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130
  
Reshaping Antenna Patterns Using Metasurface Radomes
132
  
NRL Participates in NATO Electronic Warfare Trial 
134
  
Magnetoelectric Microbeam Resonators for Magnetic Field Sensing 
137
  
Intense Laser-Driven Ion Accelerator
139
  
Normally-Off AlGaN/GaN MOS-HEMTs with Record Performance
141
  
NexGen High Frequency Surface Wave Radar
Electronics and Electromagnetics

130
2017 NRL REVIEW
  |  
electronics and electromagnetics
Reshaping Antenna Patterns Using 
Metasurface Radomes
B. Raeker and S. Rudolph
Tactical Electronic Warfare Division 
 Introduction: The radiation pattern of an antenna 
is ultimately what determines its suitability for a spe-
cific application. However, generating complex radia-
tion patterns from a single antenna requires significant 
expertise and substantial design effort. Researchers in 
the Offboard Countermeasures Branch of the Tactical 
Electronic Warfare Division at the U.S. Naval Research 
Laboratory have been interested in a method to directly 
design an antenna radiation pattern using a metasur-
face radome. A metasurface consists of subwavelength, 
two-dimensional unit cells which are designed to have 
a specific impedance. Such metasurfaces can be easily 
realized using printed circuit board fabrication tech-
niques, making the production of these radomes widely 
available and inexpensive. In this article, we will first 
demonstrate this capability using a cylindrical radome, 
and then demonstrate the flexibility of the method by 
examining a spherical radome.
 
Such radomes would be beneficial to both the U.S. 
Navy and commercial applications. The metasurface 
radomes could be used to produce nulls in areas of 
interfering signals or reallocate power along differ-
ent bearings without needing to redesign the enclosed 
antenna. Additionally, the radomes can be used to 
provide basic antennas with enhanced, mission-specific 
performance, allowing for the utility of a modular 
design while minimizing the amount of hardware that 
would need to be replaced. The next section outlines 
the method by which a radome can be designed to 
transform the radiation pattern of an existing antenna 
into any pattern that is desired.
 
 
Design Procedure: The first step in the design 
procedure is to calculate electromagnetic fields that 
must be produced on the surface of the radome. This is 
done by reverse propagating the desired field pattern. 
However, arbitrary radiation patterns cannot directly 
be propagated back and projected onto new surfaces; 
such operations can only be performed on solutions to 
the wave equation. Therefore, in our research project, 
we first decompose the desired radiation pattern into 
an infinite series of modes. This can be done in any 
separable coordinate system, but we provide examples 
here in two-dimensional cylindrical coordinates and 
three-dimensional spherical coordinates. This decom-
position takes the form of a Fourier series in cylindrical 
coordinates and a Fourier-Legendre series in spheri-
cal coordinates. Once the desired field is separated 
into these orthogonal modes, they can be propagated 
independently along the radial direction, i.e., inward or 
outward, such that the desired field on the image sur-
face can be propagated inwards to produce the required 
fields on the surface of the radome.
 
The next step in the design is to find the necessary 
scattered field that must be produced by the radome 
to transform the incident field into the desired field. 
This is done by simply subtracting the incident field at 
the surface of the radome from the desired field which 
has been propagated back to the surface of the radome, 
such that E
scattered
 = E
desired
 – E
incident

 
The subsequent step is to take the now-known 
scattered field and use it to design the metasurface 
that will actually transform the incident field into the 
desired field. By subdividing the surface of the radome 
into discrete subwavelength unit cells, we can use the 
Method of Moments to determine the current needed 
on each unit cell to produce the correct scattered field. 
Once the current is known, we can find the impedance 
of the unit cell by taking the ratio of the desired electric 
field and the current at any given location on the sur-
face of the radome: Z
i
 = E
idesired
/J
i
, where i indicates the 
unit cell number.
 
