Leeds student mixes a mm wave topology

Leeds student mixes a mm wave topology
Richard Ball Researchers at Leeds University have found a cheap way of mixing baseband signals up to gigahertz frequencies. Tiny millimetre wave basestations could provide high bandwidth wireless communications where short ranges are acceptable. Mike Roberts, a PhD student at Leeds, has developed a new topology for a millimetre wave mixer. The mixer self-oscillates at 38GHz, removing the need for a local oscillator and reducing cost. The non-linearity of the mixer results in a second harmonic at 76GHz. “A spin-off application was to interface that mixer to a fibre optic network,” said Roberts. “We took a baseband signal and modulated it onto a laser diode.” The laser light, with a modulation frequency of 100MHz, shines onto the mixer. The mixer uses a p-channel high electron mobility transistor (pHEMT), which behaves like a photodiode and up-converts the laser signal. This relatively cheap method of interfacing a fibre optic network to a millimetre wave mixer could have implications for mobile communications. A range of several hundred metres makes millimetre wave antennas ideal for communications picocells in towns and buildings.


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