Millimeter Wave Reconfigurable Antenna Based on Active Printed Array and Inhomogeneous Lens
ABSTRACT This paper deals with radiation pattern reconfigurable antenna in millimetre wave range. An active printed antenna array is designed in 24 GHz band and feed an inhomogeneous lens (Half Maxwell Fish Eye) to obtain reconfigurable patterns and in particular sectorial and directive cases. In the first part, the authors describe a four patches multilayer active array which allows achieving radiation pattern control by associating a commutator to each element and by changing the fed patches number. In a second part, this array feed an inhomogeneous lens to shape radiation pattern.
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ABSTRACT: A design procedure for spherical lens antennas is described. A particle swarm optimization (PSO) algorithm is coupled to a mode matching technique based on spherical wave expansion to analyze the lens antennas. The proposed methodology is applied to three optimization problems using real-number and binary PSO. First, the maximization of the directivity of Luneburg lens antennas is addressed. Then, amplitude shaped radiation patterns are synthesized by optimizing both amplitude and position of each element of an array that illuminates a lens. Finally, a dual-beam reconfigurable lens antenna is optimized. By only switching properly the elements of an array, the lens antenna radiates either a directive or a sectoral beam. Numerical comparisons with a full wave commercial software successfully validate the proposed design procedure. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1655–1659, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25278Microwave and Optical Technology Letters 06/2010; 52(7):1655 - 1659. · 0.59 Impact Factor
Millimeter Wave Reconfigurable Antenna Based on
Active Printed Array and Inhomogeneous Lens
O. Lafond1, M. Caillet2, B. Fuchs3, S. Palud1, M. Himdi1, S. Rondineau4, L. Le Coq1
1 Institute of Electronic and Telecommunication of Rennes , University of Rennes 1 (France)
2 Royal Military College of Canada , Kingston, Ontario (Canada)
3 Ecole Polytechnique fédérale de Lausanne, EPFL, (Switzerland)
4 University of Colorado, Boulder, (USA),
reconfigurable antenna in millimetre wave range. An active
printed antenna array is designed in 24 GHz band and feed an
inhomogeneous lens (Half Maxwell Fish Eye) to obtain
reconfigurable patterns and in particular sectorial and directive
cases. In the first part, the authors describe a four patches
multilayer active array which allows achieving radiation pattern
control by associating a commutator to each element and by
changing the fed patches number. In a second part, this array
feed an inhomogeneous lens to shape radiation pattern.
This paper deals with radiation pattern
Far field radiation pattern control antennas have strong
potential in wireless communication and radar. In particular,
short range and ‘’Stop and Go’’ radars are studied to obtain
beam shaping antennas for automotive cruise control radars
. If printed antennas are well suited with active device
report, they can introduce bad results in term of efficiency if
high gain antennas are wanted. Then, it could be interesting to
combine active printed antennas array and lens to achieve
control pattern and high efficiency by reducing losses in
feeding line network. The authors have been working on
inhomogeneous lenses  for several years. Thus, this type of
lens has been chosen to be associated with an active printed
antenna array. This array is composed of four patches with a
switch for each patch. This design allows to change the
number of fed patch to control the beamwidth [3, 4].
The paper is organized as follows. In section II, the
reconfigurable printed antenna array is discussed when using a
low cost switch based on LNA amplifier configuration. For
this active antenna array, one obstacle appears to maintain a
good matching whatever the number of fed patches. A
solution is proposed and implemented here. Then, results of
simulation and measure are compared at 24 GHz and show a
good consistency in terms of radiation pattern and gain. In
section III, the Half Maxwell fish Eye lens is briefly described
before being associated to the active patch antenna array
which will become the feeder of the lens. The lens allows to
achieve directive radiation pattern in E plane because only one
patch feed the lens. In H plane, depending on the number of
fed patches, a sectorial or a directive beam can be obtained.
The results of simulation and measurements are given to
demonstrate the reconfigurable radiation pattern feasibility.
II. RECONFIGURABLE PRINTED ANTENNA ARRAY
A. Technology and switch configuration
To separate radiating elements from active switch, a
multilayer technology  has been chosen to design
reconfigurable printed array at 24 GHz. In this configuration,
patches are printed on top substrate (RT Duroid 5880, h =
0.127mm) and lines on bottom substrate (Duroid RO3003, h =
0.127mm). The patches are fed by microstrip lines via
coupling slots (Fig. 1) which are engraved in a thick copper
ground plane (h =0.2 mm).
