MODERN ANTENNAS

1. MODERN ANTENNAS
• PHASED ARRAYS
• FREQUENCY SCANNING ARRAYS
• SMART ANTENNAS
• ADAPTIVE ARRAYS
• SWITCHED BEAM SYSTEMS
• RFID ANTENNNAS
• WEARABLE ANTENNAS
POORNISHWAR M
2020105561

2. PHASED ARRAYS
• The objective of phased arrays is to achieve BEAM STEERING
without the mechanical and inertial problems of rotating the entire
array.
• 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.
• Let us consider the simplest beam steering technique done by
mechanical switching

3. 3-Element dipole array:
• 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 45° to the broadside :
• The dipole 1 captures the signal first followed by dipole 2 and then dipole 3 during
RECEPTION.
• And similarly ,
• During TRANSMISSION dipole 3 radiates first followed by dipole 2 and then dipole 1.

5. • Now simply by switching between connection 1 and connection 2 we can shift
the beam from broadside to 45 ° tilted angle.

6. Phased arrays using phase shifters :
• A four element dipole antenna
is considered.
• Instead of varying the length of
connecting cables,
• phase shifters are used
accordingly to steer the beam.
• Attenuates are used for
impedance matching purposes.

7. Rotatable helix phased arrays :
• Here beam steering is achieved by
rotating helix 1 and helix 3 in opposite
directions while keeping helix 2
stationary.
• Continuous rotation results in continuous
beam steering from extreme right to
extreme left of the sweep angle

8. ADVANTAGES
• High gain with low side lobes
• Steering of antenna beam
without physical movement
• Multifunctional operation
• Reduction of fault signal
components
APPLICATIONS :
• Radar tracking
• Direction tracing
• Smart antennas
DISADVANTAGES
• Complex structure
• High cost
• Low frequency bandwidth

9. Frequency scanning antenna arrays :
• In this array beam steering is done by sweeping (scanning) the
frequency.

10. Expression for beam angle ∅ :
• Example : velocity of transmitted wave v = c
(m = -1) , d = 1m , 𝝀 = 𝟏𝒎 calculate the beam angle ?
• Example : velocity of transmitted wave v = c
(m = -1) , d = 1m , 𝝀 = 𝟎. 𝟎𝟗𝒎 calculate the beam angle ?

11. Adaptive arrays and smart antennas :
• By processing the information from individual antenna an array can
become active and react intelligently with it’s surroundings by steering
a beam towards a desired direction while simultaneously steering a
null towards a undesired direction.
• Thereby reducing the interference and increasing the signal to noise
ratio (SNR) of the desired signal.
• These are called adaptive arrays.

14. Smart antennas :
• Also by suitable signal processing further enhancement can be
achieved,
• 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.
• Smart antennas uses a low cost DSP for digitizing and sampling the
signals along with advanced algorithms .

15. 2 element smart antenna :

16. Cell splitting and sectorizing :
• 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.
• 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 120◦

17. Switched beam systems :
• A switched-beam system is a system that can choose from one of
many predefined patterns in order to enhance the received signal.

18. 120 ° SECTORIZED ANTENNA :

19. Comparison : switched beam and adaptive arrays
• Adaptive array scheme is far more superior in performance than a
switched beam scheme.

20. RFID ANTENNAS :

21. WEARABLE TEXTILE ANTENNAS :
• It should be highly flexible comfortable and durable to wear.
• It should be stable lightweight and cost effective.
• 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.
• It should maintain same radiation properties due to bending crumpling
and wrinkling of textile.

23. THANK YOU