During research into using microwaves for communication it was found that the presence of boats and planes could be detected by the energy they reflected. After a link realized in 1931 by a French–English group across the English Channel, using waves of 18 cm, great interest arose throughout the world for microwave communications. C E Cleeton and N H Williams of the Michigan University performed the first spectroscopic measurements at microwave frequencies at that time, using a magnetron to investigate the absorption spectrum of gaseous ammonia. Microwave instrumentation and production techniques received a vigorous impulse between 1930 and 1945 due to the need to produce ultrashort waves for the development and construction of radar. In Russia, the employment of radio waves for communications was developed independently from Guglielmo Marconi, by Professor Aleksandr S Popov who developed one of the first receivers of electromagnetic waves.