A compact coupler design using meandered line compact microstrip resonant cell (MLCMRC) and bended lines
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A compact coupler design using meandered line compact microstrip resonant cell (MLCMRC) and bended lines Sobhan Roshani1
•
Saeed Roshani1
Accepted: 20 October 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, a novel branch-line coupler using meandered line compact microstrip resonant cell (MLCMRC) and bended lines is proposed. The presented coupler works at 0.9 GHz, with good specifications. The measured values of S12 and S13 at 0.9 GHz are 3.2 dB and 3.3 dB, respectively, which show better than 0.3 dB insertion loss in the pass band. The measured value of S14 is better than 36 dB and S11 is better than 31 dB. The proposed design can eliminate 3rd and 5th harmonic with high suppression level (more than 40 dB) and reduce the size of the circuit more than 64% compared to the conventional branch-line coupler. The presented coupler has a very simple structure, which can be used in modern communication applications. Keywords Branch line coupler Harmonic suppression Resonator Size reduction Wireless communication
1 Introduction Couplers have several applications in communication, microwave and radio frequency (RF) circuits and systems. Branch line coupler (BLC) is the symmetric type of coupler with four uniform branches, which divide or combine power with 90˚ out phase [1]. Branch line couplers (BLCs) have several applications in microwave devices, such as Doherty power amplifiers (DPAs), balanced power amplifiers, radio frequency identification (RFID) reader modules, antennas feeding networks, mixers, matched attenuators and beam forming networks [2–8]. Conventional coupler and divider suffer from large size and presence of harmonics in frequency response [9]. In the past decade, several techniques such as defected ground structure (DGS) [10], shunt open-stubs [11–13] and resonators [14–18] have been applied to design couplers and dividers with unwanted size reduction and harmonic suppression. Unfortunately, these methods are not very good & Sobhan Roshani [email protected] Saeed Roshani [email protected] 1
Department of Electrical Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
for design. In defected ground structure (DGS) technique the fabrication process is a very complicated and not desirable method. With shunt open-stubs, only a few harmonics are suppressed with not superior suppression level and applied resonator cells in branch lines of coupler/divider lead to high insertion loss. In [19], open stubs and ring resonators are used together to reduce the coupler size, but this structure is so complicated to design. In [20–23], lumped components are used to design modified coupler and dividers, unfortunately lumped component usage leads to complicated fabrication process and circuit size increasing in three-dimensional (3D) configuration [24]. In [25], large conventional quarter wave-length lines of the coupler are replaced with discontinuous lines, which results in a 60% size
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