Diffraction effects of a tape covering the gaps of a panelled 'compact range' operating at millimetre waves

Diffraction which arises at the interpanel gap edges of a panelled reflector in a 'compact antenna test range' clutters the measured radiation pattern with the formation of spurious lobes. The the approach of covering the gaps with a thin metallic tape is studied in terms of its effectiveness to suppress the spurious effects at frequencies mainly in the 180 GHz band. A ray GO/GTD like approach is employed. Diffraction from the tape edges is accounted for. The conclusion of the analysis is that the tape can itself induce a spurious lobe, the strength of which depends on factors such as tape thickness and width as well as its location on the reflector surface. In addition, the spurious lobe strength is affected by the edge misalignment of the gap which the tape covers as well as the possible pillowing of the tape over the gap. Experimental results are presented that agree with theoretical predictions. Spurious lobes with a level around -45 dB have been observed in practice, providing an average figure of 13 dB suppression relative to the bare gap case.