# Liquid Crystal-Reconfigurable Antenna Concepts for Space Applications at Microwave and Millimeter Waves

Authors: A. Gaebler; A. Moessinger; F. Goelden; A. Manabe; M. Goebel; R. Follmann; D. Koether; C. Modes; A. Kipka; M. Deckelmann; T. Rabe; B. Schulz; P. Kuchenbecker; A. Lapanik; S. Mueller; W. Haase; R. Jakoby
Journal: International Journal of Antennas and Propagation
 (2009)

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## Abstract

Novel approaches of tunable devices for millimeter wave applications based on liquid crystal (LC) are presented. In the first part of the paper, a novel concept of a tunable LC phase shifter realized in Low Temperature Cofired Ceramics technology is shown while the second part of the paper deals with a tunable high-gain antenna based on an LC tunable reflectarray. The reflectarray features continuously beam scanning in between±25∘. Also first investigations on radiation hardness of LCs are carried out, indicating that LCs might be suitable for space applications.


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## Body

## 1. Introduction

The shortage in the available frequency
spectrum for radio communications and the requirement for more functionality in
ever smaller volume requires the development of new concepts in RF technology, especially
for space missions. A general approach to solve this problem is the concept of
dynamically reconfigurable RF front ends. One possibility for the realization
of tunable RF components is the use of special substrate media such as
controllable dielectrics. Especially for the higher frequency range (>20  GHz), liquid crystals (LCs) show very good RF performance [1]. Nevertheless,
the used fabrication processes prevented a commercialization up to now, because
of incompatibilities with standard fabrication processes. One aim of the
Liquida project is to overcome that problem in order to develop tunable
components for RF applications. The combination of both good RF properties of
LC and the advantages of the standard multilayer technology of Low Temperature
Cofired Ceramics (LTCC) has a high potential to enable the realization of cost-effective
and high-performance RF components. Therefore, the investigation in terms of
fabrication technology aims to accomplish the development of a technique for
the fabrication of a Liquid Crystal compatible LTCC material system. measurement
results of several LTCC phase shifter devices which can be the key component of
tunable-phased array antennas. In the second part of the paper another concept
of an LC-tunable high-gain antenna based on a reflectarray topology is
presented. Furthermore, some basic investigations for space qualification of
Liquid Crystal devices are aimed for.


## 2. Properties of Liquid Crystal

LCs are an anisotropic material showing both properties of a
crystal and a liquid. All further explanations are related to nematic LCs which
shows up to now the best dielectric properties at microwave and mm-wave
frequencies [2]. They can be described as rod-like molecules as shown in Figure 1. The shown rod represents the anisotropic dielectric properties of a molecule
and the unit vector n→ pointing in the same direction as the rod is
called director.Figure 1
Representation of a rod like molecule with
the anisotropic dielectric axes.εr,⊥, the permittivity perpendicular to an incident
electrical field, is usually around 2.5 while εr,∥ ranges between 2.8 and 3.5, depending
on the material.A bulk of LC molecules represented as such a rod contained
between two surfaces which have been specially treated to anchor the molecules
parallel to the surface will look like Figure2(a).Director distribution by surface alignment
without (a) and with a bias voltage on the upper electrode.
(a)(b)The two electrodes in this figure represent a microstrip line and the
respective ground plane. The reorientation of an entire bulk of LC can be
achieved by the effect of an external electric bias field. Applying such a
field, the molecule's long axis rotates such that the director points mainly
towards the same direction as the exciting electric field lines. Figure2(b) demonstrates this schematically. By using LC in such a way as a dielectric
substrate, this mechanism can be used for a continuous tuning of the effective
permittivity of transmission lines.To describe the director orientation in the biased state, it is
necessary to consider the influence of the director dynamics which is described
by the so called LC Continuum theory [3]. Looking at the rod-representation as
shown in Figure 1, an electric bias-field generates an anisotropic polarization
in the LC material. This leads to an electric torque for the considered
director given by the cross-product of the bias field with the polarization.Another torque contribution results from the elastic forces
between the molecules themselves. These elastic forces stem from deformations
of the director distribution and can conveniently be imagined to be working
like deformations in a regular crystal. In liquid crystal bulks generally three
basic types of deformations can exist simultaneously: the splay, twist and the bend
deformation. The nature of these types is shown in Figure3.(a) The splay, (b) twist, and (c) bend deformation.
(a)(b)(c)After the bias voltage is removed these torques lead the
molecules back to the original state, caused by the minimum energy principle.


