A novel coupling structure for broad-band fin-line filter design

In this paper, a novel coupling structure for broad-band band-pass fin-line filter design is analyzed by 3-D full-wave simulation and then utilized as K inverter network. Network parameters are obtained and compared with those of the traditional inductive coupling structure, indicating that higher coupling strength can be achieved by choosing the proper size of the proposed coupling structure. Meanwhile, the physical length of the presented structure is bigger than its traditional counterpart. A 7-orders Ka-band improved fin-line filter is designed and fabricated. In order to obtain broadband width and keep compact size simultaneously, both the proposed coupling structure and the traditional one are applied in the filter design. Measurements show that the fractional bandwidth of the filter is about 8%, and the insertion loss is less than 1.2 dB in pass-band of the filter. Moreover, the outmost coupling structure dimension is: w=12 mil, s=38 mil. There is no difficulty in physical realization.