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In this work, an original closed-form evaluation is performed for the continuous-spectrum field excited by a dipole source in substrate-superstrate configurations, which have been employed in microwave planar antennas. In particular, we derive an analytical representation of the continuous-spectrum field in the form of angular-dependent cylindrical leaky waves of TE or TM type, weighted by an appropriate transition function. The proposed formulation is uniformly valid as frequency is varied, i.e., also in the neighborhood of the transition region between leaky-wave and bound-wave ranges. In this way it is possible to describe in a simple and efficient way the behavioral features of guided and radiated fields excited by practical sources in open planar structures. Numerical results which show the accuracy of this approach are provided in different operating conditions.