Vector Network Analyzer Spread Spectrum Technology

The development of millimeter wave technology increases the demand of measurement capability at this frequency range. Thus, vector network analyzers (VNA) operating at millimeter wave frequencies has great significance in researching and engineering.A 26.5-40GHz broadband frequency extension technique based on Agilent 8720ET 20GHz VNA is presented and some critical problems are discussed. The technique lowers the cost and maintains the broadband characteristic by employing a new way of frequency down-conversion without using expansive broadband harmonic mixers. The frequency extension modules are connected directly to the test ports of VNA whose millimeter wave measurement capability is not required, thus the modules can be widely used. The frequency multipliers and mixers are commercial MMICs, the signal separator is a broadband high directivity waveguide directional coupler. During measurement, the synchronization between LO source and VNA is controlled by a program running on a PC. The program is written in Visual Basic under VISA standard and communicates with VNA via USB/GPIB interface. One-port and simplified TRL calibrations are aslo implemented in the program, TRL waveguide standards were made for use while calibrating the two port measurement system.A Ka band reflectometer prototype was built with frequency extension modules connected to Agilent 8720ET. Test port maximum output power was 15dBm, maximum input power was 31dBm. At 26.5-40GHz, calibrated system measurement range was up to 30dB.