Vol. 67

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2016-09-18

A Miniaturized 3-dB Microstrip TRD Coupled-Line Rat-Race Coupler with Harmonics Suppression

By Yuan Cao, Zhongbao Wang, Shao-Jun Fang, and Yuan'an Liu
Progress In Electromagnetics Research C, Vol. 67, 107-116, 2016
doi:10.2528/PIERC16072705

Abstract

A miniaturized microstrip rat-race coupler with harmonics suppression is proposed by using shorted trans-directional (TRD) coupled lines. The shorted TRD coupled lines consist of a set of capacitor-loaded λ/4 coupled microstrip lines with two shorts, which are used to replace the 3λ/4 uniform transmission-line section (UTLS) in the traditional 3λ/2 ring coupler for miniaturization. To attain perfect matching for any coupling factor of the TRD coupled lines, shorted TRD coupled lines are synthesized and the design equations are derived. To further reduce the ring size, T-type transmission-line equivalent circuits are also adopted to replace the λ/4 UTLS and associated with a transmission zero for harmonic attenuation. Using the proposed method, a microstrip ring coupler with 26.7% circuit size of a traditional one is fabricated and tested. The measured results show that the bandwidth for the return loss of better than 10 dB is 43.9% and that for isolation of better than 20 dB is 18.7% with a maximum isolation of 40.6 dB. There is no spurious passband up to the sixth harmonic of the design center frequency with more than 20 dB suppression from the third to fifth harmonics.

Citation


Yuan Cao, Zhongbao Wang, Shao-Jun Fang, and Yuan'an Liu, "A Miniaturized 3-dB Microstrip TRD Coupled-Line Rat-Race Coupler with Harmonics Suppression," Progress In Electromagnetics Research C, Vol. 67, 107-116, 2016.
doi:10.2528/PIERC16072705
http://jpier.org/PIERC/pier.php?paper=16072705

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