The work is supported by INFN, Italy and the EC FP7 Research Infrastructure projects (HadronPhysics3, GA n. 283286 and AIDA, GA 262025). The work is also supported by the MSMT CR grant LE13012.
 P. W. Gorham et al., Observations of microwave continuum emission from air shower plasmas, Phys. Rev. D 78 (2008) 032007.
 R. Gaïor, for the Pierre Auger Collaboration, Detection of cosmic rays using microwave radiation at the Pierre Auger Observatory, Proc. 33rd ICRC, Rio de Janeiro, Brazil (2013) [astro-ph/1307.5059].
 K. Louedec, for the Pierre Auger Collaboration, Radio-detection of extensive air showers at the Pierre Auger Observatory - Results and enhancements, in proceedings of EPS-HEP 2013, PoS(EPS-HEP 2013)027.
 J. Alvarez-Muñiz et al., Search for microwave emission from ultrahigh energy cosmic rays, Phys. Rev. D 86 (2012) 051104(R).