Investigations of the radio signal of inclined showers with LOPES

We report in this paper on an analysis of 20 months of data taken with LOPES. LOPES is radio antenna array set-up in coincidence with the Grande array, both located at the Karlsruhe Institute of Technology, Germany. The data used in this analysis were taken with an antenna configuration composed of 30 inverted V-shape dipole antennas. We have restricted the analysis to a special selection of inclined showers - with zenith angle θ>40∘. These inclined showers are of particular interest because they are the events with the largest geomagnetic angles and are therefore suitable to test emission models based on geomagnetic effects.The reconstruction procedure of the emitted radio signal in EAS uses as one ingredient the frequency-dependent antenna gain pattern which is obtained from simulations. Effects of the applied antenna model in the calibration procedure of LOPES are studied. In particular, we have focused on one component of the antenna, a metal pedestal, which generates a resonance effect, a peak in the amplification pattern where it is the most affecting high zenith angles, i.e. inclined showers. In addition, polarization characteristics of inclined showers were studied in detail and compared with the features of more vertical showers for the two cases of antenna models, with and without the pedestal.