TARC is the method of manipulating all S parameters for the N-port network and displaying a single curve that has all information of S parameters. A single curve of TARC can be used to determine the resonance frequency and impedance bandwidth of the whole antenna system for specified phase excitation between ports. In other words, this MIMO parameter depicts how much or what degree of interference is going between antenna elements.
Formula for calculating TARC for a two port system is attached below.
The curve in the question shows S parameter of MIMO antenna for various values of input feeding phase.
The total active reflection coefficient (TARC) relates the total incident power to the total outgoing power in an N-port microwave component. The TARC is mainly used for multiple-input multiple-output (MIMO) antenna systems and array antennas, where the outgoing power is unwanted reflected power. The name shows the similarities with the active reflection coefficient, which is used for single elements. The TARC is the square root of the sum of all outgoing powers at the ports, divided by the sum of all incident powers at the ports of an N-port antenna. Similarly to the active reflection coefficient, the TARC is a function of frequency, and it also depends on scan angle and tapering.
The parameter of Total Active Reflective Coefficient (TARC) in terms of S-parameter is evaluated by using the relation same is given attached figure.
Pl. go through and try to generate data in excel sheet and plot.