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    \$\begingroup\$ The presence of the pins will extend the effect of the copper area into the antenna zone and reduce the electrical length of the connected strip line somewhat. There are so many variables that equations are for a starting point. Make a few prototypes and get them tested with the local university RF lab network analyser, then you will know. \$\endgroup\$
    – KalleMP
    Feb 25, 2020 at 14:31

2 Answers 2

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The 4 ground pins are provided for more than just mechanical stability.

Whether or not you can get away with only 2 of the 4 GND pins connected to a ground plane (or return) depends on what your RF concerns are. Depending on the frequency of operation, only having 2 of the 4 pins connected to GND would cause an impedance mis-match at the connector that may (at 10 GHz) or may not (at 100 MHz) cause you problems.

Also, only having 2 of the 4 pins connected to GND provides a path for noise and coupling onto your RF trace.

You need to perform the proper modeling and simulation to be sure.

EDIT1 - In answer to OP's question

It would better if you could extend the copper GND plane under the SMA connector to pick up the "top" 2 pins.

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  • \$\begingroup\$ Would it make a difference if I was to add a tin line from the other 2 pins onto the copper plate? The frequency of operation is 2.4GHz btw and I intended to add components for impedance matching at later stage. \$\endgroup\$
    – Jaacob
    Feb 25, 2020 at 13:23
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The 4 ground pins are for better stability. If you have soldered at least 2 ground and the middle pin, don't worry, go ahead!

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