Conventional Branch-line Coupler Research Articles

A MINIATURIZED BRANCH-LINE COUPLER WITH WIDEBAND HARMONICS SUPPRESSION

This paper presents a miniaturized branch-line coupler with suppression of wideband harmonics based on a unit of transmission-line section with triple-stub. This fundamental unit produces three transmission zeros and exhibits wide stopband response due to the triple stubs. It is used to replace a quarter-wavelength line in conventional branch-line coupler, leading to size reduction and wideband harmonics suppression. The closed-form equations are given for the coupler design. As an example, a branch-line coupler operating at 1.0GHz is designed, fabricated and measured. Measurements agree well with simulations, and show that the proposed branch-line coupler occupies 56% size of a conventional one and achieves wideband harmonics suppression (better than 17dB) from 1.8GHz to 6.4GHz. The 2nd, 3rd, 4th, 5th, and 6th harmonics are suppressed better than 34dB, 19dB, 30dB, 17dB, and 32dB, respectively. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and wideband harmonics suppression.

REALIZATION OF A COMPACT BRANCH-LINE COUPLER USING QUASI-FRACTAL LOADED COUPLED TRANSMISSION-LINES

An extremely compact branch-line coupler operating at 900MHz is presented without the use of via-holes, multilayered technique, or air-bridged. The technique presented here uses the concept of fractals to load a coupled transmission-line in order to realize a compact quarter-wavelength transmission-line, which forms the couplers arms. It is shown that the proposed branch-line coupler's performance is analogous to a conventional branch-line coupler with the beneflt of substantially reduced physical dimensions by a factor of 78%. The measured result of the fabricated microstrip branch- line coupler is compared with the simulation data. The agreement of the measurement and simulated conflrms the theory and validates the proposed coupler design.

To compact ring branch‐line coupler using nonuniform transmission line

AbstractA compact ring Branch‐Line Coupler (BLC) with size reduction of about 50%(in circuit area) of conventional BLCs at frequency 2 GHz is introduced. The coupler is designed by using nonuniform transmission lines (NTL) instead of Uniform Transmission Lines in each arm. The normalized width w (z)/h function of the NTLs is expanded in a truncated Fourier series. The reduced size couplers are potential building blocks for the growing wireless communication markets. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2679–2682, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24703

Analysis and design of novel dual‐band branch line coupler with patterned ground plane

AbstractThis article presents the novel dual‐band planar 90° branch line coupler with patterned ground plane, sometimes referred to as ‘defected ground structure.’ In the new layout, two cross coupling branches are added to the conventional branch line coupler. The additional branches make the design of dual‐band coupler at two arbitrary bands more flexible. Moreover, the used patterned ground plane makes an implementation of high impedance microstrip line easy and increases the electrical length of microstrip line. The basic principles of the novel coupler are analyzed and the design procedure is presented. For method validation, a dual‐band microstrip coupler operating at 2.1 GHz and 3.6 GHz was designed, tested, and analyzed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1000–1005, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24246

Quasi-circulator for effective cancellation of transmitter leakage signals in monostatic six-port radar

A quasi-circulator, composed of two branch-line couplers and an asymmetric power combiner, is proposed to effectively cancel the transmitter leakage signals in a monostatic six-port radar. The effective isolation is improved by 12.2 dB at 24 GHz. With the proposed quasi-circulator, the maximum detectable range of the six-port radar is improved by 167 , compared with that of the six-port radar with a conventional branch-line coupler.

Design of Multipassband Microstrip Branch-Line Couplers With Open Stubs

The microstrip branch-line coupler with multiple passbands is proposed; moreover, the design equations are provided in this paper. In order to obtain multiple passbands, open stubs are added to the conventional branch-line coupler's ports; in addition, these open stubs' impedance and electrical length need to be properly chosen. The proposed couplers can be easily fabricated on the printed circuit board without any lumped element. The agreement between measured results and the theoretical prediction validates the feasible configuration of the proposed coupler.

Branch-Line Coupler Based on Edge-Coupled Parallel Lines With Improved Balanced Response

A conventional branch-line coupler is flat-balanced, in terms of magnitude and phase, in a narrow frequency band due to the quarter-wave length requirement in the transmission lines. In this paper, a novel branch-line structure is presented in order to overcome this limitation. Loading the horizontal transmission lines with a pair of open-end series stubs, the magnitude and phase balance becomes flatter in a wider frequency range. However, the proposed structure cannot be fabricated, for which an equivalent circuit using edge-coupled parallel lines has been used. The measurement of this device shows a relative bandwidth of 82.5% for 2 dB magnitude and 72% for plusmn5deg phase balance condition.

Exact design of novel miniaturised fractal-shaped branch-line couplers using phase-equalising method

Although miniaturised and fractal-shaped branch-line couplers have been reported by many researchers, their operating bandwidth are narrowed and shifted because the phase-shifting properties of the fractal-shaped microstriplines with different iteration orders are different to each other; thus the application of these techniques were limited. In this paper, an exact design technique is presented to obtain compact and fractal-shaped branch-line couplers for a given frequency. By using the length reduction formulae of the chamfered bend and equalising the transmission phase of the fractal-shaped microstriplines of the proposed fractal-shaped branch-line couplers to their counterparts of the conventional branch-line coupler, the phase-shifting phenomenon of the fractal branch-line couplers can be compensated. As an example, novel fractal-shaped branch-line couplers operated at 2.4 GHz using Koch fractal shapes of different iteration orders have been designed successfully, and the designed couplers all operated at the designed frequency and achieved a maximum 81.8% size reduction. And furthermore, the operating frequency and its bandwidth are virtually unaltered. The proposed method is verified by the measurement results.

