Abstract:In this article, a compact branch-line hybrid coupler (BLC) which can suppress upper order harmonics of the conventional BLC is proposed. By adding a radial stub in the center of each branch, a compact BLC which can suppress the upper order harmonics are achieved. The proposed BLC is designed and simulated at 0.93 GHz. The proposed structure is 27% of the conventional BLC, while maintaining the characteristics of the conventional BLC at the center frequency. There are two transmission zeroes at 3.6 and 5.6 GHz. The third upto seventh harmonic are suppressed at least 20 dB. Keywords: branch-line hybrid coupler, compact size, harmonic suppression, microstrip transmission line, radial stub Classification: Microwave and millimeter wave devices, circuits, and systems References[1] S. Jung, R. Negra, and F. M. Ghannouchi, "A design methodology for miniaturized 3-db branch-line hybrid couplers using distributed capacitors printed in the inner area," IEEE Trans.

Abstract-A compact composite ultra wide-band elliptic-function low-pass filter is introduced by combining in cascade a microstrip stepped-impedance resonator using interdigital capacitor and an admittance inverter. A triple cascade low-pass filter is designed, analyzed and tested with this technique accompanied by its equivalent circuit model. This composition acts similar to a composite filter with desired attenuation and matching properties in order to obtain wide bandwidth and broad stop-band. The proposed low-pass filter features the sharpness of cut off frequency, low insertion loss, enhancement of bandwidth up to X-band frequencies and very compact size.Corresponding author: M. Nosrati (nosrati 1359@yahoo.com). 88Nosrati, Faraji, and Atlasbaf

In this article, two compact structures of the branch-line hybrid coupler (BLC) which can suppress upper order harmonics of the conventional BLC are proposed. By replacing the microstrip transmission lines at any electrical length of the conventional BLC with their equivalent new T-type transmission lines, two compact BLCs that can suppress upper order harmonics are achieved. Design equations of the proposed T-type line are achieved by ABCD matrices. To validate the design concept, first, a compact BLC which utilises a proposed T-type line in each of its branch is designed and fabricated to suppress the second to the eighth harmonics. Furthermore, the first BLC is analysed by even-and odd-mode analyses and the scattering parameter matrix of the first BLC is calculated at the first to eighth harmonics. There is an excellent agreement between simulated and measured results. Then, a compact BLC which uses two proposed T-type lines in each of its branch is designed at 1 GHz to suppress the second to the fifth harmonics and the second to sixth harmonics, simultaneously. The first-and second-proposed structures are 50% and 46% of the conventional BLC, respectively, while maintaining the characteristics of the conventional BLC at the fundamental frequency.

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