Below-resonant-length slot radiators for traveling-wave-array antennas

For a frequency-scanning-radar project, a traveling-wave-array antenna was designed. It employs radiating slots in the narrow wall of a meander-rectangular waveguide, which is milled in a flat metal block. Due to the restriction of the waveguide width, the maximum slot length that could be implemented is less than a half wavelength, i.e., below the resonant length. Although such slots are commonly deemed useless, it is shown that traveling-wave-array antennas can be designed successfully. This paper describes the design and results of low-sidelobe arrays, starting from the measurement of basic slot characteristics in an array simulator. The realization of a prescribed amplitude distribution, by tapering the slot length, is shown. The creation of phase errors, due to the reactive nature of the slots, and the associated pattern-degradation effects, are discussed in detail.