An Electro-Optic E-Field Probe
The aim of this project is to develop small sized, broadband antennas for up to about 6 GHz. Since for distributed antenna systems the attenuation in the feeding line is of great importance, special attention is focussed on the antenna feeding and the total system costs.
A novel concept for an electric-field (E-field) receiving antenna is investigated. The reactive near field, induced by an impinging E-field, of a very short, short-circuited dipole is picked-up with the aid of an electro-optical modulator. The modulator can be designed as a Fabry-Perot etalon. The laser light guided in the etalon is modulated proportionally to the near field of the dipole. The advantage of the etalon is to considerably increase the sensitivity of the antenna compared to known electro-optic probes. Other structures of the modulator are also under investigation. It has been shown analytically for an ellipsoidal dipole and numerically for a cylindrical dipole, that only the quasi electrostatic terms of the dipole field are relevant. The advantage of using a dipole much shorter than the wavelength is to minimize the interaction of the antenna with the environment and the impinging electromagnetic (EM) field.
The proposed antenna may either be used as E-field probe or receiving antenna. It features low coupling because of the small size, low signal attenuation in the fibre optic feeding line and large bandwidth.