Faculty of EngineeringElectrical and Electronic Engineering

Department

EE521

(Antenna and Propagation )

حنيش محمد الدين عالء

021090651

Group VIII

This Report is divided to two Parts :

Part one : Theory

Including Antenna definition , principle of operation ,Characteristics , types, and

horn antenna as an example .

Part two: Experiment

Including Objectives, equipments , Procedures of the measurements with comments ,then finally a conclusion.

Part one : Theory

The aim of this experiment is to investigate the basics of an antenna system , it is very clear how the antenna systems are very important in this era and we can say that they are one of the biggest evolutions in the

20th century.

What is an Antenna ?

The antenna is a directional device that convert the electrical energy to a radiated electromagnetic energy , what we mean by a directional is that

it will radiate the power to the desired direction according to its design.

The antenna may also be used in the reverse operation to get the original electrical signal from the electromagnetic radiated power.

Principle of Operation :

It simply states that to create radiation, there must be a time-varying

current or an acceleration (or deceleration) of charge.

Thus , we have in general those conditions:

1. If a charge is not moving, current is not created and there is no radiation.2. If charge is moving with a uniform velocity:a. There is no radiation if the wire is straight, and infinite in extent.b. There is radiation if the wire is curved, bent, discontinuous, terminated, or truncated .

3 .If charge is oscillating in a time-motion, it radiates even if the wire is straight.

Antenna characteristics:

They are the properties that we can express the antenna performance in term of them , some of them are radiation characteristics such as the directivity , the gain and the radiation pattern while the others are

impedance characteristics such as the input impendence and efficiency.

In this experiment we measured the gain and the radiation pattern of a horn antenna .

Here are some of the basic Antenna properties :

1-Radiation pattern:

An antenna radiation pattern is defined as a mathematical function or a graphical representation of the radiation properties of the antenna as a

function of space coordinates.

This property is defined in the far field region.

2-Beamwidth :The beamwidth of a pattern is defined as the angular separation between two identical points on opposite side of the pattern maximum. In an antenna pattern, there are a number of beamwidths. One of the most widely used beamwidths is the Half-PowerBeamwidth (HPBW ), which is the angle between the two points in which the radiation intensity is one-half value of the beam.

3-Directivity :Is the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions .

4-effeciency :The total antenna efficiency eo is used to take into account losses atthe input terminals and within the structure of the antenna. Such losses may be due to the reflection or the ohmic loss .

5-The gain :the ratio of the intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically.This property account the efficiency of the antenna as well as its directional capabilities .

6-The Bandwidth :

the range of frequencies within which the performance of the antenna, with respect to some characteristic, conforms to a specified standard .

Antenna types :

According to the Antenna dimensions we can get a different a various characteristics , therefore according to shape that the antenna take , antennas are classified to different types here are some of them with a

figures that show examples of each type :

1-Wire Antenna:

2-Apreture Antenna :

3-Microstrip Antenna :

4-Reflector Antenna :

5-Lens Antennas:

Horn Antenna :

In this experiment we are dealing with the Horn antenna:

is an aperture antenna . a very simple antenna and it is therefore widely used . used as a feed element for large radio astronomy, satellite

tracking, and communication dishes . Its widespread applicability stems from its simplicity in

construction, ease of excitation, versatility, large gain, and preferred overall performance

The horn is nothing more than a hollow pipe of different cross sections, which has been tapered (flared) to a larger opening.

The type, direction, and amount of taper (flare) can have a profound effect on the overall performance of the element as a radiator .

Some of horn Antenna forms are shown:

Part two : the Experiment

Objective:

1. Find the antenna gain.2. Find the relation between received power and distance between

two antennas.3. Draw the polar radiation patterns for horn antenna.4. Find the beam width.5. Find the directivity of the antenna.

Equipment list:1. Gunn oscillator operating frequency 10.5GHz.

Power MeterGunn Oscillator

r

2. Power meter.3. Two identical horn antennas.4. Crystal detector.

Procedure :

Free-space loss analysis1) Make sure that all power switches are in the O (off) position.2) Set up the components of the experiment as shown.

3) Make the following adjustments:

On the Gunn Oscillator Supply

Voltage ..................................Min. Mode .....................................1 kHz. Meter Range .......................... 10 V.

On the SWR Meter

Range .................................... 30dB. Gain ................................. 10 dB (fully cw). Scale ...................................... Normal Bandwidth ............................. 20 Hz.

