Aese2014 Automotive Radar System Design

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Highly Accurate and Robust Automotive Radar System Design Markus Kopp Lead Application Specialist ANSYS Inc.

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Transcript of Aese2014 Automotive Radar System Design

Page 1: Aese2014 Automotive Radar System Design

Highly Accurate and Robust Automotive Radar System Design

Markus Kopp Lead Application Specialist

ANSYS Inc.

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• This presentation is an overview of a proposed design methodology for automotive radar systems.

• This presentation is meant to illustrate the advantages of simulation, as well as what can be reasonably simulated using state of the art electromagnetic field solvers.

• This presentation will concentrate on how to address some of the challenges faced when designing radar systems at, the very high, 77 GHz frequency.

• All results shown in this presentation were created using ANSYS HFSS RF.

Introduction

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Both interfaces are included within the new unified desktop environment

Mechanical CAD (MCAD)

Electrical Layout (ECAD)

HFSS RF

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• HFSS RF using the new unified design environment also allows • RF and μwave frequency domain circuit design

– Analysis types • Linear • Harmonic Balance • Transient • Loadpull • Envelope • PXF Analyses • Oscillator • TV Noise • Phase Noise

– PlanarEM Simulations

HFSS RF

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• Single Antenna Element Design

Creating an Antenna Array

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• Initial Design is implemented

in HFSS for Layout interface • Initial Designs are

synthesized using built in calculators

• Transmission Line (TRL) Tool

• Antenna Estimator Tool

• Both tools use stackup definition provided by engineer

Initial Design

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Initial Antenna Design Initial Design is created in layout Then solved using a planar MoM solver For simple structures MoM solver is extremely fast

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Initial Planar EM Results (MoM) After some “tweaking” excellent S11 results are obtained However, Mom solver prefer 2D infinitely thin conductors At 77 GHz the finite thickness of the metal may change performance

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3D thick Metal Results Re-simulating same antenna with 0.017 mm (half ounce) thick metal produces different S11 results HFSS 3D clearly shows that more “tweaking” is needed Fine tuning will be done in HFSS-3D using adjoint derivatives

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Rapid Antenna Tuning using Adjoint Derivatives Functionality (only available in HFSS 3D)

• Extremely efficient method used for • tuning, sensitivity studies, and

optimization • Computes the derivatives of SYZ

parameters with respect to project and design variables

• Eliminates need to solve multiple variations with small differences and numerical noise

• Allows real-time tuning of reports to explore effects of small design changes

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Final Antenna Element Performance

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• Antenna Array Design

Creating an Antenna Array

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• Creating an array once the unit antenna has been design is a straight forward process

• Antenna elements are arranged in a specific pattern, and then a net resultant antenna performance can be calculated

• This final antenna performance metric can be obtained using an antenna factor calculation or using an infinite array approximation or a finite sized antenna array can be simulated.

• Both the Antenna Factor calculation or the infinite array calculation are likely to produce erroneous results with regard to side lobes and back lobes

• A finite array calculation will provide the best results • Simulating a finite array can be time consuming

especially when the exact array spacing is still being determined

Creating an Antenna Array

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Finite Array Domain Decomposition (FA-DDM) • Utilizes Replicated DDM Unit Cell to Address Array

Concerns • Geometry and Mesh copied directly from Unit Cell Model

– Unit Cell geometry expanded to finite array through a simple GUI – Adaptive Meshing Process imported from Unit Cell Simulation

• Dramatically reduces the meshing time associated with finite array analyses.

• Mesh periodicity reinforces array’s periodicity.

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Finite Array Calculation using FA-DDM Efficient solution for repeating geometries (array) with domain decomposition technique (DDM)

Patterns from 8X8 Array

Finite Array DDM with 12 cores 00:44:53 1.8 GB

Direct solver with 12 cores 5:05:14 60.8 GB RAM

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• Unit cell model uses the HFSS Linked Boundaries

• Master and slaves boundaries are applied on opposite faces

• With and depth of unit cell determines antenna array element spacing

• Optimal array spacing (it’s not lambda) can be determined efficiently and quickly

Unit Cell Model for FA-DDM

Master

Slave

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Finite Array Capability Initial Array was modeled using FA-DDM Array spacing was optimized using FA-DDM Final 1 x 10 Array shows good performance

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Explicit 1 X 10 Array Solution Final 1 X 10 Array was also explicitly simulated in HFSS 3D

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• Results between explicit HFSS 3D simulation and FA-DDM show excellent agreement

• FA-DDM has clear time advantage however and lends itself to rapid tuning of element spacing

Comparison of Explicit and FA-DDM Results

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• Power Divider Design

Creating an Antenna Array

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Initial Divider Design

Initial Design was again created in HSS Layout and analyzed using MoM solver for efficiency reasons However, similarly to antenna, finite thickness of metal makes a difference so Power divider was tuned in similar manner

