# 1 EMLAB Antennas. 2 EMLAB Hertzian dipole antenna Heinrich Hertz (1857-1894)

## Presentation on theme: "1 EMLAB Antennas. 2 EMLAB Hertzian dipole antenna Heinrich Hertz (1857-1894)"— Presentation transcript:

1 EMLAB Antennas

2 EMLAB Hertzian dipole antenna Heinrich Hertz (1857-1894)

3 EMLAB Schematic diagram of Hertz’ experiment

4 EMLAB Electric field : red Magnetic field : blue Propagation of electromagnetic wave

5 EMLAB V Reception of EM wave current Transmitting antenna Receiving antenna The charges on the receiving antenna move toward the antenna terminal, which causes voltage drop across them.

6 EMLAB E H Example – Radiation from current filament

7 EMLAB Example – Radiation from a dipole antenna

8 EMLAB Far field radiation from a dipole antenna

9 EMLAB Example – Radiation from current loop

10 EMLAB Radiation from a tapered transmission line

11 EMLAB Dipole antenna - resonance

12 EMLAB Example of resonance

13 EMLAB Advantage of a resonant circuit At resonance Generate higher voltage than input voltage. Maximum current level depends on internal resistance.

14 EMLAB How to generate time varying currents Electronic circuit generate oscillating voltages Output voltage Alternating currents accelerate electrons which emit electromagnetic waves propagating in perpendicular direction

15 EMLAB Antenna types

16 EMLAB Radiation from an infinitesimally small current segment Exact solution :

17 EMLAB Far field approximation Electrostatic solution Biot-Savart’s law Coulomb’s law Near field approximation

18 EMLAB Radiation pattern of an infinitesimally small current

19 EMLAB Isotropic pattern Omnidirectional pattern Directional pattern Gain and directivity of an antenna : Gain takes into account losses and reflections of the antenna. Directivity 정의 : (Efficiency)

21 EMLAB Example – half wavelength dipole antenna

22 EMLAB Array antenna

23 EMLAB

24 EMLAB Array factor : Array factor z-directed array

25 EMLAB Array factor x-directed array Top view

26 EMLAB Typical array configurations

27 EMLAB How to change currents on elementary antennas? Magnitudes and phases of currents on elementary antennas can be changed by amplifiers and phase shifters.

28 EMLAB Huygens principle

29 EMLAB Equi-phase surface Pattern synthesis

30 EMLAB (1) Two element array (2) Two element array Examples

31 EMLAB (3) Five element array (4) Five element array (5) Five element array 3dB Beamwidth Beam direction

32 EMLAB phi=0:0.01:2*pi; %00.).*E; polar(phi,E); %Generating the radiation pattern Sample MATLAB codes

33 EMLAB N-element linear array antenna Uniform Array : Magnitudes of all currents are equal. Phases increase monotonically.

34 EMLAB Difference : Universal Pattern is symmetric about  =  Width of main lobe decrease with N Number of sidelobes = (N-2) Widths of sidelobes = (2π/N) Side lobe levels decrease with increasing N.

35 EMLAB Visible and invisible regions Array Factor 의 특성  Array factor has a period of 2  with respect to ψ.  Of universal pattern, the range covered by a circle with radius “kd” become visible range.  The rest region become invisible range 1 visible region Visible range of the linear array

36 EMLAB Grating Lobes Phenomenon  If the visible range includes more than one peak levels of universal pattern, unwanted peaks are called grating lobes.  To avoid grating lobes, the following condition should be met. 1 visible region grating lobes major lobe They have the same strength ! Example :, no grating lobe occurs

37 EMLAB 77GHz 에서 array element 들이 모두 동위상을 갖도록 설계함. 10mm 17mm 두께 0.127mm 비유전율 2.2 표면 전류 분포 Example : array antenna (77GHz)

38 EMLAB Radiation pattern (77GHz) elementary pattern Radiation pattern of 8-element array