Research And Design On Balanced Dual-band Bandpass Filter And Filtering-antenna

In resent years, with the rapid development of mobile and wireless communication technlogy, the requirement for higher performances are proposed for the wireless devices. RF front-end, which is the key part of the wireless communication, not only needs to be compact, high-performance and low loss, but also can immune to the environmental noise. Due to their good common-mode rejection capabilities which result in high immunity to environmental noises, banlaced circuits, as compared with their single-ended counterparts, have been widely used. In addition, intergating multiple components in RF front-end together can reduce the system size and cost, by integrating the functions of the circuit, the device configuration and utilization can be improved. In this thesis, the balanced dual-band bandpass filter and the filtering antenna with the characteristic of filter and radiation are researched for WLAN. The main works are as follow:In chapter2, a banlaced dual-band bandpass filter is proposed based on SIR and UIR. By adjusting the parameters of the SIR and UIR, the designed filter can operate at two expected resonant frequencies. The circuit characteristic under differential-mode and common-mode exciting is analyzed using the equivalent circuits. By folding SIR Structure, an extra transmission zero is introduced near the common-mode resonant frequency, and the common-mode signal is suppressed.In chapter3, a balanced dual-band bandpass filter is proposed based on the asymmetrical coupled lines formed by the stepped-impedance resonators (SIRs). The high-impedance lines of one SIRs are coupled with the low-impedance lines of the other SIRs respectively, and two segments of asymmetrical coupled lines have different coupled gaps. Better differential-mode performance and common-mode signal suppression are obtained by adjusting the two coupled gaps.In chapter4, a balanced dual-band bandpass filter is proposed based on the double-sided parallel-strip line (DSPSL). The filter structure in chapter2is arranged in two sides of dielectric symmetrically and formed a type of DSPSL structure. Then, an H-shaped ground plane is inserted in dielectric. The inserted H-shaped ground plane has no effect on the differential-mode performance, but is helpful for suppressing the common-mode signal.In chapter5, a compact filtering-antenna is proposed. The second port and the second resonator of the previous filter are substituted by a fan-shaped patch antenna with DGS and form a filtering-antenna with flat gain response. Owing to adopting the DGS, the size of filtering-antenna is decreased. Moreover, the fan-shaped patch antenna with DGS acts as a radiator as well as the second resonator of the filter, so the filtering-antenna has the performance of the filter and antenna.