## 3. Fabrication Process

The realization of phase shifters based on Liquid Crystal
combined with LTCC requires the fabrication of cavities which can be filled
with LC. Figure4 shows schematically the cross section of an inverted microstrip
line (IMSL) consisting of a ground plane on the bottom of the center cavity and
a top electrode. This structure is stacked here by using six layers of LTCC.
The challenge is to fabricate a wide cavity or channel (e.g., dimensions of
W=400μm by H=100μm height) and maintaining these dimensions also over a
channel length of, for example, 50 mm.Figure 4
Cross-section of an LTCC-based inverted microstrip line.The LTCC manufacturing process uses a screen printing to generate
metalized circuit patterns on so called green sheets which make the LTCC
layers. Afterwards, the sheets are stacked and laminated by utilizing a
combination of multiple lamination steps which also include forming rectangular
cavities in the process.Although the structuring of planar LTCC foils, which are
processed and screen printed with thick-films, is straight forward, major
problems arise such as delamination or bending of the cavity's top and bottom
wall during the sintering process. Therefore, the investigation in terms of the
fabrication is focused on the optimization of the process parameters needed to
create integrated and well-defined cavities in LTCC.After the burnout and co-firing process the LTCC device is filled
with Liquid Crystal and finally sealed. The whole device is shown in Figure5.Figure 5
Prototype of a LTCC phaseshifter device.


## 4. LTCC Phaseshifter

Figure6 shows the prototype of a LTCC phase shifter schematically.
A coplanar waveguide (CPW) is used for the external connection, whereas an
inverted microstrip line (IMSL) realizes the liquid crystal filled transmission
line phase shifter. This line type provides a high tuning efficiency [4] in the
meaning of a big change of the effective permittivities in the steered and
unsteered case. After applying an electrical bias field to the CPW center
electrode (which has a galvanic connection to the top electrode of the IMSL),
the LC can be continuously steered depending on the applied voltage as
described in Section 2.Figure 6
LTCC
structure of the CPW to IMSL transition.


### 4.1. Measurement Results

The following
measurement results where obtained by using the standard nematic LC K15. This
commercial available LC is well investigated and its microwave properties are
also known at the targeted operation frequencies. These parameters are
summarised in Table1.Table 1
Material
parameters of K15 and MDA-03-2838.
Mixtureεr,∥εr,⊥tan(δ)∥tan(δ)⊥K152.852.550.010.03Table 2
Capacitance and conductivity values before and after proton
irradiation.
SampleAfter irradiationbeforeC/pFR/MOhmC/pFR/MOhmK15-1826,56,482526K15-2836,06,383429,2M_A-1927,52,9909,522,3M_A-2775,93,6759,530,2M_B-1220,3138,5216infiniteM_B-2229,4182,0225infiniteM_C-1153,9infinite151,4infiniteM_C-2158,0infinite157,4infiniteThe results of
the measured insertion lossS12 and the attenuation are shown in Figure 7.Figure 7
Measurement
results of the LTCC phaseshifter, without bias voltage (black curves).As depicted in Figure7, the insertion loss of the whole devise is
better than −8.5 dB in the range of 25 to 30 Ghz and the reflection is lower
than −15 dB for both the biased and unbiased state.The phase shiftΔΦ which can be achieved by using K15 is between
120° and 200° in the measured range from 25 to
40 GHz (Figure 8).Figure 8
Measured phase shift.In order to compare this results an quality factor of a
phaseshifter as commonly called Figure-of-Merit (FoM), can be defined by the
relation of the phase shift to the highest insertion loss at the corresponding
frequency. Figure9 shows the FoM which could be achieved with the presented structure.Figure 9
FoM of the
LTCC phaseshifter.


