The narrow-wall slot array is a popular microwave frequency antenna, which is especially useful for RADAR applications where mechanical robustness, low-loss and the ability to withstand high transmit power are advantageous. A single instance of the linear array produces a fan beam, while a pencil beam may be created by stacking a number of arrays to realize a planar configuration.
The magnitude of the wave launched from the feed of the traveling-wave slotted waveguide array decays towards the load as the energy is coupled out and radiated by the slots. At the termination side of the waveguide, the remaining un-radiated power is absorbed by a matched load. For a correctly designed array the absorbed power should only be a small percentage of the input power. ...Fan-beam radiation patterns of linear traveling-wave narrow wall slotted guide arrays at the center frequency of the operating band for (a) 12-element (with negative squint) and (b) 54-element (with positive squint) arrays.
The antenna is well matched over a reasonably wide bandwidth and the bandwidth does not degrade with increasing array length, as is the case for a resonant array. The antenna is designed such that coupling between the travelling wave and the radiating slots increases towards the load, such that the radiation intensity from the second half of the array is comparable to that from the first half. The slots are spaced such that there is a progressive phase shift between slots, resulting in a fan beam which squints off broadside at an angle that increases with excitation frequency - a property that is leveraged in many applications.Typical main beam scan versus frequency for a 54-element array