Antenna Midterm Exam 2019

Note: Write down your answers in detail. Indicate which equations, figures or tables

you refer to. All answers must have at least 4-digit accuracy.

1. An antenna has a far-field pattern which is independent of but which varies with

as follows:

a. Find the directivity. (10%)

b. Find the half-power beam width. (10%)

2. Compute the radiation efficiency of a short dipole antenna at 900 MHz and 1800 MHz

if it is made of No. 20 AWG copper wire and has a total length of 2 cm. (20%)

3. A wireless network access point operating at 2.4 GHz delivers 1 W into a 10 dB gain

antenna. Compute the power in W received from a 3 dB gain mobile receiving

antenna 10 m away. (20%)

4. A manufactured standard gain horn antenna operates in Ka band has a WR-28

waveguide input. The gain is 20 dB at 33 GHz. (1) Use optimum gain design

principles to determine the horn geometry values. (2) Compute the E-plane and H-

plane half-power beam width HPE and HPH. (20%)

Hint: use MATLAB roots function to compute the root of Eq. 9-159 as follow:

roots([ ])

5. Design an optimum LPDA to operate from 470 MHz to 890 MHz with 9-dB gain.

Add one extra element to each end over that required by (6-86). (20%)

Solution1.

a. From Eq. (1-146b)

b.

2. From appendix

Diameter of the wire 0.812 mm.

L = 2 cm

a. Ideal dipole assumption

from Eq. 1-172

From Eq. (1-176)

From Eq. (1-175)

From Eq. (1-174)

b. Short dipole assumption

From Eq. (1-177)

From Eq. (1-180)

3. From Eq. (2-94)

4. WR-28:

At frequency 33 GHz,

Solve Eq. 9-159 with and , we have

From Eq. 9-147,

From Eq. 9-121,

From Eq. 9-152,

From Eq. 9-98,

From Eq. 9-135,

From Eq. 9-153,

From Eq. 9-125,

From Eq. 9-124,

From Eq. 9-138,

Verify the gain by 9-95,

Verify the gain by numerical method,

5. From Example 6-3, .

,

n L(m) d(m)

0 0.348 0.118

1 0.319 0.108

2 0.293 0.099

3 0.268 0.091

4 0.246 0.083

5 0.226 0.076

6 0.207 0.070

7 0.190 0.064

8 0.174 0.059

9 0.160 0.054

10 0.146 0.049