10-12-2012, 06:14 PM
ANTENNA DESIGN
[attachment=43290]
Abstract:
This project involves study of different types of antennas.
• We have designed following 2 types of antenna:-
1. Circular loop : Designed for f.m. broadcasting, the antenna gives a substantially circular radiation pattern in the horizontal plane, it is a simple mechanical structure (at least from the commercial viewpoint), and can be mounted without insulation on a grounded metal pole.
2. Array type antenna (Endfire) : An antenna array is a similar antennas oriented similarly to get greater directivity in a desired direction. It may also be defined as a radiating system consisting of several spaced and properly phased radiators.
• Working frequency of both antennas = 175 MHz .
• Both the types of antennas were not available in the Lab so this project is useful for the college.
Problem statement:
• In our college, in communication lab we have antennas working at 750MHZ which are able to transmit as well as receive only audio signals.
• These antennas have negligible BW and very low gain.
• Size of these high frequency antennas is also very small.
• Thus we have built two antennas -
1) Circular loop antenna
2) Endfire array antenna
Working at 175MHZ frequency.
This frequency is very less than what our college antennas have.
This will enable us to pass audio as well as video signals proving flexibility.
Introduction to antenna
Our project focuses on the hardware fabrication and software simulation of circular and endfire antennas. In order to completely understand the above it is necessary to start off by understanding various terms associated with antennas.
An antenna (or aerial) is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter applies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified. An antenna can be used for both transmitting and receiving.
Antenna parameters
An antenna is an electrical conductor or system of conductors
Transmitter - Radiates electromagnetic energy into space
Receiver - Collects electromagnetic energy from space
The IEEE definition of an antenna as given by Stutzman and Thiele is, “That part of a transmitting or receiving system that is designed to radiate or receive electromagnetic waves”. The major parameters associated with an antenna are defined in the following sections.
Antenna Gain
Gain is a measure of the ability of the antenna to direct the input power into radiation in a particular direction and is measured at the peak radiation intensity. Consider the power density radiated by an isotropic antenna with input power P0 at a distance R which is given by S = P0/4πR2. An isotropic antenna radiates equally in all directions, and its radiated power density S is found by dividing the radiated power by the area of the sphere 4πR2. An isotropic radiator is considered to be 100% efficient.
Radiation Pattern
The radiation pattern of an antenna is a plot of the far-field radiation properties of an antenna as a function of the spatial co-ordinates which are specified by the elevation angle (θ) and the azimuth angle (φ). More specifically it is a plot of the power radiated from an antenna per unit solid angle which is nothing but the radiation intensity. It can be plotted as a 3D graph or as a 2D polar or Cartesian slice of this 3D graph. It is an extremely parameter as it shows the antenna’s directivity as well as gain at various points in space. It serves as the signature of an antenna and one look at it is often enough to realize the antenna that produced it. Because this parameter was so important to our software simulations we needed to understand it completely. For this purpose we obtained the 2D polar plots of radiation patterns for a few antennas in our lab using a ScienTech antenna trainer kit. The transmitter of the kit was rotated through 360 degrees in 20 degree intervals and the received power was measured (in µV – converted to dB) by a receiver to plot the radiation patterns of a few antennas.
ELECTRICALLY LARGE LOOPS
As the electrical size of the loop antenna is increased, the current distribution in the loop departs from the simple uniform distribution of the electrically small loop. For single-turn loops, this departure has a significant effect on performance when the circumference is greater than about 0.1l.
End-Fire Array Antennas :
The endfire array is nothing but broadside array except that individual elements are fed in, out of phase. Thus in the endfire array, a number of identical antennas are spaced equally along a line and individual elements are fed with currents of equal magnitude but their phases varies progressively along the line in such a way as to make the entire arrangement substantially unidirectional. In other words, individual elements are excited in such a manner that a progressive phase difference between adjacent elements becomes equal to the spacing (in wavelength) between the elements.
In end fire array the maximum radiation can be directed along the axis of the uniform array by allowing the progressive phase, shift between element to ± fid. This produces a maximum field in the direction 0=0 but does not give the maximum directivity.
Conclusion
The overall working of antennas was understood. The major parameters (such as Return Loss curves, Radiation Patterns, Directivity and Beamwidth) that affect design and applications were studied and their implications are understood.
We have first simulated our antenna in NEC software. The results which we got for simulation were matched with the actual results using the antennas which we have designed.
For loop antenna radiation resistance is improved and for endfire antenna directivity is improved.
