URSI GASS 2020, Rome, Italy, 29 August - 5 September 2020 A Compact and Lightweight Ultra-Wideband Interferometer for Direction Finding Applications L. Scorrano (1) , A. Calcaterra (1) , P. Bia (1) , S. Maddio (2) and G. Pelosi (2) , M. Righini (2) , S. Selleri (2) (1) Elettronica S.p.A., Roma, Italy, (2) DINFO - University of Florence, Florence, Italy Abstract In this work it is proposed the design of a couple of UWB two-arm sinuous antennas working in 2-18 GHz (Antenna A) and 6-18 GHz (Antenna B) frequency bands assembled in a ultra-wideband array for direction finding applications. Both antennas work with a slant 45° polarization ensuring good matching impedance and stable radiation characteristics in the considered frequency bands. The design has been optimized in order to reduce the geometrical dimensions. The proposed antennas have been manufactured and tested in order to validate the simulation performances. Finally the evaluation of accuracy performances in estimating the direction of arrival of an incoming wave-front is presented. 1 Introduction The sinuous antenna is a very appealing and versatile ultra- wideband (UWB) antenna. Originally introduced and patented by Du Hamel in 1987 [1], it has been used both in its dipole and slot versions, both with two or four arms [2– 6]. In particular, two-arm dipole sinuous antennas are very interesting for homeland security applications. Their UWB characteristic and linear polarization allow the design of interesting systems for passive detection of targets. Effective radio-goniometers can be devised by employing a limited number of sinuous antennas in slant 45° polarization. UWB and slant polarization allows to effectively detect any incoming signal generated by the targets. In this contribution the design of two sinuous antennas, one covering the 2-18GHz band and one covering the 6-18GHz band is presented. Stringent constraints on overall size are given to be able to pack the antenna tightly enough to build an effective radio-goniometer. An overview of the backing lossy-loaded cavity and balun, necessary for single mode operation, will also be given. 2 Antenna design The sinuous antenna layout is reported in Fig. 1. The equation of the profile can easily be retrieved in literature [3-6] and will not be reported here for brevity. Key points are that lower working frequency is limited by the outer diameter of the antenna, while the upper frequency is limited by how close the feeding point can be manufactured. The 6-18GHz, hereafter indicated as “Antenna A” diameter must be at maximum 20mm, while the 2-18GHz, hereafter indicated as “Antenna B” diameter must be at maximum 60mm, furthermore photolithographic process cannot create lines/slots thinner than about 100m, limiting upper frequency. These dimensional requirements are very hard to comply. In particular the theoretical analytic profile has been modified so as to never produce lines thinner than 100m in the feeding area. Figure 1. Two arm microstrip antenna layout. With zoom on the feeding point area. Figure 2. Side view of the antenna (top plate) backed by a shaped cavity loaded with lossy ECCOSORB-MF190.