Matching an On-Board Antenna - Part 1

RE: Matching an On-Board Antenna - Part 1

clem57 — Fri, 30 Jan 2015 13:45:46 GMT

For people that know, does a balun help antenna matching?

Thanks,

Clem

RE: Matching an On-Board Antenna - Part 1

hctiming — Fri, 30 Jan 2015 12:28:15 GMT

Hi,

http://www.miniradiosolutions.com has got a new VNA that goes up to 3 GHz for about 400 Euro. I just bought it and will test it for matching at 868 MHz. If anyone else has it, it would be nice to hear your experience with it.

Edit: I have tested it now. It seems to work very good for antenna matching. I have included some pictures so you can see the results.

I calibrated it on-board.

Antenna before match (ignore red trace) - actually quite good RL.:

[View:/resized-image/__size/806x612/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/6835.contentimage_5F00_175496.png:806:612]

In Smith Chart:

[View:/resized-image/__size/620x334/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/5430.contentimage_5F00_175497.gif:620:334]

So, after matching:

[View:/resized-image/__size/781x606/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/8562.contentimage_5F00_175498.png:781:606]

In Smith Chart:

[View:/resized-image/__size/620x334/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/8176.contentimage_5F00_175499.gif:620:334]

Setup:

[View:/resized-image/__size/620x349/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/5023.contentimage_5F00_175500.jpg:620:349]

[View:/resized-image/__size/620x349/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a3ed39b4-1cac-4870-9651-d628b4447e87/5751.contentimage_5F00_175501.jpg:620:349]

I would need another VNA in order to verify that the measurement is correct regarding the initial point in Sm Ch before match. But I end up exactly at Z=50 in correspondence to simulation. This must be a good indicator.

Best Regards

RE: Matching an On-Board Antenna - Part 1

Former Member — Fri, 10 May 2013 18:38:27 GMT

You reference "the least expensive" VNAs. Actually, there is a small company that is focused on the amatuer radio market that makes a sub $1000 VNA (either $500 or $750, don't actually remember). The miniVNA from http://www.miniradiosolutions.com It's not as fancy or as fast (sweep speed), but based on my testing it's good enough to do antenna matching. I'm operating at 13.56Mhz for all my work, so probably much lower than many other requirements, but this unit does go up to 2.5Ghz I believe. It doesn't have screen, you use your own computer and a free Java app for the interface. This tool has allowed me to do all of my antenna matching for my customers in house instead of renting a VNA every time (at a cost of about $1k a pop) or paying someone else to do the matching.

Very nice article!

RE: Matching an On-Board Antenna - Part 1

DAB — Mon, 06 May 2013 20:14:13 GMT

I would like to clarify for the readers that by "matching" you are talking about Impedence matching so that you get the maximum amount of power transfer from the driver circuit to the antenna so that it has the maximum range and recieving sensitivity.

It would be an interesting project to look at the various hand held devices to see how well each has managed to couple their power to the antenna. I suspect that there is a lot of wasted RF energy just do to sloppy antenna designs.

A very good post from someone who knows the benefits of antenna matching.

I used to watch the RF engineers changing the bend in the on board waveguide tubes to get the most power and least noise from their circuits.

Of course in those days, we only had an Oscilloscope and at best a power meter to debug the devices.

Thanks

DAB

RE: Matching an On-Board Antenna - Part 1

Former Member — Mon, 06 May 2013 17:27:34 GMT

A good article once again, thanks!

Elias