Prof. Dejan S. Filipović

Antenna Research Group - ARG Department of Electrical, Computer, and Energy Engineering

University of Colorado, Boulder, CO dejan@colorado.edu

Acknowledgments: ARG students and alumni. This work was sponsored by the Office of Naval Research.

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Introduction Future EW Systems

Frequency Independent Antennas (FIAs)

Commonly accepted “truths” about FIAs: Spiral antennas are dispersive and they can not be used in UWB

systems unless some pre-distortion is applied

Multi-octave planar FIAs handle low-powers (a few tens of watts)

Wideband MMW DF with FIAs requires use of diodes/bolometers

Future Research Outlook

3

Figure courtesy of Dr. Peter Craig, EW Program Manager, Office of Naval Research.

ESProcessor

AndTechniques

EAController

AndTechniques

ES/EAApertures

EA TransmitterHPAs, DACs, Beam Formers, Lasers, Combiners

ES ReceiverLNAs, Filters, Mixers, LOs, ADCs, FPAs, ROICs

DigitalSignal

ProcessorsAnd

Modulators

CirculatorIsolator EW NetworkApertures

EASystem

ESSystem

Processing

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Only class of antennas able to maintain consistent properties over decade BWs Spiral, sinuous, and log-periodic antennas in planar or conical form Concept first proposed by Rumsey (1957), spiral by Turner (1955), sinuous by DuHamell (1985), MAW spiral by Ingerson (1975)

True FI antenna must: have infinitely large aperture and infinitesimally fine feed region have geometry described by angles insure the non-radiated currents decay to zero after passing their active region and before entering the next active region D. S. Filipovic and T. P. Cencich, "Frequency independent antennas", in Antenna

Engineering Handbook, 4th ed., J. L. Volakis, Ed. New York: McGraw-Hill 2007.

[1]

5

Patent in 1955 by E. Turner[1]*

Main application: ESM sensor Multi-octave bandwidth Range: few MHz – 45GHz Above V-band with diode Power handling < 20W Good axial ratio and WoW Input impedance stable Planar or conical shape Planar are absorber backed Number of arms: 2 and 4 (typical) [1] Edwin M. Turner, “Spiral Slot Antenna,” United States Patent 2,863,145, October 1958. * To my knowledge, first mentioned by J.S. Chatterjee in ‘Radiation Field of a Conical Helix,’ Journ. App. Phys., Vol. 24, May 1953.

C. Fumeaux, et.all, “Finite-Volume Time-Domain Analysis of a Cavity-Backed Archimedean Spiral Antenna,” IEEE TAP, vol. 54, 844–851.

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Electronic Support Measures (radar warning sensor, DF, polarimetry)

Ground Penetration Radar Imaging Navigation Communications Radio Astronomy Ionosphere Probing EMC/EMI Testing Antenna Testing Hyperthermia RF Energy Harvesting

[1]

[2] [1] http://indiandefence.com/threads/eurofighter-typhoon.4731/page-184 [2] http://en.wikipedia.org/wiki/AS-17_Krypton

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Spiral antennas are dispersive and they can not be used in UWB systems unless some pre-distortion is applied

Application to UWB systems Detection of LPI signals

Use for Electronic Attack Longer range communications Deeper penetration GPRs

ESM through MMW Tx mode available

Multi-octave planar FIAs handle low-powers (a few tens of watts)

Wideband MMW DF with FIAs requires use of diodes / bolometers

8

Statement

Spiral antennas are dispersive and they can not be used in UWB systems unless some pre-distortion is applied

* Mohamed A. Elmansouri, Joint Time/Frequency Analysis and Design of Spiral Antennas and Arrays for UWB Applications, PhD Thesis, University of Colorado Boulder, 2013 (now with Univ. of Colorado, Boulder)

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Short pulse (SP)/IR-UWB systems based on Tx/Rx short pulses

Employed antennas can distort these pulses (at Tx or Rx or both)

Thus, communication quality and ranging accuracy will be degraded

Understanding antenna dispersion, its effects on pulse distortion, and characterization thereof are important

Note that the antenna pattern, gain, polarization, and other FD features must be maintained

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Radar Application [1]

[1] J D McKinney, et.al. “Dispersion limitations of UWB links and their compensation via photonically enabled arbitrary waveform generation,” IEEE TMTT, pp 710–719, Mar 2008

UWB Communications [1]

(a) Input pulse(s)

(a) (a)

(b)

(c)

(b)

(c)

(b) Rx waveform (c) Rx waveform after compensation

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Question: Can we use spiral antennas for pulsed UWB applications?