Once the impedance distribution across the meta-
surface has been calculated, we can then realize those 
impedances through printed circuit board methods, as 
can be seen in Fig. 1(b). This is typically done by solv-
ing for a few key points and then extrapolating to find 
the intermediate values.
1
 
 
Results: To prove the validity of our approach, we 
sought to transform the isotropic radiation pattern of 
an infinite filament of current into a binary radiation 
pattern such that radiation is permitted over a 180° 
sector and prohibited over the other 180° sector (see 
Fig. 1(a)).
2
 The field patterns are remarkably consis-
tent between the theoretical, simulated, and measured 
results, as shown in Fig. 1(c), with the measured field 
having a normalized RMS error of 0.034. Addition-
ally, this proved to be a much more precise method of 
realizing our desired field distribution when compared 
with an alternative method for realizing the prescribed 
binary pattern, such as a conducting shield, as shown in 
Fig. 1(d).
 
Finally, to demonstrate the fully arbitrary nature of 
the radiation patterns that can be synthesized using this 
method, we sought to transform the radiation pattern 
of a small dipole into the shape of a nautical anchor, 
with the geometry shown in Fig. 2(a).
3
 The resulting 
simulated three-dimensional far-field pattern is pre-
sented in Fig. 2(b). A flattened version is compared to 
the ideal pattern we sought to achieve in Fig. 2(c). Fig. 
2(d) presents individual linear cuts along the azimuthal 
angle of 180° and the elevation 90°.
 
[Sponsored by the NRL Base Program (CNR funded)]

131
electronics and electromagnetics
 
 |  
2017 NRL REVIEW
FIGURE 1
(a) Geometry of the cylindrical metasurface radome. (b) The fabricated metasurface radome, manufactured using 
printed circuit board techniques. (c) Plot of the theoretical, simulated, and measured radiation patterns. (d) Plot 
comparing the radiation patterns low-loss substrate radome, a radome with a conducting sector to block radiation 
over a 180° sector, and the metasurface radome.
FIGURE 2
(a) Geometry of the spherical metasurface radome. (b) Simulated far-field pattern of the antenna enclosed in the 
metasurface radome displaying the shape of a nautical anchor on its side. (c) Comparison between the design 
radiation pattern (left) and the radiation pattern of the antenna enclosed in the radome (right). (d) Comparisons of 
the ideal and simulated far-field patterns along the E-plane (φ = 180°) and the H-plane (θ = 90°).

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2017 NRL REVIEW
  |  
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References

B.O. Raeker and S.M. Rudolph, “Arbitrary Transformation 
of Antenna Radiation Using a Cylindrical Impedance Meta-
surface,” IEEE Antennas Wireless Propag. Lett. 15, 1101–1104 
(2016).
2
 B.O. Raeker and S.M. Rudolph, “Verification of Arbitrary Radia-
tion Pattern Control Using a Cylindrical Impedance Metasur-
face,” IEEE Antennas Wireless Propag. Lett. 16, 995–998 (2017).
3
 B.O. Raeker and S.M. Rudolph, “Arbitrary Transformation of 
Radiation Patterns Using a Spherical Impedance Metasurface,” 
IEEE Trans. on Antennas and Propag. Lett. 64(12), 5243–5250 
(2016).
    
ª
NRL Participates in NATO Electronic 
Warfare Trial
A. Allegrezza and C. Maraviglia
Tactical Electronic Warfare Division 
 
Introduction: During the week of June 6, 2016, 
the U.S. Naval Research Laboratory’s (NRL) Tactical 
Electronic Warfare Division and the Royal Norwegian 
Navy cohosted the Naval Electromagnetic Operations 
(NEMO) Trials in Andøya, Norway. The trials, con-
ducted by the NATO Above Water Warfare Capabilities 
Group, involved the participation of eight countries 
that provided 10 warships, four air assets, and several 
shore-based assets. The trials were conducted in the 
area of Andøya, Norway, about 200 miles north of the 
Arctic Circle. The Norwegian Air Force’s 133rd Air 
Wing, based at Andøya Air Station, was the host loca-
tion for the trials. Facilities and test support were pro-
vided by Andøya Air Station, the Andøya Space Launch 
Center, the Norwegian Navy Operational Logistics 
Unit, and associated Surface and Air Operations Areas.
 
