Frequency characteristics of alternating-phase single-layer slotted waveguide array with reduced narrow walls

There are strong demands for high gain and mass produceable planar arrays at millimeter waves. However the planar arrays reported in the literature adopt microstrip or triplate lines as the feeder, which inherently suffer from serious losses at millimeter-wave frequencies. On the other hand, the transmission loss is so negligible for the waveguide that a slotted waveguide array antenna is a leading candidate for a high-gain flat antenna at millimeter-wave frequencies. The authors show two types of single-layer slotted waveguide array antenna; one is a co-phase type and the other is an alternating-phase one. The former has already achieved a high-efficiency and a high-gain performance at microwave frequencies, but is slightly degraded at millimeter-wave frequencies due to the incomplete contact between the slot plate and groove structure electrically. The electric contact is not important in the latter because no total currents flow across them. Furthermore, all the side-walls can be removed in principle at the center frequency. This reduced side-wall structure is expected to have higher-efficiency than the co-phase feeding type because reduction of side-walls reduces the loss as well as cost for fabrication. But the distance between null points of the guided standing wave and slots varies according to frequency changes. This results in a narrow antenna bandwidth. In this paper, characteristics of single-layer waveguides are surveyed in terms of efficiency and mass produceability. Secondly, bandwidth is evaluated for reduced side-wall antennas.