Design of Compact Multi-band Microstrip Bandpass Filters

• Main Authors: Huang Kai-Lun, 黃楷倫
• Other Authors: 尤正祺
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/45645787075522491775

碩士 === 逢甲大學 === 通訊工程學系 === 104 === This paper presents of microstrip bandpass filters with small size, and high selectivity. The filters have been realized on RT/Duroid 5880 substrate with a dielectric constant of 2.2, and a thickness of 0.787 mm. They are suitable for wireless communication applications. The first band-pass filter is a high selectivity and compact tri-band bandpass filter. The filter is composed of a multi-mode resonator and parallel coupling input/output strips. Through adjusting the coupling strip and length, we control the position of transmission zero. The method of source-load coupling is also used to add transmission zeros to improve the selectivity. The main size of the filter is only 17.6 mm × 16.4 mm. The bandpass filter can be applied in WLAN(2400-2488 MHz ; 5150-5300 MHz) and LTE(3400-3600 MHz) bands. Second, a diplexer constructed by stepped impedance resonators and uniform impedance resonators is proposed. The first design step is using a stepped impedance resonator to realize two pass band. Then, we use another stepped impedance resonator and uniform impedance resonator to filter out another unwanted passband individually. Finally, a quarter-wavelength open branch line is used to improve the isolation between the two outputs. The diplexer main size is only 19mm × 25.8mm. It can be applied in WLAN(2400-2488 MHz ; 5150-5300 MHz) bands. The third filter is a tri-band bandpass filter which is designed by using multipath asymmetric stub-loaded resonators. By changing the feeding position and the coupling space between resonators, the required bandwidth can be achieved. The source-load coupling technique is also used to add transmission zeros to improve selectivity. The main size of the filter is only 18.2mm × 22.3mm. The filter can be applied in LTE(2500-2690 MHz ; 3400-3600 MHz) and WLAN(5150-5300 MHz) bands. All of the filters are proposed in this paper have good agreement in the simulation and measurement. The characteristics of compact size and high selectivity make them suitable for application in communication products.