Scalar Network Analyzer Rf Signal Source

Network analyzer are used mostly at high frequencies, they are used to measure microwave S parameters of a linear circuit network, which are known as transmission and reflection parameters. These parameters are often vectors. A scalar network analyzer(SNA) only measures the amplitude of S parameters. A SNA consists of a signal source, signal detection and separation equipment, data processing and display unit. The signal source will be discussed through this paper.This paper presents a 0.3~1300MHz sweep generator based on DDS + PLL +Frequency mixing structure. The project uses two PLLs, one of which is designed as a N-integer synthesizer; the other is designed at 1900MHz. The output signals are obtained from a mixer which has these two PLL output signals as inputs. A feasibility study is carried out., which involves phase noise, spurs, output power and so on.The design procedures include several modules which are a sweep circuit, a fixed-frequency circuit, a detection circuit, a PIN attenuation circuit, a mixer circuit, system filters,PCB design.Besides, we introduce the SNA software structure, and focus on the process of frequency setting and on the ARM controlling over the signal source.Finally, a PCB board of the signal source is made, we conduct full measurement of its spectral characteristics, including phase noise and spurs which are the most important items to be observed.Above all, this paper presents the improvement structure of the signal source, in which a N1-integer PLL is inserted into the other N0-integer PLL by a mixer. The combination can lower the value of N, and other problems are supposed to be eliminated.