An antenna assembly comprising: an open-ended coaxial waveguide (150; 300; 350; 360; 380; 390; 400; 410; 430; 440; 600; 620), comprising: an inner electrically conducting surface having a substantially uniform cross section extending along a central axis; and an outer electrically conducting surface having a substantially uniform cross section extending along the central axis, the outer conductive surface spaced apart from and opposing the inner electrically conducting surface; a first electromagnetic coupling module (160'; 200; 212) disposed at least partially within the coaxial waveguide and aligned substantially along a radius; a second electromagnetic coupling module (160"; 200; 212) disposed at least partially within the coaxial waveguide and aligned substantially along a different radius, each of the first and second electromagnetic coupling modules comprising: a respective pair of opposing transducers (202, 204; 214, 215), each transducer adapted to convert between an electromagnetic field and at least one of a voltage and a current; and a respective electronic circuit (206; 216) in electrical communication between the respective pair of opposing transducers, at least one of the respective electronic circuits comprising a phase-adjusting element adapted to introduce a phase difference between the at least one of a voltage and a current of the first and second electromagnetic coupling modules. an open-ended coaxial waveguide (150; 300; 350; 360; 380; 390; 400; 410; 430; 440; 600; 620), comprising: an inner electrically conducting surface having a substantially uniform cross section extending along a central axis; and an outer electrically conducting surface having a substantially uniform cross section extending along the central axis, the outer conductive surface spaced apart from and opposing the inner electrically conducting surface; an inner electrically conducting surface having a substantially uniform cross section extending along a central axis; and an outer electrically conducting surface having a substantially uniform cross section extending along the central axis, the outer conductive surface spaced apart from and opposing the inner electrically conducting surface; a first electromagnetic coupling module (160'; 200; 212) disposed at least partially within the coaxial waveguide and aligned substantially along a radius; a second electromagnetic coupling module (160"; 200; 212) disposed at least partially within the coaxial waveguide and aligned substantially along a different radius, each of the first and second electromagnetic coupling modules comprising: a respective pair of opposing transducers (202, 204; 214, 215), each transducer adapted to convert between an electromagnetic field and at least one of a voltage and a current; and a respective electronic circuit (206; 216) in electrical communication between the respective pair of opposing transducers, at least one of the respective electronic circuits comprising a phase-adjusting element adapted to introduce a phase difference between the at least one of a voltage and a current of the first and second electromagnetic coupling modules. a respective pair of opposing transducers (202, 204; 214, 215), each transducer adapted to convert between an electromagnetic field and at least one of a voltage and a current; and a respective electronic circuit (206; 216) in electrical communication between the respective pair of opposing transducers, at least one of the respective electronic circuits comprising a phase-adjusting element adapted to introduce a phase difference between the at least one of a voltage and a current of the first and second electromagnetic coupling modules.