Low PIM coax to PCB interface and method of constructing the same

A coaxial-to-printed circuit board (PCB) interface, comprising:

• a PCB comprising:
• a lower surface partially covered by a PCB lower ground plane;
• an upper surface partially covered by a PCB upper ground plane opposite the lower surface;
• a dielectric slab between the PCB lower ground plane and the PCB upper ground plane;
• a via extending through the dielectric slab from the lower surface to the upper surface;
• and
• an electrical conductor trace between the lower surface of the PCB and the upper surface of the PCB, the electrical conductor trace of the PCB being in electrical contact with solder deposited into the via;
• and
• a coaxial structure comprising:
• an outer conductor terminating at a first end;
• and
• an inner conductor being inserted into the via before deposition of the solder, the inner conductor of the coaxial structure extending beyond the first end, and terminating above the PCB lower ground plane;
• and
• a metallic cylinder below the PCB lower ground plane, the metallic cylinder being concentric with and exterior to the outer conductor of the coaxial structure when the inner conductor of the coaxial structure is inserted into the via, the metallic cylinder terminating at a second end flush with the first end of the outer conductor.

A method of constructing a coaxial-to-printed circuit board (PCB) interface to couple signals between an electrical conductor trace in a PCB and an inner conductor of a coaxial structure, the coaxial structure having an insulator surrounded by an outer conductor, the method comprising:

• inserting a metallic cylinder over the outer conductor of the coaxial structure, the metallic cylinder being configured to at least partially surround the outer conductor and form a capacitive gap between the outer conductor of the coaxial structure and a PCB lower ground plane, the metallic cylinder terminating at a second end flush with a first end of the outer conductor;
• positioning the coaxial structure with respect to the PCB so that:
• the outer conductor and insulator of the coaxial structure lie below a lower surface of the PCB;
• and
• the inner conductor of the coaxial structure is inserted into a via and extending beyond the first end of the outer conductor from the lower surface of the PCB to an upper surface of the PCB;
• and
• depositing solder in the via to provide an electrically conductive path between the electrical conductor trace of the PCB and the inner conductor of the coaxial structure.