Cubical Quads

Part #6 of the "Roger Writes" series - September 2023


I was looking for an easy to build, short length beam, with reasonable gain. The classic is the Yagi, but for decent gain you need many elements and the length adds up. For short beams the Cubical Quads offer more gain in a much shorter length. Upto 4 elements, the Cubical Quad offers good gain, after that adding elements doesn't increase the gain by much (around 0.2dB extra per element). For more than 4 elements, a combined quad + Yagi (aka Quagi) is worth looking at.
The Cubical quad has many options. For a given number of elements, by varying the loop circumference and the spacing, you can balance the bandwidth, length, the forward gain, and the front to back ratio.


I've been using 4nec2 to simulate a few antennas. Until this project I had been experimenting with existing published designs, to get a feel for how they work, or to calculate dimensions for difference bands.
For the cubical quad, there are lots of parameters, and none of the existing web calculators did what I wanted. Given the simple nature of the elements, it was easy to create a model for 4nec2, with some optimising, this is the result for a 3 element beam for the 2 meter band, I'm pretty happy with 9.81dBi forward gain in 1.03meters.

The wireframe looks like this:

The gain plot looks like this (viewed from above):

With good SWR over the band (tuned for UK mid-band):

The build

It's one thing testing the model, but another to actually build it. Many of the designs I found used insulating supports with wires strung between them. I prefer using copper pipe, as it's self supporting. Copper water pipe is quite expensive now, so I searched for something smaller diameter and cheaper. I found car hydraulic line, it's copper/nickel plated, 3/16" steel pipe, cheap (30m/100ft for £17 delivered, from eBay), easy to bend by hand, holds its shape reasonably well, can be soldered, and doesn't rust (if the ends are covered).

These are the dimensions I used:
ElementLength in metersLength in inches
Reflector circumference2.14m84.3"
Reflector to driven gap0.44m17.3"
Driven element circumference2.06m81.1"
Driven to director gap0.59m23.2"
Director circumference1.98m78.0"


For other beam lengths, bandwidths, or gains, load the 4nec2 software, and the model. Change the S to change the bandwidth, the D for overall length, then optimise for V & L to find a solution (I tend to use 100% SWR, 5% Gain, 2% Front/back).

I did a quick test with it connected to the VNA+PC, so just rested it on the landing (with lots of metal in the walls!)
This gave these results:

I took it outside:

It was down to 1:1.05, with a reasonably wide bandwidth.

What next

I was going to build a 4 element for 4m, but will probably get this up in the loft and pointing at a nearby repeater. I'll turn the driven element through 90 degress, so that it's vertically polorised.

The Roger Writes series

I research / dabble with lots of things, and figured that if I write my notes here, I can quickly reference them, also, sometimes, they are useful to others!
Here is what I have so far:

This page was lasted updated on Tuesday, 28-Nov-2023 14:57:31 GMT

This content comes from a hidden element on this page.

The inline option preserves bound JavaScript events and changes, and it puts the content back where it came from when it is closed.

Click me, it will be preserved!

If you try to open a new Colorbox while it is already open, it will update itself with the new content.

Updating Content Example:
Click here to load new content