How to Design A Passive RF Diode Single-Ended Mixer
Actually, what is Mixer? Mixer is a 3 port device both active or passive that sum or difference frequency of RF wave. Mixer have 2 input port and a output port. One of the input port is used for wave from Local Oscillator (LO) with higher or lower frequency from RF wave in another input port. After “mixing”(sum or difference) those frequency, an Intermediet Frequency is created in output port. This article explain how to design one of passive mixer that commonly used.
A Passive RF Diode Single-Ended Mixer
properties : Narrow Bandwidth, low cost, poor port to port isolation, low intercept point, and inferior intermodulation supression.
This type of mixer only used one diode (commonly a silicon or Schottky diode), and to upgrade the specification, we can add a diode so the power of LO can be increased.
How to Design
1. Select an appropriate diode for the frequency of interest ( can be silicon or Schottky doide)
2. Design L4 and C5 for series resonance at IF frequency with high L to C ratio for narrow passband
3. Design l5 and c6 for parallel resonance at IF frequency with high C to L ratio for narrow passband
4. Design 50 Ohm Low Pass Filter for RF Wave (to attenuate high radiaton from LO)
5. Design 50 Ohm matching circuit for diode
6. Add 8-dBm LO signal, which will supply the mixer with an RF-to-IF conversion loss of 10-dB