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Antenna Engineering

by: Karolann Wiegand

Antenna Engineering ECE 5318

Karolann Wiegand
GPA 3.51

Stuart Long

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Stuart Long
Class Notes
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This 43 page Class Notes was uploaded by Karolann Wiegand on Saturday September 19, 2015. The Class Notes belongs to ECE 5318 at University of Houston taught by Stuart Long in Fall. Since its upload, it has received 67 views. For similar materials see /class/208298/ece-5318-university-of-houston in Electrical Engineering at University of Houston.

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Date Created: 09/19/15
ECE 53186352 Antenna Engineering Chapter 11 Frequency Independent Antennas ITHE BEGINING Antenna performance is I typically a function of length wavelength A gt same performance both are the same size in wavelengths depends on some characteristic length 39S CALING PRINCIPLE YZDNT IANGLE PRINCIPLE quot TRU NCATION PRINCIPLE 39TRUNCATION PRINCIPLE CONT 66296981 eg TV channels A 00 Jammers 1006 0 EQUIANGULAR SPiRAL log Spiral IEQUIANGULAR SPIRAL v ON T called SELFCOMPLEMENTARY IEQUIANGULAR SPIRAL CONT gt current I fell off faster than i aver a 1 frequency independent band I gt before truncation upper rrv ii dfep nos onily39on a of the feed region But needed linear polarization LP as well as circular polarization CP 39EQUIANGULAR SPIRAL 3 Spiral pm 17 Spiral slm IEQUIANGULAR SPIRAL econm Fig 114 Conical spiral metal strip antenna g t a E d but nt PRIN needed to cause currents to fall off more rapidly 3 introduced discontinuities teeth in fins to increase radiation and increase decay of 1 LDG PERiODIC L41 KIM F0 UT HOW TO DEI39ERMINE S P39ACING 7 5i a Q ILOG PERIODIC CONT 3 Soradii of successive teeth were chosen such that Feed ILOG PERIODIC CONT If the p th tooth is i at f0 then the 10 p1th tooth is i at A 10 r ILOG PERIODIC CGNU as long as the Structure is accurate at thief eewd and there are negligible currents at the truncation point Feud Rquot g NRA FI 116 Planar and wire lo arithmicall eriodic antennas I LOGPERIODIC ANTENNAS Experimentally they found that the variation in pattern between the periods were relatively minor for designs where r was not too far from 10 21 qu penod ere f Ofund to have linear pglariza tion in the x dir along dir of teeth instead of perpendicular to them BIFIN LOG PERIODIC 22 39LOG PERIODIC COSvi Tl could be made straight trapizbdal A most currents Were in teeth whose length was near 39 4 see model Also found they could onlyjust outline the periphery of the sheet structure with a wire and it would still work Fiq 116 Planar and wire trapezoidal toothed qu LQGvPE R IOD C mom us mount d tav backed logg riodicslot antenna I39LOG PERIODIC com in Ig piei39r iddi sstyle 26 Source 27 IILPDA CQNT rtee x 39 When wage parallel pairs of equal Iangth39 teeth almost lined up successive teeth came out in opposite direction Equivalent to criss crossing wire between elements introducing a 1800 phase shift between successive elements 29 criss cross connection A lt alternate coaxial connection alternate pairs from opposite sides found gt 39LPDA CONT currents mostly on elements near in total length frequency band bounded on high side by size of smallest element and on low end at frequency where largest dipole is approximately g in length 31 but R 33 1 a 21am V E 4 0639 or a tan3911 T 4o 34 35 dB 7 3 MB 75 dB 1 1 n m 1 1 034 080 o 6 1 10 096 0 0 Scale factor 1 Fi 1113 Com uted contours of constant directivit versus 5 and r for loggeriodic digole arrays design aciivg rie gi cm B BW correction v 1 1 B 11 77 1 r2cota lengthLfT l cota ar S 36 Iflongestelement l 39the nextis rim Ti 431 max max maxv Zrm until shortest elemenf is shorter than 2 high end of band B ILPDA DESIGN CONT Precedure 39 V find optimum Given DodB 39quot gandz39 9 om Fig1113 calculate H ottan 4039 Bar and BK find define lengths and N and L gt positions of elements 38 From Fig11 13 optimum D0 9 dB BW 320 60MHZ 00172 10917 mm m 65 w m x Ba 11771 72c0ta154 By 2 Q 154456 20 388 0354 Scale factor x 0 30 39 1 ILPDA DESIGN com I Example TocenterBSaroundBgt 2456 and l iz l 20 60 l A L1 12 fH centered so same above and below fL and fH where f1 and f2 are ends of band BS and fL and fH are ends of band B more generally want 1 f1 159MHz and f2 724MHZ 4o check fL f2 fH Q f1 and atfl 159MHz 215 92795 gt 205 20 724 1205gt205 60 E456 159 x7 Longest element E at low frequency of BS A max below above gt 2m 2 3189m f1 I 22943 m 41 ILPDA DESIGN CONT L 1 1 1 c0ta162gtL305m quot Am 4 BS 1 In 11n4i185gt180r19elements ln j ln j T 917 Igt 42 Rm 391 T 2865 mm 358 Tszax 2 326 Total L ng 2 82 TotalL 391 82 309 m 43


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