Abstract: Systems and methods for operating an antenna assembly. The methods comprise: receiving, at the first circularly polarized antenna, a first signal comprising a desired signal emitted from a first signal source located at a first altitude higher than a second altitude of the antenna assembly and an interfering signal emitted from a second signal source located at a third altitude lower than the second altitude; receiving the interfering signal at the second circularly polarized antenna (where the first and second circularly polarized antennas are disposed on opposite sides of an antenna reflector and having opposite circular polarizations); generating a second signal by shifting a phase of the interfering signal which was received at the second circularly polarized antenna by an amount to cause the second signal to be out-of-phase with the first signal; and providing an antenna pattern with a null at or below a horizon by destructively combining the second signal with the first signal.

Abstract: Adaptive tunable antenna system includes a first radiating element having an elongated length and a second radiating element extending from a distal end of the first radiating element. The first radiating element is for a high band of operation and the second radiating element is for a low-band of operation. The second radiating element is a helical member including a plurality of turns. A low-band circuit selectively bypasses one or more of the turns of the second radiating element in response to a control signal.