diode mixer vs harmonic mixer-difference between diode mixer and harmonic mixer
This page on diode mixer vs harmonic mixer mentions difference between diode mixer and harmonic mixer. The other difference between terms are also provided here.
At frequency range of about 1GHz, silicon crystal diode is used as mixer to produce low frequency IF signal.
It has low conversion loss and low noise. Figure-1 depicts coaxial line single diode mixer used upto
frequencies of 3GHz. This type of circuit is used where signal levels are large in comparison to noise power signal.
In the situations where signal levels are not always large, balanced mixer configurations are used having 2 or 4 diodes in hybrid or magic-T configurations.
READ MORE Balanced mixer configurations➤➤
Fig:1 Diode Mixer
Fig:2 Harmonic Mixer
These type of mixers are used in frequency calibration set-ups. Here standard low frequency signal will cause harmonic generation in nonlinear device(e.g. crystal diode) and later heterodyned with another microwave test signal to generate frequency at IF. Harmonic amplitude or power is inversely proportional to the order of the harmonic. The figure-2 depicts harmonic mixer made using crystal diode and other components.
The figure depicts RF choke and IF choke. RF choke provides DC return for the crystal. RF bypass will prevent RF leakage through IF terminals. IF choke provides DC return with negligible effect on IF power.
Let us understand how harmonic mixer circuit works:
• The LO signal ( Vp*cos(Wp*t) generates currents in the crystal which contains fundamental frequency plus harmonics n*Wp, where n =1,2,3,....
• Incoming signal (Vs*cos(Ws*t) will beat with these frequencies and will produce sum as well as difference frequency components n*Wp +/- Ws.
• The difference component is tuned out through this IF amplifier.
• In this harmonic mixer, harmonic along with low frequency LO is used to generate IF frequency.
Like normal RF mixer, conversion loss is expressed as follows:
Conversion Loss(dB) = 10* Log10 (IF output power/RF input power)
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