An alternating-phase fed slotted waveguide array with a double-layered feed structure and meandering radiating waveguides in 60 GHz band

Abstract

An alternating-phase fed single-layer slotted waveguide array is an attractive candidate for high gain and mass producible millimeter wave planar antennas because of small transmission loss of a waveguide even in millimeter wave and its simple structure suitable for mass-production [1]-[5]. It consists of several radiating waveguides with a resonant shunt slot array and a feed waveguide arranged at the end of the radiating waveguides. The whole structure is accommodated in a single layer. The radiating waveguides are excited 180-degree out of phase with adjacent ones by a cascade of T-junctions arrayed at a spacing of a half guided wavelength in the feed waveguide. A great advantage of the alternating-phase fed array is cost reduction for assembling; a slotted plate and a groove feed structure are just tacked and fixed screws together with a choke structure at the periphery [3]. This array has already been put into practical use for 26GHz wireless IP access service (WIPAS) system [4]. 31.5 dBi gain with 65 % efficiency in 26 GHz and 34.8 dBi gain with 57% efficiency in 76 GHz [5] are achieved by the prototypes, respectively. The authors have also developed the alternating-phase fed array with a sector shaped pattern for radar applications in 60 GHz [6]. A problem of this array is narrow bandwidth, that is, side lobe level is increased in case that the operation frequency is changed from the design one, since the feeding network of the alternating-phase fed array is a series circuit. In order to solve this problem, a novel alternating-phase fed array is proposed in this paper. A double-layer feeding network, the upper layer for the alternating-phase fed slotted waveguide array and the lower layer for a tournament-type parallel-fed power divider, is introduced to reduce the long line effect. Furthermore, meandering structure is adopted for the radiating waveguides to eliminate grating lobes due to the staggered slot arrangement. In this paper, design of the proposed array and experimental results of the prototype array in 60 GHz are described.