The Initial presentation of the Coaxial Cavity Antenna occurred at the Antenna Applications Symposium 2000. Additional work has been undertaken using the coaxial cavity antenna in taking advantage of the fourfold feed symmetry and out of band roll-off. This antenna is unique in its configuration providing the capability for multiple polarizations as described previously. The new performance data illustrates the relevant use of this element for interferometry and direction finding systems. The flat phase and amplitude over an octave in frequency and a +/- 60 degree field of view demonstrate the use of these elements in numerous wideband systems. The latest performance data, to be presented, shows a slow out of band roll-off on the lower side and a sharp roll-off on the upper side of the designed operating band edges. The four-fold symmetry has been demonstrated with a simple four element butler matrix resulting in a classic mode 0 and mode 1 (alternatively mode 1 and mode 2) radiation pattern shape. Based on the latest performance enhancements, a new version 360 degree circular DF antenna can be built in a smaller volume. A design that is being fabricated and tested has a volume of only 9.0 inches in diameter with approximately a 4.5 inch height. This DF antenna works over the 2 to 18 GHz frequency range.
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