AP-S Session 5, 1630, Tuesday, October 12, Room 163-173 A FREQUENCY-SCANNED SLOT-ARRAY ON A COAXIAL SLOW-WAVE STRUCTURE

SUKHARY Frequency-scanned antenna m a g s usually emplaJr a sinuous feed to obtain a high frequency sensitivity [ l ] , [2]. It has been redized [I] that this effect can alternatively be produced by using a slow-wave feed, such as a helix, in place of the more commonly employed "Efi-line or waveguide feed. Such a feed system can be made quite compact and lightweight as compared to the lat ter tspes of feed. In this paper, a structure consisting of a coaxial line with a corrugated inner conductor is examined es an array feed (Fig. 1) . The radiating elements are transversely out half-wavelength slots on the outer conductor snd constitute a unipormly spaced linear me;y. The absorber at the end of the feed ensures that the array is excited in the traveling-wave mode. In an approximate analysis of the feed, radiation from the structure is neglected. Such slow-wave structures have been studied earlier [3], 141 with a view to applications in traveling-wave tubes. However, the present analysis Uses a SOIlleWhat different approach in obtaining the dispersion characteristics. It considers the presence of higher order space harmonics in Region 2 which were neglecterl in the eerlier studies. At the same time, it assumes that the coITu&ations are narrow and closely spaced so that higher order modes in Region 1 can be neglected. Under these assumptions, the characteristic equation of the slm-wave structure is given by