After the design and successful use of the active dipole antenna for CODALEMA2, attempts were made to improve again the sensitivity of the antenna.

Coted drawing of the Butterfly antenna used by the autonomous stations. Coted drawing of the Butterfly antenna used by the autonomous stations.

In 2008, after having tested several possibilities, the “butterfly” shape of the aerial was chosen. It is still equivalent to a fat dipole, for what rules the behaviour of the antenna is the external path of the current in the antenna poles: the latter could as well be plain metallic plates, however the proposed design minimizes the weight and quantity of matter used. The definitive Butterfly design was adopted in 2011 and, at first with the CODALAMP LNA then the LONAMOS, further equipped all the CODALEMA autonomous stations.

Spectral response of the Butterfly antenna Due to the longer arms and a fine tuning of the LONAMOS LNA, the spectral response of the Butterfly extends up to 250 MHz, with still a bit sensitivity above (here the power spectral densities of a cosmic ray event detected by a station). This very wide bandwidth, from 20 to 250 MHz, makes the Butterfly antenna and the LONAMOS unique in their field.

Evolution of the Butterfly antenna Mosaic picture of the various successive designs of the Butterfly. A “tripole” and a low frequency version were made in 2013 and 2014 in the scope of EXTASIS.