Harmonic mixers in low noise heterodyne millimetre radiometry

Provided adequate local oscillator (LO) power is conveniently available, fundamentally pumped single ended mixers remain a good choice in narrow band applications requiring good radiometric sensitivity. In aerospace applications however, where there are often severe constraints on system design, and performance trade offs may need to be made, harmonic mixers have a number of attractive features. Single diode subharmonically pumped mixers are particularly economical of LO power and are relatively simple to build, but have inherently inferior sensitivity compared with fundamentally pumped types. However, subharmonically pumped double diode mixers show promising sensitivity and have excellent bandwidth capabilities, and are now being chosen for a number of projects. Evolving diode technology and mixer fabrication techniques are likely to increase their attractiveness in the future