Microstrip linear array with polarisation control

A new configuration of microstrip series-fed linear array is presented; in which the choice of the specific array geometry permits selection of the dominant radiated polarisation from a wide range. The array consists of a series of right-angle bends in a microstrip line whose spacing determines the polarisation. Using an equivalent magnetic current analysis, closed-form expressions are derived for the geometry required for specific polarisations. Design limitations are noted and, in particular, the appearance of grating lobes in the radiation pattern in some cases indicates the use of high dielectric-constant substrates. Measured results for four arrays, having polarisations of current interest, verify the design technique for crosspolarisation levels down to -25 dB and sidelobe levels down to -20 dB. The performance limitations are critically assessed, and it is concluded that the new configuration will result in arrays having reduced bandwidth, or efficiency, with radiation-pattern control comparable to other microstrip arrays, combined with polarisation control which may well make them attractive in some system applications.