What is a quadrifilar helix antenna?
A quadrifilar helix antenna (QFH or QHA) consists of four helical arms, typically fractional-turn, fed with equal amplitude and 0°, 90°, 180°, 270° phase. It produces a circularly polarized, broad cardioid pattern covering most of the upper hemisphere with good axial ratio at low elevation, which suits LEO satellite, weather-satellite and GNSS reception.[1][2][3]
How is the quadrature feed produced?
Either with an external feed network of hybrids, or self-phased: two bifilar loops of slightly different size, one resonant above and one below the operating frequency, give ±45° phase shifts so the pair is in quadrature at the design frequency, with an infinite balun integrated into the structure.[3]
Why use a QFH instead of a patch?
A patch beam narrows toward the horizon and loses CP purity at low elevation, while a QFH maintains a broad beam and good axial ratio down to low elevation angles and does not need a large ground plane, important for handheld GNSS, satellite phones and drones.[2]
Frequently asked questions
Is the QFH large?
Printed and dielectric-loaded versions are compact enough for handheld GNSS receivers.
What polarization does it give?
RHCP or LHCP depending on winding sense.
Where is it used at VHF?
Common for 137 MHz weather satellite reception.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “Understanding GPS/GNSS: Principles and Applications, 3rd ed.”. E. D. Kaplan and C. J. Hegarty (eds.), Artech House. 2017.
- “Antenna Engineering Handbook, 4th ed.”. J. L. Volakis (ed.), McGraw-Hill. 2007.