1. ANTENNAS Presented By :- Dr. Ganga Prasad Pandey PDPU, Gandhinagar, Gujarat Dated : 15 February 2017

2. HISTORY The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. He published his work in Annalen der Physik und Chemie (vol. 36, 1889).

3. Antenna—introduction Electric currents Electromagnetic waves Radiation is dependent on relative value of signal wavelength and device size. An accelerating charge can make the radiation Radiation from corner and bend Even a DC current source may cause radiation if there is bend---causing charge acceleration.

4. Transmitting Antenna--- radiating electromagnetic wave in preferred direction. Antenna  free space At t=T/4at t=T/2at t=T/4 (T=time period) Receiving Antenna: antenna intercepts electromagnetic wave  tiny voltage at its terminals  receiver  amplifier. An antenna can be used for both transmitting and receiving  reciprocity theorem

5. TYPES OF ANTENNAS Based on radiating field: Radiation pattern Isotropic Antenna:– radiate equally in all directions  all planes have equal radiation

6. Omnidirectional Antenna Radiates equally in a given plane  different planes different radiations.

7. Directional Antenna Preferentially Radiate or Receive in a particular Direction  Different Radiation in the same plane.

8. Based on length of antenna: 1. Resonant Antennas – Length of antenna=n X λ/2 Open ended 2.Non-resonant Antennas – Length of antenna ≠ n X λ/2 Terminated ends Z0 No standing waves Unidirectional Like travelling wave antenna—rhombus antenna

9. RADIATION PATTERN

10. ANTENNA GAIN Measures the degree of directivity Ratio of the radiation intensity in a given direction and the radiation intensity that would be obtained, if the power fed to the antenna were radiated isotropically. Measured in dBi  isotropic

11. The gain of an antenna is a passive phenomenon - power is not added by the antenna, but simply redistributed to provide more radiated power in a certain direction than would be transmitted by an isotropic antenna. High-gain  longer range  better signal quality, Less foot print  precise positioning Low-gain  shorter range Large foot print  positioning less bothered

12. EFFICIENCY 1. Antenna Efficiency: ratio of power actually radiated to the power fed to the antenna. losses--- radiation loss, dielectric loss, surface wave loss, reflection loss. Pin=Prad+Pd+Pc+Psw+Pref Antenna efficiency=Prad/Pin 2. Radiation efficiency: excluding reflections from antenna ports Prad/(Pin-Pref)

13. POLARIZATION Defined by the orientation of the electric field Polarization of transmitter and receiver should match Orientation mismatch  bad signal reception Linear polarization: Horizontal & vertical Elliptical Polarization: : Circular  LHCP & RHCP

14. BEAM-WIDTH Angular separation between two 3dB down points on the field strength of radiation pattern

15. Microstrip Antenna

16. RMSA

17. Advantages of Microstrip Antennas  Low profile  can even be “conformal,” i.e. flexible to conform to a surface.  Easy to fabricate  Easy to feed  Easy to use in an array or incorporate with other microstrip circuit elements.  Patterns are somewhat hemispherical, with a moderate directivity (about 6-8 dB is typical). 17

18. Disadvantages of Microstrip Antennas  Low bandwidth  Low Efficiency  Only used at microwave frequencies and above (the substrate becomes too large at lower frequencies).  Low power handling capacity 18

19. THANKS