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Antenna Synthesis:Evolutionary Optimization Supports

Design by Specification

Antenna Systems 2016

November 3, 2016

3ni.com | NIni.com/awrni.com/awr

Outline• Antenna Synthesis Introduction

• Example #1: CP Hemispherical design• Using Antenna Synthesis for Challenging Antennas

• Example #2: Robust UHF RFID antenna• Using Antenna Synthesis to Gain Insight

• Example #3: UWB antenna design


Antenna Design Challenges• Increasingly challenging size, cost & performance goals• Shortage of experienced designers• Time and budget are under pressure to be reduced• Productivity and consistency are difficult when wrestling

with physics by hand

UHF Reconfigurable

0.03 Self-resonant

Altshuler, AFRL

S-band high-gain Yagi

2-18 GHz Spiral

Wideband Phased Array

0.3 – 10 GHz Vivaldi

0.4 – 40 GHz LPA

Spacecraft Comm Antenna

Deployed on 3 NASA ST5 Spacecraft

2.4 GHz Wi-Fi antenna


Difficult to Design?• Enormous range of possible solutions for even the

simplest antennas• Limitless number of antenna shapes to choose from• Optimum design is often non-intuitive and difficult to find• EM simulation is very expensive for “blind” optimization


How Difficult is Antenna Design?

Drive point

(in center of element)

Reflector element 0 - 4

Driven element 0.5

Separation distance

0.04 - 2

Linden, 1997

A Simple Wir e Antenna Example


How Difficult is Antenna Design?

0.02

0.22

0.42

0.62

0.82

1.02

1.22

1.42

1.62

1.82

2.02

2.22

2.42

2.62

2.82

3.02

3.22

3.42

3.62

3.82

0.08

0.28

0.48

0.68

0.88

1.08

1.281.48

1.681.88

-2

0

2

4

6

8

10

Gain

Length

Separation


Genetic Algorithm Optimization

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 10

0.2

0.40.6

0.81

0 0.2 0.4 0.6 0.8 10

0.2

0.40.6

0.81

0 0.2 0.4 0.6 0.8 1

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Generation 1 Generation 2 Generation 5



A Genetic Algorithm can focus in on most useful areas of search space


What is Antenna Synthesis

• Software that automates the antenna design process for Systems/RF Engineers and Antenna Experts

• Expert system for antenna selection, fitness scoring, representation, etc.

• Antenna optimization engine• EM solver (WIPL-D) used to provide accurate evaluation of

candidate antennas

Antenna specs Antenna DesignAntSyn


Antenna Template Library• Many “textbook”

styles• “Underconstrained”

designs that allow more open-ended design

• The wider the range of templates, the more problems can be solved

• Expected to be an unending area of expansion

10


Synthesis Benefits• Decrease risk

• Eliminate failure as much as possible• Lower risk when setting specs for RF systems (e.g., in

proposal phase)• Decrease cost and schedule

• Reduce the expense and time of “horse-race” trade studies• Increase availability of the underlying technology

• Allow computer-generated designs to be available to those not experts in antennas, EM simulation, and optimization

• Resolve customer issues• Moving goalposts: changing specs, esp once a solution is

found for the original spec• Customers that want to be assured that they didn’t miss

any good designs, but don’t want to pay for the exploration• Unreasonable expectations regarding physics


Philosophy of Synthesis• What You Want is What You Get (with a

bit of persistence)• More like managing a grad student

instead of the normal design process• Approaches used

• The “Single Shot”o Run one spec sheet with all specs in it

• The “Spiral of Success”o Get to a partial spec with successful designso Build on that success to get to your real

spec

vs

vs


Mindset for Synthesis• Effective mindset: “what happens if…”

• AntSyn is set up for low-cost, rapid experimentation• Failure is always an option!

o Can be very useful in showing the trade space edges• Don’t give up – keep runs going, even you can’t think of anything

other than specs that seem likely to fail• Duplicated runs are often useful on hard problems


What Synthesis Can Do• Solve problems when given specs

that respect the physics• The easier the problem, the faster the

solve• Generate designs 24/7• Scale with compute power• Require just a few minutes or even

seconds of labor to kick off a new iteration

• AntSyn allows login from anywhere on almost anything with a browser


What Synthesis Can’t Do• Violate physics (with valid designs)

• It might find a clever, yet useless, way to solve the problem• Know if all specs are reasonable a priori

• Solve complex or difficult specs with one shot (usually)


Example #1: CP Hemispherical Antenna

• Demo


Hemispherical S-band Satellite Comm Antenna• Frequency: 2 – 2.3 GHz • Wire antenna with choke ring

– Ring prevents currents from flowing from antenna to platform at frequencies of interest

– Packaged version shown with anti-static film

– Packaged for flight, antenna is about 4” tall and 3.1” in diameter, not including mounting flange

• Radiator itself is about 1.5" tall

• RHCP or LHCP• Hemispherical coverage• 4 Flight units flown on NASA’s IRIS and

LADEE missions in 2013– 2 RHCP units, 2 LHCP units


Antennas on LADEE18

Omni

OmniDirectional


Google Project Ara Smartphone

Antenna


Do’s and Don’ts for Antenna Synthesis• Do’s

• Understand the effect of default antenna orientations• Start and cancel runs and antennas frequently• Use the smallest set of specs that meets needs• Experiment

• Don’ts• Over-specify • Add more bands than needed• Quit trying


Example #2 – Robust UHF RFID Antenna• Demo


Expert usage - gaining insight with synthesis• An iterative process, usually using the “spiral of success,”

but with an eye for gaining physical insight, not just a final design

• Pushes on different aspects of the problem to see how solutions change

• AntSyn solutions are then analyzed to find common and divergent features

• EM tools are used to simplify designs to their most basic forms, examine operation methods, arrive at design rules and final designs


Exploring antenna types• AntSyn can explore many antenna types with the same

spec • Helps the expert user to determine which type of antenna

and mode of operation may be most natural for solving the problem


Exploring antenna features• Underconstrained designs, like meshes and crooked

wires, can have common features that behave predictably• Certain parts of a mesh may control impedance, while others

control radiation • AntSyn will automatically invent and optimize these

regions, allowing an expert to take an AntSyn design and tweak it for their own purposes

Deployed on 3 NASA ST5 Spacecraft

2.4 GHz Wi-Fi antenna


Exploring limits of physics• Exploring the limits of physics requires significant iteration

and experimentation• Having an understanding of the basic physical limits (e.g.,

Chu limit) is helpful for saving time and runs


Spiral synthesis process in more detail• Explore

• Which specs are hard?• Which design types look promising?• Gate: specs (mostly) finalized

• Generate initial viable designs• Use defaults, possibly with tweaks• Usually don’t have all the performance• Design tradeoffs examined• Gate: final design type selected

• Finalize design• Use parameters to constrain design• Use “high quality” run(s)• Gate: good design obtained


Exercise #3: UWB Antenna Design• Exploring physical limits – demo with AntSyn• For more information, see application note at

http://www.awrcorp.com/sites/default/files/content/attachments/AN-AS-UWB-2016.4.10.pdf

http://www.awrcorp.com/sites/default/files/content/attachments/AN-AS-UWB-2016.4.10.pdf


The End• Thanks for your attention!• Any questions?

Documents

ni.com/awrni.com/awr - Antenna Magazine€¦ · • Wire antenna with choke ring ... • Underconstraineddesigns, like meshes and crooked wires, can have common features that behave