This paper aims to design a 2Ã—2 antenna array testbed to serve as a complete tower-top calibration system that is able to eliminate the effect of transmitter differences of an array elements. The testbed architecture is based on an advanced tower-top interlinear reference calibration scheme where a non-radiative reference sensor is located in the centre of the array and four transmitter elements are coupled to its. The prototype system was built using commercial off the shelf components and it operates in the 2.4 GHz ISM band. A software control capability via a PC parallel port interface makes it flexible for testing other calibration algorithm implementations. Continuous real time calibration is also possible and easy to apply. Experimental results of tower-top calibration accuracy in transmit mode operation are presented. The measured performance of prototype system calibration shows amplitude and phase imbalance better than 0.15 dB and 1.1Â°.