Wireless and Microwave Instructional Laboratory
Laboratory #3 Notes
The purpose of this laboratory exercise is to introduce you to the
following:
1. Harmonic Balance, Power Budget, and Frequency Characterization
Simulations using Advanced Design System (ADS)
2. Communication System Design Techniques for Optimal Image
Frequency Rejection and Noise Figure
3. The Principles of Mixing
4. Re-emphasis of the use of dB, dBm Units
For this exercise you will need to turn in the following items:
1. One-Page Post-Laboratory Report Including Summary and Discussion
Pertaining to Topics Listed in the "Laboratory Report" section of the
experiment
Note: Please omit Part 4(c) given in the "Laboratory Report" section. No
power budget was performed at the image frequency in this
experiment.
2. Worksheets Containing Results
3. Printouts and Tables as Specified in the "Laboratory Report" section
of the experiment.
Please Note: If you want extra credit for performing optional sections,
please make a note of this on your one-page post-laboratory
report.
Important Concepts
Mixing
Mixers are imperfect multipliers. Mixers are devices used for
downconversion based upon the mathematical principles of sinusoid
multiplication.
Example: Multiplication of sinusoidal waves
v1(t) = A cos at
v2(t) = B cos bt
Note that a and b are the radian frequencies of the signals.
v1(t)v2(t) = AB cos at cos bt = (AB/2) cos (a - b)t + (AB/2) cos (a +
b)t
It should be noted that the sum and difference of the radian frequuencies
a and b of the original signals are present in the resultant signal.
This is due to the trigonometric identity
cos x cos y = [cos (x - y)]/2 + [cos (x + y)]/2
(1)
You may have previously been exposed to the identity
cos x cos x = 1/2 + (1/2)cos 2x
which is a special case of (1).
.
Image Frequency Rejection
We convert down to an intermediate frequency before converting to
baseband by using the principle of mixing. We utilize the mixing of
the local oscillator frequency and the desired RF frequency to downconvert
the signal to the desired IF frequency. Thus, the local oscillator should
be the sum of the RF and IF frequencies. However, another frequency that
will produce a difference frequency (with the LO frequency) at the IF is
the image frequency, equal to the sum of the IF and the LO
frequencies. Thus it is necessary to greatly attenuate the image
frequency at the first stage to prevent signal distortion.
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