I have been honing the rigid Quad beam, pushing the boundaries of its capabilities and utilising the thicker elements for more performance, thin wires always having been a hindrance to the performance of the more traditional quad.
Additionally, like all my designs I have optimised these with a 50Ohm impedance feed point in order to remove matching devices of any kind. There is no method of matching or transforming anything known to science that is 100% efficient. Those inefficiencies mean the RF changes form from the desired and most commonly in antenna this loss presents itself as heat in the matching device and this heat is was restricts the power handling capability of an antenna.
As yourself this, if your antenna input is limited to a few hundred Watts or even a few thousand Watts, whys is that? How many of your transmitted Watts converted into heat would it take for a matching device to fail? You would think it would be quite a significant amount wouldn’t you? And yes, it is.
In addition to the removal of loss and massive increase in radiating efficiency a direct feed provides, performance is increased too. More traditional quads have had an input impedance of 110Ohm allowing for impedance matching to be performed by a 1/4 wavelength of 75Ohm coax (to 50Ohm). Lowering of feedpoint impedance does increase performance so producing with a 50Ohm feed point has multiple benefits.
The rigid quads I have developed consist of a dual-boom supporting the elements top and bottom with only the element width varied in order to created the change in element size (reflector to directors).
There are many myths about Quads, one of the biggest being they ‘open and close the band sooner and later than a Yagi’. While this is very difficult to accept without any substantiated evidence, they do possess a number of benefits over a Yagi but these are limited.
If optimised correctly, the Quad can produce much higher gain (per foot or metre of boom) than a comparative Yagi. However, this benefit diminishes as the boom length increases. After around one wavelength, any benefits in performance in favour of the Quad are minimal and certainly, where this rigid Quad is concerned, do not warrant twice the material usage (two booms rather than one, full wav elements rather than half wave elements).
I will cover more on this subject in my soon-to-be-published article on the evolution of the Quad and my experimentation and development relating to stacking and phasing quads.
This example below is for a customer who wants the ultimate performer on 28Mhz. This has just 4 elements on an 8m (26’) boom. 11.5dBi free space gain and 26+dB F/B.
Stay tuned for more very soon!
The 4el 28MHz Rigid Quad placed 10m above average ground 16.2dBi
An impressive 11.5dBi free space gain
Element layout (in model) of the rigid Quad
SWR betweel 28.2MHz and 28.6MHz
A Dual Boom 4 element Rigid Quad @ EI7BMB
Justin Johnson G0KSC is the owner of InnovAntennas Limited and contributing author to the ARRL Antenna Book 23rd edition