Abstract: A microwave horn antenna comprising a hollow cylindrical horn (11) having a rear section of tapered internal dimension extending towards a tubular radiation open end. The open end incorporates a number of parallel-sided slots (17), which extend at angles of 45 degrees to the horn axis. The slots (17) terminate at the open end in semi-circular cut-out portions (17B). A dielectric lens (19) is fitted over the open end of the horn. The antenna provides a wide beamwidth of approximately 90 degrees over a frequency ban of 8 to 18 GHz.

Abstract: An exponentially tapered slot (Vivaldi) antenna for producing an end-fire beam. The antenna features a novel balun for coupling with a feed line. The conventional Vivaldi antenna is fed by means of a stripline section (1) underlying the ground plane (5) and lying perpendicular to the axis of the slot line (3). This balun arrangement has an inherent narrow bandwidth. In the proposed antenna arrangement the slot line (14) and the stripline (16) each have a 45.degree. twist centered on a common cross-over point (X.sub.o,Y.sub.o). The stripline (16) is terminated by a short-circuit to the ground plane (12) and the slot line (14) is terminated by an open-circuit in the form of a circular slot (15). The E-plane and H-plane radiation characteristics are similar to those of the conventional Vivaldi antenna, but the arrangement has a broadband capability enabling operation over any 3 to 1 bandwidth in the frequency range 1 to 40 GHz.