Constant beamwidth spiral antenna

Claim 1

A spiral antenna comprising two elongated antenna arms each extending outwardly and spiraling about an axis, each said antenna arm having an innermost end and an outermost end, each said antenna arm further having broad sections and narrow sections alternately from said innermost end to said outermost end such that said antenna arms with said broad and narrow sections form a series of filter means each blocking energy progressively at higher frequency, the nth of said sections from said innermost end along each said antenna arm having a length given approximately by (V h /ω i ) sin -1 (Z l g n /Z h ) if n is odd and (V l g n /ω i ) if n is even, where Z l /Z h is the ratio of low-impedance to high-impedance sections of a Tchebyscheff filter, V l and V h are velocities of propagation along the low and high impedance lines of said filter, ω i is the angular band edge frequency of said filter and g n are the known element values of said Tchebyscheff filter.