The Galactic Emission Mapping Project

GEM Backfire Helix Antenna Design

GEM Backfire Helix Antenna

• The receivers can be put in an easy access, protected position with a very short feed cable run.
• The feed antenna can be mounted well without an obscuring, scattering, diffracting spider.
• The backfire helix antenna is naturally and simply circularly polarized. This was important for the first maps in that the synchrotron radiation that dominates at low frequencies is partially linearly polarized and the received signal would depend on the angle of observation otherwise. We are depending upon observing each position in the sky from multiple positions to remove striping and cross link the maps for calibration.

  We monted an effort to develop backfire antennas for the 408 MHz and 1.5 GHz observations. Giovanni De Amici then provided documentation on the backfire antenna designed for GEM in an IEEE paper Here is some documentation about the backfire antennas

  • Text of IEEE paper postscript
  • Figure 1 postscript drawing showing the backfire helix antenna installed in the GEM dish
  • Figure 2 postscript figure showing the backfire helix antenna beam pattern.
  • Figure 3 postscript extra figure not in published paper showing design parameters for helix backfire antenna.
  • Figure 4 postscript three figures showing beam pattern for various parameters.

  Return to the GEM Home page

  Return to the Smoot Group page for a complete description of Dr. Smoot's group's research activities.