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A coaxial microwave applicator radiating in a liquid medium contained inside a chemical reactor is described. The applicator consists of an insulated asymmetrical dipole antenna that radiates almost isotropically. Hence, it appears well suited to directly heat the medium that fills the vessel, making it unnecessary to use a microwave oven as currently done in microwave assisted chemistry. The electromagnetic (EM) properties of the insulated dipole antenna emitting in high permittivity lossy media are first reviewed to define the applicator design criteria. A 3-D numerical EM solver is then employed to analyze the radiation of the applicator in the surrounding medium taking into account the whole structure of the reactor. Safe operations are always assured by the proper design of the applicator-vessel mechanical connection that drastically reduces unwanted stray radiation. The agreement between the theoretical analysis and the experiments performed is good, thus confirming that the coaxial applicator compares favorably with the traditional methods of activation, which use a single or multimode resonant EM cavity.