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|A Design Approach for the Miniaturization of Embedded RF Filters for System-in-Package (SiP) Applications|
|Keywords: Communication Systems and Circuits, Embedded RF Filters, System-in-Package (SiP)|
|Various design and integration approaches for embedded filters have been widely studied and reported in several publications. This paper presents a design approach for embedded RF filters focussing on the design miniaturization and performance improvement. From the synthesized LC-networks, the design procedure for embedded filters started with the definition of the integration medium supporting RF/high-speed signals. A hybrid laminate multilayer board consisting on 3 cores and 2 prepreg materials (RO4450B, IS620, and RO4350B) has been defined. Then, optimal topologies and configurations for filter structures within the multilayered board system have been determined, followed by the optimization and evaluation through full-wave analysis. Finally, the implemented circuits have been fabricated and tested. As illustration, 2nd-order bandpass filters for Wi-Fi systems operating around 5GHz U-NII band have been designed and implemented in different design configurations (e.g., Config.-1: lateral configuration, Config.-2: vertical configuration with off-set between the resonant components, Config.-3: vertical configuration without any off-set between the resonant components). As results, the 5.2GHz-Bandpass filter implemented in config.-2 has exhibited a total lateral dimension of 4.6mmx3.2mm=14.72mm² (including all proximity area around the filter), and an insertion loss (IL) and return loss (RL) of 2.8dB and 15dB at 5.2GHz, respectively. The same filter realized in Config.-3, has presented a total lateral dimension of 3.4mmx3.2mm=10.88mm², and an IL and RL of 2.7dB and 15dB, respectively. Thus, a size reduction of more than 25% could be met without any significant impact on the electrical performance within the passband. Indeed, to reduce the filter dimension, ground planes with appropriated electromagnetic windows have been inserted within the inner metal layers, between the resonant structures. Thereby, the amount of the electromagnetic flux between the coupled resonators could be controlled. Thus, based on this design approach, filters for various applications have been successful designed and implemented, with remarkable size improvement.|
|Mohamadou Baba, Research Engineer
Fraunhofer Institute for Reliability and Microintegration (FhG-IZM)