In our assignment, the antenna that we study is called TERK TV5 Indoor Amplified TV Antenna. The model is SU-112 and is manufactured from PANASONIC. This indoor amplified do not have any advantages to the conventional rabbit ears antenna. The rabbit ear antenna is relatively short which stand about five inches high. From the side, the antenna looks like an infinity sign and from the top, it looks like two loops. The antenna only uses a cable to connect to the television which means that the antenna is powered from the television and only works when the television is on.
Objectives
The objectives of this assignment are to understand the principles on how the rabbit ear antenna works, the radiation of a TERK TV5 Indoor Antenna patterns, signal strength of the antenna, characteristics of the antenna, strengths and weaknesses an indoor antenna and the designation of the antenna.
Outcomes
We learn that this antenna have a unique type of signal strength and polarization pattern. We also learn that friends, library and internet sources are important to gain more knowledge on antenna. Beside that, we learn that by distributing the work among us, it can be done faster and teamwork is very important among us.
Theory
Antenna is a device use to propagates and receive radiated electromagnetic waves. Antenna helps transformed guided electromagnetic waves propagates freely in free space (or vise versa) from the transmission line (waveguides) to a specific direction depending on the directional characteristics of the antenna. A few of the important characteristics discussed in this assignment are antenna’s radiation pattern, power gain, directivity, and polarization.
Antenna Radiation Pattern
Radiation pattern describe the relative strength involve in the radiated field where the antenna radiates in various direction. Radiation pattern can also called reception pattern as it shows how the properties receiving of the antenna. The radiation pattern is three dimensional plots from the source. Usually, we take the measurement in two dimensional which is slices of the three dimensional pattern. The two forms that we take are the elevation pattern and the azimuth pattern. The elevation pattern takes the measurement from the side where the antenna radiates while the azimuth pattern takes from the top as the antenna radiates.
When both the elevation pattern (Figure 1.1a) and the azimuth pattern (Figure 1.1b) combines, it shows the three dimensional radiation pattern of the energy radiated from the antenna (Figure 1.1c).
These pattern measurements can be represented using rectangular form or polar form. Rectangular form shows great details but it is difficult to visualize the antenna behavior from different directions. This is because the radiation pattern only shows how high the power gain is different angle without showing the effectiveness of it.
Polar form however, is widely used because the polar coordinate graph can show the points by projecting in a rotating axis to an intersection with one of the several concentric circles. Polar coordinates can be divided into two classes which are linear and logarithmic.
Linear class is where the concentric circle are equally spaced, and also when graduated. This kind of grid can be used to prepare a linear plot of the power in the signal. For comparison, the concentric circles are then replaced with appropriate decibel response. Lobes with higher peaks (approximately 15 dB) or below the main lobe will disappear because the power gain is small. This actually helps enhance the plots with high directivity and small minor lobes. This will let the voltage of the signal to be able to be plotted on a linear coordinate system instead of the power of the signal but the degree in the linear power grid will then differ.
In logarithmic class, the polar coordinate system concentric lines are spaced periodically depending on the logarithm of the voltage of the signal. This can affect the appearance of the plotted patterns if different values a used. Therefore, if 0 dB is used as reference for the outer edge, the lobes (around 30 dB) that are below the main lobes can still be distinguish. This means that the spacing between 0 dB and -3 dB will be greater than the spacing between -20 dB and -23 dB and it so on. The spacing will then correspond to the significance changes in the antenna performance.
There are two types of radiation patterns, which are absolute and relative. Absolute patterns are used with absolute units of field strength or power while relative patterns are used relatively to the unit of the field strength or power.
The radiation patterns are different depending on the distance. The term near-field is used where the field pattern exists close to the antenna. The term far-field (or radiation filed) is used where field patterns are at large distances.