Andøya Air Station is in Andenes, on the north-
ern end of the island of Andøya. The area provided 
a protected fjord (Andfjorden) to the east and open 
ocean to the north and west. The air station provided 
ground sites for test and measurement stations as well 
as airfield and aircraft support.
 
U.S. Government objectives for the trials included 
collecting electro-optical and imaging infrared (EO/
IIR) data for the various NATO warships, assessing 
the effectiveness of decoy deployment tactics against 
imaging seekers, evaluating detection ranges of various 
seeker platforms, and creating a multi-threat environ-
ment with the radiofrequency (RF) stimulator. To 
meet these objectives, the Tactical Electronic Warfare 
Division flew captive-carry IIR and EO seeker simula-
tors on a Lear jet and set up shore sites at Andøya Air 
Station to support an IIR seeker simulator and an RF 
stimulator system (Fig. 3). 
 
NRL Objectives: NRL researchers focused on 
objectives established by a NATO capabilities group 
for both operational interoperability and scientific 
objectives. For the EO/IIR group, objectives included 
collection of EO/IIR imagery of various platforms, 
evaluating the effectiveness of decoys and tactics, and 
evaluating ship detection based on signature measure-
ments. For RF researchers, the objective was to create a 
multi-threat environment using the Complex Arbitrary 
Waveform Synthesizer (CAWS) radar stimulator in 
conjunction with a German anti-ship cruise missile 
simulator. 
 
Test Asset Descriptions: Description of FOXTROT 
Anti-ship Missile (ASM) Simulator: The FOXTROT 
simulator is a programmable, human-in-the-loop, 
real-time image tracking system designed to simulate 
IIR anti-ship missile threats. Developed as a research 
tool, the simulator can represent both modern and 
future classes of threats, with an imaging front end and 
sophisticated image processing capabilities. Video data 
from an imager can be processed in real time or saved 
as raw data that can be post-processed for target track 
evaluation and algorithm development. The FOX-
TROT simulator is composed mainly of off-the-shelf, 
commercially available components. The simulator is 
maintained under the U.S. Navy’s Effectiveness of Naval 
Electronic Warfare Systems program. Control and inte-
gration software was developed by NRL’s Tactical Elec-
tronic Warfare Division. Two versions of the simulator 
were fielded: (1) a flyable version, housed in a standard 
instrument pod (SIP) for captive-carry under the wing 
of the Learjet, and (2) a portable version, packaged in 
lightweight containers and located in a shelter at the 
ground operations IR test site. The FOXTROT simula-
tors consist of several major subsystem components: 
commercially available infrared imager, wide field-of-
view reference TV camera (visible band), video image 
processing and analysis computer, gyro-stabilized 
FIGURE 3
NRL used a Lear jet to fly sensors that captured electro-optical 
and imaging infrared data for the various NATO warships in-
volved in the 2016 Naval Electromagnetic Operations (NEMO) 
Trials in Andøya, Norway.

133
electronics and electromagnetics
 
 |  
2017 NRL REVIEW
gimbal with an electronic control loop, data recording 
devices, and standard PC for I/O control. The infra-
red imager and the reference camera are installed on 
the same gimbal. Both FOXTROT simulators (flyable 
and portable) were based on a NightConqueror II-256 
IIR camera from L-3 Cincinnati Electronics (Mason, 
Ohio) as the primary tracker. The NightConqueror is a 
ruggedized, staring focal plane array-based, mid-wave 
infrared camera. 
 
FOXTROT simulators also use a visual reference 
camera. The flyable system contains a Cohu Closed 
Circuit Television wide field-of-view visible band 
camera. The FOXTROT portable system uses a Photon 
Focus 14-bit monochrome visible band camera.
 
FOXTROT relies on manual acquisition by an 
experienced operator to select the target of interest, 
after which the target is auto-tracked. The tracking al-
gorithm is based on a binary threshold, centroid track. 
The digital image is passed into the video processing 
PC, which determines a target pixel value threshold 
based on imagery inside several gates. Outer clutter 
gates adjust the threshold based on the amount of clut-
ter in the scene/image. A background gate and track 
gate then determine the final threshold based on the 
image in their gates and clutter data from the clutter 
gates. The result is a binary color image of the target. 
This image is centroided, and new track gate dimen-
sions are calculated for the next image. The resulting 
data is then passed back to the gimbal to maintain 
pointing accuracy.
 
