Sentence:  Very recently , observations have been made at 8 - mm wave length with a reflector 22 meters in <WSD>diameter</WSD> with a resultant beam width of only about 2 ' ( Amenitskii , Noskova , and Salomonovich , 1960 ) . 
Meaning of the word marked with <WSD> tags:  the length of a straight line passing through the center of a circle and connecting two points on the circumference