Compact Microstrip Branch-line Coupler Research Articles

An Ultra Compact Microstrip Branch Line Coupler with Wide Stopband Using LCL Filter and Meandered Stubs for Microwave Applications

A branch line coupler (BLC) with ultra-compact size and harmonic suppression ability using an LCL filter and meandered stubs is proposed in this paper. There are some important factors in microstrip coupler design, including size reduction, harmonic suppression, and low insertion loss. Thus, improving each of these factors will contribute to a more efficient design. In the proposed circuit, for the first time, LCL filters, including four T-shaped circuits and four meandered line open-ended stubs, were used together to reduce the circuit size and suppress unwanted harmonics. The proposed LCL filters, incorporated in the BLC branches, resulted in superior size reduction and harmonic suppression for the presented BLC. The proposed BLC correctly worked at 900 MHz with 300 MHz operating bandwidth, which showed 33% fractional bandwidth (FBW). Additionally, a wide suppression band from 1.4 GHz to 8.8 GHz, with more than 20 dB attenuation level was obtained, which suppressed the second to ninth unwanted harmonics. The overall size of the proposed 900 MHz coupler was only 11 mm × 10.4 mm (0.044 λ × 0.042 λ) while the size of the conventional 900 MHz coupler was 61.5 mm × 62.5 mm (0.25 λ × 25 λ). The proposed BLC had a very small size and only occupied 3% of the size of the conventional coupler, which corresponded to a 97% size reduction. To the best of the authors’ knowledge, to date, the best size reduction has been obtained among the published couplers. Furthermore, the experimental results verified the simulated and analyzed results of the proposed technique and demonstrate its potential for improving the performance and miniaturizing the size of other similar BLCs.

A Branch Line Coupler with improved stopband and miniaturized size for L-band applications

This paper offers a compact microstrip branch line coupler with amended stopband performance using stepped impedance resonators. The operational frequency is adjusted at 1.174 GHz for L-band applications. The proposed coupler has a 75% decrement of size compared with a typical branch line coupler at the operational frequency. Embedded stepped impedance resonators make attenuation (more than 12 dB) on 2nd to 17th harmonics. The insertion loss and coupling are −3.1 dB and −3.1 dB, respectively. The proposed branch line coupler has been simulated, fabricated and tested. Good accord has been attained between simulation and test results.

Design of compact microstrip branch line coupler using semi-circular and rectangular resonators with wide range suppressed harmonics

In this paper, a novel compact branch line coupler (BLC) with 10 suppressed harmonics is proposed. To achieve small size, four semi-circular and eight stepped impedance resonators are used instead of 35 Ω and 50 Ω conventional branch line coupler transmission lines. The operational frequency of the presented branch line coupler is 0.85 GHz. The size of the proposed circuit is reduced about 78% in compared with the conventional branch line coupler. To verify the design and analysis, the proposed coupler is simulated using full-wave EM simulator Advanced Design System and fabricated. Simulation results are in good agreement with measurement results.

Compact microstrip branch-line coupler with wideband quadrature phase balance

This letter presents planar microstrip branch-line (BL) couplers with improved phase and amplitude stability bandwidth along with significant size reduction. The prototypes are designed to operate at 433 MHz frequency band suitable for ISM 433 MHz applications. The prototypes with symmetric polygonal modification (SPM) and asymmetric polygonal modification (ASPM) offer a wide quadrature phase bandwidth of 37.8% and 35.5% respectively, over which the phase imbalance is within 90°±5°. In SPM all four transmission lines of the BL coupler have been symmetrically modified to bring in 75.99% size reduction compared to the conventional design. Further asymmetric modification has been performed to bring an additional 12.34% size reduction, compared to symmetric, and providing an overall size reduction of 78.95% compared to conventional BL coupler. The prototypes are able to offer compactness without compromising much on the matching, transmission and isolation parameters. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1369–1374, 2016

Miniaturization of Microstrip Branch-Line Coupler With Dual Transmission Lines

The dual transmission lines are proposed to replace conventional quarter-wavelength transmission lines for a compact microstrip branch-line coupler in this study. The developed coupler can be easily fabricated on the printed circuit board without lumped element; moreover, its size is greatly reduced compared to the conventional branch-line coupler. Furthermore, simulated and measured frequency responses match well to validate the proposed coupler with dual transmission lines.