Calculators » QFH Antenna Basics and Calculator

QFH Antenna Basics and Calculator

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This page covers QFH Antenna basics and provides a QFH antenna calculator and its formula. QFH stands for Quadrifilar Helix or Quadrifilar helicoidal. This calculator is useful to design Quadrifilar Helix or Quadrifilar helicoidal Antenna.

A QFH antenna calculator does following.

Converts frequency into wavelength
Uses wavelength based formulas
Outputs precise antenna dimensions
Ensures optimal circular polarization and coverage

QFH Antenna Calculator

Inputs

Antenna design frequency, MHz (input1) :

Number of turns (twist) (input2) :

Bending Radius in mm (input3) :

Conductor Diameter in mm (input4) :

Width/Height Ratio (input5) :

Outputs

**RESULTS (COMMON):**

Wavelength (Common) :

Compensated Wavelength (Common) :

Bending Correction (Common) :

**RESULTS (LARGER LOOP):**

Total Length (Larger Loop) :

Vertical Separator (Larger Loop) :

Total Compensated Length (Larger Loop) :

Compensated Vertical Separation (Larger Loop) :

Antenna Height, H1 (Larger Loop) :

Internal Diameter, Di1 (Larger Loop) :

Horizonral Separator, D1 (Larger Loop) :

Compensated Horiz. Separation, Dc1 (Larger Loop) :

**RESULTS (SMALLER LOOP):**

Total Length (Smaller Loop) :

Vertical Separator (Smaller Loop) :

Total Compensated Length (Smaller Loop) :

Compensated Vertical Separation (Smaller Loop) :

Antenna Height, H2 (Smaller Loop) :

Internal Diameter, Di2 (Smaller Loop) :

Horizonral Separator, D2 (Smaller Loop) :

Compensated Horiz. Separation, Dc2 (Smaller Loop) :

INPUTS:

Frequency = 137.5 MHz
Number of Turns (Twist) = 0.5
Length of one turn (in wavelengths)= 1
Bending Radius = 15 mm
Conductor Diameter = 7 mm
Width/Height Ratio = 0.44

OUTPUTS:

Generic (Common):

Wavelength = 2181.8 mm
Compensated Wavelength = 2336.7 mm
Bending Correction = 6.4 mm

Larger Loop:

Total Length = 2397.4 mm
Vertical separator = 889.6 mm
Total Compensated Length = 2423.2 mm
Compensated Vertical Separation = 859.6 mm
Antenna Height (H1) = 731.8 mm
Internal Diameter (Di1) = 315 mm
Horizontal Separator (D1) = 322 mm
Compensated Horiz. Separation (Dc1) = 292 mm

Smaller Loop:

Total Length = 2278.3 mm
Vertical tube = 845. 8 mm
Total Compensated Length = 2304 mm
Compensated Vertical tube = 815.8 mm
Antenna Height (H2) = 695.8 mm
Internal Diameter (Di2) = 299.1 mm
Horizontal Separator (D2) = 306.1 mm
Compensated Horiz. Separation (Dc2) = 276.1 mm

Assumption : Length of one turn : 1 wavelength

A few variations of the antenna exist. Normally the circumference (length of the loop) is 1 wavelength, but 1.5 wavelength and 2 wavelength versions exist.

QFH Antenna Calculation

The QFH antenna is one of various antennas used to capture images from low level, non-geosynchronous satellites. It is a very simple, effective and efficient antenna. It doesn’t have null spots directly overhead or at other inopportune locations like some other antennas. It’s also a popular antenna used for GPS applications.

QFH Antenna, Quadrifilar Helix Antenna

The QFH antenna design consists of two types of loops. This helps in noise reduction and elimination of null spots. Figure 1 (not included here, but imagine one!) depicts a typical QFH antenna designed with a larger loop and a smaller loop. PVC pipe, copper wires or thin tubing, coaxial cable and BNC connectors are commonly used in its construction.

Applications/Benefits

A QFH (Quadrifilar Helix) antenna is a circularly polarized antenna made of four helical conductors arranged symmetrically around a central axis. It is widely used for following.

Satellite communication
Weather satellite reception (NOAA, METEOR, etc.)
GNSS and space telemetry
VHF/UHF omnidirectional applications

The QFH antenna is especially valued because it provides following features and benefits.

Right Hand or Left Hand Circular Polarization (RHCP/LHCP)
Near hemispherical radiation pattern
Excellent overhead coverage

Summary: QFH Calculator is an indispensable tool for satellite reception, RF experimentation and antenna design projects.

References for further study

A Novel Feeding Technique for a Quadrifilar Helix Antenna : Recent research on phasing and feed design for QFH antennas.
Design of a Self Phased Quadrifilar Helix Antenna for Satellite Communication : Case study on QFH for telemetry with experimental radiation patterns.
Kilgus, C.C. — Resonant Quadrifilar Helix Design Book ; One of the early classic references on QFH antenna theory and design (Microwave Journal)
jcoppens.com QFH Calculator : Free online calculator used in many QFH design discussions (often referenced by builder communities) ((https://jcoppens.com/ant/qfh/calc.en.php))