Suppression of Parallel Plate Modes in Low Frequency Microstrip Circuit Packages Using Lid of Printed Zigzag Wires

This work deals with the suppression of parallel plate and cavity modes in shielded microstrip circuits operating at the lower microwave frequency range. The suppression is achieved by using a lid made of zigzag wires printed periodically on narrow slices of ungrounded circuit boards, located vertically side by side. This structure is very compact both in periodicity and height, it suppresses cavity modes over about an octave 2:1 bandwidth, and it does not interfere with the packaged microstrip circuit.