Abstract: A broad passband pressure barrier arrangement is provided for insertion in circular waveguide between a source and a receiver of radio frequency (RF) energy with a spatially circumferential electric field characteristic of the TE.sub.01 mode. At least three abutting cylindrical barrier regions are coaxially aligned a arranged symmetrically in mirror image fashion about a radial plane of the circular waveguide. The cylindrical barrier regions include: at least one solid cylindrical plug region sealed in a cross-section of the circular waveguide and having a longitudinal thickness sufficient to withstand a predetermined pressure load, and at least one solid cylindrical tuning region having a radius less than that of the circular waveguide and further having a longitudinal thickness. Each of the cylindrical barrier regions are defined by a characteristic impedance at opposing end faces thereof and a by characteristic impedance between the opposing end faces.

Abstract: A broadband quadrifilar phased array helix antenna is comprised of a pair of bifilar arrays spaced 90.degree. on a coaxial fiberglass tube. A 90.degree. feed phase exists between the bifilar arrays. Each bifilar array has three elements with the longest element having approximately twice the length of the shortest element and all three elements being of a length to give good broadband coverage over a specified range with specified shaped patterns being required. A 180.degree. feed phase exists between adjacent elements. A number of trimming adjustments to the design of the antenna are presented for obtaining improved performance.