This paper investigates the impact of a rectangular slot on the performance of a sensor patch antenna designed for ice detection at 5.6 GHz. The study evaluates and compares variations in the resonant frequency of the patch antenna, both with and without a slot, when loaded with an ice layer. The results reveal that the slot strengthens the near electric field by creating an open coupling area with the material under test, which in this case is ice. The sensitivity of the antenna, measured as the frequency shift in response to the ice layer, is significantly improved with the rectangular slot, showing an increase of approximately 4.5 times for the same ice layer. Furthermore, the slot enhances the radiation efficiency and gain by approximately 58% and 5.449 dBi, respectively, setting it apart from previous patch antennas with slots placed between the patch and an external slab for ice detection, which exhibited a reduction in gain. These findings underscore the effectiveness of incorporating a slot in improving patch antenna performance for sensing and detection applications, while also paving the way for future research on slotted base structures specifically tailored for sensor antennas.