| dc.description.abstract | This dissertation focuses on the key components of RF front-end systems for various wireless communication application. A new design scheme for the wideband filters with the low temperature co-fired ceramic (LTCC) technology is proposed in this letter. Based on the traditional second-order combline filter, an extra shunt capacitor is added in the middle of the coupled line, and a new transmission zero is thus obtained. The proposed design not only possesses excellent selectivity at both sides of the passband, the fractional bandwidth can also be as wide as 86%. To validate the design scheme, the proposed technique is applied to the third-order ombline filter and realized by using the LTCC technology. The wide-band filter with passband of 3.1–5.1 GHz is obtained. With four transmission-zeros, the selectivity and out-band rejection of the third-order filter is further improved from those of the second-order designs. A systematic design scheme for multi-band filters is proposed based on the conventional single-band combline filter. In the proposed design, the coupled line in the filter is divided into two sections, and one of the sections is replaced with a ladder circuit consisting of parallel capacitors and series coupled lines. The center frequency and fractional bandwidth of each passband can be adjusted without significantly affecting those of the other passbands. The design scheme is illustrated with a dual-band (2.4 and 5.5 GHz) and a tri-band (2, 4.1, and 7.2 GHz) combline filters. Both designs are realized using low-temperature co-fired ceramic technology. Not only the design procedures are given and explained in detail, experimental validation is also conducted.
In addition, convenient techniques of selectivity enhancement for lump-distributed baluns are proposed in the paper. With these techniques, transmission zeros are introduced by adding circuit components to the balun. First, novel balun circuits which possess a transmission zero in the differential-mode operation are proposed. A shunt capacitor is then added to the balun to provide a mechanism for tuning the position of the zero. To further improve the frequency selectivity, one more transmission zero which appears in both three-port and differential-mode operations is introduced by adding one transmission line and two capacitors to the balun. Not only equations required for circuit designs are derived, also the proposed circuits are realized by using LTCC process and validated by measurements.
Furthermore, this dissertation proposes a triband antenna design for Wi-Fi (2.4–2.48 and 5.15–5.8 GHz) and WiMAX (3.3–3.7 GHz) applications. In order to accommodate the antenna into the limited space, two L-shaped monopoles are stacked on top of each other. These stacked monopoles are used for the radiation in 2.4- and 3.5-GHz bands. Additionally, one parasitic U-shaped strip is placed alongside the stacked monopoles for the radiation in the 5.5-GHz band. Two on-chip inductors are inserted into the monopoles for impedance matching and further miniaturization. The proposed design can be contained in a volume of 8x8x1.6(mm) and built on the printed circuit board. Simulation and measurements are conducted, and both results have proven to be in good agreement.
| en_US |