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.

A compact branch‐line coupler using defected ground structures

AbstractA compact branch‐line coupler (BLC) with a size reduction of about 70% of a conventional BLC has been introduced. The coupler has been designed using a defected ground structure (DGS). No bonding wire or via holes have been used. The simulation results have been verified by measurement with good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 386–389, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23118

A Compact Slow-Wave Microstrip Branch-Line Coupler With High Performance

One compact slow-wave microstrip branch-line coupler is presented. The new structure not only effectively reduces the occupied area to 28% of the conventional branch-line coupler at 2.0 GHz, but also has high second harmonic suppression performance. The measured results indicate a bandwidth of more than 200 MHz has been achieved while the phase difference between S21 and S31 is within 90deg plusmn 1deg. Furthermore, the measured insertion loss is comparable to that of a conventional branch-line coupler. The new coupler can be easily implemented by using the standard printed-circuit-board etching processes and is very useful for wireless communication systems.

Size reduction and harmonic suppression of microstrip branch-line coupler using defected ground structure

A new method, with branches having an equivalent series inductance using defected ground structure, is proposed for size reduction and harmonic suppression of branch-line coupler. The proposed structure is 35% of the conventional branch-line coupler at 1 GHz and the measured third harmonic signal is less than −30 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1966–1969, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21830

A compact quadrature coupler based on coupled artificial transmission lines

A new compact quadrature hybrid based upon artificial transmission lines (ATLs) is presented. Miniaturization is achieved through reduced even- and odd-mode phase velocities which are achieved using capacitive loading with interdigital open-circuited stubs. A proof-of-concept microstrip implementation of the quadrature hybrid exhibits performance comparable to a conventional branch-line coupler while occupying only 14% of the area. The compact structure of the hybrid is useful for RF applications and is suitable for scaling to frequencies above 100GHz where the size of shielded-microstrip components must be limited to prevent excitation of high-order modes.

A novel compact-size branch-line coupler

A novel compact-size branch-line coupler without any implementation of lumped-elements, bonding wires, and via holes is proposed. In this study, the size of the proposed coupler occupied only 45% of the conventional branch-line coupler at 2.4GHz. The performances of the circuit can be competed with the conventional coupler. The element sizes of this coupler can be realized easily by using simply standard printed-circuit-board etching processes. It is very useful for applications in the wireless communication systems.

Branch-Line Couplers Using Defected Ground Structure

In this letter, a novel design of a branch-line coupler with considerable reduction in its size and suppressed harmonic passband is proposed. By embedding a defected ground structure (DGS) unit cell under a microstrip line, compact branch-line couplers are easily achieved. The electrical length is scaled appropriately according to the slow-wave effect. In this case, the experimental coupling (S 21 or S 31 ) is comparable to that of conventional branch-line couplers. Also, experimental results indicate that DGS section is quite effective for the suppression of higher order harmonics.

Phase-agile branch-line couplers using metamaterial lines

Two branch-line couplers are introduced that utilize a combination of regular microstrip (MS) and negative-refractive-index (NRI) lines. Interesting phase compensation (0/spl deg/ phase shift) at the output port and a choice of /spl plusmn/90/spl deg/ phase shift at the through port, with respect to the input, are possible. On the other hand, one of the dimensions of the coupler is significantly reduced, compared to a corresponding conventional branch-line coupler, but without any bandwidth degradation.

Branch-line couplers using unequal line lengths

General solutions for branch-line couplers using different line lengths are provided in this paper. Explicit expressions are derived with which a hybrid with any given power division ratio can be designed. In the design, one of the characteristic impedances or lengths of the branches can be chosen arbitrarily to suit a given design specification. This approach brings flexibility in choosing the characteristic impedances or the lengths of the branches, and is helpful especially in monolithic-microwave integrated-circuit applications where restrictions imposed on microstrip transmission lines do not allow the use of conventional branch-line couplers employing quarter-wave-long lines. However, the resultant bandwidth is narrower compared to that of the conventional coupler.

Analysis and Design of Branch-Line Hybrids with Coupled Lines

The scattering parameters of four-ports consisting of coupled lines with coupled or uncoupled connecting branches are derived in terms of the even- and odd-mode impedances and the lengths of the lines. These are used to analyze and formulate basic design procedures for the application of these structures as directional couplers including 0° and 90° 3-dB hybrids. The proposed new structures are quite compact at lower frequencies as compared to conventional uncoupled branch-line and rat-race hybrids. The results for the case of the coupled-line four-port with uncoupled branch lines also lead to closed-form expressions for the lengths and impedances of the lines required to nullify the effect of coupling between the main lines of a conventional branch-line coupler for use at higher frequencies. The measured response of the fabricated couplers is in good agreement with the theoretical predictions.