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