Abstract
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 50/spl Omega/ microstrip line with DGS at the output section, while the other has only 50/spl Omega/ straight line. Measured results show that DGS suppresses the second harmonic more than -20dBm at the output and yields improved output power by 3-5%.
Highlights
There has been an increasing interest in studying the microstrip line with various periodic structures including photonic bandgap (PBG) [1,2,3,4] and defected ground structure (DGS) [5,6,7,8,9] in the design of microwave circuits such as filters, divider, amplifiers and so on
The second harmonic was suppressed more than À20 dBm at the output and yields improved output power
This means that DGS terminates the second harmonic perfectly
Summary
There has been an increasing interest in studying the microstrip line with various periodic structures including photonic bandgap (PBG) [1,2,3,4] and defected ground structure (DGS) [5,6,7,8,9] in the design of microwave circuits such as filters, divider, amplifiers and so on. DGS, which is realized by etching only a row of defects on the ground plane, is a kind of periodic structure. DGSs have similar and=or superior characteristics to the conventional PBGs. DGSs have prominent advantages in extending their applicability to other microwave circuits. One important parameter of designing microwave VCO is output power. The output power mainly depends on the active device, bias conditions, matching networks, and so on. The second harmonic is especially in want of controlling, ISSN 0882-7516 print; ISSN 1563-5031 online # 2003 Taylor & Francis Ltd DOI: 10.1080=0882751031000116106
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