A method for calibrating a radar apparatus, comprising: measuring a first electrical length which is a round-trip electrical length of a sub-array transmit path from a first radar signal input port to a first terminal of a circulator in a sub-array driver module of a sub array of the radar apparatus using time domain reflectometry when the sub-array transmit path from the first radar signal input port to the sub-array driver module is terminated by a first short circuit at the first terminal of the circulator, the first terminal being located between the first radar input port and the circulator; measuring a second electrical length which is a round-trip electrical length of the sub-array transmit path from the first radar signal input port through the circulator via the first terminal of the circulator using time domain reflectometry when a transmit/receive path between the sub-array driver module and a solid state module 'SSM' of the sub array is terminated with a second short circuit at a second terminal of the circulator, and when the sub-array receive path from the first radar input port through the circulator in the sub-array driver module to receiver circuitry is terminated with a third short circuit at a third terminal of the circulator, the second terminal being located between the circulator and the SSM, and the third terminal being located between the circulator and the receiver circuitry; measuring a third electrical length which is an electrical length of a sub-array receive path of the sub-array from the first radar input port through the circulator to the receiver circuit when the transmit/receive path between the sub-array driver module and an array element module of the radar is terminated with the second short circuit at the second terminal of the circulator; measuring a fourth electrical length which is an electrical length in the radar apparatus of a transmit and receive path between the sub-array driver module of the sub-array and the SSM of the sub-array by injecting an exciter signal into the sub-array driver module, through a passive calibration loop in the SSM, and measuring the exciter signal at the receiver circuitry; measuring a fifth electrical length which is an electrical length in the radar apparatus of a receive path between the sub-array driver module and the SSM; measuring a sixth electrical length which is an electrical length in the radar apparatus of a transmit path between the sub-array driver module and the SSM; based upon the measurements, adjusting the transmit path between the sub-array driver module and the SSM by adjusting a phase control circuit in the SSM; and based upon the measurements, adjusting the receive path between the sub-array driver module and the SSM by controlling the phase control circuit in the SSM. measuring a first electrical length which is a round-trip electrical length of a sub-array transmit path from a first radar signal input port to a first terminal of a circulator in a sub-array driver module of a sub array of the radar apparatus using time domain reflectometry when the sub-array transmit path from the first radar signal input port to the sub-array driver module is terminated by a first short circuit at the first terminal of the circulator, the first terminal being located between the first radar input port and the circulator; measuring a second electrical length which is a round-trip electrical length of the sub-array transmit path from the first radar signal input port through the circulator via the first terminal of the circulator using time domain reflectometry when a transmit/receive path between the sub-array driver module and a solid state module 'SSM' of the sub array is terminated with a second short circuit at a second terminal of the circulator, and when the sub-array receive path from the first radar input port through the circulator in the sub-array driver module to receiver circuitry is terminated with a third short circuit at a third terminal of the circulator, the second terminal being located between the circulator and the SSM, and the third terminal being located between the circulator and the receiver circuitry; measuring a third electrical length which is an electrical length of a sub-array receive path of the sub-array from the first radar input port through the circulator to the receiver circuit when the transmit/receive path between the sub-array driver module and an array element module of the radar is terminated with the second short circuit at the second terminal of the circulator; measuring a fourth electrical length which is an electrical length in the radar apparatus of a transmit and receive path between the sub-array driver module of the sub-array and the SSM of the sub-array by injecting an exciter signal into the sub-array driver module, through a passive calibration loop in the SSM, and measuring the exciter signal at the receiver circuitry; measuring a fifth electrical length which is an electrical length in the radar apparatus of a receive path between the sub-array driver module and the SSM; measuring a sixth electrical length which is an electrical length in the radar apparatus of a transmit path between the sub-array driver module and the SSM; based upon the measurements, adjusting the transmit path between the sub-array driver module and the SSM by adjusting a phase control circuit in the SSM; and based upon the measurements, adjusting the receive path between the sub-array driver module and the SSM by controlling the phase control circuit in the SSM.