A laminated balance filter using LTCC technology

In this paper, a laminated balance filter is developed for wireless communication systems such as Bluetooth and wireless LAN (local area network) applications. By using full-wave electromagnetic simulation, a 2 pole bandpass filter and 3 line balun operated in the 2.4 GHz ISM band frequency are designed, and combined to be a 3 pole balance filter with a imbalance input and two balanced outputs, which has advantages of a lower insertion loss and smaller size than the electrical connection of a chip filter and balun on PCB (printed circuit board). By using multi-layer configuration provided by LTCC (low temperature co-fired ceramic) technology, an experimental filter is fabricated. According to the measured results, the maximum insertion loss is 1.8dB, the maximum in-band phase imbalance is within 2.2°, and the maximum in-band amplitude imbalance is less than 0.46dB.