Millimeter-wave Vector Modulator

The vector modulator has been widely applied into RF and microwave communication systems since its development, and become into a very important component. High performance vector modulators direct modulate millimeter wave as electronic control units in the operation of millimeter-wave receiver. The research work about vector modulator in foreign countries has achieved advanced technology, while domestic scholars'research is only in its infancy in this field, and papers about vector modulator are rare, especially above Ka band. Most of the foreign scholars usually realize vector modulators by Lange couplers and MMIC technology at the present time, while used hybrid integrated circuits in our country because of bad fabricating technique. The innovation of this paper is that it designed a balanced I-Q modulator in Ka band by combining branch-line couplers and PHEMT. This paper realized a vector modulator at rather low cost relative to MMIC techniques in foreign countries.The balanced I-Q vector modulator this paper designed in Ka band is applied to reflected power canceller in LFMCW (Linear Frequency Modulated Continuous Wave) radar, and it is one of the most important components in the canceling system. This paper will elaborate the development and application of vector modulator, compare operation principles of alternative types of vector modulators, select the key components of designed scheme, then simulate the circuit by simulation software, such as HFSS, ADS. Finally, the balanced I-Q vector modulator working at Ka band is designed and fabricated on Rogers5880 substrate. Moreover, a microstrip-to-waveguide antipodal finline transition in Ka band and PCB control circuit were designed so as to connect with cancellation loop. This paper analyzed the measured results and discussed of the approaches to improve the circuit performance after testing the vector modulator.