Alternating-phase single-layer slotted waveguide arrays at 25 GHz band

High-gain and mass-producible planar antennas are strongly demanded for millimeter-wave applications such as high-speed wireless LAN, automotive collision avoidance radar and subscriber radio link systems such as LMDS. Single-layer slotted waveguide arrays (Goto 1988) are a leading candidate for these purposes because the transmission loss of hollow waveguides is quite small even at millimeter-wave frequencies in comparison with other planar lines like microstrip or triplate lines. The authors present the structure of an alternating-phase single-layer slotted waveguide array, where all the radiating waveguides are excited in the same amplitude but with opposite phase between the adjacent waveguides by T-junctions. This antenna is suitable for mass-production because it consists of a slot-plate and a groove feed structure. Electrical contact between the slot-plate and the groove feed structure except the periphery of the antenna can be omitted. The authors have already confirmed this principle experimentally (Sakakibara et al.1997). This paper estimates the change in the guided wavelength of the co- and alternating-phase single-layer waveguides due to a small gap between the slot-plate and the narrow walls on the groove feed structure, in order to show how tolerant the latter is against the gap. This paper also confirms a high-gain performance of 35.5 dBi with 67% efficiency of the alternating-phase fed array in the 25 GHz band experimentally, with the new design of a tilted main beam in the backfire direction. The design is used by a slot analysis including mutual coupling effects.