Quadrifilar Helix Antennas

The purpose of this page is to provide information and links about Quadrifilar Helix Antennas. There are a few links at the foot of the page - if you want me add yours please email the details.

What is a Quadrifilar Helix Antenna (QHA) ?

Simply - It's the best antenna to use for APT satellite reception - the featured antenna is depicted on the left. 

To paraphrase M. Walter Maxwell

"It comprises two bifilar helical loops oriented in mutual orthogonal relationship on a common axis. The terminals of each loop are fed in antiphase and the currents in the two loops are in phase quadrature. By selecting the appropriate configuration of the loops, a wide range of pattern shapes is available". The basic form of resonant QHA was developed by Dr. C. C. Kilgus of the Applied Physics Laboratory, John-Hopkins University, Silver Spring, Md. and published in December 1970 in "The Microwave Journal". Since then a lot of research has been done into the number of turns and length/diameter ratios. All of these affect the radiation pattern. The "traditional" fractional turn design produces a cardioid radiation pattern. It