[attachment=43290]
Abstract:
This project involves study of different types of antennas.
• We have designed following 2 types of antenna:-
1. Circular loop : Designed for f.m. broadcasting, the antenna gives a substantially circular radiation pattern in the horizontal plane, it is a simple mechanical structure (at least from the commercial viewpoint), and can be mounted without insulation on a grounded metal pole.
2. Array type antenna (Endfire) : An antenna array is a similar antennas oriented similarly to get greater directivity in a desired direction. It may also be defined as a radiating system consisting of several spaced and properly phased radiators.
• Working frequency of both antennas = 175 MHz .
• Both the types of antennas were not available in the Lab so this project is useful for the college.
Problem statement:
• In our college, in communication lab we have antennas working at 750MHZ which are able to transmit as well as receive only audio signals.
• These antennas have negligible BW and very low gain.
• Size of these high frequency antennas is also very small.
• Thus we have built two antennas -
1) Circular loop antenna
2) Endfire array antenna
Working at 175MHZ frequency.
This frequency is very less than what our college antennas have.
This will enable us to pass audio as well as video signals proving flexibility.
Introduction to antenna
Our project focuses on the hardware fabrication and software simulation of circular and endfire antennas. In order to completely understand the above it is necessary to start off by understanding various terms associated with antennas.
An antenna (or aerial) is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter applies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified. An antenna can be used for both transmitting and receiving.
Antenna parameters
An antenna is an electrical conductor or system of conductors
Transmitter - Radiates electromagnetic energy into space
Receiver - Collects electromagnetic energy from space
The IEEE definition of an antenna as given by Stutzman and Thiele is, “That part of a transmitting or receiving system that is designed to radiate or receive electromagnetic waves”. The major parameters associated with an antenna are defined in the following sections.
Antenna Gain
Gain is a measure of the ability of the antenna to direct the input power into radiation in a particular direction and is measured at the peak radiation intensity. Consider the power density radiated by an isotropic antenna with input power P0 at a distance R which is given by S = P0/4πR2. An isotropic antenna radiates equally in all directions, and its radiated power density S is found by dividing the radiated power by the area of the sphere 4πR2. An isotropic radiator is considered to be 100% efficient.
Radiation Pattern
The radiation pattern of an antenna is a plot of the far-field radiation properties of an antenna as a function of the spatial co-ordinates which are specified by the elevation angle (θ) and the azimuth angle (φ). More specifically it is a plot of the power radiated from an antenna per unit solid angle which is nothing but the radiation intensity. It can be plotted as a 3D graph or as a 2D polar or Cartesian slice of this 3D graph. It is an extremely parameter as it shows the antenna’s directivity as well as gain at various points in space. It serves as the signature of an antenna and one look at it is often enough to realize the antenna that produced it. Because this parameter was so important to our software simulations we needed to understand it completely. For this purpose we obtained the 2D polar plots of radiation patterns for a few antennas in our lab using a ScienTech antenna trainer kit. The transmitter of the kit was rotated through 360 degrees in 20 degree intervals and the received power was measured (in µV – converted to dB) by a receiver to plot the radiation patterns of a few antennas.
ELECTRICALLY LARGE LOOPS
As the electrical size of the loop antenna is increased, the current distribution in the loop departs from the simple uniform distribution of the electrically small loop. For single-turn loops, this departure has a significant effect on performance when the circumference is greater than about 0.1l.
End-Fire Array Antennas :
The endfire array is nothing but broadside array except that individual elements are fed in, out of phase. Thus in the endfire array, a number of identical antennas are spaced equally along a line and individual elements are fed with currents of equal magnitude but their phases varies progressively along the line in such a way as to make the entire arrangement substantially unidirectional. In other words, individual elements are excited in such a manner that a progressive phase difference between adjacent elements becomes equal to the spacing (in wavelength) between the elements.
In end fire array the maximum radiation can be directed along the axis of the uniform array by allowing the progressive phase, shift between element to ± fid. This produces a maximum field in the direction 0=0 but does not give the maximum directivity.
Conclusion
The overall working of antennas was understood. The major parameters (such as Return Loss curves, Radiation Patterns, Directivity and Beamwidth) that affect design and applications were studied and their implications are understood.
We have first simulated our antenna in NEC software. The results which we got for simulation were matched with the actual results using the antennas which we have designed.
For loop antenna radiation resistance is improved and for endfire antenna directivity is improved.