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چكيده انگليسي :

Dissipation Effects in the Performance of Reflectarray Antennas Mohammad Mehrjoofar m mehrjoofar@ec iut ac ir Date of Submission 2011 05 09 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Abolghasem Zeidaabadi Nezhad zeidabad@cc iut ac irAbstractIn the last decade there is an increasing interest in printed reflectarray antenna which combines the best features oftraditional reflector antenna and conventional phased array antenna Using microstrip technology these antennas areinexpensive and benefit from low profile nature of microstrip antennas Recent advances in printed circuit andintegrated circuit technology as well as in computational electromagnetic analysis methods have led to improveddesign and optimization methodologies of such architectures which in turn have resulted in their increaseddeployment in communication system and radar applications Usually a printed reflectarray antenna consists of a flatarray of microstrip patches printed on a thin dielectric slab A feed antenna illuminates the array whose individualelements are designed to scattered the incident field with proper phased required to form a planar phase surface infront of aperture The phase of reflected wave is controlled by changing the geometrical parameter of elements There are several methods for finding the relationship between changing the geometrical parameter of element andphase of its scattered field In this thesis we explain different methods for finding this relationship The adoptedtechnique is assumption of local periodicity of element so for finding the reflection amplitude and phase diagram ofelement a single unit cell of a periodic infinite array of such elements analyzed by Ansoft HFSS software The roleand effect of different components of the reflectarray antenna such as elements substrate ground plane feeder andetc has been considered and explained It has been observed that the reflection phase diagram of different types ofelements effect of substrate thickness and permittivity in reflection phase diagram of element effect of arraycharacteristic in aperture efficiency and effect of using an FSS as a ground plane of array on the reflected wavephase The Reflectarray antenna suffers potentially significant loss due to dielectric loss copper loss and surfacewave excitation These losses have been considered here First we simulate one unit cell that already has beensimulated and measured As it will be seen the implemented simulations are closer to the measured data than thesimulations have been published previously We ve also considered the effect of existence of losses in the reflectionamplitude and phase diagram of the element The considered element is a combined patch that is above the groundedlossy dielectric substrate The used metal is copper As we will see by increasing the loss tangent of the dielectricslab the losses increased Also by changing the loss tangent the resonance frequency of unit cell changed Thesechanges are slight because the dielectric permittivity is small Consequently by changing the resonance frequencythe reflection phase will change Finally we have designed two reflectarray antennas for beam steering in thedesirable directions One of the antennas steers beam in the broadside direction and the other steers the beam in the 200 0 00 direction Both antennas have dielectric and copper losses and consist of 7 7 elements These 0elements are square patches The feeder of the array is the open ended WR90 waveguide Keywords Reflectarray antenna Phase range Reflected phase diagram Losses

مهرجوفر، محمد

بررسي اثر تلفات بر عملكرد آرايه آنتن هاي باز تابنده

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