Printed circuit with inductively coupled printed coil elements and a printed element forming a mutual inductance therewith

A printed circuit adapted to function as a bandpass filter for a selected band of frequencies comprising:

• a. a first conductor formed as a first inductance element on an insulating plate;
• b. a second conductor formed as a second inductance element on said insulating plate electromagnetically coupled to said first inductance element, one end of each of said first and second inductance elements being connected at a common point, the other ends of said first and second inductance elements being connected to first and second input and output terminals respectively;
• and
• c. a common conductor formed as a third inductance element connected at one end to said common point of said first and second inductance elements on said insulating plate, and the other end being connected to a ground terminal, whereby said common conductor inductance element determines the mutual inductance of the printed circuit, said common conductor having a trimmed portion near the position at which said first and second conductors are connected thereto, thereby enabling adjustment of the coupling factor between said first and second conductors by changing inductance of the common conductor.

A printed circuit adapted to function as a bandpass filter for a selected band of frequencies comprising:

• a. a first conductor formed as an inductor on an insulating plate to have inductance;
• b. a second conductor formed as an inductor on said insulating plate to have inductance;
• and
• c. a common conductor formed as an inductor on said insulating plate to have inductance, one end of said common conductor being connected to one end of each of said first and second conductors and providing a connection at a point intermediate said first and second conductors;
• d. a first resonant circuit connected to an input of the printed circuit and formed of first and second plane electrodes on opposite sides of said insulating plate, said plane electrodes being shaped to provide a first coil, first capacitor, and part of a second coupling capacitor;
• p1 e. a second resonant circuit connected to said first resonant circuit by said second coupling capacitor and formed of third and fourth plane electrodes on opposite sides of said insulating plate, said third plane electrode comprising said first conductor, second conductor, and common conductor, said third and fourth plane electrodes providing second and third coils and a third capacitor for said second resonant circuit;
• and
• f. a third resonant circuit connected to said first resonant circuit and an output of the printed circuit, said third resonant circuit being formed of said fourth plane electrode and a fifth plane electrode on opposite sides of said insulating plate, said fourth and fifth plane electrodes providing a fourth coil and fourth capacitor which, together with said third coil, form the third circuit;
• whereby a symmetrical bandpass filter printed circuit is provided having accurate coupling adjustment by trimming said third plane electrode common conductor to independently change coupling without changing the location of the first and second conductors of the third plane electrode.