QFH Antenna for NOAA Satellite Reception
This Quadrifilar Helix (QFH) antenna can be used for signal reception from NOAA satellites. These are omnidirectional antennas made up of 4 wires with a helical shape. This design is about 0.14λ in diameter and the length of each helix is 0.4λ. It resonates at 137.5 MHz and has a bandwidth of 6% (SWR < 2). The purpose of the helices is to block surrounding interference.
In free space, the radiation pattern actually points downward when the coaxial cable (the source in the simulation) is connected to the top of the antenna. However, when a real ground plane is added and the antenna is placed 5 meters high, multiple lobes and a more omnidirectional pattern are obtained, as expected.