## 4.1. Measurement Results

The following
measurement results where obtained by using the standard nematic LC K15. This
commercial available LC is well investigated and its microwave properties are
also known at the targeted operation frequencies. These parameters are
summarised in Table1.Table 1
Material
parameters of K15 and MDA-03-2838.
Mixtureεr,∥εr,⊥tan(δ)∥tan(δ)⊥K152.852.550.010.03Table 2
Capacitance and conductivity values before and after proton
irradiation.
SampleAfter irradiationbeforeC/pFR/MOhmC/pFR/MOhmK15-1826,56,482526K15-2836,06,383429,2M_A-1927,52,9909,522,3M_A-2775,93,6759,530,2M_B-1220,3138,5216infiniteM_B-2229,4182,0225infiniteM_C-1153,9infinite151,4infiniteM_C-2158,0infinite157,4infiniteThe results of
the measured insertion lossS12 and the attenuation are shown in Figure 7.Figure 7
Measurement
results of the LTCC phaseshifter, without bias voltage (black curves).As depicted in Figure7, the insertion loss of the whole devise is
better than −8.5 dB in the range of 25 to 30 Ghz and the reflection is lower
than −15 dB for both the biased and unbiased state.The phase shiftΔΦ which can be achieved by using K15 is between
120° and 200° in the measured range from 25 to
40 GHz (Figure 8).Figure 8
Measured phase shift.In order to compare this results an quality factor of a
phaseshifter as commonly called Figure-of-Merit (FoM), can be defined by the
relation of the phase shift to the highest insertion loss at the corresponding
frequency. Figure9 shows the FoM which could be achieved with the presented structure.Figure 9
FoM of the
LTCC phaseshifter.


## 5. Space Qualification Tests of LC

In order to verify the capability of LCs for space applications, different basic investigations have to be carried out: one test scenario is the reaction of the material under exposing of high energetic protons.The tests has been carried out at the Forschungszentrum Jülich.The energy of the protons is fixed to 42 MeV with a maximum
current of 10μA. This energy was reduced to 15 MeV by using a special graphite
iris between the target and the proton gate in order to simulate the typical
total radiation dose of a 15 years lifetime space mission in the Low Earth
Orbit.Several test cells have been irradiated with protons, for example, LTCC packaged
phase shifters, LC-filled capacitances and pure LC-filled glass tubes each with
four different LC mixtures.The results of the measured values of the capacitances before and
after several equivalent years of a space mission are shown in Table1.  The data was obtained by using an LCR meter
at 1 KHz.As can be seen, the reaction depends on the kind of the LC. Big
changes of the conductivity could be obtained for K15 and M_A mixtures, whereas
no change of those properties could be measured for the M_C mixture. However,
the physical interpretation of all measurements is not finished yet and further
tests with electrons and gamma radiation are in planning.


## 6. Reflectarrays

In place of phase shifters to
realize a tunable-phased array another possibility to realize tunable high-gain
antennas is a reflectarray antenna.A reflectarray antenna combines, as
its name already suggests, some of the best features of reflector and array
antennas. A special type of reflectarray is the microstrip reflectarray. It
consists in a basic form of a planar, thin substrate with microstrip antenna
elements, for example, patches or dipoles, which are arranged in an equidistant grid on
the substrate. The array is illuminated by a feed antenna and the elements of
the array, in the following called “unit cells”, are designed to scatter the
incident wave with an appropriate phase, required to form a planar phase surface
in front of the aperture, as depicted in Figure10.Figure 10
Functioning of a microstrip reflectarray.This mode of
operation is similar in concept to a parabolic reflector that naturally forms a
planar phase front, when a feed is placed at its focus.One of the key
features in microstrip reflectarray implementation is how the elements are
designed to scatter with the desired phase. One method is to use microstrip
patches with different sizes to control the backscattered phase, as proposed in
[5]. This method is also the basic functionality of the tunable unit cell
presented in this contribution.Reflectarrays
have attracted increasing attention in the past years because of their
properties: low loss due to the absence of a corporate feed, ease of fabrication,
planarity, and low weight. Reconfigurability is another desirable feature of
reflectarrays that would increase their versatility a lot. A novel approach
based on nematic LCs will be presented in this contribution in order to realize
an electronically reconfigurable reflectarray.


