Ka-band I_q Vector Modulator

Vector modulator has been widely used in the microwave and millimeter wave systems, high-performance vector modulator is used in digital communication systems, radar cancellation system, pre-distortion system. The research work about vector modulator began in1980s in foreign countries, is now quite mature, mainly through MMIC process; while domestic research is started lately, mainly through hybrid integration method.In this paper, the balanced I-Q vector modulator using PHEMT switch model as an electronic control device in the Ka-band (34GHz-36GHz) is manufactured in hybrid integrated process, applying in FMCW (Linear Frequency Modulated Continuous Wave) radar cancellation system. The microstrip processes can not produce high-performance Lange couplers in Ka-band, and it can not be realized in Monolithic technology, so this paper use narrowband coupler to design branch line coupler, and use HFSS simulation software to simulate the cascaded coupler. To use vector modulator in the radar cancellation system, we integrate finline-microstrip transition to the vector modulator circuit. For the high isolation of the two combined circuit, the microstrip planar magic-T is used as the high isolation Wilkinson combiner in this paper. The dissertation consists mainly of the following parts:1. Analyzing the theory of the operation principle of vector modulator, contrasting the advantages of the balanced structure of vector modulator and the disadvantages of the simple structure.2. Discussing the different methods to realize vector modulation in different thickness of the Rogers5880substrate, applying the0.127mm thickness Rogers5880substrate to reduce the coupling between the couplers microstrip.3. Simulating the cascaded branch line coupler, achieving I_Q vector modulator in the0.127mm thickness Rogers5880substrate with PHEMT switch tube as the electronic control component. 4. Testing of the vector modulator and analyzing the measured results and discussion of the approaches to improve the circuit performance.