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Why are all PCB yagis all limited to 3 elements?

Hello micro addicts,

I’ve noticed all the microwave PCB yagis for sale are all 3 elements at most, and there’s gota be a way to homebrew or special order say a 9 element pcb yagi to squeak some extra gain out. I always prefer the non coax designs where you attach the sma adapter right to the board for minimal losses. The average SOTA backpack has room for a 14 inch long board, possibly more.

I even had a crazy idea, the reflector, DE, and some directing elements on one 14 inch long board, then another 14 inch board with just directors, you attach the two at the edges with non conductive temporary fasteners (plastic bolts, pins, or duct tape) and then deploy for a 28 inch long pcb “beam” antenna.

I feel like the PCB board is perfect for sota, its light weight, and the elements don’t get bent into modern artwork as things tumble around in the pack. I’ve never custom ordered PCB boards, so any advice or ideas would be great. I even thought of using copper tape, used for old home security systems on a plexiglass long board, to add directors to the existing 3 element boards in the above fashion.

If you are interested in performance it’s unlikely that a PCB Yagi is a good solution.

With a 4 element PCB yagi I could at least achieve the qo -100 over 36000km.
https://youtu.be/VEgwlS2z-S8

73 Chris

You could get bare board and epoxy elements to it. This seems to be the same board as PC board, but without the copper cladding.

wunder

They are not limited to 3 elements.
Have you seen the antenna supplied with the SG-LAB 3.4 GHZ transverter?
or the WA5JVB log periodic antenna?
It is an interesting idea.

When extending a yagi you have to consider what the tradeoffs are, between gain, losses, directivity, physical dimensions including weight. and how will you mount it?

For a long pcb antenna, I would consider the rule of thumb that doubling the length of a yagi usually increases the gain by about 3 db. And at the same time makes it a narrower beam requiring more attention to aligning it to point to the desired signal.

Re 3db gain, this would mean that the signals you currently receive at the noise level will be 3 db stronger with a yagi that’s twice as long, and the signals currently 3db below the noise level may increase to being equal to the noise. How many more contacts will you make with a higher gain antenna?

I have made plenty of good contacts on 1296 using a 4 element yagi, which I think was built on a design published in VHF Communications.

For a long PCB yagi you need to consider the mechanical stress on the connectors, which are designed to connect cables and not to support antennas. Most of the connectors on microwave gear are SMA and are soldered to the PC board so if you overload the connector you may also damage the board.

ie. caution recommended…

73 Andrew VK1DA/2uh

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Demand is probably a major limit on the availability of longer PCB antennas… Most of them are designed for uses where a small antenna is needed. At 23cms and up patch antennas and stacked patches are simple to make and have the same gain as a small Yagi. Reproducibility and reduction in size and cost make what maybe considered “more exotic” antennas feasible.

So you can make one that is longer but you need to be careful with the choice of PCB material as there can be significant variation in the Er between brands and even between batches. But as soon as you start considering 5 elements or more you are probably better off with stacked patches especially as the phasing lines can be etched with the patches.

The biggest PCB antenna I’ve seen is the old BSB Squarial for 12GHZ satellite reception. This was a 16 x 16 array of 12GHz PCB dipoles on a plastic flexible sheet along with all the phasing lines. Incoming RF was summed by all the dipoles and then fed to one dipole that was in the opening of the built in LNB feedhorn. i.e. it was a passive array feeding a 12GHz DBS LNB.

A number of us including Denis G3UVR(SK), Brian G3SMU(SK) and others in NW England used them on 3cms TV. The 12GHZ LNB was removed and a standard DBS LNB using WG17 could be fitted. I had one where the DRO puck was changed to 9.5GHz and it was snowflaked up and used with an old analog satellite tuner. On TX, the LNB was removed and I had a WG16 Solfan head Gunn diode into a WG16>WG17 transition which mounted to the WG17 fitting. You had to rotate the dipole PCB sheet through 90degs ISTR to get the polarisation right for TX. The pair were on the top chimney and I had a P5+++ duplex TV link with G4OAR about 5km away with about 5mW of wideband TV. That must have been 23 if not more years ago.

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A yagi is probably not the best type of pcb antenna.
Generally it is better to get more gain in V and wider in H. i.e stacked antennas.
We don’t tend to do this with tubing, because the feed and mounting complexity make a single long yagi much easier than stacked antennas
But on pcb, you can print an arbitrarily complex feed and mounting arrangement, with no penalty, so stacked phased arrays become the preferred choice for more gain, rather than long yagis

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BTW if you do make a large pcb or tape-on-plastic antenna, put large holes between the elements, it makes the windage far less. I have a 2m/70cm moxon of copper tape on corflute.
It was impossible beyond a light breeze. I installed large holes, and it reduces the wind effect far more than the surface area was reduced.

is that like pumping a vacuum into something? :slight_smile: :slight_smile:

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Well valves definitely stop working when you let the vacuum out :wink:

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Or you can buy them in different sizes from a wholesaler…

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I built a four elements yagi on a PVC boom, DK7ZB design, and is his web there is anothers designs with more elements.