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In this letter, a design of a compact, dual-band, rat-race coupler is presented. The dual-band characteristics are obtained by using two shunt open-stubs with the conventional coupler. The proposed design can cover a wide range of frequency ratio of the dual bands within the fabrication limit of a low and high impedance microstrip line. Frequency variations of the bandwidths of this coupler in terms of isolation, matching, amplitude, and phase imbalance are also discussed. Theoretical prediction has been verified in the microstrip line by fabricating a dual-band coupler at the 900/1900-MHz mobile bands. Experimental results agree well with the theoretical predictions. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 277–281, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23063 [ABSTRACT FROM AUTHOR]

A design of a miniaturized rat-race coupler with higher-order harmonic suppression is presented in this article. The slow wave effect and stopband produced by a shunt open-stub is utilized to miniaturize the occupying area and suppress higher order harmonics, respectively. Design guidelines are obtained using a transmission line model. A prototype coupler has been fabricated in microstrip line to validate the theoretical predictions. The fabricated coupler occupies 18.4% area of that of a conventional coupler. At the same time, the second to tenth harmonics are suppressed by at least 15 dB. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2812–2814, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23840 [ABSTRACT FROM AUTHOR]

In this article, a compact microstrip coupled-line configuration has been presented to design a wideband bandstop filter with three transmission zeros. These transmission zeros are utilized to obtain sharp rejection characteristics. A loss-less transmission line model is used to obtain the filter design parameters. To validate the theoretical prediction, a single section sharp-rejecting, compact, bandstop filter having a 20-dB rejection bandwidth of ∼100% at 1.5 GHz has been fabricated. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2955–2957, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23819 [ABSTRACT FROM AUTHOR]