# Antenna Theory and Communication Systems, communications homework help

1. Apply the input impedance formula for a /2 and /4 transmission lines. Compare and comment on any of the two cases which provide impedance transformation exploited in impedance matching techniques.

2. An ADSL cable, with the characteristic impedance Zo= 300  , is used to connect a computer having an impedance of 180 Ω. Assume the frequency of the signal on the line is 400 MHz and length of the line is 22.5 cm. Calculate the characteristic impedance of a quarter-wave impedance transformer to match the load with the line. Also draw the equivalent circuit of the matched system with Standing Wave Plot.

3. A lossless transmission line of length =0.3 is terminated with complex load impedance =30+ 20 Ω and characteristic impedance 0=75 Ω. Calculate:

a) The reflection coefficient at the input of the line;

b) VSWR on the line;

c) The input impedance to the line in Ω;

d) The input admittance to the line in S;

e) The distance to first minimum and first maximum from the load;

f) Use Smith Chart to find all parameters from (iii) to (vi).

4. An Ethernet cable is used to connect a computer to a server and it is found experimentally that . 120 Ω . 500 Ω. The cable is terminated with a sever having a load resistance of 500Ω at frequency of 300MHz. Design a single stub matching to minimize the reflection on this cable without using the Smith Chart.

5. The impedance of a 1 meter dipole antenna operating at 120 MHz is 44.8 – j 107Ω. The antenna is fed by a transmission line with characteristics impedance Zo = 75 Ohm. Design a series stub which will match this antenna to the transmission line. Find the position and length of the stub (by using Smith Chart).

6. Refer to at least two research papers to find the ways to increase Parabolic Reflector Antenna Signal Strength through Design. Support your explanation with suitable schematic diagrams.

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