Compact ultra-wideband bandpass filter with new coupled line structure for wireless

In this letter, a new ultra-wideband bandpass filter using microstrip parallel coupled line structure is proposed. The filter is constructed of only two sections of three-coupled lines, which is a quarter wavelength long at the midband frequency. In addition, one of the outer coupled lines of each section is shorted to the ground. As a result, the filter exhibits two new symmetric transmission zeros around the passband, which increase the selectivity of both edges of the passband significantly. The transmission zeros can be located at the desired frequency by adjusting the width or the length of the coupled lines or also by changing the gap between them. The desired bandwidth can be obtained where the bandwidth is reversely proportional to the gap between the coupled lines. The design is successfully realized verified by full-wave electromagnetic simulation and the experiment. A good agreement between the expected and measured results is obtained, and it validates the efficiency of the proposed new coupled line structure and corresponding filter design technique. (C) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:13191321, 2012