First Experimental Characterization of Microwave Emission from Cosmic   Ray Air Showers
  We report the first direct measurement of the overall characteristics of microwave radio emission from extensive air showers. Using a trigger provided by the KASCADE-Grande air shower array, the signals of the microwave antennas of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have been read out and searched for signatures of radio emission by high-energy air showers in the GHz frequency range. Microwave signals have been detected for more than 30 showers with energies above 3*10^16 eV. The observations presented in this Letter are consistent with a mainly forward-directed and polarised emission process in the GHz frequency range. The measurements show that microwave radiation offers a new means of studying air showers at energies above 10^17 eV. 
R. Smida, F. Werner, R. Engel, J.C. Arteaga-Velazquez, K. Bekk, M.   Bertaina, J. Bluemer, H. Bozdog, I.M. Brancus, A. Chiav...
astro-ph.IM astro-ph.HE