Design and Development of an Offset-Beam Slotted Waveguide Antenna

Planar slotted waveguide antennas usually have their main-beam pointed perpendicular to the antenna aperture. While this arrangement is most practical and convenient from design point of view, it suffers a serious setback in that it offers large RCS in the direction of antenna main-beam. This paper presents the design and testing of an offset-beam antenna for low RCS applications. A linear traveling wave antenna is designed at Ku-band. It consists of 18 radiating slots cut in the broadwall of the waveguide. A 25 dB Taylor aperture distribution is used to reduce sidelobes. The antenna is simulated and optimized using high frequency structure simulator (HFSS) software. Manufacturing of the antenna was done using high precision CNC milling machine. After assembly, the antenna was characterized by measuring its scattering parameters and radiation pattern. Measured results are fairly close to the theoretically predicted and simulated results. Gain of the antenna is 15.0 dB over a bandwidth of 500 MHz. Power absorbed into the load is 20% and return loss is below -30 dB. First side lobe level (SLL) is 23.5 dB down and azimuth beam width is 7.0deg with beam pointing at an offset angle of 20deg in azimuth plane.