Compact multi-notched UWB bandpass filter using E-shape microstrip structure

In order to prevent interference with some selected narrowband communication channels, UWB filters with rejections at these bands are preferred or sometimes necessary for some UWB systems. In this paper, for the first time, a technique for generating rejection notches in the miniaturized UWB filters employing the E-shape microstrip structure is presented. It is shown the attenuated bands can be achieved by capacitively coupling grounded quarter wavelength (λ_g/4) stub or E-shape microstrip structures to the main filter structure. The performances of a second-order filter with a single rejection notch and a third-order filter with one and two rejection notches are evaluated using an accurate equivalent circuit model as well as by simulation and measurement. The dimensions of the third-order filter are about 4 mm × 4.2 mm × 0.4 mm excluding the feeding ports.