Adv Electromag Waves
Adv Electromag Waves ECE 6341
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This 33 page Class Notes was uploaded by Karolann Wiegand on Saturday September 19, 2015. The Class Notes belongs to ECE 6341 at University of Houston taught by Staff in Fall. Since its upload, it has received 43 views. For similar materials see /class/208302/ece-6341-university-of-houston in Electrical Engineering at University of Houston.
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Date Created: 09/19/15
USNCURSI National Radio Science Meeting Boulder CO January 36 2008 Techniques for Scanning Through Broadside with Periodic LeakyWave Antennas Simone Paulotto Paolo Baccareli Fabrizio Frezza and David R JacksonM Electronic Engr Dept La Sapienza University of Rome Italy MDept of ECE University of Houston TX APIENZA if Outline Introduction gt Introduction to 1D periodic microstrip leakywave antennas LWAs gt Broadside scanning and openstopband OSB problems 058 Mitigation technique gt Doublestub technique OSB Suppression technique Metamaterial Design gt CLRH Design 058 Suppression technique recent new Conventional Designs gt A new periodic LWA with a Ushaped stub gt A new periodic LWA with an impedance transformer Introduction iD Periodic Printed LWAsr 1D Periodic Printed LWAs Broadside z Backward Forward 29 Air vg i x I Ground Combline structure Source Side View sketch OpenStopband OSB Region At broadside stopband null point 1871180 O Olko 9 Freespace radiation region Frequency Bound region Brillouin zone OpenStopband OSB Region At broadside gt The traveling leaky wave turns into a standing wave a shortcircuit at the ends of the unit cell for the combline structure gt The attenuation constant drops sharply to zero gt The Bloch impedance becomes pure imaginary gt The input match becomes poor gt The beamwidth changes rapidly near broadside dropping to zero at broadside for an infinite structure Example Combline Structure A Frequency range near broadSIde 39 I o 411 4205 0 005 01 M39icr39ostr39ip Stub M H 91 7QQ5V w 06 mm ls05 mm h0i67i6 mm wSO391mm a 102 Example cont Bloch Impedance Frequency range Hz Q near broadside quot12 Q 200 200 150 100 loo a 5n mn o 400 24 245 5 21 215 is 26 55 GHz Stopband null point OSB Mitigation Technique DoubleStub Method WWWWWWWWWWWWWWWW A Historically this is the first method that was used to reduce the OSB JR James and PS Hall Microstrip Antennas and Arrays part 2 New array design technique IEE J Microwave Optics and Antennas 1977 Double Stub Two identical stubs per unit cell Key idea The two reflected waves cancel out At broadside 31230 277220 llgt pZ Z g llgt Results Double Stub 3235Li b same stub dimensions a I I I i 255 I fGHZ ul 2 255 39 25 7205 one 0114 on o Even though the openstopband region has been reduced we are far from the ideal beahavior DoubleStub Optimization The distance dhas been optimized with a periodic MoM c f GHZ 2 w m 803 an nu am a n1 It does not appear to be possible to completely eliminate the openstopband region OSB Suppression Technique Metamaterial CLRH LeakyWave Antenna This structure is a quasiuniform structure that radiates from the n O harmonic L Liu C Caloz and T Itoh Dominant Mode LeakyWave Antenna with BackfiretoEndfire Scanning Capability Electron Lett vol 38 pp 1414 1416 Nov 2002 G V Eleftheriades A K lyer and P C Kremer Planar Negative Refractive Index Media using Periodically Loaded Transmission Lines IEEE Trans Microwave Theory Tee1 vol 50 pp 2702 2712 Dec 2002 Metamaterial CLRHTL LWA Artificial transmission line ATL Planar realization LR 0L Zsh l L Zse L 1 OR Balanced condition The series and shunt branches resonate at the same frequency The stub length S is varied to optimize the structure CRLH LWA ATL Analysis Ansoft Designer gt Ap r ximhte anaIVs js Propagation wavenumber Characteristic impedance 1 yaj steZsh Z0 ZseZsh 7 CLRH LWA ATL AnaIySIs Propagation constant Characteristic impedance Q 05 I I I I 01 300 I I I I 100 Re Im 250 50 200 iii i I 150 quotquot I o l I I 100 ILquot Zline quot 7 A r 50 50 1 0 0 i i 4 42 44 46 48 5 4 42 44 46 48 5 fGHZ fGHz Ansoft Designer 15165111111 i168mm ATL analysis lxl70mm CLRH LWA