Calibration network for a phased array antenna

A method of calibrating an array antenna having a plurality of antenna elements connected to a plurality of T/R modules of an RF front end of the array antenna through a plurality of corresponding coaxial transmission lines in a receiving mode of operation of the RF front end, the method comprising:

• providing a calibration network system including:
• a waveguide arrangement comprising at least one pair of rectangular waveguides having an inside height of side-walls smaller than an inside width of top and bottom walls;
• said at least one pair of rectangular waveguides being stacked in a substantially parallel relation to each other to form a lower rectangular waveguide and an upper rectangular waveguide spaced apart from the lower rectangular waveguide at a distance of about a quarter of a desired operating wavelength of the array antenna;
• said at least one pair of rectangular waveguides including a plurality of circular through-holes extending through at least one side-wall of the stacked rectangular waveguides from a bottom of the lower rectangular waveguide to a top of the upper rectangular waveguide and having a diameter sufficient to accommodate coaxial transmission lines passing through said circular through-holes;
• said at least one side-wall having openings between said circular through-holes and an interior region of said lower and upper rectangular waveguides in order to provide coupling of the coaxial transmission lines into said at least one pair of rectangular waveguides;
• at least one 90 degree phase shifter having two phase shifter terminals and coupled at one phase shifter terminal to one end of the upper rectangular waveguide;
• and
• at least one RF power divider/combiner having an input port configured for coupling to a reference Transmit/Receive (T/R) Module and two output ports being coupled correspondingly to said at least one 90 degree phase shifter at another phase shifter terminal and to one end of the lower rectangular waveguide;
• injecting from a T/R reference module an internal calibration signal having a known amplitude and phase to the input port of said at least one RF power divider/combiner of the calibration network system to obtain a first part of the divided internal calibration signal and a second part of the divided internal calibration signal,
• coupling the first part of the divided internal calibration signal into said at least one 90 degree phase shifter, and coupling a second part of the divided internal calibration signal into the lower rectangular waveguide;
• transferring the first part of the divided internal calibration signal through said at least one 90 degree phase shifter to provide a minus 90 degree phase shift thereto;
• transferring the first part of the divided internal calibration signal shifted by minus 90 degrees through the upper rectangular waveguide and coupling it to portions of the coaxial transmission lines passing through the upper rectangular waveguide;
• transferring the first part of the divided internal calibration signal shifted by minus 90 degrees through portions of coaxial transmission lines that have a length of about a quarter of wavelength from the upper rectangular waveguide towards the lower rectangular waveguide, thereby to return the phase shift of the first part of the divided internal calibration signal to 0 degrees;
• transferring the second part of the divided internal calibration signal within the lower rectangular waveguide,
• coupling the second part of the divided internal calibration signal to the portions of the coaxial transmission lines passing through the lower rectangular waveguide to combine in this portion of the coaxial lines the second part of the divided internal calibration signal with the first part of the divided internal calibration signal;
• relaying a combined internal calibration signal including the first and second parts of the divided internal calibration signal received by each coaxial transmission line to the RF front end of the array antenna;
• comparing the combined internal calibration signal for each coaxial transmission line with a corresponding predetermined reference data signal;
• and
• calculating at least one calibration parameter when the combined internal calibration signal deviates from the corresponding predetermined reference data signal.

A method of calibrating an array antenna having a plurality of antenna elements coupled to a plurality of T/R modules of the array antenna through a plurality of corresponding coaxial transmission lines in a transmitting mode of operation of the RF front end, the method comprising:

• providing a calibration network system including:
• a waveguide arrangement comprising at least one pair of rectangular waveguides having an inside height of side-walls smaller than an inside width of top and bottom walls;
• said at least one pair of rectangular waveguides being stacked in a substantially parallel relation to each other to form a lower rectangular waveguide and an upper rectangular waveguide spaced apart from the lower rectangular waveguide at a distance of about a quarter of a desired operating wavelength of the array antenna;
• said at least one pair of rectangular waveguides including a plurality of circular through-holes extending through at least one side-wall of the stacked rectangular waveguides from a bottom of the lower rectangular waveguide to a top of the upper rectangular waveguide and having a diameter sufficient to accommodate coaxial transmission lines passing through said circular through-holes;
• said at least one side-wall having openings between said circular through-holes and an interior region of said lower and upper rectangular waveguides in order to provide coupling of the coaxial transmission lines into said at least one pair of rectangular waveguides;
• at least one 90 degree phase shifter having two phase shifter terminals and coupled at one phase shifter terminal to one end of the upper rectangular waveguide;
• and
• at least one RF power divider/combiner having an input port configured for coupling to a reference Transmit/Receive (T/R) Module and two output ports being coupled correspondingly to said at least one 90 degree phase shifter at another phase shifter terminal and to one end of the lower rectangular waveguide;
• injecting from each T/R module an internal calibration signal having a known amplitude and phase into corresponding coaxial transmission line;
• coupling a small part of the internal calibration signal into the lower rectangular waveguide through the portions of the coaxial transmission lines passing through the lower rectangular waveguide, transferring this part of the internal calibration signal within the lower rectangular waveguide, and applying this part of the internal calibration signal to one output port of said at least one RF power divider/combiner;
• transferring a major part of the internal calibration signal through portions of coaxial transmission lines that have a length of about a quarter of wavelength from the lower rectangular waveguide towards the upper rectangular waveguide, thereby to provide a phase shift to the major part of the internal calibration signal of plus 90 degrees;
• coupling another small part of the internal calibration signal having a phase shift of plus 90 degrees into the upper rectangular waveguide from the portions of the coaxial transmission lines passing through the upper rectangular waveguide;
• transferring said another small part of the internal calibration signal within the upper rectangular waveguide and through said at least one 90 degree phase shifter configured to provide minus 90 degree phase shift thereto, thereby to return the phase shift of said another part of the internal calibration signal to 0 degrees;
• applying said another small part of the internal calibration signal with a phase shift of 0 degrees to another output port of said at least one RF power divider/combiner;
• combining two small parts of the internal calibration signal by the RF power divider/combiner to obtain a combined internal calibration signal having 0 degree phase shift;
• relaying said combined internal calibration signal to a reference T/R module;
• comparing the combined internal calibration signal for each antenna element with a corresponding predetermined reference data signal;
• calculating at least one calibration parameter when the combined internal calibration signal deviates from the corresponding predetermined reference data signal;
• and
• applying said at least one calibration parameter to RF front end of the array antenna for adjusting operation of the T/R modules.

A method of calibrating an array antenna having a plurality of antenna elements connected to a plurality of T/R modules of the array antenna through a plurality of the corresponding coaxial transmission lines for indicating operation of the antenna elements, the method comprising:

• providing a calibration network system including:
• a waveguide arrangement comprising at least one pair of rectangular waveguides having an inside height of side-walls smaller than an inside width of top and bottom walls;
• said at least one pair of rectangular waveguides being stacked in a substantially parallel relation to each other to form a lower rectangular waveguide and an upper rectangular waveguide spaced apart from the lower rectangular waveguide at a distance of about a quarter of a desired operating wavelength of the array antenna;
• said at least one pair of rectangular waveguides including a plurality of circular through-holes extending through at least one side-wall of the stacked rectangular waveguides from a bottom of the lower rectangular waveguide to a top of the upper rectangular waveguide and having a diameter sufficient to accommodate coaxial transmission lines passing through said circular through-holes;
• said at least one side-wall having openings between said circular through-holes and an interior region of said lower and upper rectangular waveguides in order to provide coupling of the coaxial transmission lines into said at least one pair of rectangular waveguides;
• at least one 90 degree phase shifter having two phase shifter terminals and coupled at one phase shifter terminal to one end of the upper rectangular waveguide;
• and
• at least one RF power divider/combiner having an input port configured for coupling to a reference Transmit/Receive (T/R) Module and two output ports being coupled correspondingly to said at least one 90 degree phase shifter at another phase shifter terminal and to one end of the lower rectangular waveguide;
• applying an external calibration RF radiation having a known amplitude and phase from an external reference RF source sequentially to each of said plurality of antenna elements and coupling an external calibration signal generated by the antenna elements to coaxial transmission lines;
• coupling a small part of the external calibration signal into the upper rectangular waveguide through the portions of the coaxial transmission lines passing through the side-wall of the upper rectangular waveguide;
• transferring said small part of the external calibration signal within the upper rectangular waveguide and through said at least one 90 degree phase shifter to provide plus 90 degree phase shift thereto, and applying the part of the external calibration signal shifted by plus 90 degrees to one output port of said at least one RF power divider/combiner;
• transferring a major part of the external calibration signal from the upper rectangular waveguide towards the lower rectangular waveguide through portions of coaxial transmission lines that have a length of about a quarter of wavelength, thereby to provide a phase shift to the external calibration signal of plus 90 degrees;
• coupling another small part of the external calibration signal shifted by plus 90 degrees to the lower rectangular waveguide for transferring therethrough towards said at least one RF power divider/combiner;
• applying said another small part of the external calibration signal transferred through the lower rectangular waveguide to another output port of said at least one RF power divider/combiner;
• combining the two small parts of the external calibration signal by the RF power divider/combiner to obtain a combined external calibration signal having 90 degree phase shift;
• relaying said combined external calibration signal to a reference T/R module;
• comparing the combined external calibration signal for each antenna element with a predetermined reference data signal;
• and
• providing an indication of those coaxial transmission lines for which the combined external calibration signal deviates from the corresponding predetermined reference data signal.