Description of IOTA-MIKE Unmanned Aircraft Sys-
tem Simulator: The IOTA-MIKE system is a program-
mable simulator of a visible band optical unmanned 
aircraft system payload composed of off-the-shelf, 
commercially available components. The software 
is written and maintained by the Tactical Electronic 
Warfare Division, and the software load used for 
the NEMO 2016 Trials is unclassified. The system is 
housed in a SIP slightly modified to accommodate 
its gimbal and mounted to the wing of the Learjet for 
flight. The IOTA-MIKE simulator comprises several 
major subsystem components: commercially available 
CCD NTSC visible band imager, laptop computer for 
system control, gyro-stabilized gimbal with an elec-
tronic control loop, data recording devices, and an 
onboard PC/104 embedded computer for I/O control. 
The tracker works in the same way as the FOXTROT 
tracker (Fig. 4). 
 
Description of the Complex Arbitrary Waveform:
The Complex Arbitrary Waveform Synthesizer (CAWS) 
is a programmable radar stimulator (transmit only) 
developed and built by NRL. Each waveform parameter 
can be individually programmed to provide accurate 
signals for laboratory and operational testing. CAWS 
can be packaged in both portable (configuration used 
for NEMO 2016) and captive carry flyable configura-
tions. CAWS requires a connection to an external RF 
amplifier and antenna. Amplifiers can vary in size to 
match the individual test requirements. The opera-
tional concept of CAWS is similar to Joint Electronic 
Warfare Countermeasure System ALQ-167 Stimulation 
Pods (Fig. 5). 
 
Summary: For NRL researchers, the primary 
objective of this trial was to take EO/IIR imagery of 
various platforms and evaluate the effectiveness of IIR 
decoys and deployment tactics against IIR seekers. The 
secondary objective was to support ESM operations 
by transmitting a radar signal with the CAWS system. 
All proposed U.S. test objectives were met. The flyable 
FOXTROT system collected over 776 files consisting 
of 314 megabytes of data. The flyable system col-
lected both visible and mid-wave IR imagery and GPS 
tracking data for 86 ship runs. The portable FOX-
TROT system collected over 467 files consisting of 1.6 
terabytes of data. The portable system collected both 
visible and mid wave IR imagery for 66 ship runs. The 
IOTA-MIKE system collected over 239 files consisting 
of 205 megabytes of data; the system collected visible 
band imagery and GPS tracking data for six ship runs. 
The CAWS stimulator operated for 22 runs, providing 
a multiple threat environment in conjunction with the 
German RF Simulator.
FIGURE 4
The pod of the IOTA-MIKE system. The system’s software is 
written and maintained by the NRL Tactical Electronic Warfare 
Division.
FIGURE 5
The FOXTROT pod. The FOXTROT simulator is a program-
mable, human-in-the-loop, real-time image tracking system 
designed to simulate imaging-infrared anti-ship missile threats.

134
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The collected data was post-processed by NRL 
researchers to evaluate decoy and inoperability tactics. 
The mission of NATO is to present a unified front. 
By working together in their trials and subsequent 
scientific research, a stronger alliance is formed. The 
size and scope of these types of exercises also offer an 
excellent venue for realistic data sets. 
 
[Sponsored by OPNAV]
    
ª
Magnetoelectric Microbeam 
Resonators for Magnetic Field Sensing
S.P. Bennett,
1
 J.W. Baldwin,

M. Staruch,
1
 B.R. Matis,
2
 
K. Bussmann,
1
 D. Goldstein,
2
 and P. Finkel
1
 
1
Materials Science and Technology Division
2
Acoustics Division 
 
Introduction: One of the great challenges of our 
time is to achieve maximum efficiency in the next 
generation of electronics. It is particularly crucial for 
self-sufficient platforms (e.g., autonomous vehicles and 
remote sensing) on which power requirements are a 
highly limiting factor towards performance. Of specific 
importance for the Navy is magnetic sensing technol-
ogy, which has fallen far behind other technologies in 
power consumption and performance. 
 
