Sentence:  Very recently , observations have been made at 8 - mm <WSD>wave</WSD> length with a reflector 22 meters in diameter with a resultant beam width of only about 2 ' ( Amenitskii , Noskova , and Salomonovich , 1960 ) . 
Meaning of the word marked with <WSD> tags:  the distance (measured in the direction of propagation) between two points in the same phase in consecutive cycles of a wave