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.

[2]  Chi-Yang Chang,et al.  Modified Vertically Installed Planar Couplers for Ultrabroadband Multisection Quadrature Hybrid , 2006, IEEE Microwave and Wireless Components Letters.

[3]  L. Ong,et al.  Wideband 3-dB coupler using a patterned ground plane , 2005, 2005 Asia-Pacific Microwave Conference Proceedings.

[4]  M.-J. Park,et al.  Compact foldable coupled-line cascade couplers , 2006 .

[5]  L. Yeung,et al.  A Compact Dual-Band 90° Coupler With Coupled-Line Sections , 2011, IEEE Transactions on Microwave Theory and Techniques.

[6]  Arne F. Jacob,et al.  Advanced characterization and design of compensated high directivity quadrature coupler , 2010, 2010 IEEE MTT-S International Microwave Symposium.

[7]  Yongshik Lee,et al.  An Inductor-Loaded Microstrip Directional Coupler for Directivity Enhancement , 2009, IEEE Microwave and Wireless Components Letters.

[8]  J. Lange.  Interdigitated Stripline Quadrature Hybrid (Correspondence) , 1969 .

[9]  G.V. Eleftheriades,et al.  Printed high-directivity metamaterial MS/NRI coupled-line coupler for signal monitoring applications , 2006, IEEE Microwave and Wireless Components Letters.

[10]  T. Kawai,et al.  Directivity improvement of microstrip coupled line couplers based on equivalent admittance approach , 2003, IEEE MTT-S International Microwave Symposium Digest, 2003.

[11]  M.E. Bialkowski,et al.  Design of Compact Directional Couplers for UWB Applications , 2007, IEEE Transactions on Microwave Theory and Techniques.

[12]  M. Dydyk,et al.  Microstrip directional couplers with ideal performance via single-element compensation , 1999 .

[13]  Ke-Li Wu,et al.  A Dual-Band Coupled-Line Coupler With an Arbitrary Coupling Coefficient , 2012, IEEE Transactions on Microwave Theory and Techniques.

[14]  J. Reed,et al.  A Method of Analysis of Symmetrical Four-Port Networks , 1956 .

[15]  Jin-Koo Rhee,et al.  Microstrip line directional couplers with high directivity , 2004 .

[16]  J. Lange,et al.  Interdigitated Strip-Line Quadrature Hybrid , 1969 .

[17]  Yng-Huey Jeng,et al.  New high-directivity coupler design with coupled spurlines , 2004, IEEE Microwave and Wireless Components Letters.

[18]  Sang-Won Yun,et al.  A design of wideband 3-dB coupler with N-section microstrip tandem structure , 2005, IEEE Microwave and Wireless Components Letters.

[19]  Sang-Won Yun,et al.  A design of wideband 3-dB coupler with N-section microstrip tandem structure , 2005 .

[20]  T. Kawai,et al.  A construction of coupled-line 3-dB couplers using quarter-wave connecting lines , 2005, 2005 European Microwave Conference.

[21]  Krzysztof Wincza,et al.  Theoretical limits on miniaturization of directional couplers designed as a connection of tightly coupled and uncoupled lines , 2013 .

[22]  Chieh-Pin Chang,et al.  A 3-dB Quadrature Coupler Using Broadside-Coupled Coplanar Waveguides , 2008, IEEE Microwave and Wireless Components Letters.

[23]  Krzysztof Wincza,et al.  Generalized Methods for the Design of Quasi-Ideal Symmetric and Asymmetric Coupled-Line Sections and Directional Couplers , 2011, IEEE Transactions on Microwave Theory and Techniques.

[24]  Yeong-Her Wang,et al.  A 3-dB Quadrature Coupler Suitable for PCB Circuit Design , 2006, IEEE Transactions on Microwave Theory and Techniques.

[25]  R. Mongia.  RF and microwave coupled-line circuits , 1999 .