### 6.1. Tunable Unit Cell

There have
been various attempts to achieve electronic reconfigurability of reflectarrays:
some of them made use of varactor diodes [6] in order to change the reflection
phase, others used tunable materials, such as Barium Strontium Titanate (BST)
[7]. With the advances in the field of MEM-switches, these have become
preferred to varactor diodes due to their superior RF properties [8, 9].The novel
approach, presented in this paper, makes use of a substrate which dielectric
properties can be tuned by applying a low bias voltage (<20 V) [10, 11]. Thus all patches will have the same geometrical size, while the effective
permittivity of the substrate under each patch will differ causing different electrical
dimensions of the patches. This results in different backscattered phases which
can be electronically tuned independently for each unit cell. One material that
provides this functionality is LC. Because of the anisotropy of the molecules
in combination with an orientational order, a macroscopically uniaxial
anisotropic permittivity is effective [12] as aforementioned.Using LCs as
tunable substrate introduces several constrains in the antenna design. As the
name already suggests, LCs are fluid and hence carrier substrates are required
to support the metallization and the ground plane. Additionally, the carrier
substrates have to form a cavity with a well-controlled thickness in which the
LC can be filled in later on. The cavity has to be properly sealed to avoid LC
leakage. On the ground plane and on the metallization layer a thin polyimide
film has to be spin coated to provide the initial alignment of the LC director.
Since the surface alignment mechanism is only functional for thin LC layers,
the cavity thickness should not be much larger than 100μm. This will seriously
limit the bandwidth of the microstrip structure, especially for lower
frequencies. Hence, the operating frequency of the reflectarray presented in
this work is situated in the E-band at 77 GHz.In Figure11 a schematic of the cross
section of a LC-tunable reflectarray unit cell is presented. The cell consists
of a patch printed on a carrier substrate, the ground plane printed on a
carrier as well, and the LC cavity between patch and ground. A thin polyimide
film (about 300 nm) is spin coated both on the ground plane and on the patches,
cured and finally mechanically rubbed, in order to provide the prealignment of
the LC molecules.Functioning principle of the LC-tunable
reflectarray unit cell with single microstrip patch.
(a)(b)(c)The director of the LC-molecules is
initially aligned parallel to the patch and ground, owing to the polyimide
layer (Figure11(a)). The applied bias voltage between patch and ground generates
the external electric field for reorientating the director n⇀.The RF field, given by the
microstrip patch fundamental mode is mainly confined in the LC volume and is essentially
perpendicular to the director. Thus, the RF field will perceive an effective
permittivityεr,eff=ε⊥. Applying an increasing bias
voltage, the director will begin to rotate as soon as the voltage exceeds a
certain threshold voltage Vth of a few volts (Figure 11(b)). When the bias voltage is
increased even further, the director of the LC molecules will tend to align
with the bias field lines, until the molecules are completely aligned parallel
to the bias E-field. In this state, the average direction of the main axes of
all molecules become parallel to the RF-field and the experienced effective
permittivity becomes εr,eff=εr,∥ (see Figure 11(c)).
The change in relative effective permittivity, Δεr,eff produces a change in the capacitance
per unit length of the microstrip patch. This leads to a shift in the resonance
frequency, ωr, and also to a shift of the phase
characteristic as depicted in Figure 12. Since the permittivity variation is
continuous, so is the phase tuning at a certain frequency.Functioning principle of a LC-tunable unit
cell.
(a)(b)


