In general, a vector modulator is a device that is used in a measuring machine and an amplifier, so as to simultaneously control the amplitude and phase of a signal. The vector modulator converts an input signal into an in-phase (I) channel signal and a quadrature (Q) channel signal, which have a phase difference of 90 degrees. The I/Q channel signals are output in the state in which the amplitude of each of the I/Q channel signals is not changed, but only the phase of each of the I/Q channel signals is changed depending on an external control signal. The output signals are attenuated with a certain attenuation rate by an amplitude variable attenuator and then output as a vector sum of the attenuated signals.
However, a conventional vector modulator generates four uppermost signals and variably controls the amplitude of each uppermost signal using an amplitude variable attenuator. Then, the conventional vector modulator outputs a vector sum obtained by combining the uppermost signals. In this case, the amplitude variable attenuator is necessarily required in the conventional vector modulator, and therefore, the circuit configuration of the conventional vector modulator is complicated.
In order to use the amplitude variable attenuator, the conventional vector modulator has a disadvantage in that I/Q channel signals should be respectively converted into amplitude control values so as to obtain an arbitrary phase angle. The conventional vector modulator has a problem in that the process of obtaining a phase angle output as a final vector sum is complicated.
Further, a conventional single vector modulator has a problem in that the modulation phase of a modulator is changed into two unit vectors having angles of 0 and 180 degrees, and therefore, the phase of an input signal cannot be converted into all areas in the polar coordinate system.