For many years there has been a growing need 
for a giant leap in the development of high sensitivity, 
cryogen-free, chip-based magnetic sensors that operate 
with ultra-low power consumption. To meet this need, 
a new generation of sensors must be realized based 
from a new set of physics for detection, and, if they are 
to outperform the current state of the art, they must 
operate at very low power consumption, ruling out 
the physics used by most of our current power hungry 
technologies (e.g., search-coil, Hall effect, flux gate, 
fiber optic, and the superconducting quantum interfer-
ence device).
 
Very recent advances in materials physics have 
unveiled that micron scale Magnetoelectric (ME) com-
posite resonators could hold the answer. ME resonators 
basically consist of two strain-coupled materials; one 
magnetostrictive and another piezoelectric.
1
 When the 
coupled structure is driven to mechanical resonance a 
peak in the piezoelectric signal is detected. If the reso-
nating device is placed in a magnetic field the magneto-
elastic layer responds by either stiffening, or loosening, 
the structure and in turn shifting this resonance signal. 
Similar devices have already shown remarkably high 
sensitivity and quality factors. Additionally, their direct 
coupling between magnetic and electric fields allows 
for very low power consumption, or even completely 
passive, magnetic sensors. 
 
The current state of the art for magnetoelectric 
resonators is limited to very large sizes (>1cm) as well 
as their needs for op-amp detection, battery power, 
and a relatively high equivalent noise floor of ~10
–10
 
Tesla at frequencies away from the electromechanical 
resonance. The limitations are partly due to the size of 
the resonator structure. We expect that miniaturization 
chip-based micro-scale domain is expected to increase 
the signal-to-noise ratio and allow for broadband mag-
netic field detection with an equivalent noise floor of 
~10
–12
 Tesla at 1Hz. As an added perk such miniaturiza-
tion allows for easy integration into silicon-based, low 
power, electronic systems. 
 
Using advanced nanofabrication methods, we 
have demonstrated a fully suspended two-point 
connected thin film heterostructure where precisely 
engineered internal stresses hold the structure in a 
taut tensile stressed state, preserving the shape and 
allowing for a fundamental string mode resonance 
behavior at the first harmonic. The ME heterostructure 
demonstrated here consists of a Pt back electrode, an 
AlN piezoelectric signal layer and a magnetostrictive 
FeCo layer, which also serves as the top electrode. At 
the resonance mode, the time-variant strain signal is 
detected as a piezoelectric voltage from the AlN layer. 
When subjected to a magnetic field, magnetoelastic 
effects in the FeCo layer cause a shift in the resonance 
frequency, which is proportional to the field amplitude. 
This frequency shift is what allows for highly sensitive 
measurements of very low magnetic fields. 
 
Fabrication: The fabrication process is outlined 
in the schematic diagrams given in Fig. 6(a). Double-
side polished, 100-mm diameter, <100> orientation Si 
wafers were coated with 300nm of low stress LPCVD 
silicon nitride. The device side (top surface) was coated 
with a 10nm Ti adhesion layer followed by 150 nm 
of low stress Pt film deposited with DC magnetron 
sputtered. The AlN piezoelectric films were deposited 
by reactive sputtering to a thickness of 750 nm, with 
conditions optimized for low stress (~50 MPa.). Qual-
ity of the AlN films was verified through XRD having 
FWHM values for the (002) AlN diffraction peak less 
than 2 degrees. Using standard lithography techniques, 
the top FeCo film was defined by lift-off photolithog-
raphy. The FeCo film films were co-sputtered by DC 
magnetron at a ratio of approximately (30%Fe, 70% Co) 
at room temperature to a total thickness of 500 nm. The 
AlN nitride layer was patterned using standard lithog-
raphy techniques and subsequent wet etching using a 
PECVD a silicon nitride hard mask. The Ti/Pt bottom 
electrode was patterned with standard lithographic 
techniques followed by reactive ion etching using Cl2/
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