Band rejection filter having integrated impedance inverter-tune cavity configuration

In a microwave frequency converter-filter circuit having

• a mixer circuit which combines a local oscillator frequency signal with an input frequency signal and produces an output frequency signal as an arithmetic combination of the frequencies of the local oscillator and the input signal and which contains as an unwanted component said load oscillator frequency signal, and
• a bandpass filter circuit having a center frequency at said arithmetic combination frequency for selectively filtering the output of said mixer within a selected passband
• the improvement comprising a band rejection filter arrangement coupled to said bandpass filter circuit for removing said unwanted local oscillator frequency signal component from the output of said mixer circuit, said band rejection filter arrangement comprising:
• an input terminal to which an input signal having a prescribed frequency component to be effectively rejected is to be coupled;
• an output terminal from which an output signal absent said prescribed frequency component is to be derived;
• a plurality of impedance inverter elements connected in series between said input and output terminals;
• and
• respective tunable resonator cavity elements connected between the junctions of commonly connected impedance inverter elements and a reference potential terminal;
• wherein
• one end of each of said resonator cavity elements is formed of an insulator board having first conductive material disposed on the side thereof facing each cavity;
• and wherein
• on the side of said insulator board facing away from each cavity there is provided a second conductive material, which is connected to said first conductive material, and upon which ones of said impedance inverter elements are affixed.