Compact Microwave Components with Harmonic Suppression Based on Artificial Transmission Lines

Abstract

In this paper, compact microwave components, including a Wilkinson power divider and a 3 dB branch-line coupler based on artificial transmission lines (ATLs) with harmonic suppression, are presented. A section ATL is consisted of microstrip stepped impedance transmission lines and a microstrip interdigital capacitor. To achieve a compact size, the stepped impedance transmission lines are folded into a right-angled triangle shape. For the ATL, the interdigital capacitor is used to suppress harmonics. By employing two sections of 70.7 Ω ATLs with a right-angled triangle shape to replace conventional transmission lines, the proposed power divider working at 0.9 GHz achieves a size miniaturization with the 58.8% area of a conventional case. In addition, the power divider has good harmonic suppression performance. In the design of a branch-line coupler, two pairs of ATLs with 50 Ω and 35.4 Ω are utilized. For 50 Ω ATLs, the ATLs are designed to a right-angled triangle shape. Meanwhile, to obtain a more compact size, these 35.4 Ω ATLs are modified to an isosceles trapezoid shape. The proposed branch-line coupler operating at 0.9 GHz accounts for merely 33.4% of a coupler adopting conventional microstrip transmission lines. Moreover, the harmonics of a branch-line coupler are suppressed effectively as well. Finally, measured results of the proposed Wilkinson power divider and branch-line coupler display good performance and agree with their simulated results well.