Slot array in non-radiating dielectric waveguide

The non-radiating dielectric (NRD) guide has proven to be one of the promising candidate for microwave and millimeter wave applications due to its inherently low-loss in transmission. Also, since the separation between the ground planes is less than half a free-space wavelength, the NRD effectively suppresses radiation at curved sections and discontinuities. A slotted-array antenna in an NRD thus offers one the flexibility to design low loss antennas with desirable side-lobe levels. This was proposed by Malherbe et al. (1984) Since it is constructed in the same guide system, it also avoids the need for costly transitions. However, the field produced by a slot cut in the axial direction of the NRD guide varies co-sinusoidally in the dielectric region and decays exponentially in the air region. The current distribution in the NRD is an even function about the center line so that for a broadside array, the axially directed slots can only be spaced one guide wavelength apart which will result in unwanted grating lobes in the radiation pattern. To avert this problem, slant slots, spaced half a guide wavelength apart and with alternating inclinations can be used, with coupling to the NRD adjusted by the slot inclination. The theoretical design of a slotted array NRD guide proposed by Malherbe et al. is discussed, and used for further optimisation.