Patent ID: 6072999
Filing Date: 2000-06-06
Classification: H01P

Abstract:
A receiving apparatus comprising:a frequency converter for converting a signal of a receiving channel into an intermediate frequency signal for receiving waves from broadcast satellites, communication satellites and surface wave broadcasts and signals from CATV transmission and comprising a mixer and a local oscillator which oscillation frequency is controlled by a voltage; anda tunable filter having traps of fixed tuning frequencies at the input and/or the output of said receiving apparatus in order to increase the attenuation at a local oscillation frequency outputted from said local frequency oscillator and/or the attenuation at an image frequency determined by said receiving channel frequency and said local oscillation frequency at a high band channel frequency reception;said tunable filter comprising first, second, third and fourth coils and p pieces (p=1 to n) of microstrip lines, first and second variable capacitance diodes, first and second capacitors and first and second resistors;one terminal of said first coil is connected to the input terminal of said tunable filter;the other terminal of said first coil is connected to a terminal of said second coil;the other terminal of said second coil is grounded;one terminal of said first capacitor is connected to a junction point of said first and second coils;the other terminal of said first capacitor is connected to the cathode of said first variable capacitance diode;the anode of said first variable capacitance diode is grounded;a control voltage is applied to the cathode of said first variable capacitance diode through said first resistor;one terminal of said third coil electromagnetically coupled to said second coil is grounded;the other terminal of said third coil is connected to a terminal of said second capacitor;the other terminal of said second capacitor is connected to the cathode of said second variable capacitance diode;the anode of said second variable capacitance diode is grounded;a control voltage is applied to the cathode of said second variable capacitance diode through said second resistor;one terminal of said fourth coil is connected to a junction point of said third coil and said second capacitor;the other terminal of said fourth coil is connected to the output terminal of said tunable filter;said p pieces of microstrip lines are connected between the output terminal of said tunable filter and the ground; anda channel frequency is selected by adjusting the control voltage at the cathodes of said first and second variable capacitance diodes.