Usually, a sufficiently large distance is used as the minimum permissible distance depends on the dimensions of the antenna in relation to the wavelength. Therefore, the minimum distance from the antenna is given to be two times of the square of the largest dimension of the antenna divided by the wavelength.
rmin = 2d2/
where rmin is the minimum distance from the antenna, d is the largest dimension of the antenna, and is the wavelength.
Figure 1.1
Power Gain
The gain is defined to be dimensionless ratio without any physical term such as Watt or Ohms in reference to a standard antenna. Two reference antennas that are commonly used are the isotropic antenna and the resonant antenna. The isotropic antenna can radiates equally well in all directions but real isotropic antenna do not exist. Theoretically it is used to compare with real antennas. Any real antenna radiates more energy is some directions than the other. The total power radiated is then the same as an isotropic antenna because antenna cannot create energy. Therefore, if additional energy is radiated in one direction, it will offset by equally radiating less energy in other directions.
The power gain of an antenna in a given direction is the ratio of the power input to the antenna to the power output from the antenna. Usually, the maximum gain is interested in which the gain in the direction in which the antenna is radiating the most power. The gain is referred in dBi, which is the logarithmic gain relative to an isotropic antenna while the gain will be written ad dBd, in which it is the logarithmic gain relative to a dipole antenna.
Directivity
Directivity of an antenna is how the concentrated of the radiated power in a particular direction when transmitting or when receiving energy. It is possible to direct radiated power to any wanted direction. For wireless link, fixed locations for both the receiver and transmitter antenna are used. For mobile application, an Omni-directional antenna is used as transceiver does not have any fixed position. An Omni-directional antennal can ideally radiate in all directions. Directivity measurement is usually obtained from the ratio of radiation intensity in a given direction to the average radiation intensity.
Polarization
Polarization is the orientation of the electric field of electromagnetic waves far from the source. In general, polarization is described by an ellipse. Two special types of elliptical polarization are linear polarization and circular polarization.
In linear polarization, the electric field vector stays in the same plane all the time. Electric field may then leave the antenna in vertical, horizontal, or oblique orientation. Vertical polarized radiation is less affected by reflections over the transmission path while in horizontal polarization, reflection cause variations in the received signal strength making it less likely to have man- made interference.
In circular polarization, the electric field vectors appear to be rotating with circular motion about the direction of propagation with one full turn for each RF cycle. This rotation can be circular right hand, circular left hand, elliptical right hand or elliptical left hand.
Polarization is important when we want to get the maximum performance of the antennas. Therefore, the initial polarization of the radio waves is determined by the antenna. By matching the polarization of the transmitting and receiving antenna, we can get the best performance.
Figure 1.2 Showing how the sine wave of the electric field moves in perpendicular to the magnetic field in the direction of propagation
When both the receiving antenna and the transmitting antenna have the same spatial orientation, polarization and axial ratio, maximum power can then be transfer. If both antennas are not properly aligned and do not have the same polarization, the power transfer will be lesser. Lesser power transfer will then reduce the efficiency and performance of the whole system.
If both antennas are linearly polarized but not properly aligned, it will result in mismatch loss which can then be calculated with,
Loss (dB) = 20 log (cosine )
where is the difference in the aligned angle between the two antennas.
In conclusion, the more mismatch in polarization between the two antennas, the more apparent loss it have.
Type of antenna
The antenna that we used is called the rabbit ear antenna. It two rabbit ear part can be adjusted to become shorter of longer by pulling the center part or the antenna. This will then create a reflector in the center. In our case study, we find that by putting the two rabbit ear to maximum we can get the maximum gain. The transmission line used in this case is 75 ohms and a capacitor type plug allows the antenna to just plug into the television without any power supply. In out study, we remove the capacitor plug and wired it to the spectrum analyzer to find the signal strength. This antenna does not have any switch to on/off or to amplifier the signal. Besides, this antenna also creates two loops in the rabbit ear form.
