Meaning
Transmitter testing and characterization require realistic signal environments that replicate the dense spectrum of modern communication networks. The process of applying multi-carrier excitation involves feeding several independent signals simultaneously into a single device under test. This method evaluates how the component handles multiple distinct frequencies without generating excessive distortion.
Distortion Generation
Nonlinearities in high-power amplifiers cause different input frequencies to mix and produce new spurious frequencies. When multi-carrier excitation is applied, these intermodulation products can fall directly into adjacent channels. This adjacent-channel leakage degrades the performance of neighboring wireless networks.
Power Demand
The peak-to-average power ratio of a composite signal increases significantly when multiple carrier frequencies are combined. These peak power spikes can drive the amplifier into hard saturation or trigger over-current protection circuits. To prevent this, the transmitter must be operated with sufficient output power back-off.
This back-off reduces the overall efficiency of the amplifier but is necessary to prevent signal clipping and maintain high linearity across all channels.
Test Application
RF engineers utilize multi-carrier excitation during the design verification phase to evaluate base station transmitter designs. This approach simulates the complex modulation schemes of commercial cellular systems under peak traffic loads. High-performance signal generators synthesize the composite wave, and a spectrum analyzer measures the resulting intermodulation distortion.
