Active Impedance Mismatch

An adaptive linearization strategy designed to compensate for the distortion caused by the time-varying load impedance presented to a power amplifier in a beamforming array. As the beam scans, the impedance seen by each PA changes dynamically, altering its nonlinear characteristics. Load modulation DPD tracks these impedance variations in real-time and adjusts the predistorter coefficients accordingly.

• Compensates for dynamic load-pull effects
• Often uses a look-up table indexed by beam angle
• Critical for maintaining ACLR across the full scan range

The electromagnetic interaction between antenna elements in an array where energy from one element induces currents in another, altering the impedance and radiation pattern of each element. Mutual coupling is the primary physical mechanism that causes active impedance mismatch. When beamforming weights change, the coupling environment shifts, and the impedance seen by each PA's output port varies.

• Modeled via the S-parameter coupling matrix
• Increases with reduced element spacing (< λ/2)
• Creates element-specific nonlinear distortion signatures

A digital predistortion technique that accounts for the dynamic changes in PA nonlinearity caused by varying beamforming weights in a phased array. Rather than applying a static linearization model, beamforming-aware DPD receives the current beamforming coefficient vector as an input and adapts its predistortion function accordingly.

• Integrates beam index or weight vector into the DPD model
• Prevents beam-dependent ACLR degradation
• Essential for 5G massive MIMO base stations with wide scan angles

A signal processing method to mitigate the effects of unintended electromagnetic interaction between adjacent antenna elements in a MIMO array. While active impedance mismatch describes the impedance variation problem, cross-coupling cancellation addresses the resulting signal leakage between transmit chains. The two phenomena are tightly linked: mutual coupling causes both impedance mismatch and cross-channel interference.

• Uses digital cancellation filters between adjacent branches
• Requires accurate coupling path estimation
• Often combined with DPD in a joint linearization framework

A linearization method that explicitly models the S-parameter coupling network between antenna elements to decouple and linearize the array's radiated field. The coupling matrix captures the forward and reverse wave relationships between all ports, providing a complete description of the impedance environment. By inverting this matrix digitally, the DPD system can pre-compensate for both nonlinearity and coupling simultaneously.

• Based on measured or simulated S-parameters
• Enables per-element linearization in strongly coupled arrays
• Computationally intensive but highly accurate for small to medium arrays

A linearization technique where the combined radiated signal from an antenna array is captured by a far-field observation receiver and used as feedback. This approach inherently accounts for active impedance mismatch because it measures the actual radiated field after all coupling and impedance effects have occurred. The DPD coefficients are optimized to linearize the spatial composite signal rather than individual PA outputs.

• Eliminates need for per-element couplers and feedback paths
• Captures array-level nonlinear behavior including mismatch effects
• Well-suited for mmWave and tightly integrated arrays