Research Of C-Band Linear Reflection-type360°Analog Phase Shifter

A phase shifter is a kind of microwave dual-port devices, which is used tochange the transmission phase angle of a net work without energy attenuation. Phaseshifters are widely used in many fields, such as microwave phase measurement,communication system, antenna arrays, the radar system and microwave automaticcontrol system. Phase shifters can be analog or digital. In recent years, digital phaseshifters are developing very fast. However, analog phase shifters cannot be replaced,they are still need to be researched. Analog phase shifters include ferrite phase shiftersand reflection-type varactor diode phase shifters. Compared with the former, the latterare more popular used because of their smaller size, higher speed and higherintegration.Based on large amount of literature on analog phase shifters and the consideringof some products’ performance, the design indexes of the reflection-type analog phaseshifter are determined: operating at4.0GHz, phase shift range is360°, linearity is lessthan5%, bandwidth is200MHz, and the insertion loss is less than3dB. According tothe indexes, this article uses a3dB branch-line coupler and two varactor-diode circuitsto achieve360°phase shift. The phase shifter is implemented with microstrip circuit.This article presents a detailed analysis of phase shifter’s working principle, howto improve the linearity and how to increase the bandwidth. To increase the bandwidth,it uses a three-branch branch-line coupler instead of a two-branch branch-line couplerand designs the branches. And a new reflective load is used to get more freedom ofadjustment of the linearity and bandwidth, which is composed of two parallelbranches, each one contains a series microstrip transmission line, a varactor diode anda short-circuited microstrip line. Then the phase shift range, linearity and bandwidthare all considered.For the layout design, to isolate the high-frequency signals from the DC voltage,an open stub is used in the transmission line which connect the reverse voltage, and a decoupling capacitor is added between the voltage and the ground. In addition, thedesign and production process of couplers and phase shifter is discussed in detail. Andthe article presents the theory basis of how to select the core elements, varactordiodes.The C-band reflection-type analog phase shifter is made of microstrip circuit.The final test results show that in the frequency range of3.9GHz to4.1GHz, thedesign has a360°phase shift range. The maximum reverse controlled voltage is15V.At the center frequency of4.0GHz, the phase shift error is less than15°, that meansthe linearity is less than5%. And the insertion loss is less than3.8dB in the workingband. So the results of measurement can meet the design requirements.