Budapest University of Technology and Economics

BME Students Design a Novel Mixer

 

Company Profile

The Budapest University of Technology and Economics (BME) is the most significant technological university in Hungary. Founded in 1782, it is considered the world’s oldest university of technology and was the first institute in Europe to train engineers at university level. The electrical engineering and infomatics department and is renowned for excellence in research and education throughout the years of changes in the scope of engineering. 

The Design Challenge

Under the direction of Dr. Tibor Berceli, head of the Optical and Microwave Telecommunication Laboratory, students at BME were challenged to design a novel mixer. Specifications for input signals to separate ports, multiplier-type operation, significantly lower LO power, cleaner spectrum, and easier separation of bands were all given at the onset. 

The BME students' mixer uses a microstrip distributed diplexer subcircuit to separate the RF and IF signals. The LO signal drives the FET between on and off states. To optimize the on/off ratio, some gate bias was applied. The mixer operates in a reflection mode and the signals applied to the FET channel are reflected by a time-varying reflection coefficient. The FET channel under the control of the LO signal switches between a low resistance state and a high resistance state. Furthermore, the diplexer circuit contains the IF and RF filter subcircuits. It isolates the IF and RF ports from one another, but allows transmission between these ports and the common port, which is connected to the drain of the FET.

The Solution

The students at BME used NI AWR Design Environment, specifically Microwave Office circuit design software, to achieve this novel design. The steps they followed included the design of the gate and drain bias network providing the necessary isolation of the DC bias injection ports from high-frequency signals, the development of the impedance matching circuit for the gate of the FET (source) at the 2.0 GHz LO frequency, as well as the development of impedance matching networks for the RF input and IF output signals, as well as filtering of the RF signal at the IF port. 

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