This document discusses microwave mixers, which translate the frequency of electromagnetic signals by multiplying two waveforms. Microwave mixers have applications in military radar, RF communications, radio astronomy, and biological sensing. The document discusses the fundamentals, performance parameters, and types of microwave mixers, including single-balanced, double-balanced, sampling, and image rejection mixers. It provides examples of using mixers for up and down frequency conversions.

1. Microwave Mixer
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2. translate the frequency of electromagnetic signals
What is microwave mixer?
Applications
Military radar and surveillance
RF communications
Radio astronomy
Biological sensing
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3. Mixers perform frequency translation by multiplying two
waveforms (and possibly their harmonics)
Fundamentals of Mixer
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4. The LO port of this mixer is very nonlinear
The RF port must remain sufficiently linear to satisfy the
compression and/or intermodulation requirements
Fundamentals of Mixer
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5. Performance Parameters
Gain: mixer gain is critical in suppression of noise
while retaining linearity
Noise and Linearity: The design of down-conversion
mixers entails a compromise between the noise
figure and the IP
figure and the IP3
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6. Single-Balanced Mixers
operate with a single-ended RF input and a single-ended
LO. Discarding the RF signal for half of the LO period
two switches are driven by
differential LO phases, thus
“commutating” the RF input to
the two outputs. It is called
the two outputs. It is called
“single-balanced” mixer
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7. Up & Down conversions using single-ended mixer
Down-converter
RF AMP MIxer
Local
Oscillator
IF AMP
Lowpass
filter
fRF
fRF
fLO
fIF=fRF-fLO
RF input
Oscillator
Up-converter
MIxer
Local
Oscillator
Bandpass
filter
fRF
fIF
fLO
fIF=fRF+fLO
IF input
RF AMP
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8. The advantages of conversion are
to reduce 1/f noise when convert to lower frequency
for easy tuning for a wide band with fixed IF
frequency off-set between transmitter and receiver by
using a single LO as in Radar
Up & Down conversions using single-ended mixer
Drawbacks of single-ended mixer
Single -ended mixer produces output consisted of all harmonics.
The balanced mixer using hybrid suppresses all even harmonics
of the LO
Double balanced mixer suppresses all even harmonics both LO
and RF
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9. Double-Balanced Mixers
two single-balanced mixers
are connected in such a way
that their output LO feed-
throughs cancel but their
output signals do not
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10. Sampling Mixer
If the resistor is replaced with a capacitor, such an
arrangement operates as a sample-and-hold circuit and
exhibits a higher gain because the output is held
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11. Image rejection mixer
Mixer A
90o hybrid
90o
hybrid
The RF with frequency ωr= ω o + ω i will also produce the IF (ωi) when
mixed with LO
The frequency produced will be USB (ωr= ωo + ωi ) and LSB (ωr= ωo - ωi )
The undesired frequency either USB or LSB is called image frequency.
The mixer can produce one single side band is used as modulator.
3dB
power
divider
RF input
Mixer A
Mixer B
90 hybrid
LO
LSB
USB
IF out
90o
hybrid
Zo
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