3- to 5-GHz Ultra-Compact Bandpass Filter With Independent Transmission Zeros Using PCB Embedding Passive Technology

A compact ultra-wideband bandpass filter was newly designed and implemented by embedding all the passive components into a printed circuit board with a high dielectric composite film layer. It was designed using a modified third-order Chebyshev circuit topology to obtain a large bandwidth. J-inverter transformation technology was then applied in order to reduce the size of the filter and avoid unwanted electromagnetic coupling among the filter circuit elements. A capacitor and two inductors connected in series with three parallel resonators were newly applied to generate three independent transmission zeros for improving the rejection characteristics at the lower and upper stopbands of the proposed filter. The measured maximum insertion loss in the passband range from 3.1 to 4.75 GHz was better than 1.68 dB and the return loss was higher than 12 dB. The transmission zeros of the measured response occurred at 2.2 and 5.15 GHz and provided suppressions of 31 and 20 dB in the wireless local area networks bands of 2.4 and 5.15 GHz, respectively. The group delay in the passband was lower than 0.62 ns. The size of the fabricated filter was 2.9 × 2.8 × 0.55 (H) mm³.