Direction finding

A direction finding system comprising:

• a) a plurality of antennas;
• b) means for determining individual antenna signal strengths, the means for determining individual antenna signal strengths comprising a first multipole switch having input poles connected to receive signals from respective antennas;
• c) combining means for deriving combined antenna signal strengths by forming combinations of a first and second antenna signals derived from different antennas, wherein the second antenna signals are in two sets with signals in one set having a non-zero phase difference relative to signals in the other set, the combining means incorporating a second multipole switch having input poles connected to receive signals from respective antennas and a third multipole switch for switching phase shifting means into and out of an antenna signal path extending via the second multipole switch;
• d) the combining means also incorporating adding means for combining signals, the adding means being arranged to add an antenna signal in a first signal path extending via the first multipole switch to another antenna signal in a second signal path extending via the second and third multipole switches;
• and
• e) means for determining at least one emitter bearing from antenna signal strengths.

A method of direction finding using a plurality of antennas comprising the steps of determining:

• a) individual signal strengths of signals received by each of the plurality of antennas;
• b) combined antenna signal strengths by forming combinations of first and second antenna signals derived from different antennas, wherein the second antenna signals are in two sets with signals in one set having a non-zero phase difference relative to signals in the other set;
• and
• c) at least one emitter bearing from the individual and combined antenna signal strengths measured.

A method of direction finding using a plurality of antennas comprising the steps of determining:

• a) individual antenna signal strengths;
• b) combined antenna signal strengths by forming combinations of first and second antenna signals derived from different antennas, wherein the second antenna signals are in two sets with signals in one set having a non-zero phase difference relativerel-a-tiftg to signals in the other set;
• and
• c) at least one emitter bearing from the antenna signal strengths, wherein step a) comprises switching signals from antennas via a first path;
• and step b) incorporates:
• i) switching signals from antennas via a first path for combining;
• ii) switching signals from antennas via a switch selectable second path or a third path for combining, the third path being arranged to phase shift antenna signals therein relative to antenna signals in the second path;
• and
• iii) adding a first path antenna signal to second and third path antenna signals individually.

A method of direction finding using a plurality of antennas comprising the steps of determining:

• a) individual antenna signal strengths by switching signals from the antennas via a first path;
• b) combined antenna signal strengths by forming combinations of first and second antenna signals derived from different antennas, wherein the second antenna signals are in two sets with signals in one set having a non-zero phase difference relative to signals in the other set;
• and
• c) covariance matrix elements using the individual and combined antenna signal strengths measured, and determining at least one emitter bearing therefrom;
• wherein the step of determining combined antenna signal strengths incorporates:
• i) switching signals from antennas via a first path for combining;
• ii) switching signals from antennas via a switch selectable second path or a third path for combining, the third path being arranged to phase shift antenna signals therein relative to antenna signals in the second path;
• and
• iii) adding a first path antenna signal to second and third path antenna signals individually.

A direction finding system incorporating:

• a) a plurality of antennas;
• b) measuring apparatus for determining strengths of signals received by each of the plurality of antennas;
• c) a combining circuit for deriving combined antenna signal strengths by forming combinations of first and second antenna signals derived from different antennas, wherein the second antenna signals are in two sets with signals in one set having a non-zero phase difference relative to signals in the other set;
• and
• d) digital signal processing apparatus for determining at least one emitter bearing from the individual and combined antenna signal strengths measured.