To address the insufficient near-field coupling efficiency in traditional Passive Intermodulation(PIM) test systems, a compact near-field coupling test board operating at 2.6 GHz has been designed and fabricated. The board employs a Substrate-Integrated Waveguide(SIW) architecture and incorporates, for the first time, an adjustable rectangular-slot structure whose dimensions can be optimized to match different materials under test, thereby markedly enhancing the near-field test intensity. While maintaining stable RF electrical performance, the board achieves a high test sensitivity of -170 dBc with a measurement deviation kept within 3 dB. Experimental results demonstrate that the compact geometry is especially suited for evaluating the PIM characteristics of common microscale conductive materials, offering excellent repeatability and stability. The proposed design provides an effective test method for material-level PIM investigations and holds significant value for PIM analysis of components and materials used in mobile-communication systems.