Abstract— A fully planar UWB monopole with dual feed is designed for low cost applications over the [3.1-6] GHz frequency band. The achieved input bandwidth is [2.9-7.9] GHz for a size of 40 x 24 x 3 mm. The chosen stripline technology allows a feeding circuit isolation from antenna radiation, and provides robustness to the 20 mm height protruding square-like monopole. The main drawback of such a fully planar design is the degradation of the omni- directionality beyond the first octave. The frequency radiation pattern dependency is investigated and evaluated with specific UWB characterization tools. At last a comparison between 2 monopoles with different technologies helps to settle the compromise between complexity/cost and global performance. Index Terms—small UWB antenna, planar dual feed monopole, fidelity characterization. I. INTRODUCTION everal UWB communicating and/or positioning devices require small-sized, omni-directional, easy to integrate and particularly low complexity/cost antennas. Satisfying these requirements will probably degrade antennas performance. Designer’s role is also to propose relevant characterization tool to quantify that degradation in order to compare antennas. While cylindrical symmetry [1-3] and planar monopoles [4-5] are qualified as good UWB omni antennas, in a mass production and handset integration contexts, the orthogonal ground plane constraint may be relaxed and replaced by purely or quasi-planar antenna design. Thus an UWB planar monopole with dual stripline feed is designed and realized, keeping in mind low cost production and small size. However pure planar monopoles are not fully omni- directional particularly over the upper part of the frequency band. Two specific tools are proposed to quantify the quasi omni-directionality radiation pattern. One the one hand, mean gain balanced with pulse spectrum highlights global behavior; on the other hand angular deviation fidelity points out main lobe deviation vs. frequency. At last a comparison between 2 identical monopoles but with different technologies (metal sheet monopole in the air, embedded into substrate) gives an example of the necessary compromise between complexity/cost and performance. II. ANTENNA DESIGN The proposed antenna is derived from a previous works on the dual stripline feed metal sheet monopole [8], which shows wide impedance bandwidth and reduced radiation pattern degradation as regards the other monopole shapes [5]. The double feeding is in particular responsible for a significant improvement of the vertical current distribution resulting in better matching notably over the upper-band part [4]. (a) (b) Fig. 1. (a) UWB monopole prototype; (b) insight of the power divider circuit and dimensions in mm. Robust Planar Stripline Monopole for UWB Terminal Applications Serge Bories, Hassan Ghannoum, and Christophe Roblin, Member, IEEE ENSTA UEI 32 Bd. Victor 75739 PARIS FRANCE (serge.bories@ensta.fr) S Y w2 w1 17 18 2.2 24 40 19 Z