Compact BandStop Filter Utilizing Low Cost Solution Cast Nanomagnetic Thin Films

A compact integrated microstrip bandstop filter(BSF) with low cost magnetic nanoparticle thin film loaded in the air substrate has been designed, fabricated and characterized. First, an optimized microstrip BSF patterned on a thin Liquid Crystal Polymer (LCP) was mounted on a partially 3D printed air substrate through a lego-like process to have the rejection of 41 dB at 8.5 GHz. To achieve the compactness, various magnetic nanoparticles were deposited within the air substrate to have the magnetic film thickness of 30 µm and 100 µm, which gave the self-resonances of the BSFs from 7.6 GHz to 8.3 GHz. The filter can also operate at higher a center frequency with a rejection over 30 dB by applying an external DC magnetic bias of 2500 Oe that is normal to the filter. Detailed comparison of the filter performance in terms of types of magnetic materials, film thicknesses and magnetic bias strength is provided. This work demonstrates a low cost and compact BSF utilizing the magnetic nanoparticle film which could find many applications in RF and microwave circuits and devices.