lecture32 - Lecture 32 Circuit Properties of Antennas In...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 ECE 303 – Fall 2006 – Farhan Rana – Cornell University Lecture 32 Circuit Properties of Antennas In this lecture you will learn: • Circuit properties of transmitting and receiving antennas • Thevenin circuit models for receiving antennas • Antenna theorem ECE 303 – Fall 2006 – Farhan Rana – Cornell University Circuit Properties of Transmitting Antennas - I How does an antenna look to a driving circuit? d Z o ( ) ( ) ( ) ( ) y x z I z r J δ δ ˆ = r r x z I Z o I Z A P = Net time-average power going into the antenna Antenna appears as a load impedance Z o P Poynting theorem: ( ) ( ) ( ) ( ) t r E t r J t t r W t r S , . , , , . r r r r r r r + = Time-average form for time-harmonic signals: ( ) ( ) ( ) t r E t r J t r S , . , , . r r r r r r = P rad P rad P rad P rad Note the distinction between P and P inc and P rad P = P inc - P ref P = P inc - P ref P inc P ref
Image of page 1

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

View Full Document Right Arrow Icon
2 ECE 303 – Fall 2006 – Farhan Rana – Cornell University Circuit Properties of Transmitting Antennas - II Z o P Time-average form for time-harmonic signals: ( ) ( ) ( ) dv t r E t r J a d t r S ∫∫∫ = ∫∫ , . , . , r r r r r r r Net power dissipated Z o I Z A P Net power going in diss rad R I P P 2 2 1 = P rad P rad P rad P rad But: rad rad R I P 2 2 1 = So we get: ( ) rad diss R R I P + = 2 2 1 But from the circuit model: [ ] A Z I P Re 2 1 2 = [ ] diss rad A R R Z + = Re P = P inc - P ref ECE 303 – Fall 2006 – Farhan Rana – Cornell University Circuit Properties of Transmitting Antennas - III Z o I Z A P Z o I P jX A R A ( ) A diss rad A A A jX R R jX R Z + + = + = The reactive part is due to the net inductance or capacitance of the antenna structure Not all the power P going into an antenna is converted into radiated power P rad – some is dissipated due to the less-than-infinite conductivity of real metals (i.e. non-zero R diss ) Definition of Antenna Gain for real antennas: ( ) ( ) 2 4 ˆ . , , r P r t r S G π φ θ r r = ( ) ( ) 2 4 ˆ . , , r P r t r S G rad π φ θ r r = NOT: The Antenna Efficiency η rad is defined as: + = = diss rad rad rad rad R R R P P η ( ) ( ) rad d d G η π φ θ θ φ θ π π 4 sin , 2 0 0 = ∫ ∫ P = P inc - P ref P = P inc - P ref
Image of page 2
3 ECE 303 – Fall 2006 – Farhan Rana – Cornell University Z o P P rad P rad P rad P rad Transmitting and Receiving Antenna Systems Z o P out Need to determine the following: i) From the net power P going to the antenna how much is the total radiated power P rad ii) From the total radiated power how much power is coupled into the receiving antenna iii) From the total power coupled into the receiving antenna how much ends up as the useful power P out in the receiving circuit Transmitting antenna Receiving antenna P = P inc - P ref ECE 303 – Fall 2006 – Farhan Rana – Cornell University
Image of page 3

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

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern