Overview

Concept

Electromagnetic Vector Sensor (EMVS), first described by Dr. Nehorai [1],[2] in 1991, is currently a subject of active scientific research. It is used in mobile communications for direction finding, beam forming, and polarization matching.

In its classical form, EMVS consists of three mutually orthogonal dipoles, and three mutually orthogonal loops. All six antennas are collocated (their geometric centers coincide). An array of six synchoronized SDR receivers serves as an interface between the sensor and a computer. Using this setup, it is possible to measure the X,Y,Z components of the E and H vectors of the impinging radio wave.

Full information about the E and H vectors allows the PC software to do many interesting things [3],[4], such as:

determine the direction of arrival of the radio waves, both in the azimuth and elevation planes, with high accuracy. This may be done simply by computing the cross product of the E and H vectors;
determine the complete polarization state of the radio wave, linear, circular or elliptic, and adaptively match the polarization of the receiving system;
separate multiple signals on the same frequency if they come from different directions, or at different vertical angles, or if they at least have different polarization.

Advantages

EMVS exploits the pattern and polarization diversity of its receiving elements, and this gives it several advantages over the phased arrays of identical elements that exploit spatial diversity:

it can receive signals from any direction and with any polarization;
collocation of its elements results in a compact design that does not require a lot of real estate;
the EMVS system can be made wideband because it does not depend on the distances between the elements being a certain fraction of the wavelength.

Fig.1. A commercial EMVS antenna

Possible Applications in Ham Radio

EMVS used as a receiving antenna will eliminate most of the QSB by tracking the Faraday rotation of the polarization vector and adaptively changing the polarization of the antenna.
Automatic separation of multiple signals on the same frequency will counteract deliberate QRM in the pileups.
The ability to measure the azimuth and elevation of the radio wave arrival with high accuracy will be extremely valuable for propagation research;
High resolution azimuth estimation will make detection of the pirate stations much easier;
Azimuth information will provide another clue for finding DX signals on the crowded bands. Just imagine a color-coded waterfall display on the HF bands, similar to what DF6NM has done on VLF, where the color indicates the direction of arrival:

Fig.2. Color-coded waterfall display on VLF