Radio communications apparatus

Radio communications apparatus comprising:

• a quadrature modulator for making the transition of the phase of a modulated wave via a in-phase component and a quadrature component;
• a first voltage-controlled oscillator for outputting a first transmission signal;
• a second voltage-controlled oscillator;
• a first mixer for frequency-converting the first transmission signal based on the output signal of the second voltage-controlled oscillator;
• a phase comparator for comparing the phase of the output signal of the quadrature modulator with the phase of the output signal of the first mixer;
• a low-pass filter for filtering the component below a predetermined frequency of the output signal of the phase comparator and supplying the resulting signal to the frequency control terminal of the first voltage-controlled oscillator;
• and
• a first band-pass filter for outputting a signal obtained by filtering the component in a predetermined frequency band of the output signal of the quadrature modulator as a second transmission signal.