This work introduces an orthogonal amplitude modulation (AM) technique for simultaneous measurement of phased-array elements. The approach leverages a code-modulated embedded test (CoMET) technique in which a test signal is injected to the array, on-off keying is applied to each element using the existing variable-gain amplifiers and vector interpolators, signals are combined and then squared using a power detector, correlations are demodulated from the squared response, and then amplitude and phase are estimated using an equation solver. The amplitude modulation technique can be used in systems where phase modulation is either difficult or erroneous. This paper presents the theory for AM-CoMET and demonstrates its operation using an eight-element phased array transmitter operating at 8 GHz. The extracted gain and phase from the new technique are compared with a vector network analyzer (VNA), showing that AM-CoMET extracted gain and phase are accurate to within 0.25 dB gain error and 2° phase error.