Laser-cut QO-100 POTY patch antenna

Two friends have asked me to assemble dual-band 2.4GHz/10.4GHz patch/horn antenna feeds, known aa a POTY (for Patch of the Year).

The first one I made was from 1.5mm brass sheet, and I made it on the lathe and milling machine, but for these, a group buy was arranged on the UKMicrowaves group to get them cut on a CNC laser. The cuts are very slightly oversize, by about 0.2mm, but the edges are very clean and only needed minimal fettling to remove the inevitable pip at the start/finish of each cut. I had to open up the centre holes using a deburring tool to make the fit perfect. I also had to mark up and drill/ream the hole for the socket. I made a custom collet for the previous one, it supports the reflector at exactly 90 degrees. It is relieved near the solder joint.

Reflector and central waveguide/support mounted on the custom collet and clamped
Drilled the pilot hole in the reflector ready to open up to 8.8mm then ream to 9.0mm
Reaming the mounting hole in the reflector for the N socket

It was a lot of effort and actually it would have taken about the same amount of time to machine them from scratch, but for folks without a machine shop, they are excellent.

The Radiall N socket my friend supplied is not the usual small-format N with 4.1mm PTFE sleeve over a 1.27mm gold-plated brass pin. It has a solder spill. I had to cut it back a little and solder in a suitable extension pin. Again, a lot of work for no benefit.

In addition the N socket and the TNC supplier by the other friend for hit POTY both have a 1.5mm raised boss behind the socket.

TNC with solder spill just like the Radiall N

The N connectors I use are like this:

4.1mm PTFE shrouded N socket like the one I use for POTYs, but much longer
Six-slot N socket that I prefer for the POTYs

On the 0.9mm laser-cut material, that means the boss would intrude into the space between the element and reflector. I made up a precision washer to ensure the boss was flush with the reflector surface.

24mm OD washer bored 9mm and parted-off then superglued to a custom mandrel
Turning the washer to 0.46mm thick
Finished spacer washer under the Radiall N socket
Rear of the N socket now flush with the reflector face

I soldered the reflector to the tube at the right spacing from the machined top edge of the tube (6mm+0.9mm+3mm) using 183C tin-lead solder paste, which makes a neat joint,

I used a 3mm U-shaped spacer to fix the driven element in place and clamped it, then soldered it. to the tube. Then I stuffed paper towel into the tube and soaked it with water to prevent the existing joints from melting, then soldered the N connector and spacer to the rear of the reflector.

After a good cleaning with isopropyl alcohol then hot water and detergent, I fitted the 10GHz dielectric lens and connected the 2,3GHz port to an HP directional coupler, signal generator and spectrum analyser

POTY patch under test on 2.4GHz
Return loss versus frequency from 2320 to 2480MHz

So far, I have not been able to get the correct double-dip response. I can get a very deep single dip to -33dB (!) but even doing asymmetric bends or dielectric slips, I can’t split the dips. At max RL, the axial ratio is pretty much that of a linear feed, and with it much flatter, the axial ratio is still around 6dB. I am making another of the original patter with 1.5mm brass parts and machining them on the lather and mill, with a good small-format N socket with 4.1mm PTFE over 1.27mm brass pin so see if I can find what is going on. Then I need to make another with these TNCs…

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