Pre-Fractal Resonant Rings for Compact Spiral Antennas

J. Valleau1, H. Aubert1, A. Bellion2, P. Pouliguen3, P. Potier3

1LAAS-CNRS Toulouse, 2CNES DCT/RF/AN Toulouse, 3DGA DS/MRIS Bruz

State of Art

Choice of Profile

Measures

Introduction

Pre-fractal profiles

Conclusions

Energy harvesting Wireless Power Transmission

Antennas need to receive energy over

wideband

Use of UWB antennas required Issue: Antenna sizes for low frequency applications Objective: Miniaturized UWB antennas

An innovative architecture for miniaturization of UWB antenna is reported in [1] :

Antenna with stacked crenelated metallic rings

rings

substrate

spiral -40

-35

-30

-25

-20

-15

-10

-5

0

0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8

|S11

| (d

B)

Frequency (GHz)

D=127mm D=80mm

D=80mm

Principal: Lowest operating frequency of such an antenna depending on:

Number of stacked metallic rings Unfolded length L of the ring’s contour (or fres) Position of different rings above the spiral

37% reduction of the antenna No degradation of the radiating performances

antenna thickness (height=λ/25) Limitation in fres & miniaturization with crenel profile Time-consuming EM simulation (difficult optimization)

Iteration Order Von-Koch Hilbert-

Inspired (HI) Peano-

Inspired (PI)

1

2

3

Modified Von Koch (MVK) [2]

New degree of freedom : the sine amplitude A high number of points required for a good definition

[1] O. Ripoche, H. Aubert, A. Bellion, P. Pouliguen, P. Potier, “Spiral antenna miniaturization in very high frequency band”, Antenna Technology and Applied Electromagnetics (Antem), 25-28 juin 2012

New degree of freedom :

iteration order

[2] H. Diez, H. Aubert, D. Bellot, A. Takacs, ‘Antenne hélice compacte à profil sinusoïdal modulant un motif fractal’, french patent pending CNES-CNRS n°04576-01/20.

1,05

1,1

1,15

1,2

1,25

0 0,05 0,1 0,15 0,2 0,25 0,3 0,35

Log

qual

ity fa

ctor

Q

Log (L/L0)

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,1

0 0,05 0,1 0,15 0,2 0,25 0,3 0,35

Log

reso

nant

freq

uenc

y in

log(

GHz

)

Log (L/L0)

lowest Q

Reference

Reference

lowest fres

Best trade-off

The choice of the most suitable profile in a given application is the results of a trade-off between two criteria

Primary criteria For a given L, a compromise needs

to be made between:

lowest Q lowest fres !

Two antagonist parameters

Application criteria In a given application, a profile

needs to be realizable and limit the computation time. We will choose a

profile with : lowest fractal

iteration

lowest number of replicas

-50-45-40-35-30-25-20-15-10

-50

0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8

|S11

| (d

B)

Frequency (GHz)

Gain (dBi) φ=0° φ=90°

Lowest frequency

1,8 GHz

3 GHz

5 GHz

9% diminution of the lowest operating frequency with the MVK profile without deteriorating the

radiation performances

9% 7%

Chosen L

State of Art

Pre-fractal profile

Profile Choice Measures

Characterization of new profiles Comparison of their resonant frequency and quality factor to the crenel Definition of criteria to choose the most suitable profile depending on the application

Measures of an antenna with the selected profile: 9% diminution of the lowest operating frequency without deteriorating radiation performances Greater reduction expected with more stacked rings