About possibility to create a small antenna based on inhomogeneous biconical line

Design of efficient electrically small antennas is very important for miniaturization of radio communication devices. However besides some technical difficulties there is a fundamental problem: an antenna with the size much smaller than the wavelength cannot radiate efficiently. As a result for an antenna there exists a lower cut-off frequency f_c. For frequencies f <; f_c an antenna cannot radiate and all the fed energy is reflected back to the generator. The cut-off frequency f_c depends on the size of an antenna, so the problem of miniaturization can be considered: for given size to design the antenna with the lowest possible cut-off frequency. From this point of view we are going to consider one of the simplest antenna geometries based on irregular biconical line with dielectric filling.