EXAMINER: Dr. J Zhou
DEPARTMENT: EE&E EMAIL: zhouj@liverpool.ac.uk
SECOND SEMESTER EXAMINATION REPLACEMENTS 2019/20
WIRELESS SYSTEMS AND CAD DESIGNS
INSTRUCTIONS TO CANDIDATES
The numbers in the right hand margin represent an approximate guide to the marks available for that question (or part of a question). Total marks available are 100.
Copying any material from another source, or colluding with any other person in the preparation and production of this work will be considered suspected academic misconduct and will be dealt with according to the University’s Academic Integrity Policy.
PAPER CODE NO.
ELEC462
Additional Information:
This is an open-book test.
Answer ALL Questions.
The use of a calculator IS allowed.
Smith Chart Formula Sheet
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1. a)
Sketch a diagram and explain how a two-way Wilkinson power divider can 10 be designed using transmission lines and resistor(s). Explain why, at the
centre frequency, the divider can realize equal power splitting and achieve perfect isolation between the two output ports.
b) Such a Wilkinson power divider can operate over a relatively narrow 15 bandwidth. To broaden the bandwidth, a multi-section power divider can be designed. Use the table provided in Lab 9 to design a two-way divider that
can cover the bandwidth of 0.5 GHz to 2 GHz for a 50 Ω system. Sketch the circuit diagram and specify the values of all transmission lines and components used in the design.
c) In addition to Wilkinson power dividers, there are many other types of circuits 15 that can realise power splitting. A resistive network, which is a circuit using
only resistors, and a branchline coupler, which is a four-port network, can be
used as power dividers as well. Please discuss the advantages and disadvantages of using these three types of structures to realise power splitting.
Total 40
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2. a)
It has been discussed in Lecture 6 that an active filter can be designed using 10 operational amplifiers. Please explain why the circuit shown in Fig. Q2a has a lowpass response.
Fig. Q2a
b) Please design a highpass filter using an operational amplifier in a similar way 10 as that shown in Fig. Q2a.
c) A bandpass filter can be designed by combing a lowpass filter and a highpass filter. Please design a bandpass filter with a passband of 100 MHz to 1 GHz using one operational amplifier with as many capacitors and resistors as you need. Please
i) Draw the circuit diagram of your design. 5
ii) Specify all the values of the capacitors and resistors used in your design. 10
iii) Sketch the frequency response of your design. 5
Total 40
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3.
a)
b)
c)
A solid state amplifier can be developed using transistors with properly designed
input and output matching networks.
Please explain why transistors are usually not pre-matched when manufactured. 5
Which one is more important when designing high efficiency power amplifiers, the 5 input matching network or the output matching network? Explain why.
A chain of low noise amplifiers can be used to amplify weak signals. Are the gain 10 and the noise figure of each stage of the amplifiers important? Explain why. What
are the main considerations when designing a low noise amplifier?
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Total 20
Smith Chart
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Formula Sheet
Constants
Free space speed of light c = 1 = 3 × 108 ms−1, 0 = 8.85 10−12 Fm−1 0 = 4 10−7 Hm−1
√μ0 ε0
Impedance of free space η = √μ0 = 377 Ω ε0
Transmission Lines
vph = 1 = c = LC r
=a+j= (R+jL)(G+jC)
Z0 = (R + jL) (G + jC)
=ZL −Z0 ;Z =Z1+L
L Z+Z L 01− in L
=e−2L
Z =Z ZL + jZ0 tan(L) VSWR=1+L ; =VSWR−1
L0L L
in 0Z +jZ tan(L) 1− VSWR+1 0LL
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Lowpass Prototype Filter Element Values
Friis Formula
G 2G G P=PtA=Ptr
r t 4r2 er t 162r2
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