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New Optimised Wideband Low Impedance Yagi Designs

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Justin, G0KSC

Wed Dec 30 2009, 10:45AM

All, some exciting news for the New Year!

As I am sure most will know, I developed the LFA (Loop Fed Array) Yagi which has become very popular at home and abroad already providing low-noise, wide bandwidth performance with good levels of gain too for many hams.

The Yagi is a big compromise antenna however. If you look at one end of the scale you have the OWA (Optimised Wideband Array) Yagi with 50 Ohm input impedance which has a number of benefits. First, you need no matching so have no matching losses or induced pattern degradation and it is super wide band so easy to build and get right.

At the other end of the scale is the very low impedance antenna, exceptional performance very high gain BUT very narrow band. The problem being when it rains or snows (etc.) the antenna shifts in frequency and sometimes can not be used until the weather is right again! additionally, they can be very hard to build and get set up in the first place. Last of all, the patterns on Low Impedance antennas are no the cleanest.

DK7ZB has got it right with the 'mid way' antennas providing the 28Ohm impedance variety which give a balance of performance and bandwidth. The only issues being the patterns (elevation) are poor and not conducive to low-noise and the match requires the use of 75Ohm coax. finding good quality, RF grade coax can be troublesome.

The Holy Grail would be a very low impedance Yagi which had all the gain and benefits of the Very Low impedance antenna, has a very low loss matching arrangement with very limited impact on antenna pattern which provides a symmetrical, clean pattern and is wide band too. Not possible? I have done it.

I sent some of my designs to Ian GM3SEK who said 'I have never seen anything like this before'

Lionel VE7BQH who hosts the 2M G/T table received some 2M examples from me and had this to say 'I summary, I believe this may well be the optimum antenna for 2 M due to its high gain per bandwidth considering the other parameters have been brought under control. '

I have a 25 page article explaining how this is possible and why it has not been done before which will be published in DUBUS early next year. If anyone is interested in building one in the meantime, do let me know.

Justin G0KSC

[ Edited Wed Dec 30 2009, 10:47AM ]

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