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An Intro to LFA Yagis

Premium commercial versions of G0KSC antennas at Innovantennas

 

An introduction to the Loop Fed Array Yagi

The Loop Fed Array Yagi is one where a rectangular loop is placed upon the boom in-line with the parasitic elements instead of a traditional split dipole.

What are the benefits of the LFA?

The LFA presents a 50 Ohm feedpoint impedance and therefore no matching is needed. The loop itself is infact the matching system and driven element in one and this gives the LFA many advantages while being modelled.

The 'real' impedance of each LFA varies greatly. However, the presented impedance at the feedpoint is always 50 Ohm. Therefore any optimisation tool is not limited in the results it can achieve from a single input impedance, instead it is able to alter the width and length of the loop in order to maintain a 50 Ohm impedance. This feature is important when ensuring good patterns, bandwidth and flat SWR are maintained within an antenna.

This additional flexibility also allows the modeller to supress more side lobes and achieve more front to back (F/B) ratio that with traditional Yagis. If time is taken, an excellent balance between pattern cleanliness, F/B, gain and bandwidth can be achieved.

Additionally, the close loop at the feedpoint deems the LFA less susceptible to man-made noise and static. Adding this to the low level side lobes of the LFA provides a winning formula for a super low-noise antenna!

A 5 element 4M LFA Yagi installed at G4ZTR

 

Further benefits include the ability to use simple baluns at the feedpoint due to the 50 Ohm direct feed. The higher impedance also provides a much more stable antenna within wet weather and icy conditions and very wide acceptable bandwidths can be achieved too so ultimatley the user is not limited to the CW portion or SSB portion of any given band!

 

G0KSC recently instroduced the 'Antenna Balun' a simple but fully symmetrical 1:1 balun which can be easily built and installed while the antenna is being made. The Antenna Balun and how it works is taken from the Pawsey Stub concept. However, with G0KSC version becomes an integral part of the antenna itself and hence the name. The antenna balun consists of a 1/4 wave length of wire, tube or rod which is used to connect the terminal at the feedpoint that the inner core of the feeding coax will connect to, to and the boom further along the antenna. See the picutres below of the great job done by VE7XDT did on his 8el 2m LFA Yagi.

 

The G0KSC Balun installed at VE7XDT

 

 

The inner core of the coax connects to the terminal shorted to the boom by th 1/4 wave length aluminium bar

 

Many users around the World now enjoy the superior performs of the LFA Yagi which has only been made possible by the utilization of the very latest computer modeling techniques along with the employment of Particle Swarm Optimization. Many professional manufacturers of the LFA and even now, military 'customers' use and supply G0KSC designed antennas. If you want to benefit from the many performance benefits and want the additional satisfaction of building one yourself, please read fully all the information on this site to make it a very simple and enjoyable task for you to undertake.

As always, mail me with any questions

justin 'at' g0ksc.co.uk

73

Justin G0KSC

 
 
 
 

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