Re: Harmonic Mixer
Dear MobiNaz:
If you use a good Schottky diode as a frequency doubler, the efficiency will be poor. A better idea is to use a pair of such diodes; they act as switches controlled by the input signal. You can build even a wideband multiplier but its efficiency is usually ~ 13 dB. You will still need a post-amplifier to obtain a useful signal for e.g. a mixer.
Typically, a two-diode doubler needs an input > 15 dBm to operate well. Any lower input will strongly diminish its efficiency.
A subharmonically- pumped mixer can work as a harmonic mixer, but its conversion loss is usually >10 dB higher than a "straight" mixer, and >10 dB higher for each next harmonic.
There are varactor frequency multipliers; they utilize "parametric" action and are better in efficiency, but very demanding in design. They need THREE tuned circuits (or more) named "idler (s)" and they usually work best at a single frequency. A good frequency doubler with a varactor diode, from 5 to 10 GHz can have a conversion loss of <6 dB, but typically needs > 100 mW input power to generate ~30 mW at twice the input frequency.