Novel Compact Waveguide Flange Adapter for Passive Intermodulation Measurement Systems

Passive intermodulation (PIM) measurement is necessary for microwave and antenna products to evaluate their PIM performance. To achieve stable low residual PIM level of measurement system and make accurate PIM test, a compact waveguide flange adapter is proposed based on gap waveguide, dielectric filled bed of nails is adopted to construct compact double-sided artificial magnetic conductor (AMC) structure. When the adapter is connected between standard waveguide flanges, double-sided contactless electromagnetic band gap (EBG) structure with air gap is formed inside the flange connection. Electromagnetic leakage is prevented by stop band of the EBG structure. Meanwhile, metallic contact nonlinearity is almost eliminated by the contactless structure, and PIM can be therefore suppressed. A Ku band prototype of the adapter is designed for a Ku band PIM measurement system. By using the adapter, the system’s residual PIM is significantly improved with a maximum improvement better than 30 dB, achieving a stable low level.