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MODERN ANTENNAS.pptx
1. MODERN ANTENNAS
โข PHASED ARRAYS
โข FREQUENCY SCANNING ARRAYS
โข SMART ANTENNAS
โข ADAPTIVE ARRAYS
โข SWITCHED BEAM SYSTEMS
โข RFID ANTENNNAS
โข WEARABLE ANTENNAS
POORNISHWAR M
2020105561
2. PHASED ARRAYS
โข The objective of phased arrays is to achieve BEAM STEERING
without the mechanical and inertial problems of rotating the entire
array.
โข Another important objective of phased arrays is to provide beam
steering at a fixed frequency or at a number of frequencies within a
certain bandwidth in a frequency independent manner.
โข Let us consider the simplest beam steering technique done by
mechanical switching
3. 3-Element dipole array:
โข For impedance matching purposes resistance of the
cable to the receiver/transmitter should be 1/3 the
resistance of the individual cables.
4. Now consider incident wavefront 45ยฐ to the broadside :
โข The dipole 1 captures the signal first followed by dipole 2 and then dipole 3 during
RECEPTION.
โข And similarly ,
โข During TRANSMISSION dipole 3 radiates first followed by dipole 2 and then dipole 1.
5. โข Now simply by switching between connection 1 and connection 2 we can shift
the beam from broadside to 45 ยฐ tilted angle.
6. Phased arrays using phase shifters :
โข A four element dipole antenna
is considered.
โข Instead of varying the length of
connecting cables,
โข phase shifters are used
accordingly to steer the beam.
โข Attenuates are used for
impedance matching purposes.
7. Rotatable helix phased arrays :
โข Here beam steering is achieved by
rotating helix 1 and helix 3 in opposite
directions while keeping helix 2
stationary.
โข Continuous rotation results in continuous
beam steering from extreme right to
extreme left of the sweep angle
8. ADVANTAGES
โข High gain with low side lobes
โข Steering of antenna beam
without physical movement
โข Multifunctional operation
โข Reduction of fault signal
components
APPLICATIONS :
โข Radar tracking
โข Direction tracing
โข Smart antennas
DISADVANTAGES
โข Complex structure
โข High cost
โข Low frequency bandwidth
9. Frequency scanning antenna arrays :
โข In this array beam steering is done by sweeping (scanning) the
frequency.
10. Expression for beam angle โ :
โข Example : velocity of transmitted wave v = c
(m = -1) , d = 1m , ๐ = ๐๐ calculate the beam angle ?
โข Example : velocity of transmitted wave v = c
(m = -1) , d = 1m , ๐ = ๐. ๐๐๐ calculate the beam angle ?
11. Adaptive arrays and smart antennas :
โข By processing the information from individual antenna an array can
become active and react intelligently with itโs surroundings by steering
a beam towards a desired direction while simultaneously steering a
null towards a undesired direction.
โข Thereby reducing the interference and increasing the signal to noise
ratio (SNR) of the desired signal.
โข These are called adaptive arrays.
12.
13.
14. Smart antennas :
โข Also by suitable signal processing further enhancement can be
achieved,
โข By appropriate sampling and digitizing the signals at the terminals of
each element and processing them with a computer a very intelligent or
a smart antenna can be built.
โข Smart antennas uses a low cost DSP for digitizing and sampling the
signals along with advanced algorithms .
16. Cell splitting and sectorizing :
โข Cell splitting subdivides a congested cell into smaller cells called
microcells, each with its own base station and a corresponding
reduction in antenna height and transmitter power.
โข Sectorizing is where a single omnidirectional antenna is replaced at the
base station with several directional antennas. Typically, a cell is
sectorized into three sectors of 120โฆ
17. Switched beam systems :
โข A switched-beam system is a system that can choose from one of
many predefined patterns in order to enhance the received signal.
21. WEARABLE TEXTILE ANTENNAS :
โข It should be highly flexible comfortable and durable to wear.
โข It should be stable lightweight and cost effective.
โข It should be safe to wear and should have proper provisions to protect
against any possible health hazards by creating a proper isolation
between body and antenna.
โข It should maintain same radiation properties due to bending crumpling
and wrinkling of textile.