The conical antenna as a sensor or probe

It is shown that the electrically small wide-angled spherically capped conical monopole has frequency-related properties closely resembling those of the electrically thin cylindrical dipole. It is pointed out that the frequency dependence of the current in the load of a conical receiving antenna can be determined by applying the reciprocal theorem. At each frequency, there are three steps to be followed. The first is determining the radiation field of the conical antenna when driven by unit voltage. The second is locating a thin cylindrical dipole in the far field of the conical antenna and determining the current in its load. The application of the reciprocal theorem demonstrates that this is also the current in an equal load in the conical antenna when the cylindrical dipole is driven by unit voltage. The third step is determining the field arising from the cylindrical dipole at the location of the conical antenna. This, it is pointed out, is the incident field that excites the current in the load of the conical antenna.