ECE 4370: Antenna Engineering TEST 2 (Spring 2015)

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1 Name: GTID: ECE 4370: Antenna Engineering TEST 2 (Spring 205) Please read all instructions before continuing with the test. This is a closed notes, closed book, closed friend, open mind test. On our desk ou should onl have writing instruments and a calculator. No internet-enabled devices. Show all work. (It helps me to give partial credit.) Work all problems in the spaces below the problem statement. If ou need more room, use the back of the page. DO NOT use or attach etra sheets of paper for work. Work intelligentl read through the eam and do the easiest problems first. Save the hard ones for last. All necessar mathematical formulas are included either in the problem statements or the last page of this test. You have 80 minutes to complete this eamination. When the proctor announces a last call for eamination papers, he will leave the room in 5 minutes. The fact that the proctor does not have our eamination in hand will not stop him. I will not grade our eamination if ou fail to ) put our name and GTID number in the upper left-hand blanks on this page or 2) sign the blank below acknowledging the terms of this test and the honor code polic. Have a nice da! Pledge Signature: I acknowledge the above terms for taking this eamination. I have neither given nor received unauthorized help on this test. I have followed the Georgia Tech honor code in preparing and submitting the test.

2 . Uniform Linear Antenna Arras: In the blanks below, place the letter of the arra pattern sketch that corresponds to the design parameters (number of elements, element phase offset, and element spacing) net to each blank. Assume that the arra elements are placed along the -ais and that all points of observation are in azimuth (θ = 90 ). (40 points) (a) (b) (c) (d) (e) (f) (g) (h) (i) () N = 4, (2) N = 4, β = 90, d = 4 (ordinar endfire) β = +90, d = 4 (ordinar endfire) (5) N = 4, (6) N = 8, β = 2.5, d = 3 6 (Hansen-Woodward endfire) β = 0.75, d = 7 32 (Hansen-Woodward endfire) (3) N = 5, β = 20, d = 2 (7) N = 2, β = 0, d = 5 (4) N = 3, β = 0, d = 2 (8) N = 0, β = 0, d = 2 2

3 2. Small-Scale Fading: The single antenna of a mobile device is operating in a heav multipath fading environment in which an average of -85 dbm is available within the local area. Answer the questions below based on this scenario (25 points) (a) What percentage of the time would ou epect this antenna to have an instantaneous received power below 5 0 mw? (0 points) (b) What percentage of the time would ou epect this antenna to have an instantaneous received power above -78 dbm? (0 points) (c) If link outages are too frequent for this device under these conditions, what could ou change about the RF design of the mobile device to mitigate the fading? (5 points) 3. Design of a Helical Antenna: (25 points) An aial-mode helical antenna is designed at 3 GHz to have a wavelength circumference, a pitch angle of α = 3, and a peak gain of 4 dbi. Answer the following questions based on this scenario. (25 points) (a) How long is this antenna in cm if the target gain is 4 dbi? (0 points) (b) Given the same 4 dbi requirement, what is the half-power beamwidth of this antenna? (0 points) (c) If the helical antenna can be used for 3 4 does this correspond to? (5 points) C 4 3, what frequenc range of operation 3

4 4. Horn or Yagi?: You are the lead antenna design engineer for the following scenario. Write H for Horn antenna or Y for Yagi antenna beside each scenario for the antenna that would work best for the specification. (0 points) (a) You need to put a directional antenna high on a thin, steerable mast with minimal wind shear forces. (b) (c) You need to make a directional antenna that operates at 20 GHz. You need to make a directional antenna that operates at 300 MHz. (d) You need to make an antenna that operates at 2 GHz with 9 dbi of peak gain and maimal bandwidth. (e) You need to make an antenna named after a Japanese professor. 4

5 d Cheat Sheet N Uniform Linear Arra 3 2 AF = sin ( π sin ( π Nd sin φ + Nβ/2) d sin φ + β/2) for θ = 90 G arra (θ, φ) G element (θ, φ) AF (θ, φ) 2 sin for small f = c c = m/s µ o = 4π 0 7 H/m ɛ o = F/m k = 2π Aial-Mode Helical Antenna Design (for operation over 3 4 C 4 3 ): ( ) G peak = 5N C2 S C 3 R rad 40 Ω HPBW = 523/2 C NS degrees S N C α h turn spacing number of turns circumference, πd pitch angle, tan (S/C) total height, NS Link Budget Formula (Logarithmic) P R = P T + G T + G R 20 log 0 (4π/) 0n log 0 (r) Raleigh Fading Probabilit Pr{P a P P b } = P b P a ( ep p ) dp P R P R 5

ECE 4370: Antenna Engineering TEST 2 (Fall 2012)

Name: GTID: ECE 4370: Antenna Engineering TEST 2 (Fall 2012) Please read all instructions before continuing with the test. This is a closed notes, closed book, closed friend, open mind test. On your desk