CHAPTER 5

week 13 to 15, student has finish chapter 5 which is microwave antennas. 

.....student know the definition and the function of antenna on week 13.....

—DEFINITION:

ANTENNA (OR AERIAL)

is a metallic conductor that act as transducer which converts electric currents into electromagnetic waves and vice versa.

Function of antenna

1.As radiator / transmitter

       Electrical energy from the transmitter is converted

       into electromagnetic  energy by the antenna and

       radiated into space.

2. To transmit/radiate energy with high efficiency (kW).

3.As sensor/ receiver

     Electromagnetic energy is converted into

     electrical energy by the antenna and fed into

     the receiver.

4.To receive the lowest energy from the space (mW)

5.As impedance matching device – to ensure the characteristic impedance of transmission line is equal to impedance of free space.

......student has describe the type of microwave antenna on week 14 to 15.....

TYPES OF  MICROWAVE ANTENNA

1.HORN

ŸWas first invented in 1987 by Indian  radio researcher, Jagadish Chandra Bose.

ŸIt is  constructed in a variety of shapes with a flared  open ended  waveguide.

ŸThe shape of the horn determines the shape of the field pattern.

4 type of horn attenna

2.PARABOLIC

¢Function:

—To convert the spherical waveform produced at a focus point to the plane wave.

—All the energy received from the free space which is the same as the parabolic axis (Rx) will be reflected to the focus point.

¢Application:

1.Used in microwave frequencies UHF, SHF which the size of wavelength λ is small enough compared to size of reflector.

2.Point-to-point communication such as Satellite communication

3.Microwave Relay links that carry telephone and TV signals.

ADVANTAGES

1.The gain can be increased whenever needed.

2.Can be operated at any frequency in the microwave zone.

3. Simple Installation.

DISADVANTAGES

1.Difficult to install with high accuracy.

2.Operational frequency limited to the types of dish used.

3.SLOTTED

¢Slot antenna was first invented in 1983 by Alan Blumlein while his working for EMI.

¢Consists of a metal flat plate with a hole @ slot cut out.

¢The slot typically narrow width with less than 0.1λ and 0.5λ long.

¢Increasing the width of slot, a,  will increases the bandwidth.

¢Advantages:

i.Easy to fabricate

ii.Have low loss. So, it has high antenna efficiency, ηr 

iii.Radiate in linear polarization with low cross-polarization.

¢Application:

i.Often used at UHF and higher microwave frequencies which need radiation pattern control such as Radar.

ii.Sector antennas for Radio Base Station

iii.Marine Navigation Radar

iv.Often used in aircraft because it can be made to conform to the surface.

4.DIPOLE

¢Dipole is a 2 pole antenna. It is a basic antenna.

¢Has 2 types:

1.Quarter wave  (ʎ/4) @ Marconi antenna

2.Half wave (ʎ/2) Dipole @ Hertzian antenna .

¢APPLICATION:

vUsed as a feeder to feed an electromagnetic energy to Parabolic Antenna.

vAs Radio Base Station antenna in Cellular Communication System.

5.DIELECTRIC LENS

¢Also known as Dielectric Resonator Antenna (DRA).

¢Mostly used at microwave frequencies or very high microwave frequencies (millimeter frequencies) due of it is made of Dielectric material.

¢Consists of a block of ceramic(dielectric) material at various shapes (rod, cube etc.).

¢This dielectric rod mounted on a metal surface which act as a ground plane.

¢Advantages:  DRA is made of dielectric material not a metal. Because of it is made of dielectric, there are some advantages of DRA:

1.No inherent conductor loss in DRA. So, it is lossy at millimeter frequencies à Less dissipating energy.

2.Because less dissipating energy, so it has lower losses and more efficient than metal antennas at very high microwave frequencies (mm frequencies).

¢Application 

1.Dielectric waveguide is used in some compact portable wireless device.

2.Because of its advantages, DRA is very suitable to operates at millimeter microwave frequencies, eg, Military millimeter-wave Radar equipment.

3.Dielectric cone is use as feeder for Cassegrain Parabolic Antenna.

6.PRINTED (PATCH/ MICROSTRIP)

TYPES OF PATCHED ANTENNAS:

Application:

i.common used in Mobile phone antenna – PIFA

ii.Mobile radio communication devices.

iii.Portable Radar systems

iv.Missile Guidance systemaircraft and military application.

7.PHASE ARRAY

¢Phased Array Antenna is a group of array antenna that when connected together, function as a single antenna whose its beamwidth and direction (i.e radiation pattern) can be changed electronically without having to physically movement of  any individual antenna.

¢That why it is also known as SMART ANTENNA because it capable to vary its radiation pattern without change the antenna physically.

¢It was first developed in 1905 by Nobel Laureate Karl Ferdinand Braun, Germany. This antenna is used during World War II as a military Radar system.

¢Advantages:

1.No need mechanically rotating antenna elements. It is electronically controlled  by phase shifter.

¢Application:

1.In navy, it used as a Radar system to detect and tracking the ships. While, in air force, it is used for air detection & tracking the aircraft.

2.Radio Frequency Identification (RFID)

3.Human-machine Interfaces (HMI)

5.Ultrasonic & Medical Imaging application.

6.Optics – as a wavelength selective splitter

7.Multiband TV antenna

8.SONAR (Sound Navigation And Ranging) in submarine - beam forming