Cad and Mechanical Realization of Planar, Ka-Band, 8x8 Butler Matrices

Butler matrices of order four (4x4) have been recently investigated concerning their electromagnetic modelling, mechanical/thermal design and actual realization. However, from a practical viewpoint, planar Butler matrices of order eigth (8x8) are the minimal to be considered for effective graceful degradation when using multiport amplifers. The transition from 4x4 planar Butler matrices to 8x8 configurations is by no means trivial, due to the large increase in components' number and crossings. Moreover, while at X and Ku-bands mechanical tolerances are a relatively small problem, manufacturing of matrices for applications at higher frequencies such as at Ka-band adds a further difficulty. In this paper we describe a planar 8x8 Butler matrix baseline layout and a possible arrangement for realizing such a high complexity network in a compact manner. A prototype operating at Ka-band has been designed, implemented in reduced height waveguides, and measured, showing very good performances.