Frequency converter used for a receiver which receives signals of a UHF band or a microwave band

A frequency converter comprising:

• (a) a signal divider, having an input terminal for receiving an input signal containing a main signal and an image signal supplied to said input terminal, for dividing said input signal supplied to said input terminal into a first divided input signal and a second divided input signal;
• (b) a first local oscillation signal generator circuit having a frequency control terminal supplied with a channel select voltage, and a first voltage-controlled oscillator for generating a first local oscillation signal having an oscillation frequency which changes depending upon said channel select voltage supplied to said frequency control terminal;
• (c) a second local oscillation signal generator circuit including a second voltage-controlled oscillator supplied with said channel select voltage from said frequency control terminal for generating a second local oscillation signal having a frequency which changes depending upon said channel select voltage and which is equal to the frequency of said first local oscillation signal generated by said first local oscillation signal generator circuit, said second local oscillation signal having a phase different by 90 degrees from the phase of said first local oscillation signal;
• (d) a phase detector, connected to receive said first local oscillation signal from said first voltage-controlled oscillator and said second local oscillation signal from said second voltage-controlled oscillator, for comparing said phase of said first local oscillation signal with said phase of said second local oscillation signal, and for generating a phase error signal based on the comparison;
• (e) a loop filter connected to said phase detector so as to be supplied with said phase error signal;
• (f) an adder connected to said loop filter for adding an output signal of said loop filter to said channel select voltage;
• (g) a first mixer circuit connected to said signal divider and to said first local oscillation signal generator circuit, and being supplied with said first divided input signal from said signal divider and with said first local oscillation signal from said first local oscillation signal generator, for generating a first intermediate-frequency signal of a wavelength .lambda. that contains a first necessary signal obtained from said main signal and a first unnecessary signal obtained from said image signal in response to said first divided input signal and said first local oscillation signal;
• (h) a second mixer circuit connected to said signal divider and to said second local oscillation signal generator circuit, and being supplied with said second divided input signal from said signal divider and with said second local oscillation signal from said second local oscillation signal generator, for generating a second intermediate-frequency signal of a wavelength .lambda. that contains a second necessary signal obtained from said main signal and a second unnecessary signal obtained from said image signal in response to said second divided input signal and said second local oscillation signal;
• and
• (i) a hybrid coupler connected to said first and second mixer circuits, and being supplied with said first intermediate-frequency signal from said first mixer circuit and with said second intermediate-frequency signal from said second mixer circuit, said hybrid coupler having at least one output terminal for outputting said first intermediate-frequency signal and said second intermediate-frequency signal, said second intermediate-frequency signal being delayed by a quarter of a wavelength (1/4.lambda.) behind said first intermediate-frequency signal, such that the phase of said first unnecessary signal is different by 180 degrees from the phase of said second unnecessary signal, and such that said first and second unnecessary signals are cancelled by each other.