A Rydberg sensor for detecting radio signals comprising: - A computer processor and data storage medium arranged to receive data from photodetectors, provided with instructions to control the computer processor compare their time variation of intensity, to determine a radio signal incident on the vapour cell. - A detector unit comprising at least one Rydberg vapour cell exposed to receive radio signals incident thereon, and a probe laser input unit and a coupling laser input unit; Characterised in that: - The probe laser input unit comprises a first row of beam splitters (2a 2b 2c) arranged to accept and direct a probe laser input from a probe laser input port at an input end of the row, into a respective vapour cell window area of the Rydberg vapour cell(s), as an array of at least three probe laser beams; - The coupling laser input unit comprises a second row of beam splitters arranged to accept and direct a phase or frequency modulated coupling laser input beam, from a coupling laser input port at an input end of the row, into a respective vapour cell window area of the Rydberg vapour cell(s), as an array of at least three coupling laser beams; - In use, the two arrays of laser beams are aligned to each other to provide opposed pairs of laser beams, each pair intersecting within the vapour of the Rydberg vapour cell(s) with parallel and opposite beam directions; - For each of the two rows of beamsplitters, either: - the beam splitting ratio of the beam splitters regarding the proportion of laser light directed to the Rydberg vapour cell(s), increases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and/or - an optical density of optical filters or reflectors associated with respective output paths to the vapour in the Rydberg vapour cell(s) decreases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and - The photodetectors comprise an array of at least three photodetectors, each arranged to measure the time variation of intensity of laser light from a respective one of the probe laser beams exiting the vapour cell(s) from a vapour cell window area; - The coupling laser input unit is arranged to direct each respective probe laser beam from the Rydberg vapour cell(s) to a respective photodetector of the array such that each photodetector receives light from only one of the probe lasers of the at least three probe laser beams; - A computer processor and data storage medium arranged to receive data from photodetectors, provided with instructions to control the computer processor compare their time variation of intensity, to determine a radio signal incident on the vapour cell. - A detector unit comprising at least one Rydberg vapour cell exposed to receive radio signals incident thereon, and a probe laser input unit and a coupling laser input unit; - The probe laser input unit comprises a first row of beam splitters (2a 2b 2c) arranged to accept and direct a probe laser input from a probe laser input port at an input end of the row, into a respective vapour cell window area of the Rydberg vapour cell(s), as an array of at least three probe laser beams; - The coupling laser input unit comprises a second row of beam splitters arranged to accept and direct a phase or frequency modulated coupling laser input beam, from a coupling laser input port at an input end of the row, into a respective vapour cell window area of the Rydberg vapour cell(s), as an array of at least three coupling laser beams; - In use, the two arrays of laser beams are aligned to each other to provide opposed pairs of laser beams, each pair intersecting within the vapour of the Rydberg vapour cell(s) with parallel and opposite beam directions; - For each of the two rows of beamsplitters, either: - the beam splitting ratio of the beam splitters regarding the proportion of laser light directed to the Rydberg vapour cell(s), increases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and/or - an optical density of optical filters or reflectors associated with respective output paths to the vapour in the Rydberg vapour cell(s) decreases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and - the beam splitting ratio of the beam splitters regarding the proportion of laser light directed to the Rydberg vapour cell(s), increases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and/or - an optical density of optical filters or reflectors associated with respective output paths to the vapour in the Rydberg vapour cell(s) decreases from a first beamsplitter thereof to a second beamsplitter thereof, from the input end along the row; and - The photodetectors comprise an array of at least three photodetectors, each arranged to measure the time variation of intensity of laser light from a respective one of the probe laser beams exiting the vapour cell(s) from a vapour cell window area; - The coupling laser input unit is arranged to direct each respective probe laser beam from the Rydberg vapour cell(s) to a respective photodetector of the array such that each photodetector receives light from only one of the probe lasers of the at least three probe laser beams;