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Active and Passive Electronic Components
Volume 26 (2003), Issue 4, Pages 205-211

A VCO with Harmonic Suppressed and Output Power Improved Using Defected Ground Structure

1Department of Electronic Engineering, Shanghai Jiaotong University, Shanghai 200030, China
2Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China

Received 14 January 2003; Revised 21 March 2003

Copyright © 2003 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In this paper, a novel defected ground structure (DGS) is proposed for suppressing harmonic and increasing the output power of a voltage-controlled oscillator (VCO) in microwave circuits. The DGS is formed with connecting in parallel two periodic structures which have different center frequencies (in a ratio of 2:3) of the stopband and provides the bandgap characteristic in certain frequency bands. Simulated and experimental results show that the microstrip line with DGS has a wide low-pass band for the fundamental frequency and a stopband for the second harmonic with good performance. To evaluate the effects of DGS on microwave VCOs, two GaAs field-effect transistor (FET) VCOs have been designed and fabricated. One of them has a 50Ω microstrip line with DGS at the output section, while the other has only a 50Ω straight line. Measured results show that DGS suppresses the second harmonic more than 20 dBm at the output and yields improved output power by 35%.