The waveguide slot antenna is shown in Figure (a). In the figure, the waveguide transmits TE10 mode. There is a current distribution on the inner wall of the waveguide. The slot antenna on the wall cuts the current line. . In order to enhance the directivity of the slot antenna, a series of slots of the same size can be opened on the waveguide according to a certain rule to form a waveguide slot array. Figure (b) shows a resonant slot array. To ensure that all slots are excited in phase, the distance between adjacent slots should be λ.