161_1_Class16

161_1_Class16 - EE161 Electromagnetic Waves Spring, 2010...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: EE161 Electromagnetic Waves Spring, 2010 Prof. Y. Ethan Wang Electrical Engineering Dept. UCLA Lesson 16 Dipole Antenna Large Aperture Antenna Rectangular Aperture with Uniform Field Distribution Friss Transmission Formula Antenna Impedance A I A I A R rad R ohmic R A A A jX R Z + = 2 2 2 2 1 2 1 2 1 A ohmic A rad ohmic rad A A in I R I R P P I R P + = + = = 2 2 ) ( 2 2 A rad in A ohmic ohmic I P P I P R = = 2 2 A rad rad I P R = A rad ohmic rad rad ohmic rad rad in rad r R R R R R P P P P P = + = + = = A X , represents the energy stored in near field Ignore the reactive part, we have Radiation resistance Antenna impedance: Antenna resistance Radiation resistance Ohmic resistance Total input power is, A I A Z Equivalent Circuit Current at the terminal Radiation Resistance Example Find out the radiation resistance for a Hertzian dipole! max 2 4 S D R P rad = rad P S R D max 2 4 = According to the definition of 2 2 2 2 2 2 2 2 2 max 15 32 = = l R I R l I k S [ ] 2 max 2 2 2 2 2 2 * sin sin 32 Re 2 1 S R R l I k R = = = H E S av The radiated power is given by, Previously we have the power density, Therefore, 2 2 2 2 2 2 2 40 15 5 . 1 4 = = l I l R I R P rad The radiation resistance is finally given by, If given R ohmic, one can find the radiation efficiency from R rad , thus the gain of the antenna! 2 2 2 80 2 = = l I P R rad rad I I A = D Half-Wave Dipole elsewhere z 2 / I ) ( z I 4 z z=0 Total length of the Dipole is /2!!! Dipole: an antenna with 2 arms According to transmission line approximation, the current on the dipole is given by, = cos ) ( ~ kz I z I ) ( z I z Folded TRL Half wave dipole can be considered as a group of short dipole elements aligned in space, thus the radiation fields of the half wave dipole should be the superposition of the contribution from every short dipole element!!!...
View Full Document

Page1 / 19

161_1_Class16 - EE161 Electromagnetic Waves Spring, 2010...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online