Feeding line of patchFeeding line of patch
Feeding lineFeeding line
Slot / line transition Slot / line transition
Ground planeGround plane
Duroid 5880Duroid 5880
Duroid RO3003Duroid RO3003
Fig. 1 : Multilayer technology with active and radiating patches layers
A brief description of reconfigurable antenna is shown in Fig.
2 where switches and radiating elements are shown. Many
technologies exist for RF swith design. The most common are
semiconductors , MEMS  and also electromechanical
switches . Semiconductor technology has been selected in
this case because it allows to have high speed switching and
relatively low cost. PIN diodes and transistors can be
employed but the last one provide gain and better isolation.
Thus, a FET transistor (NEC NE3210s1) has been retained.
Because a transistor has been selected, design constraints are
different according to the considered configuration of the
antenna, transmission or reception. Considering a reception
configuration, a Low Noise Amplifier (LNA) has been
designed by minimizing the Noise Figure (NF) characteristic.
To achieve the switch functionality, the idea is to use a
variable gain amplifier by controlling the drain bias voltage.
At the ON-state, the gain will be positive and the input return
loss equals to Γopt to minimize NF and the output return loss
matched to 50Ω. At this OFF state, the gain will be negative
to achieve a good isolation and the output return loss should
be equivalent to an open circuit. After, the feed network
design is based on these constraints. The FET-switch has been
optimized for 24 GHz and good results have been obtained
revealing an isolation close to 20 dB and a 5 dB gain in ON-
Fig. 2 : Multilayer Reconfigurable antenna array composed of microstrip
patches, aperture slot transitions and switches
B. Feed network design to achieve antenna matching
For the reconfigurable patch antenna array, the number of ON
switches is variable to provide beamwidth tunability.
Moreover, the antenna array has to be matched whatever the
number of fed patches. Using a classical feeding line network,
the number of fed patches is stable and quarter-wave
transformers are chosen to match the global antenna array. But,
in our case, if a classical feeding line network is employed,
the active antenna array will be matched when 4 patches will
be fed, but completely mismatched when one patch will be fed.
Then, the authors proposed to add a quarter wave transformer
having an optimized impedance at the input port of the
antenna to achieve an acceptable matching for all
configurations (1 to 4 fed patches corresponding to D1, D2,
D3, D4 configurations). A detailed demonstration of this
original matching technique is described in . The complete
active antenna prototype is pictured in Fig. 3 for both
radiating element and active layers. The switches are put ON
with VDS = 2V and put OFF with VDS = 0V.
The simulated normalized radiation patterns are plotted in Fig.
4 for all configurations (D1 to D4) at 24.2 GHz. The
directivity depends of the number of fed patches and is
respectively equals to 7.3, 11.2, 13.6 and 15.1 dBi.
Concerning prototype characterization, S11 magnitude
parameter has been measured for all configurations and results
are presented in Fig. 5. The antenna array is matched whatever
the number of fed patches close to 24 GHz even if only -8 dB
is achieved for the D4 configuration. The measured radiation
patterns are also shown on Fig. 6 for the same configurations
to compare with simulation results. This reception antenna
configuration has been measured in a millimeter wave
Fig. 3 : Active antenna prototype showing both substrate layers
Fig. 4 : Simulated normalized radiation patterns of the different
configurations at 24.2 GHz
23 23.5 24 24.5 25
angle (° )
Fig. 5 : Measured S11 magnitude parameter of the different configurations
The measured gains are respectively equal to 9 dB, 12.3 dB,
15.3 dB and 16.4 dB. These results are higher than the
simulation predictions, but it could be due to the active switch
-80 -60 -40 -20 0 20 40 60 80
angle (° )
Fig. 6 : Measured normalized radiation patterns of the different
configurations at 23.9 GHz
C. Concluding remarks
An active directivity diversity printed antenna has been
demonstrated at 24 GHz. This prototype allows to tune the
half power beamwidth of the antenna by changing the number
of fed patches in the array. To achieve this result, a switch
design based on FET transistor has been shown. The matching
of this antenna is obtained whatever the number of fed patches
by modifying the characteristic impedance of a quarter
wavelength. If this design permits to change directivity, it
doesn’t allow obtaining shaped radiation pattern. This kind of
shaped beam, sectorial for example, could be a good solution
for automotive cruise control radar to ensure ‘’Stop and Go’’
system. To design a sectorial radiation pattern antenna array,
the radiating elements have to be tapered in terms of phase
and amplitude. In millimetre waves, phase shifter and
attenuators or amplifiers used to design beam forming antenna,
are scarce and expensive. Then, in the following section of
this paper, a new solution investigated by the authors to get a
sectorial shaped pattern with only switches is presented. It is
shown that it is possible to achieve this functionality by
associating the active antenna array with an inhomogeneous
III. INHOMOGENEOUS LENSES - CAPABILITY
IETR has been working over the last years on
inhomogeneous lenses based on gradient index technique.