FullWave Solution 1 012 BkO 39 ocko 39 FullWave 01 I 05 quotI 39 I e 008 quot39 39 006 004 002 1 I I I I 0 4 4 2 44 4 6 4 8 5 f GHz The fullwave results show that a further optimization is necessary CLRH LWA Optimization by FullWave Solution 012 3k ock ATL MoM The fullwave MoM solution predicts an optimum stub length of 16 mm compared with 168 mm predicted by ATL theory 1 l l l 0 4 42 44 46 48 5 fGHz CLRH LWA Finite Structure A finite structure formed by 42 cells is simulated with Ansoft Designer using a voltage source at the input end 15 dBi 1o 5 o 5 fGHz Gain dBi 10 430 129 446 131 460 135 Gain 4O 20 O 20 40 9 161 mm 60 OSB Suppression Technique Novel UShaped LWA This LWA radiates from the n 1 harmonic not a metamaterial LWA This structure showed for the first time that the open stopband could be eliminated in a LWA that radiates from the 1 harmonic S Paulotto P Baccarelli F Frezza and D R Jackson A Microstrip Periodic LeakyWave Antenna Optimized for Broadside Radiation IEEE APS Symp Honolulu Hawaii June 2007 UStub LWA The design uses a and The thickness 139 of the end cap is varied in the optimization study UStub LWA ATL Analysis llku propagation wavenumber um Raga Characteristic impedance Iimzn 05 i I am an 0015 quot n ne i M 56 new UStub LWA FullWave Analysis 04 u Imloz n 055 mm I Phase quot05 050 mm a constant n2 Leakage 005 C O n S ta n t 39039 t 004 415 002 436 I nutm on o o ol Innnu o 1 I I n I o E 82 54 55 56 9 fGHz The fullwave MoM solution predicts an optimum endcap thickness of 050 mm instead of 055 mm predicted by ATL theory UStub LWA Finite Structure 192 cm Gap source 48periods W W W W W W W W W W W W Pom Ansoft Designer GaindBi f 84 85 86 87 88 Gain dB 14 142 141 141 140 Perfectly equalized gain 80 60 40 20 0 20 40 60 80 9 OSB Suppression Technique Impedance Transformer Design This LWA radiates from the n 1 harmonic not a metamaterial LWA This design was discovered after the Ustub design S Paulotto P Baccarelli F Frezza and D R Jackson A Novel Technique to Eliminate the Open Stopband in 1D Periodic Printed LeakyWave Antennas Proc EuCAP Edinburgh Scotland Nov 2007 QuarterWave Transformer Design OSB Suppression Technique Assume that at broadside the input impedance looking to the right at point A is Z0 the unit cell is matched to the impedance of the main line B C D Z Z t k d 1 ZOZS ZOM 0T 20R Z0 ZS Z0 st tanke d1 Results Optmized Design substrate W d1 L1ne 1 ma1n 39l1ne 06 s102 h0676 mm W mm L d1071 mm stub 5 WT 1 wll Line 2 transformer ls17mm WQ1mm wT049 mm p 4 mm T lt T dz09776mm 2 Phase and attenuation constants Bloch impedance Q Gain Pattern Near Broadside Note Gain accounts for directivity and input mismatch a degree Finite structure 32 cells 32 x 4mm 128 mm Simulated with Ansoft Designer Conclusions It has been shown how openstopband effects impair broadside scanning in 1D periodic printed LWAs Metamaterial Design 71 0 gt The CLRH metamaterial LWA can eliminate the open stopband but fullwave optimization is necessary in order to achieve this Conventional Designs 71 1 gt A doublestub mitigation technique reduces but does not completely remove the openstopband problem gt A new Ushaped stub design can eliminate the open stopband gt A new quarterwave transformer design can eliminate the open stopband Backup Viewgraphs QuarterWave Transformer Design Procedure Usually 2 or 3 iterations V 3 V 5 The broadside frequencyf0 can be estimated through the Brillouin diagram of the unperturbed microstrip line Using a commercial software Z1 in is extracted atfo considering a unit cell with Z0 as load The length of the delay line all is determined to obtain a real input impedance R The quarterwave transformer is designed to match Z0 to the impedance R The dispersion behavior of the initial desing is determined by using a fullwave analysis V The broadside frequency usually differs from the one predicted at step 1 Steps 15 are repeated until the actual broadside frequency is the same that assumed in the design Some finetuning using a fullwave solver is done to optimize the structure and to obtain a complete suppression of the open stopband
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