Research On Vector Modulator For W-Band

Compared to the traditional impulse radar system, the FMCW radar has the advantages of small size, high efficiency, accurate long distance resolution and strong anti-interference ability. However, its inherent signal leakage problem restrict its wide application. The radio frequency cancellation technology, which is recongnized as one of the most effective solutions. it can inhibit most of the leakage signal of transmitter and prevent receiver saturation, so as to avoid reducing the performance of the receiver. The vector modulator is the core component of the technology, it has been widely studied and applied. Frequency of the research from the original radio frequency near to terahertz band now, and the technology from hybrid integrated to today’s monolithic integration and 3D integration. However, compared with foreign countries that have more than 20 years of history and development experience, the domestic research in this area is not much, also are concentrated in relatively low frequency band.The main purpose of this thesis is to design a kind of balanced I-Q vector modulator, which is at the center frequency of 94 GHz and its bandwidth is approximately about 500 MHz. The phase of its output signal can be adjusted in the range of 0 ~ 360° and amplitude attenuation can be from 10 dB to infinity. In the first, this paper introduces the domestic and foreign research and development status, discuses the working principle of various types of vector modulators in detail and gives the reasons of using the balanced structure I-Q vector modulator. Through the analysis of the advantages and disadvantages of several kinds of coupler with different structure, the Lange coupler and Wilkinson power divider are selected acccording to the application’s requirements. Subsequently, we use the HFSS software to model and simulate their structures. The isolation resistance of Wilkinson power divider is designed as thin film resistor due to the characteristics of monolithic integrated technology. Then, we use the ADS software to import the Sparameters data from HFSS model for circuit simulation. First we verify the advantages and disadvantages of simple structure and balanced structure, make it sure that the balanced structure of vector modulator can effectively inhibit the parasitic parameters of the PHEMT transistor. Then we carry out the simulation of the whole circuit by using the I-Q vector modulator with balanced structure to achieve the results in 0 ~ 360° of phase and amplitude adjustable, it proves that the scheme is feasible.Because the processing requirement of the monolithic integrated circuit chip is very high, and the processing cycle is long, so we take second option as an alternative. The second scheme uses a hybrid integrated structure. A waveguide branch line couple and a waveguide annular bridge are designed by using HFSS software. Then we construct the layout for biphase amplitude modulator chip and create a separate module. Finally, modules are connected and tested through the flange interface. This program is designed by a mature technology with low processing requirement, so it has a strong realizability.