This type of lens has pattern focusing and beam forming
capability. The refraction index n(r) inside the lens follows a
radial distribution. The most known inhomogeneous lens is
‘Luneburg’ one , but another case of lens that has been
investigated  is named Half Maxwell Fish Eye (HMFE).
This lens consists on a hemispherical shape and the refraction
index law is given by :
where r is the normalized radial position.
No reliable technique is currently able to yield the
continuous gradient index. Then, the easiest technique for the
implementation consists of assembling a finite number of
concentric homogeneous dielectric shells . The radius and
dielectric constant of the shells have been chosen to optimize
directivity when the lens is fed by a source antenna (Fig. 7a).
For our reconfigurable antenna application, a 9-shells lens has
been made with dielectric constant between 1 and 4 to
approach the law (Fig. 7b). The radius of the lens equals 60
mm for this prototype.
Fig. 7 : HMFE lens fed by a waveguide source (a), the 9-shells HMFE lens.
B. Capability of reconfigurable radiation patterns
If only one feeder illuminates the lens, highly directive
antenna is achieved. But, if the lens is associated with a
sources array, it becomes possible to shape the radiation
pattern . Depending on the number of fed sources, the
global antenna system gives the capability to get directive and
sectorial radiation patterns. An example is given at 77 GHz
where 9 waveguide feeders are put under the lens in H plane
(Fig. 8). If only one source feed the lens, a directive radiation
pattern is shown with a gain close to 30 dB. But, if the 9
sources feed the lens, a sectorial radiation pattern is achieved
with a gain close to 20 dB. In E plane, only one waveguide
exists then a directive pattern is maintained.
Fig. 8 : Capability of reconfigurable radiation pattern with lens and
Based on this lens capability, the precedent active printed
antenna array in the 24 GHz band has been placed under the
lens to demonstrate the feasibility of reconfigurable active
antenna based on inhomogeneous lens.
IV. RECONFIGURABLE FINAL PROTOTYPE AT 24 GHZ
Radiation pattern at 24 GHz have been simulated using
CST Microwave Studio. For this simulation, a passive printed
antenna array (without switches) is considered with the HMFE
lens (Fig. 9). Two configurations have been considered : two
fed patches to obtain a directive pattern and four fed patches
to obtain a sectorial one (Fig. 10). The measured radiation
patterns are shown in Fig. 11 for the same cases.
Fig. 9 : Simulation of global system with feeders and lens.
-80 -60 -40 -20 0 20 40 60 80
angle (° )
Two fed patches
Four fed patches
Fig. 10 : Simulated radiation patterns at 24 GHz for both configurations
-80 -60 -40 -20 0 20 40 60 80
angle (° )
Two fed patches
Four fed patches
Fig. 11: Measured radiation patterns at 23.9 GHz for both configurations
A comparison of the half power beamwidths between
measures and simulations is given in Tab. 1 and shows a good
consistency. Concerning gain characterization, the two
configurations give respectively 22.5 dB and 19 dB. These
results illustrate that the switch brings a gain close to 7 dB in
our case. It is important to talk about the matching of the
global antenna prototype. Indeed, the lens doesn’t modify the
matching of the active printed antenna array, because the law
inside the lens does not generate reflections toward the feed.
Two fed patches
Four fed patches
Tab. 1 Beamwidths for both configurations
V. CONCLUSIONS AND PROSPECTS
In this paper, the authors have studied, designed and
realized a directivity diversity printed antenna array based on
multilayer technology and FET switches. The switches allow
to change the number of fed patches and thus to modify
electronically the beamwidth of the radiation pattern. This
active patch array has been associated to an inhomogeneous
lens (HMFE). Depending on the number of fed patches (2 or
4), it becomes possible to shape radiation pattern to get
sectorial or directive patterns. This solution is very attractive
to reconfigure millimetre wave antennas without phase
shifters or attenuators but only by using switches. One
objective of the future work will be to design reconfigurable
antenna in 77 GHz band by using active waveguide feeding
line network to optimize efficiency in millimetre wave
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