10-8] 



TWO-ARM SPIRAL ANTENNAS 



529 



Fig. 10-8 A Hughes Aircraft Co. AEW Antenna, Showing (a) the 20-Element 



"Bow Tie" Structure and (b) the Corporate Feed Structure of Coaxial Lines at the 



Rear of the Antenna. 



described by angles alone (at least within its region of radiation), and thus 

 it has no lengths to be frequency sensitive. Physically, the antennas consist 

 of dipole-like conductors with boundaries defined by a geometric growth, 



r = ^^^ (10-13) 



and wound in a spiral in a plane perpendicular to its radiating direction (see 

 Fig. 10-9a). When the spiral is so proportioned that the antenna is in its 



Fig. 10-9 The Basic Two-Arm Spiral Antennas: (a) Geometric Spiral, (b) Arith- 

 metic Spiral. 



