Microstrip circuits, such as low-pass filters and mixers, often require stubs with a low impedance level and an accurate localization of a zero-point impedance [Giannini and Sorrentini et al.], [Giannini and Ruggieri et al.]. Shunt-connected quarter-wavelength rectangular microstrip lines can be used for this purpose, but suffer from narrow impedance bandwidths. The bandwidth can be increased by increasing the rectangular stub width, but this can lead to the generation of higher order modes and also result in a badly defined insertion point on the microstrip line. Radial stubs provide low impedance levels with a well-defined insertion point over a wide frequency range [Sorrentino and Roselli], [Atwater].Typical transmission coefficient versus frequency
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