My first attempt at building an RHCP patch aerial for GPS use was such a success I decided to build yet another one, for my second RFZero board. The RFZero is a multifunction Arduino based signal source / GPS receiver and relay driver board... see my other posts.
I found some rather nice 2mm thick copper plate in the junk pile, so I built a second DIY GPS patch for RFZero No.2 board. I was so impressed with the vastly superior performance of my last DIY patch over a commercial ceramic patch + amplifier that it was obviously the way to go.
While an air-spaced patch is rather large compared to a ceramic one, it's performance benefit over even amplified ceramic patches makes it a no brainer. These patches are very simple to construct and this one is a chunky job made from 2mm thick copper plate with nylon bolts to get the correct spacing. This patch is obviously for the GPS L1 frequency, (1575.42Mhz), but you can easily alter this for other frequencies by scaling *all* of the dimensions.
Just Google 'Antenna Scaling'.
Just Google 'Antenna Scaling'.
The aerial is constructed from a pair of metal plates, accurately cut to size and spaced apart by 5.0mm. Dimensional accuracy is important... a 1mm error in the size of the patch will shift its resonant frequency by as much as 20Mhz, and you don't want that.
The patch dimensions, feed point and spacing above the reflector are fairly critical. The size of the reflector is rather less so, just don't go below the measurements given. I couldn't find nylon washers so instead I used 3mm thick nuts plus others carefully filed down to 2mm, to preserve the required spacing. It's fiddly.... but you can do it!
File/measure, file/measure file/measure file/measure v etc...till it's right! The same goes for making the actual patch. In the real World, I think this is called 'fitting'.
A tip! 2mm copper sheet is tricky to solder to. Even my BIG old-school iron wasn't up to the job. Thinner sheet is easier to solder!
The 2mm plate soaked up so much heat I ended up soldering the co-ax to the plate using the gas cooker! I recommend using 'half hard' copper over softer material The extra stiffness is desirable. You could use any suitable metal sheet... even tinplate would do, so long as you varnish or paint it afterwards so it doesn't rust!
The components of a patch. Two copper sheets, nylon nuts & bolts and some RG402 mini-coax with fluoroplastic dielectric. The airspaced patch is deceptively simple from a mechanical standpoint but must be accurately constructed.... especially the actual patch element and reflector to patch distance.
Centring the patch on the reflector. If you take a ruler and draw and X in pencil across the reflector you can eyeball the centre point by sliding around the patch on top of the pencilled X. That's the quick and simple way, or you can place it by measurement. It's up to you.
The finished patch. Being air-spaced rather than using a ceramic dielectric means the finished article is a LOT bigger than those titchy wee patches, but it as a reward it delivers a far stronger signal than even the commercial ceramic patch I bought with a built-in amplifier stage!
After I tested the patch, I wrote the design frequency on with a Sharpie and sprayed it with conformal lacquer so in future I won't mix it up with the ones I've made for 2.4Ghz.
If you use GPS at all, you might want to try building your own aerials, They'll run rings around commercially made ceramic ones.
73 Al.
GM1SXX
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