MATRIX CIRCUITS AND BETTER BEAM CHARACTERISTICS FROM MBFN PRODUCED BEAMS
Systems and methods for mitigating beam squint and for producing better beam characteristics from MBFN (multi-beam forming network) generated beams. Matrix circuits are provided that operate as MBFNs where judicious assignment of input beams to specific rows in the matrix produce reduced or mitigated beam squint. As well, phase errors and other issues can be accounted for by adjustment of characteristics in the circuit elements that form the matrix circuit.
1 . A matrix circuit for coupling a plurality of input signal beams to a plurality of output antennas in an antenna array, the matrix circuit comprising:
a matrix of couplers, horizontal phase delay lines, and vertical circuit element lines;
wherein said matrix is configured to form:
a plurality of rows of circuit elements, each row of circuit elements comprising couplers and horizontal phase delay lines, each row receiving an input signal beam and each row comprising couplers coupled in series with at least one horizontal delay line between each pair of adjacent couplers; and
a plurality of columns of circuit elements, each column of circuit elements comprising couplers and vertical circuit element lines, said couplers being coupled in series with at least one vertical circuit element line between each pair of adjacent couplers, each column being coupled between an output antenna and ground;
wherein
at least one column of circuit elements further comprises a load coupled between a coupler and ground;
an output of each column of circuit elements is received by an output antenna element;
said matrix circuit is for forming multiple output beams based on said input signal beams.
2 . The matrix circuit according to claim 1 , wherein at least one row of circuit elements is coupled between an input signal beam and a load.
3 . The matrix circuit according to claim 1 , wherein each coupler is one of: a directional coupler and a hybrid coupler.
4 . The matrix circuit according to claim 1 , wherein phase compensation is applied to at least one of said couplers.
5 . The circuit according to claim 1 , wherein each row of said matrix circuit provides a distinct signal beam having a unique azimuth within a predetermined azimuth range, such that at least three distinct signal beams are provided by said antenna array, said at least three distinct signal beams comprising at least a negative-extreme-azimuth beam corresponding to a negative extreme of said azimuth range, a center azimuth beam corresponding to a center of said azimuth range, and a positive-extreme-azimuth beam corresponding to a positive extreme of said azimuth range,
wherein
said center azimuth beam is provided to a bottom row of said matrix circuit.
6 . The matrix circuit according to claim 5 , wherein a center row of said matrix circuit is provided with one of: said negative-extreme-azimuth beam and said positive-extreme-azimuth beam.
7 . The matrix circuit according to claim 5 , wherein bottom rows of said matrix circuit are assigned with beams having highest directivity.
8 . The matrix circuit according to claim 1 , wherein a cumulative effect of characteristics of said vertical circuit elements for each column is to compensate for a phase error at an input to an output antenna element.
9 . The matrix circuit according to claim 8 , wherein said vertical circuit elements are phase shifters.
10 . The matrix circuit according to claim 8 , wherein said vertical circuit elements are vertical phase delay lines.
11 . The matrix circuit according to claim 9 , wherein said vertical circuit elements are cascaded phase shifters.
12 . A method for improving beam characteristics of beams produced by an antenna array fed by a multibeam forming network (MBFN), the method comprising:
a) providing a matrix circuit of rows and columns of circuit elements to operate as said multibeam forming network;
b) providing input signal beams to said matrix circuit such that specific input signal beams are assigned as input to specific rows of circuit elements in said matrix circuit;
c) executing at least one of:
c1) assigning a specific input signal beam from said input signal beams to a specific row in said matrix circuit, said specific input signal beam having a lowest absolute value azimuth angle among said input signal beams and said specific row being a row most adjacent to ground;
c2) configuring at least one specific column in said matrix circuit to compensate for errors in antenna outputs for said at least one specific column;
wherein said matrix circuit comprises:
a plurality of rows of circuit elements, each row of circuit elements comprising couplers and horizontal phase delay lines, each row receiving an input signal beam and each row comprising couplers coupled in series row-wise with at least one horizontal delay line between each pair of adjacent couplers; and
a plurality of columns of circuit elements, each column of circuit elements comprising couplers and vertical circuit element lines, said couplers being coupled in series column-wise with at least one vertical circuit element line between each pair of adjacent couplers, each column being coupled between an output antenna and ground.
13 . The method according to claim 12 , wherein, for step c1), said specific input signal beam is a center azimuth beam.
14 . The method according to claim 12 , wherein step c1) comprises assigning an input signal beam having a highest absolute value azimuth angle to a row of said matrix circuit that is most adjacent to output antennas to which said matrix circuit is coupled.
15 . The method according to claim 12 , wherein each row of said matrix circuit receives a distinct input signal beam having a unique azimuth within a predetermined azimuth range, such that at least three distinct input signal beams are received by said matrix circuit, said at least three distinct signal beams comprising at least a negative-extreme-azimuth beam corresponding to a negative extreme of said azimuth range, a center azimuth beam corresponding to a center of said azimuth range, and a positive-extreme-azimuth beam corresponding to a positive extreme of said azimuth range, and
wherein said specific input signal beam in step c1) is said center azimuth beam.
16 . The method according to claim 15 , wherein step c1) further comprises providing said negative-extreme-azimuth beam to a center row of said matrix circuit.
17 . The method according to claim 15 , wherein step c1) further comprises providing said positive-extreme-azimuth beam to a center row of said matrix circuit.
18 . The method according to claim 15 , wherein step c1) further comprises providing said negative-extreme-azimuth beam and said positive-extreme-azimuth beam to a first and second top two rows of said matrix circuit.
19 . The method according to claim 12 , wherein step c1) further comprises assigning said rows to signal beams such that each matrix row is adjacent another matrix row receiving an opposite azimuth value, said opposite azimuth value being a same absolute value and an opposite sign.
20 . The method according to claim 12 , wherein step c2) comprises configuring said at least one specific column such that a cumulative effect of characteristics of said vertical circuit elements for said at least one specific column compensates for a phase error at an input to an antenna element for said at least one specific column.
21 . The method according to claim 20 , wherein said vertical circuit elements are one of: phase shifters and vertical phase delay lines.
22 . The method according to claim 21 , said vertical phase delay lines are specific lengths of transmission lines such that a cumulative effect of said vertical phase delay lines is to compensate for said phase error.
23 . The method according to claim 21 , wherein said phase shifters are constructed and arranged to compensate for said phase error.
24 . The method according to claim 21 , wherein step c2) comprises calculating said phase error and adjusting characteristics of said phase shifters to compensate for said phase error.
25 . The method according to claim 12 , wherein said errors in antenna outputs for said at least one specific column is at least one of:
beam squint;
side lobe levels; and
phase errors.
26 . The method according to claim 12 , wherein said matrix circuit is used to generate beams for use in cellular applications.
27 . The matrix circuit according to claim 1 , wherein said matrix circuit is any one of a Nolen matrix, a Blass matrix, a modified Nolen matrix, and a modified Blass matrix.