Microstrip Coupled-line Coupler Research Articles

Simple and High-Sensitivity Dielectric Constant Measurement Using a High-Directivity Microstrip Coupled-Line Directional Coupler

Simple methods using a microstrip coupled-line directional coupler (CLDC) are presented for dielectric constant measurements. The material under test (MUT) is placed on the coupled-line section of the coupler, and either the coupler’s coupling ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{31} \lvert $ </tex-math></inline-formula> ) or its isolation level ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{41} \lvert $ </tex-math></inline-formula> ) is considered as the sensor’s response. Putting different MUTs on the microstrip line leads to a change in the effective dielectric constant of the structure and consequently causing a change in the coupling coefficient. In addition, since the isolation level of a microstrip coupled-line coupler depends on the phase velocity difference between the substrate and the medium above the signal strips, putting different MUTs on the line significantly changes the isolation level. This change is significantly greater than the change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{21} \lvert $ </tex-math></inline-formula> level of a microstrip line when loaded with different MUTs. Validation of the method is presented through measurements for both solid and liquid MUTs.

Single-Layer Microstrip High-Directivity Coupled-Line Coupler With Tight Coupling

A novel symmetrical coupled-line circuit structure without patterned ground plane is proposed to design tight-coupling high-directivity couplers, which would be found in numerous applications in a microstrip RF front end because of its simple structure and inherent excellent compatibility. Based on a traditional even- and odd-mode technique, closed-form mathematical equations for both circuit electrical parameters and scattering parameters are obtained. Due to the use of two coupled-line sections placed in the vertical direction, the directivity of this novel coupler without any other compensation techniques can be enhanced while maintaining tight-coupling performance of almost 3 dB. For demonstrative purposes, three typical full-wave simulation examples with realized physical dimensions in microstrip technology are presented, indicating high directivity and tight coupling coefficient. Finally, a practical microstrip coupled-line coupler is designed and fabricated to operate at approximately 2 GHz. The measured results show good return loss, quadrature phase characteristics, high directivity, and strong coupling performances.

A broadband and compact asymmetrical backward coupled-line coupler with high coupling level

A new wideband asymmetric microstrip coupled-line coupler with 3dB coupling value and quadrature phase difference is presented. Compared with the conventional edge-coupled couplers, this structure, consisting of two different transmission lines (interdigital and conventional microstrip transmission lines) as coupled lines, achieves wider operating bandwidth and larger coupling level. The coupled-line length of the proposed structure is approximately λg/4. To characterize the structure, an equivalent circuit model has been established. A 3dB designed and fabricated coupler with 0.2mm spacing between coupled lines exhibits an amplitude balance of 2dB from 2.2GHz to 4.2GHz. Good agreements between the full-wave simulation and equivalent circuit model results has been achieved and verified the effectiveness of the proposed circuit model. Also, measurement results have been presented.

A Novel Broad Bandwidth and Compact Backward Coupler with High Couplinglevel

A novel backward microstrip coupled-line coupler which has been designed based on the metamaterial and composite right/left handed (CRLH) transmission line (TL) concepts is proposed. Coupling coefficient, bandwidth and size of proposed microstrip coupler are improved by coupled interdigital TLs which have been realized only by one interdigital capacitor. The design procedure to reach the coupler with predefined coupling coefficient and characteristic impedance of its ports is clearly presented. The designed and fabricated prototype is a 3-dB microstrip coupler with 0.2 mm spacing between its coupled lines over a wide bandwidth of 60% from 2. 3∼ 4 GHz centered at 3.2 GHz. The coupled-line length and the width of the proposed structure are approximately λg/4 and λg/36, respectively, which makes it more compact than the conventional cascaded CRLH microstrip coupledline couplers.

A Novel 3-dB Directional Coupler With Broad Bandwidth and Compact Size Using Composite Right/Left-Handed Coplanar Waveguides

A wideband composite right/left-handed (CRLH) coplanar waveguide (CPW) coupler with 3-dB coupling value and quadrature phase difference is presented. Compared with the conventional edge-coupled CPW coupler, this symmetrical structure, consisting of a gap capacitor, a broadside-coupled capacitor, and a meandering short-circuited stub inductor, achieves wider operating bandwidth and larger coupling level. The 3-dB CRLH CPW coupler with 0.7mm spacing between coupled lines exhibits an amplitude balance of 2dB and a phase balance of 900 plusmn 50 from 3.2 to 7.6GHz. The coupled-line length and the port impedance of the proposed structure are approximately lambda/4 and 50Omega, respectively, which makes it more compact than the cascaded CRLH microstrip coupled-line coupler. To characterize this structure, the equivalent circuit model including the unique coupling mechanism within CRLH CPWs is established and verified by measurement. The signal with less dispersion on output ports is demonstrated based on the standard deviation of group delay time

A fully planar microstrip coupled-line coupler with a high coupling level

A fully planar microstrip coupler with a high coupling level up to 4 dB is fabricated on PCB. Based on the conventional coupled-line structure, a gap size of coupled lines about 14 μm is realized by low cost IC process. It has a single stage and requires no bond wire. In measurement, a bandwidth more than 50% and isolation and return loss better than −20 dB are achieved. The measured responses have good agreement with EM simulation data. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 170–172, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20934