Antenas Remote Test Submission deadline: 5.30pm€¦ · 2nd Test of Antennas –25 June 2020 Antenas 2nd Test 25 June 2020 Remote Test Submission deadline: 5.30pm _____ Instructions:

Departamento de Engenharia Electrotécnica e de Computadores – Instituto Superior Técnico _________________________________________________________________________________________

_________________________________________________________________________________________

2nd Test of Antennas –25 June 2020

Antenas

2nd Test 25 June 2020

Remote Test Submission deadline: 5.30pm _________________________________________________________________________________________

Instructions:

Please submit your resolution through Fenix as a project (2nd Antennas test). The submission

deadline is 5.30pm.

If possible the resolution should be returned in a single .pdf file.

Together with the test, you should return a signed declaration of honor stating the following:

Declaration of honor:

For Portuguese students: Declaro por minha honra que a resolução que apresento foi preparada

exclusivamente por mim sem auxílio de terceiros. Em particular, declaro por minha honra que não

recebi auxilio nem auxiliei outros colegas.

For non-Portuguese speaking students:

I hereby declare by my honor that the present work was prepared exclusively by me without the

assistance of third parties.In particular, I declare on my honor that I have not received assistance or

helped other colleagues.


_________________________________________________________________________________________


Problem 1. Consider a lossless receiving dipole antenna with height 15L cm . The antenna is

connected to a load with impedance 73.1LZ and is used to receive a signal with frequency

1GHz and bandwidth of 5%. The load is matched to the antenna at 1GHz.

a) (10%) Suppose that the brightness temperature of the “sky” is uniform and equal to 300K. Find

the noise power captured by the antenna.

b) (10%) Find the minimum value for the intensity of the Poynting vector of the incoming signal

wave so that the signal to noise ratio (SNR ) exceeds 2 (SNR>2 ). The SNR is the ratio of the

power captured by the antenna due to the incoming signal and power captured by the antenna due

to the incoming thermal noise.

c) (10%) Supposing that the physical temperature of the antenna is 300K, find the noise power

radiated by the antenna.

Problem 2. A Dolph-Chebyshev broadside array of 7 elements was designed to perform with a

side-lobe level identical to 0.1. The spacing between the array elements 0 / 2 and the feeding

currents ( 1 2 3 4 5 6 7, , , , , ,I I I I I I I ) are such that

1 3 4 61.02 , 1.73 , 1.88 , 1.31 I A I A I A I A .

a) (10%) Find 2 5 7, and I I I .

b) (10%) Find the mainbeam width.

c) (10%) Make a plot of the array spatial factor (you can use computational tools to solve this

question).


_________________________________________________________________________________________


Problem 3.

A Yagi-Uda antenna is formed by 3 elements (director, reflector, and driven element) spaced by

1 2 0.15d d d .

The coupling between the reflector and the director is negligible. It can be shown that in order that

the Yagi-Uda operates as a endfire array the heights of the director and reflector must be such that:

22 33 0arg arg 0.3Z Z k d

a) (10%) Suppose that the quality factor of the dipole antennas is Q=15. Find the heights of the

director and reflector relative to the height of the energized element.

b) (10%) Find the input impedance of the Yagi-Uda antenna. Take into account that the mutual

impedance of two (half-wavelength or nearly half-wavelength) dipoles side-by-side is

0.15 65mZ d .

c) (10%) Find the feeding current required so that the electric field intensity at a distance of

10km from the Yagi antenna (in the direction of maximum gain) is at least 1mV/m. The frequency

of operation is 1GHz.


_________________________________________________________________________________________


Problem 4 (10%). The antenna shown in the figure is

typically fed through the apex of the structure (near the

shortest dipole). Is it acceptable to feed the antenna from

the other end (near the largest dipole)? Please explain

carefully your answer.

XXXXXXXXXX34.1pW/m^2

Documents

Antenas Remote Test Submission deadline: 5.30pm€¦ · 2nd Test of Antennas –25 June 2020 Antenas 2nd Test 25 June 2020 Remote Test Submission deadline: 5.30pm _____ Instructions: