Introduction
The non-resonant waveguide multi-slots antennas (see Fig. 1) are passive radiating structures which are commonly used in the microwave transmitter and receiver devices. Such antennas radiate energy from a feeding waveguide to a free space through longitudinal slots cut in a broad or narrow wall of an air rectangular waveguide. The special interest of such antennas is caused by their planar and compact structure, a high power handling capacity and electrical parameters, such as a high efficiency, a relatively wide frequency band and a good return loss. Their additional advantage is the ability to combine vertical slotted waveguides as a phased array with shaped and electronically switched multi-beam radiation patterns, which enables to observe many moving targets at the same time. The advantages mentioned above cause that these antennas are a subject of many publications.