25-08-2017, 09:32 PM
Helical Antenna
Helical Antenna.docx (Size: 188.87 KB / Downloads: 45)
helix antennas are referred to as axial-mode helical antennas. The benefits of this helix antenna is it has a wide bandwidth, is easily constructed, has a real input impedance, and can produce circularly polarized fields.
The parameters of the helix antenna are defined below.
• D - Diameter of a turn on the helix antenna.
• C - Circumference of a turn on the helix antenna (C=pi*D).
• S - Vertical separation between turns for helical antenna.
• - pitch angle, which controls how far the helix antenna grows in the z-direction per turn, and is given by
• N - Number of turns on the helix antenna.
• H - Total height of helix antenna, H=NS.
The antenna in Figure 1 is a left handed helix antenna, because if you curl your fingers on your left hand around the helix your thumb would point up (also, the waves emitted from this helix antenna are Left Hand Circularly Polarized). If the helix antenna was wound the other way, it would be a right handed helical antenna.
The radiation pattern will be maximum in the +z direction (along the helical axis in Figure 1). The design of helical antennas is primarily based on empirical results, and the fundamental equations will be presented here.
Helix antennas of at least 3 turns will have close to circular polarization in the +z direction when the circumference C is close to a wavelength: