This paper presents a compact and highly integrated triple-band RF front-end module (FEM) for worldwide interoperability for microwave access (WiMAX) applications using multilayer low temperature co-fired ceramic (LTCC) technology. The proposed RF FEM is composed of a TX triplexer, an RX triplexer, and a TX/RX switch. Both TX and RX triplexers are fully embedded in an LTCC substrate and the TX/RX switch is placed on the substrate. The TX triplexer consists of 2- and 5-GHz lowpass filters, a 3-GHz highpass filter, and a matching circuit. On the other hand, the RX triplexer consists of miniaturized 2-, 3-, 5-GHz coupled-resonator bandpass filters and a matching circuit, which are stacked up for space saving. In TX path, the RF FEM provides an insertion loss of 1.8 dB, 2.1 dB and 2.5 dB at 2-, 3-, and 5-GHz band, respectively, with a high second-harmonic suppression characteristic. In RX path, the RF FEM also provides a low insertion loss at three passbands with high attenuation at other passbands. The size of the proposed RF FEM is only 4.0 mm5.0 mm with a substrate thickness of 0.73 mm. The measured results are in good agreement with the simulated results.

This paper investigates intermodultation distortion in ferroelectric phase shifters depending on bias voltage. Two analog phase shifters based on barium-strontium-titantate (BST) coated sapphire substrates have been fabricated with interdigital capacitors (IDCs) which have 2 and 4 µm spacing between adjacent fingers. In case of the phase shifter with 4 µm-spaced IDCs, a phase shift of more than 121was obtained with a maximum insertion loss of 1.8 dB from 2.4 to 2.5 GHz over a bias voltage range of 0-140 V. The phase shifter with 2 µm-spaced IDCs exhibited a phase shift of more than 135with a maximum insertion loss of 2.37 dB in the same frequency range. In this case, a bias voltage of 80 V was used. Using 2 and 4 µm-spaced phase shifters, a third-order intermodulation (IM3) measurement was carried out with a two-tone cancellation setup to investigate nonlinearity, resulting in an input third-order intercept point (IIP3) of about 30.5 dBm and 38.5 dBm, respectively.

The design, fabrication, and characterization of monolithic analog phase shifters based on barium-strontium-titanate (BST) coated sapphire substrates with continuously variable 180and 360phase-shift ranges are presented. The phase shifter using a single series resonated termination can provide 180phase shift with the chip area of 4 mm 4 mm. A double series resonated termination in a parallel connection can reach over 370phase shift with better than 6.8 dB-loss at 2.4 GHz. Also, an all-pass network phase shifter composed of only lumped LC elements was described here. This phase shifter demonstrated 160phase shift with an insertion loss of 3.1 dB 1 dB and return loss of better than 10 dB at 2.4 GHz. The total size of the phase shifter is only 2.4 mm 2.6 mm, which is the smallest reported BST phase shifter operating at S-band, to the best of the authors' knowledge.