Microwave heating is a novel solution for milk pasteurisation but the non-uniformity of thermal distribution is still a significant problem that hampers its application especially for milk pasteurisation. This paper reports on the isotherm heating of a coaxial slot antenna applicator with a microwave signal generation using a fabricated mono-mode microwave system designed to improve the temperature uniformity of batch milk pasteurisation. In this paper, applicator simulation, design, characterisation, and fabrication are described in detail. The fabricated microwave pasteurisation system was implemented using a digitally controlled water-cooled magnetron with a waveguide circulator, a three-screw waveguide tuner, a water-based waveguide terminator, and a rectangular to coaxial adapter to channel the output. The impedance matching and power calibration routines of the fabricated microwave pasteurisation system …