Advantages
The advantages of the rabbit ear antenna are fewer adjustments needed to find the best reception, by pulling the rabbit ear out or by pushing the rabbit ear in, we can find that the reception of the TV channel is well receive. Furthermore, the easy rotation can exploit deep response nulls for all polarizations. This can help rejects co-channel or adjacent channel interference despite transmit polarization. This rabbit ear antenna can minimize multipath distortion of circular polarized signal which null the opposite circular polarized signal.
Disadvantages
The disadvantages of the antenna are that when every channel changes the person need to readjust the antenna and as time goes by, the signal might receive some man- made interference that cause disruption in the picture quality.
Ways to Improve
This antenna overall can provide better signal if a reflector is placed behind the antenna that can help amplified the signal. By putting it in higher places, we can minimize the interference when a person passes by.
Details of Case Study and Its Finding
First we find that the maximum signal strength is 89.5cm we -20.0dBm. This is to find the power gain of the antenna. This is actually done by increasing the distance of it by 10 cm. First, we find the maximum signal strength by moving the antenna towards the transmitter. Then, by increasing the distance between the transmitter and receiver antenna, we get the following results:
Separation between transmitterand receiver (cm) Signal strength (dBm)
89.5 -20.0
99.5 -20.5
109.5 -21.8
119.5 -29.6
129.5 -26.8
139.5 -25.9
149.5 -24.3
159.5 -23.0
169.5 -20.0
After this finding, we proceed to find the polarization of the antenna. First we mark the maximum signal strength as 0 degree. By using the same distance throughout experiment and by turning it anti- clockwise every 30 degree, the following results are obtained:
Degrees Signal strength (dBm)
0 -20.0
30 -22.5
60 -22.7
90 -22.2
120 -21.2
150 -20.0
180 -20.0
210 -20.0
240 -20.0
270 -23.7
300 -24.6
330 -21.7
360 -21.8
After obtaining the result, the graph of separation between the transmitter and receiver versus the signal strength are draw (see next page). The polarization graph is also sketched (see the page after).
From the experimentation, we find that the rabbit ear antenna have a maximum signal strength at 89.5 cm and decreasing as the distance increase until a certain distance (129.5cm) the signal strength begin to increase again and reaches the maximum signal strength. We can conclude that this is a far-field antenna. This antenna increase in certain distance might be due the back part of the ear that helps reflect and receive signal making the signal strength increase. As the maximum strength is received at 169.5cm, we can conclude that the signal strength will decrease again as the distance increase and the signal continues.
For the second part, as we continue to turn, we find that at certain degree (0,150,180,210,240) the signal strength is at maximum. This is because the polarization is aligned. As for the 150,210and 240 case, we find that it is maximum might be due to the antenna received signal at that point is maximum as the degree is near to the 180. We can also conclude that this antenna have a front and back which the signal when approaching 0 and 360 the signal is lesser. As for the 360 case, we find that it might be due to transmission line is turned together making the receiver signal has minor interference.
The study has been repeated 3 times before the final results are obtained.
Discussion:
The low-noise broadband amplifier built into this indoor antenna features a simple one-touch adjustment for all stations, and TERK's patented selectable amplifier bypass prevents over modulation of stronger incoming signals. These controls allow you to provide the right amount of amplification to weaker signals, and yet not over do it with signals that don't need amplified. This amazing antenna also takes advantage of TERK's unique Complementary Symmetry technology that incorporates a pair of tuned receiving elements for excellent reception range and incredible clarity.
Conclusion:
In this assignment, we find that the TERK TV5 indoor antenna also known as rabbit ear antenna, is outdated in a way as more and more newer antenna is being designed. In a way, this antenna actually have more advantages compare as if no power supply is needed only the television. The best way to improve the antenna radiation is reduce the interference made by placing it a distance from any electronic devices that is not related (hand phones, radio). We also find out that this antenna have a radiation pattern in a figure eight and the signal strength depends on the distance and it can oscillates from low signal strength to high signal strength as the distance increase.
Antenna Comparison:
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