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Final 10 way Power Divider Design

Final 10 way Power divider was designed To have the following power distribution 0.0625, 0.125, 0.25,0.5, 1,1,0.5, 0.25,0.125, 0.0625

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Final 10 way Power Divider Design

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• Designing a 77 GHz Automotive Radar Module

Creating a Transmit/Receive Module

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Effect of Feed Network on Antenna Pattern

No Feed With Feed

The feed network will effect the antenna array performance. Simulating our array with attached feed network can show how detrimental the feed network is to our overall array performance

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• Final Module consisted of

• 1X 10 Transmit Array • 1 X 10 Receive Array • Matching feed networks

for TX and RX sides • Radome of 1mm

thickness • Duroid er=9.8, 5 mil thick

substrate

Radar Tx/RX Module

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Antenna Pattern for full TX/RX Module

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Effect of Radome on Array Performance

Radome housing reduces back lobes but also flattens and widens main lobe Radome and antenna spacings can be optimized to reduce this effect

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Final Module Design

These optimized results are inclusive of plastic Radome, finite ground planes, feed network and TX/RX antenna structures

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• Placing an Antenna Module inside a Car

Full System Simulation

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• Placing an Antenna Module in its deployment environment can be a very large and time consuming simulation.

• Using advanced modeling techniques and hybrid solvers can make these very large and time consuming simulations be manageable and efficient.

• Creating a hybrid FEM-MoM approach to solving very large simulations can be highly efficient and yield highly accurate results.

Modeling an Antenna Array in its Deployment Environment

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TX/RX Module in Deployment Environment

Car Hood (Perfect Electric Conductor)

Car Bumper (Plastic)

TXRX Module

TXRX Module

At 77 GHz this simulation is extremely large! Conventional simulation methods are not efficient.

Using a Hybrid Finite Element Method of Moments Approach can be used to solve this model in an efficient and accurate manner

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Hybrid Finite Element-Integral Equation Method

Finite Elements vs. Integral Equations

• Integral Equation Based Method – HFSS-IE – Efficient solution technique for

open radiation and scattering – Surface only mesh and current

solution

Airbox not needed to model free space radiation

Airbox required to model free space radiation

• Finite Element Based Method – HFSS – Efficient handle complex material

and geometries – Volume based mesh and field

solutions

This Finite Element-Boundary Integral hybrid method leverages the advantages of both methods to achieve the most accurate and robust solution for radiating and scattering problems

Conformal radiation volume with Integral Equations

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• True solution to the open boundary condition – Surface currents directly computed by IE

solver – Very accurate far fields

• No minimum distance from radiator – Advantage over ABC

• Reflection-free boundary condition – Ability to absorb incident fields is not

dependent on the incident angle • Arbitrary shaped boundary

– Outward facing normal's can intersect – Can contain separated volumes

• FE-BI does come with a computational cost – Ability to create air box with smaller

volume than ABC or PML can significantly offset this cost

– Air volumes that much smaller than ABC/PML boundaries will be solvable in less RAM with FEBI

Finite Element-Boundary Integral = FEBI

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FEBI Compare with Friis Transmission • Two rectangular waveguide radiators contained in two separately spaced finite

element and IE boundary domains • Parametrically sweep separation and compare to theoretical Friis formula for

free space transmission • Pr/PI = [(1- |S11 |2)2 G2]/[16(πd/λ)2] • S11, ~0.3 and G ~4.5 computed from single radiator analysis

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Transmit Antenna Location Investigation

Proposed TX Antenna Location (Entire module not shown for clarity)

• Using The FEBI method it is possible to investigate placement of Module within a deployment platform (Car, Truck, etc.)

• Effect of various plastic and metal “obstructions” can be evaluated

• Optimal Transmit antenna location can be determined

“High” Location

“Low”Location

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Transmit Antenna Location Investigation

“Low” Antenna Pattern “High” Antenna Pattern

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Transmit Antenna Location Investigation

“Low” Antenna Pattern “High” Antenna Pattern

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• FEBI also allows engineers to place large or infinitely large obstructions at considerable distance from Antenna array.

• This can then be used to determine antenna performance in presence of obstruction or in a full system simulation where EM field solvers are combined with driving circuitry.

• This combined EM/circuit simulation is possible in HFSS RF but beyond the scope of todays presentation.

Obstructions at a Distance

TX Array

Large or infinite Metal Obstruction

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Obstructions at a Distance

No Obstruction Large Obstruction at 5 m Distance

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Obstructions at a Distance

No Obstruction Large Obstruction at 5 m Distance

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• Electromagnetic simulation can aid in the design of advanced radar modules helping to reduce time to market, design variability and manufacturing issues

• Advanced methods such as FEBI can be used to integrate Radar Modules into their deployment environment aiding design teams to ensure that Radar modules perform according to specifications

• Any questions?

Final Thoughts