Miniaturization of Embedded Bandpass Filter in LTCC Multilayer Substrate for WiMAX Applications

The explosive advancement of wireless communication devices for multiband and multi-standard applications such as Wi-Fi, WiMAX, Bluetooth, and cellular networks demands low-cost, lightweight, small form factor, and high performance radio frequency (RF) front-end modules. In the multiband or multi-standard devices, the bandpass filter (BPF) is an essential functional block to avoid signal interference between the different bands or standards. An example of a BPF using surface mountable chip inductors and capacitors is shown in Fig. 1. This design, however, is too bulky to integrate with active components such as amplifiers, mixers, and oscillators in communication devices. On the other hand, embedded passives are suitable for a system-on-package approach. A variety of embedded BPF design efforts can be found in the literature. A popular design approach is embedding BPF in a low temperature co-fired ceramic (LTCC) such as the interdigital BPF [1] using distributed components or a balanced filter design in a low profile LTCC [2] using lumped circuit elements. Multi-layer organic substrate has been used for embedded passives [3]. Electromagnetic bandgap resonators in a coplanar waveguide [4] or bulk acoustic wave resonators using zinc oxide thin film [5] are used to fabricate a 5 GHz BPF.