### 6.2. Tunable LC-Reflectarray at 77 GHz

The reflectarray designed for an operating frequency
of
77 GHz has been briefly presented in [13]. It consists of 16 times 16 unit
cells with an interelement spacing of 0.55λ. The size of a single unit
cell is 2.2 mm. From [14], it can be recognized that the single patch unit cell
with an LC cavity height of 50 μm has the best overall performance regarding
losses and tunable phase range. Hence, this unit cell topology is used to
realize the reflectarray.For the substrate carrying the microstrip patches a
glass carrier and for the substrate with the ground plane a metalized silicon
wafer is employed. The rigidity of these materials ensures a sufficient
precision for the 50μm cavity.Spherical spacers having a diameter of 50μm are mixed
together with glue, which is then used to bond the two substrates together. The
glue also acts as a seal for the liquid crystal cavity.Figure13 shows a photograph of the fully assembled
LC reflectarray with feed mounted for measurements. The feed is an open WR-10
waveguide, which is bended to radiate on the reflector.Figure 13
Fully assembled 77 GHz LC reflectarray with
feed.To simplify the bias control of this first
demonstrator, all patches on one row are connected altogether with a thin bias
line. Therefore, the same bias voltage will be applied to the entire row and
hence this reflectarray is only steerable in one plane. For this reason, there
will be no beam focusing on the nonsteerable plane, the H-plane.The cavity has been filled with the LC mixture BMW10
developed at TU Darmstadt for maximum optical anisotropy, but featuring also
acceptable microwave performance. Its characterization with the cavity
perturbation technique at
30 GHz yielded forεr,⊥=2.49 and εr,∥=3.18. The dielectric
losses are tan(δ)⊥=0.017 and tan(δ)∥=0.004.The power pattern measurements shown in Figure14 were
performed at 77.2 GHz, this is being the frequency where the maximum adjustable
phase range of the unit cells was recorded.Figure 14
Three
recorded E-plane patterns for three different voltage configurations, with the
main beam pointing at different angles:−10°,0°, and +25° (at 77.2 GHz).In order to illustrate the beam steering capability in
the E-plane of the reflectarray, three selected patterns are presented: the
main beam directed toward−10°,0°, and 25°, respectively. The main beam of the
reflectarray can be continuously scanned between −25° and +25° with a side lobe
level of 8 dB for the main beam steered to 0°. Nevertheless, it can be observed
that the pattern for the main beam directed to −10° is deteriorated in
comparison to the other two. This can be caused by the beam-focusing algorithm,
which evaluates only a very limited number of phase/amplitude distributions
from the totality of all possible combinations [10]. It is thus not guaranteed
that the obtained pattern is the best in terms of gain or side lobe level.


