This paper aims to find the most effective port position for a microwave oven operated in TE10 mode at 2.45 GHz with 1.1 kW of input power. We examine the electromagnetic field distribution inside the cavity using waveguides made with ports at different locations, focused on dimensions a (wider) and b (narrower) of rectangular waveguides and their behaviour at a quarter wavelength (λ/4) in the x, y, and z directions is studied. The λ/4 transformer is employed to adjust the impedance for maximum power transfer and to avoid reflections. Among the configurations designed, there is one with dimension a along the y-axis, dimension b along the z-axis, and λ/4 (quarter wavelength) along the x-axis, placed distantly from the microwave cavity, that perform best with S11 −21.01 dB, power output of 1100.5 W, and power efficiency of 99.2%. This study can help improve microwave oven design in relation to electric field distribution and exposure uniformity both at domestic and industrial applications.