mixer_testbench_please_explain

why voltage controlled voltage source are used in mixer test bench? dont understanding the test bench for RF mixer in cadence

Mixers to be tested require a local-oscillator to operate. MOst often, a VCO is used for a required frequency coverage.
LO frequency and power should be adjusted to mixer specification.

ya vco is required but in test bench of mixer the input LO signal is given through vcvs al