Compact WiMAX filter with three independent transmission zeros using PCB embedded passive technology

In this paper, compact modified 3^rd order Chebyshev bandpass filter was designed and fully embedded into organic packaging substrate for 2.3 - 2.7 GHz WiMAX applications. In order to reduce a size of the filter and avoid unwanted EM coupling between the 3D embedded filter circuit elements, the proposed filter was designed by using J-inverter transformation technology. It was comprised of three shunt-type LC resonators, two capacitance J-inverters, two extra transmission zero inductors, and one extra transmission zero capacitor. The grounding capacitor and two grounding via inductors generate three finite transmission zeros to enhance rejection characteristics at independent proper sides. The measured maximum insertion loss in the passband ranged from 2.3 to 2.7 GHz was better than 1.8 dB, with a minimum value of 1.58 dB at 2.6 GHz. And the return loss was higher than 15 dB in the passband. The transmission zeros of the measured response occurred at 1.71 and 5.1 GHz, and provided suppressions of 45 dB at 1.71 GHz, and 54 dB at 5.1 GHz, respectively. The size of the designed bandpass filter was 2.6 times 2.6 times 0.55 mm³ which was the smallest one in the reported devices.