10.6GHz

3.1GHz

12

Good frequency-domain characteristics

Spirals are naturally dispersive antennas

Dispersion can be compensated or mitigated

Compensation means extra complexity and cost

Spiral can be designed to have less pulse distortion

Good frequency- domain performance will be sacrificed

Well, the developed spiral must have simultaneously good TD

and FD signatures How?

Yes No

Establish FoM Define Pulses Compute Baseline

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Group Delay Fidelity Factor

fg TF

d ∂∂

−=ϕ

π21

+

=

∫∫∫

∞+

∞−

∞+

∞−

∞+

∞−

dttdtt

dtttFF

rt

rt

22 )()(

)()(max

υυ

τυυτ

The variation of the group delay through the frequency band of the transmitted pulse means that the transmitted pulse will experience different delays at different frequencies

Constant group delay is ideally desired; with low dispersive antennas having a standard deviation < 0.05 ns

Fidelity factor is the maximum correlation coefficient between the two signals obtained for varying time delay

Thus, it describes the similarity between the input and received or radiated pulses

Maximum value of 1 indicates the radiated or received pulse is identical to the input pulse

Establish FoM Define Pulses Compute Baseline

14

0 0.2 0.4 0.6 0.8 1-1

-0.5

0

0.5

1

time (ns)

Nor

mal

ized

Am

p.

1st Derivative

0 0.2 0.4 0.6 0.8 1-1

-0.5

0

0.5

1

time (ns)

Nor

mal

ized

Am

p.

2nd Derivative

0 0.2 0.4 0.6 0.8 1-1

-0.5

0

0.5

1

time (ns)

Nor

mal

ized

Am

p.

5th Derivative

[ ] ( ) 2/)2(2/ 2222

22)()( σπσ πσπ fnn

tn

n

n efjfPedtdtp −− =⇔=

0 2 4 6 8 10 12 14-35

-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

Nor

mal

ized

PS

D (d

B)

1st Derivative2nd Derivative5th DerivativeFCC Mask

Establish FoM Define Pulses Compute Baseline

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2 0.66 0.95 4 0.50 0.86 8 0.35 0.72

Best frequency domain spiral (N=8) has bad fidelity factor As N increases, fidelity factor reduces (group delay is higher at low end)

Archimedean Spiral: r(ϕ) = rin + aϕ

N=2 N=4 N=8

Establish FoM Define Pulses Compute Baseline

16

Question: How to reduce dispersion of tightly wrapped spirals while

maintaining their good frequency-domain behavior? (with 2-arm spirals)

17

0 0.5 1-1

-0.5

0

0.5

1

Norm

alize

d Am

p.

time (ns)

Input Pulse

Before (After) Before (After) N 1st Derivative 5th Derivative 4 0.50 (0.84) 0.86 (0.97) 8 0.35 (0.77) 0.72 (0.96)

Norm

alize

d Amp

.

2 2.5 3 3.5-1

0

1

N=4

2 2.5 3 3.5-1

0

1

N=8

time (ns)

Dots – before compensation Solid – after compensation

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nar /1)( ϕϕ =

−

+

= ++

11

)(2)1(

nin

n

nd rf

ccan

ngπ ( )

+∝ + 21

1 constf

constg nd

New spiral configuration that minimizes group delay variation over the frequency band of interest - power spiral is derived

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n = 1

n=2n = 2

n=4n = 4

n=6n = 6

N=4

20

2 4 6 8 10 120

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Gro

up D

elay

(ns)

Frequency (GHz)

n=1 (Arcimedean)n=2n=4n=6

3.1-10.6 GHz

Archimedean

nar /1)( ϕϕ =

2 4 6 8 10 12Frequency (GHz)

21

1

2

3

4

Frequency (GHz)

VS

WR

n=4, N=4 (Meas.)n=4, N=4 (Sim.)

1

2

3

4

VS

WR

n=6, N=4 (Meas.)n=6, N=4 (Sim.)

4

Antennas remain well matched throughout the bandwidth

2 4 6 8 10 120

Frequency (GHz)

0

2

4

6

8

AR

(dB

)

Frequency (GHz)

n=4, N=4 (Meas.)n=4, N=4 (Sim.)

0

2

4

6

8

AR

(dB

)

n=6, N=4 (Meas.)

Fre

n=6, N=4 (Meas.)n=6, N=4 (Sim.)

The effect of the bow-tie section

As frequency increases, the effect of the center bow-tie section becomes more noticeable, and the quality of circular-polarization starts to deteriorate

Combined Archimedean – Power spiral: Patterns maintain good circular polarization at wider angles (AR<4dB at 30º)

1

2 4 6 8 10 121

2

3

4

Frequency (GHz)

VS

WR

Combined: n=6, N=4 (Meas.)Combined: n=6, N=4 (Sim.)Arc.:N=6 (Meas.)Arc.:N=6 (Sim.)

0

Frequency (GHz)

2 4 6 8 10 120

2

4

6

8

AR

(dB

)

Frequency (GHz)

Combined: n=6, N=4 (Meas.)Combined: n=6, N=4 (Sim.)Arc.:N=6 (Meas.)Arc.:N=6 (Sim.)

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Fidelity factor (FF) at different elevation angles along xz-plane (φ=0˚) for the input 1st and 2nd derivatives of Gaussian pulses

Up to 23% and 40% improvements in fidelity factor are achieved Up to 63% improvement in fidelity factor is achieved compared with N=10 spiral

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Spiral antennas can be designed to have simultaneously good time and frequency domain performance over very wide

instantaneous bandwidths

24

Statement

Multi-octave planar FIAs are low-power receive-only (up to a few tens of watts)

*Matthew Radway, Mode Theory of Multi-Armed Spiral Antennas and Its Application to Electronic Warfare Antennas, PhD Thesis, University of Colorado Boulder, 2011 (now with JPL, Pasadena, CA) *Rohit Sammeta, Low-Profile Antennas for Wideband Transmit Applications in HF/UHF bands, PhD Thesis, University of Colorado Boulder, 2014 (now with Amazon, San Jose, CA) *Jaegeun Ha, Wideband Antennas for Electronic Warfare and Directed Energy Applications, PhD Thesis, University of Colorado Boulder, 2016 (expected)

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EDO CS-8599 Antenna System

Multi-band whip Horn Vivaldi (HF to L-band) (VHF/UHF – MM-waves) (L-band to Ka-band)

Pros Cons

Low-cost LP only

Simplicity Quasi-omni

Easy maintenance

Highly visible

100’s of W Dumb jamming

Pros Cons

High power Size and weight

Multiple octave Pattern instability

Variable polarization

Phase center stability

Well underst. Dumb jamming

Pros Cons

Variable polarization

Bulk & complexity

Multiple octave Pattern variation

Smart jamming Cost

http://www.arawideband.com/PDF%20Files/JAMMING%20SET%20SUV.pdf Cobham/UMAS 6-18GHz Vivaldi

Array

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Needed are new antennas that outperform UHF to S-band EA horns in: size and weight functionality and flexibility bandwidth ERP pattern purity

while maintain & increase high-power ability allow seamless scaling to lower/higher bands

BW Size Power Gain VSWR Func ITT/EDOAS-4850

0.5-2GHz

18”×18”×20”

70W 7-13dB

3:1 EA

Cobham Horn

0.2-2GHz

36”×36”×36”

200W 3-13dB

2.5:1 EA

ITT/EDO AS-4810

0.75-4.5GHz

- 40W 7-12dB

3:1 EA

36”36”

36”

Cobham Sensor Systems Model 9DL1 Quad-Ridged Horn (0.2-2 GHz)

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eliminate major bottleneck for power and efficiency: carbon-loaded foam absorber

use more than two-arms exploit modal theory of operation to keep wide bandwidth (match, gain, AR, WoW, etc.)

use high-power materials / parts when necessary, use dielectric lenses to alter power distribution in favor of the radiating side perform detailed high-power tests: temperature, radiated field, VSWR, visual

Drawbacks: higher complexity and cost, dependability on BFN, some deterioration in FI performance

Parameter Value Bandwidth 0.6- 2.5 GHz

VSWR** < 1.5:1 Axial Ratio < 2.5 dB

Gain 1 - 12 dBiC HPBW 50-10 deg WoW < 2 dB (over HPBW)

Power ≥200W CW

*All data are measured **VSWRs measured at the input of power dividers

0.6 GHz 2.5 GHz

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Planar frequency independent antennas can be designed to handle high CW powers while maintaining good frequency

domain performance

30

Statement

Wideband millimeter-wave electronic support FIAs require use of diodes/bolometers

* Honguy (Eric) Zhou, Wideband Microwave, Millimeter-Wave and Light-Wave Antennas, PhD Thesis, University of Colorado Boulder, 2011 (now with Samsung Research Lab, Fort Worth, Tx) *Joseph Mruk, Wideband Monolithically Integrated Front-End Subsystems and Components, PhD Thesis, University of Colorado Boulder, 2011 (now with First RF, Boulder, CO) *Nathan Jastram, Passive Front-Ends for Wideband Millimeter Wave Electronic Warfare, PhD Thesis, University of Colorado Boulder, 2014 (expected) *Nathan Sutton, Millimeter-Wave Single-Aperture Based Components for Electronic Support and Methods of Fabrication Thereof, PhD Thesis, University of Colorado Boulder, 2014 (expected)

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Use surface micromaching, specifically a PolyStrata™ process developed by BAE, Nuvotronics, and UCB [1]: two-conductors transmission line rectangular or square cross-section inner conductor supported by periodic dielectric supports or shorted stubs support placed under or over or within the central conductor built from at least 5-strata use release holes to remove photoresist realized Zc from <10Ω to >110Ω

Antenna demonstrated: patch antennas and arrays, planar and end-fire LP, 2- and 4-arm spirals, sinuous, Vivaldi, waveguide, etc.

[1] D.S. Filipovic, et.all. “Modeling, design, fabrication, and performance of rectangular μ-coaxial lines and components,” in 2006 Proc. IEEE MTT-S Int. Microwave Symp. Dig., San Francisco, California, June 2006, pp. 1393-1396.

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LPDAs-18-110

18-110 2-arm-spiral

18-110 PLP-ImpTrans

75-110 4-arm spiral

50-100 PLP

18-50 PLP

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• Antenna is built out of 8 strata with thicknesses varying from 20um to 120um • Spiral is self-complementary with radius of 3.375mm and 1.4 turn arms • A four-stage impedance transformer is integrated within a Dyson balun feed • Dielectric straps are utilized inside the balun to hold the central conductor • Central conductor is kept offset from the geometrical center • Probe measurements are conducted at NIST from 18 to 110GHz • EM design with HFSS & FEKO. Launch does not support far-field testing

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Wideband millimeter wave sensors can be developed to extract complex voltage; thus they can also be used for a

single aperture direction finding

35

Miniaturization: how to do it right way?

High-power: do FI antennas have place in Directed

Energy applications?

Arrays: multi-arm FIAs as true wideband arrays?

How about HF: is this possibility?

Smart wideband antenna systems: what can we do

by mixing the modes?

Can we simultaneously jam and sense from the same

FI aperture?

36