A Hierarchical Optimization Procedure for CAD of Antenna Waveguide Components B. Piovano, G. Bertin, M. Ludovico, G. Zarba, L. Accatino and M. Mongiardo* CSELT- Via Reiss Romoli, 274 - 10148 Turin, Italy,* DIEI, Universita di Perugia, I - 06100 Perugia, Italy Abstract - Modern CAD tools for antenna waveguide components design require the introduction of optimization strategies in order to reduce both the computer effort and the overall complexity of the optimization task. We introduce a hierarchical optimization procedure which breaks down the overall problem in a sequence of simpler tasks, hence also reducing the parameter space dimensions and avoiding local minima traps. Examples of manufactured components illustrate the methodology and confirm the quality of the electrical performances obtained via the suggested optimization procedure. I. INTRODUCTION In the field of high performance waveguide components for satellite applications there is an increasing demand for efficient computer aided design (CAD) tools, able to exploit the great capacities of modem computing machines to carry out, entirely at computer level, the design of a wide number of complex devices, with no need of mechanical adjustments after manufacturing [1], [2], [3]. The use of powerful CADs entails improvements of electrical performances, owing to the increased accuracy of the design, and significant advantages in the reduction of time and cost of the global production cycle. In efficient and reliable CAD tools the optimization procedure assume noticeable relevance. Recent efforts in the latter topic have mainly dealt with methods for reducing the overall computation times; these methods range from space-mapping techniques [4], [5] to the adjoint network method [6], [7] and to the analytical gradient evaluation [8]. The above approaches if on the one hand significantly accelerate the optimization procedure, on the other hand don't help the designer to select an efficient general optimization procedure and useful objective functions. In this contribution we introduce a novel approach for the optimization of waveguide components, in the following referred to as 'hierarchical', which introduces a hierarchy of the critical design specifications. We also illustrate some of the results achieved using this design technique by referring to specific examples. This paper is structured as follows: in the next section we describe the typology of waveguide components we are considering; in section III the hierarchical optimization approach is introduced and illustrated with reference to a couple of examples; finally, the section on results illustrates the actual capabilities of the proposed procedure on manufactured components. II. ANTENNA FEED COMPONENTS AND THEIR ELECTROMAGNETIC MODELING A typical set of antenna waveguide components is reported in Fig. 1, which also shows some possible arrangements for single polarization or dual polarization (linear or circular) antennas. A rectangular to circular transition (Fig l.a) is sufficient to generate a single polarization. A dual linear polarization can be achieved by using an OMT (Ortho-Mode Transducer: Fig l.b): this is a reciprocal device that is able to merge or split two linear polarizations. Finally circular polarization can be obtained by adding an iris polarizer between the feed and the circular port of the OMT (Fig. l.c). The polarizer is a device able to transfer each linear polarization present at the OMT output into a left-hand or right-hand circular polarization. 02 ( a) (D I 9 (3) (b) (c) O Horn Antenna OZ Rectangular to circular transition 3 Waveguide to coax adaptor O Orthomode Transducer (®) Iris Polarizer Fig. 1 - Antenna feed systems: a) single polarization; b) double linear polarization; c) double circular polarization mmmmm7.- I -A I .-Dj milmon. (3) (3) u d " w . (--i) Authorized licensed use limited to: UNIVERSITA PERUGIA. Downloaded on December 7, 2009 at 07:12 from IEEE Xplore. Restrictions apply.