A FULL-WAVE ANALYSIS OF HIGH GAIN RADIAL LINE SLOT ANTENNAS USING CST STUDIO SUITE

Munich Airport Marriott Hotel, 17-19 May 2011 6th EUROPEAN USER GROUP MEETING A FULL-WAVE ANALYSIS OF HIGH GAIN RADIAL LINE SLOT ANTENNAS USING CST STUDIO SUITE Simone Ledda, Matteo Cerretelli, Guido Biffi Gentili Laboratorio di Antenne e Microonde Dipartimento di Elettronica e Telecomunicazioni Università di Firenze

Overview of Presentation Design of an optimized Radial Line Slot Antenna Page 2

Overview of Presentation Design of an optimized Radial Line Slot Antenna 1 STEP : Development of a Visual Basic Software for designing the 3D layout 2 STEP : Exporting the 3D layout of the structure in SAT Format compatible with CST Studio 3 STEP : EM Simulation of the first structure created 4 STEP : Using various CST capabilities for optimize the structure and obtain the desired antenna s performance Page 3

Requirements and Difficulties Frequency: 23.5 GHz Requirements RHCP Right Hand Circular Polarization High Gain: > 30 dbi Cross-Polarization Isolation: > 25 db (Broadside) High Antenna Efficiency: > 75% Difficulties High Complexity of structure: The desired Gain involves a large number of radiating elements estimable in a various hundreds of slots. An extra software is needed for designing the 3D layout. Page 4

STEP 1 - Designing the 3D Layout Design of a Radial Line Slot Antenna [RHCP] Development of a Visual Basic Software indispensable for design the 3D layout Page 5a [Anim.]

STEP 1 - Designing the 3D Layout Page 5b [Anim.]

STEP 1 - Designing the 3D Layout Archimedean Spiral LHCP ( a < 0 ) RHCP ( a > 0 ) λ r(θ) = a θ a = λ / 2π 34 cm 1000 pairs of slots 26 λ Page 5c [Anim.]

STEP 2 Importing.SAT Model into CST Page 6a [Anim.]

STEP 2 Importing.IGS Model into CST [Nickel] Coaxial Cable Feeder Matching Hole 3,9064 mm Waveguided Structure [Air] 3,2 mm Discrete Edge Port [50 Ω ] 0,456 mm RG 316/U [50 Ω ] [Copper] Thickness 0,1 mm Page 6b [Anim.]

STEP 3 Meshing the structure in CST Mesh Level : λ / 30 Number of MeshCells : over 76 Millions! Page 7

STEP 3 Using the E-Field Probes Use of 13 E-Field Probes for control the E-Fields in the middle of the waveguide structure and between two couples of adjacent slots Page 8

STEP 3 EM Results : Decay of EM Energy Total Time of Decay of EM Energy: 2 ns Energy Accuracy : -40 db Page 9

STEP 3 EM Results : Time Signals Total Time of Decay of EM Energy: 2 ns Reflection over the Edge Port due to mismatch Page 10

STEP 3 EM Results : Array s Matching Reflection Coefficient S 11 < -20 db Page 11

STEP 3 EM Results : E-Field Probes Perfect Phase of EM Signals for a Broadside contribution Fast decreasing of E-Field Probes amplitude due to the high EM power radiated by the first turnings of slots Page 12

STEP 3 EM Results : E-Fields Page 13

STEP 3 EM Results : E-Fields Phase Page 14

STEP 3 EM Results : Farfield [23.5 GHz] Circular Right Polarization RHCP LHCP Page 15

STEP 3 EM Results : Comments A Full-Wave Time-Domain EM solver software involves some benefits useful for the next optimization of the planar array The E-Field Probes show the outward travelling waves. The E-amplitude values become an index of the power already radiated by the array related to the spatial positions of the slots. The rapid decay of the EM Energy in Time-Domain can be an index of absence of Energy reflections Those information can be easily used for the optimization of the antenna in order to obtain better antenna s performance Page 16

STEP 4 Optimization of the structure The aim we want to obtain is to decrease the radiation of the first slots, so it can increase the EM power that feeds the latest slots This concept can be realized modulating the length values of the slots progressively from a shorter value (internal slots) to an higher (external slots) Optimum Slot Lenght at 23.5 GHz [mm] Page 17

STEP 4 Optimization EM Results RHCP Gain Improved from 19.7 to over 32 dbi Page 18a [Anim.]

STEP 4 Optimization EM Results RHCP Gain Comparison [w/o Lenght Modulation] LHCP Gain Comparison [w/o Lenght Modulation] Page 18b [Anim.]

STEP 4 Optimization EM Results Higher Amplitude Values of E-Field Probes Energy Reflection due to the edge discontinuity Page 18c [Anim.]

STEP 4 Absorbing Ring Enclosure Outward RHCP Contribute (Desired) Page 19a [Anim.]

STEP 4 Absorbing Ring Enclosure Edge Discontinuity Page 19b [Anim.]

STEP 4 Absorbing Ring Enclosure Inward LHCP Contribute (Undesired) Page 19c [Anim.]

STEP 4 Absorbing Ring Enclosure Possible Solution: Absorbing Material Ring Pro. Reduction of the cross-polar component without increase the dimensions Cons. Increase of the production costs Page 19d [Anim.]

STEP 4 EM Final Results: Time Signals Reduction of the edge reflection and absorbing the residue of energy Without absorbing Ring With absorbing Ring Page 20

STEP 4 EM Final Results: 3D FarFields RHCP Gain Pattern LHCP Gain Pattern Page 21

STEP 4 EM Final Results: Comparison Cross-polar Left Polarization Comparison (w/o Absorbing Ring Enclosure) Co-polar Right Polarization Comparison (w/o Absorbing Ring Enclosure) Page 22

STEP 4 First prototype of the RLSA The first prototype is under construction and it will be available in the next few days Page 23

STEP 4 Conclusions The High-Gain Radial Line Slot Antenna was designed and optimized with a highly improvements of the performances During the optimization the requirements has been meet quickly using various CST Studio Suite capabilities, analyzing the E-Field Probes and the EM Energy in time domain The time-domain information are useful trying to modulate the EM Power radiated by the slots, so every pairs of slots ideally radiate the same EM Power improving the array s performance as result for further informations: simone.ledda@gmail.com Page 24