4) Move the antennas to an appropriate apart. Adjust the horns so that they are at the same height and directly facing each other.Comment: For our measurements we need to separate the antennas at least by r > 2D2/λ which is the far field diameter (Fresnel range ).D : is the antenna largest dimension which is for our Horn antenna 6.6 cm , the frequency of operation is 10.5GHz , and by substituting we get :

r=30.49cm

5) Power the Gunn Oscillator power supply and the SWR Meter, Wait 1-2 minutes to allow the power supply to warm up. Adjust the Gunn Oscillator’s supply voltage to 8.5V.

6) For different values of r > 2D2/λ, we record the values of received signal power.

r (cm) Pr(dB)32 -2238 -22.542 -23

7) Plot signal level against r and see if equation (1) is satisfied .

Gunn Oscillator Power Meter

30 32 34 36 38 40 42 44

-23.2

-23

-22.8

-22.6

-22.4

-22.2

-22

-21.8

-21.6

-21.4

Series2

Power in dB versus the distance in cm

Comment :

We note that the signal level decreases as the distance grows , this due to the free space loss that described in equation 1 :

PL=20 log( λ4 πr )

We did observe experimentally the effect of the distance on the free space loss and assure the theoretical equation.

Gain measurement :

8) Using same previous setup, record the values of Pr and r.They are shown in the Table .

9) Connect the same setup bypassing the two antennas (Remove both antennas), connect directly input of transmitting antenna to the output of the receiving antenna as shown below, record Pt. use the power meter to calculate the left hand side of the following equation. Note that it’s negative in sign.

Pt = -9 dB.

Equation 3 is : Pr(dB) – Pt(dB) = 20log( λ4 πr )+2G (dB )

Now by calculating the left hand side :

r (cm) Pr(dB) Pr-Pt (dB)32 -22 -1338 -22.5 -13.542 -23 -14

10) Knowing that frequency is 10.5 GHz, use equation (3) to calculate the gain of each horn antenna in dB, ie, G(dB).

r (cm) Pr(dB) Pr-Pt (dB) G(dB)32 -22 -13 14.9838 -22.5 -13.5 15.4842 -23 -14 15.66

Comment : theoretically the gain of an antenna is constant since it is a function of the radiation which a function of the antenna dimensions , and in our case we didn't change the antenna dimensionthe variation in the gain value is therefore an error and is due to many factors such as errors in the instruments , error from the observer and also the reflection from the nearby bodies as will as

travelling fields in the area .

Radiation pattern plotting :

11) Make sure that the antennas are aligned correctly. Adjust the Antenna Azimuth indicator to read 00 with the antennas correctly aligned. Record different values of azimuth angles and the corresponding values of received signal level Pr.

At θ=0 P= -22dB

θ P (dB) θ P(dB)5 -22.2 -5 -22.25

10 -22.52 -10 -22.515 -23 -15 -23.120 -23.8 -20 -2425 -25.25 -25 -24.530 -27.1 -30 -2740 -33 -40 -32.550 -39 -50 -4155 -46 -55 -45

Comment : as written above the maximum power received is -22dB at the center of the radiation pattern , however the power received for other angles (cw & ccw) from the maximum are in the table . ideally the data should be even (e.g. both 5 & -5 degree angels should have the same power received ), practically that is not the case since the environment is not symmetrical which means the reflection and the travelling fields in the area are not symmetrical with respect to the antenna , all those factors affect the power measurements .

12) Plot the radiation of the antenna and evaluate the beamwidth .As shown in the Theory part we are going to compute the H.P.B.W and for this we will compute the angles at which the power fall bb 3dB from the maximum (-22-3=-25dB) .Using this concept I did adjust the Antenna until I get the record of the power meter equals -25dB . This will result in a H.P.B.W ≅ 44 ° We can also compute it from the curve as :

H.P.B.W =47 °Now to plot the data let us convert it to watt :

θ P (watt) θ P(watt)5 0.006026 -5 0.005957

10 0.005598 -10 0.005623

15 0.005012 -15 0.004898

20 0.004169 -20 0.003981

25 0.002985 -25 0.003548

30 0.00195 -30 0.001995

40 0.000501 -40 0.000562

50 0.000126 -50 7.94E-05

55 2.51E-05 -55 3.16E-05

Using Matlab we plot the data :

13) Turn the voltage control knob on the Gunn Oscillator power supply to its MIN position, place all power switches in the O (off)

position, disassemble the setup, and return all components to their storage compartments.

Conclusion:

1- We did see experimentally that the antenna is a directional device where in this device the positions of the transmitter and the receiver and their orientation are the basic factors in the transmission process .

2- We also investigate the effect of free space loss and prove that it is a function of the distance .

3- We computed the gain of an antenna using the transmission equation .

4- We also observe that the electromagnetic propagation is highly affected by the environment , that was free clear as we get a non-symmetrical radiation pattern .

5- It is important to do all the measurements in the far field region .