## 6.1. Tunable Unit Cell

There have
been various attempts to achieve electronic reconfigurability of reflectarrays:
some of them made use of varactor diodes [6] in order to change the reflection
phase, others used tunable materials, such as Barium Strontium Titanate (BST)
[7]. With the advances in the field of MEM-switches, these have become
preferred to varactor diodes due to their superior RF properties [8, 9].The novel
approach, presented in this paper, makes use of a substrate which dielectric
properties can be tuned by applying a low bias voltage (<20 V) [10, 11]. Thus all patches will have the same geometrical size, while the effective
permittivity of the substrate under each patch will differ causing different electrical
dimensions of the patches. This results in different backscattered phases which
can be electronically tuned independently for each unit cell. One material that
provides this functionality is LC. Because of the anisotropy of the molecules
in combination with an orientational order, a macroscopically uniaxial
anisotropic permittivity is effective [12] as aforementioned.Using LCs as
tunable substrate introduces several constrains in the antenna design. As the
name already suggests, LCs are fluid and hence carrier substrates are required
to support the metallization and the ground plane. Additionally, the carrier
substrates have to form a cavity with a well-controlled thickness in which the
LC can be filled in later on. The cavity has to be properly sealed to avoid LC
leakage. On the ground plane and on the metallization layer a thin polyimide
film has to be spin coated to provide the initial alignment of the LC director.
Since the surface alignment mechanism is only functional for thin LC layers,
the cavity thickness should not be much larger than 100μm. This will seriously
limit the bandwidth of the microstrip structure, especially for lower
frequencies. Hence, the operating frequency of the reflectarray presented in
this work is situated in the E-band at 77 GHz.In Figure11 a schematic of the cross
section of a LC-tunable reflectarray unit cell is presented. The cell consists
of a patch printed on a carrier substrate, the ground plane printed on a
carrier as well, and the LC cavity between patch and ground. A thin polyimide
film (about 300 nm) is spin coated both on the ground plane and on the patches,
cured and finally mechanically rubbed, in order to provide the prealignment of
the LC molecules.Functioning principle of the LC-tunable
reflectarray unit cell with single microstrip patch.
(a)(b)(c)The director of the LC-molecules is
initially aligned parallel to the patch and ground, owing to the polyimide
layer (Figure11(a)). The applied bias voltage between patch and ground generates
the external electric field for reorientating the director n⇀.The RF field, given by the
microstrip patch fundamental mode is mainly confined in the LC volume and is essentially
perpendicular to the director. Thus, the RF field will perceive an effective
permittivityεr,eff=ε⊥. Applying an increasing bias
voltage, the director will begin to rotate as soon as the voltage exceeds a
certain threshold voltage Vth of a few volts (Figure 11(b)). When the bias voltage is
increased even further, the director of the LC molecules will tend to align
with the bias field lines, until the molecules are completely aligned parallel
to the bias E-field. In this state, the average direction of the main axes of
all molecules become parallel to the RF-field and the experienced effective
permittivity becomes εr,eff=εr,∥ (see Figure 11(c)).
The change in relative effective permittivity, Δεr,eff produces a change in the capacitance
per unit length of the microstrip patch. This leads to a shift in the resonance
frequency, ωr, and also to a shift of the phase
characteristic as depicted in Figure 12. Since the permittivity variation is
continuous, so is the phase tuning at a certain frequency.Functioning principle of a LC-tunable unit
cell.
(a)(b)


## 6.2. Tunable LC-Reflectarray at 77 GHz

The reflectarray designed for an operating frequency
of
77 GHz has been briefly presented in [13]. It consists of 16 times 16 unit
cells with an interelement spacing of 0.55λ. The size of a single unit
cell is 2.2 mm. From [14], it can be recognized that the single patch unit cell
with an LC cavity height of 50 μm has the best overall performance regarding
losses and tunable phase range. Hence, this unit cell topology is used to
realize the reflectarray.For the substrate carrying the microstrip patches a
glass carrier and for the substrate with the ground plane a metalized silicon
wafer is employed. The rigidity of these materials ensures a sufficient
precision for the 50μm cavity.Spherical spacers having a diameter of 50μm are mixed
together with glue, which is then used to bond the two substrates together. The
glue also acts as a seal for the liquid crystal cavity.Figure13 shows a photograph of the fully assembled
LC reflectarray with feed mounted for measurements. The feed is an open WR-10
waveguide, which is bended to radiate on the reflector.Figure 13
Fully assembled 77 GHz LC reflectarray with
feed.To simplify the bias control of this first
demonstrator, all patches on one row are connected altogether with a thin bias
line. Therefore, the same bias voltage will be applied to the entire row and
hence this reflectarray is only steerable in one plane. For this reason, there
will be no beam focusing on the nonsteerable plane, the H-plane.The cavity has been filled with the LC mixture BMW10
developed at TU Darmstadt for maximum optical anisotropy, but featuring also
acceptable microwave performance. Its characterization with the cavity
perturbation technique at
30 GHz yielded forεr,⊥=2.49 and εr,∥=3.18. The dielectric
losses are tan(δ)⊥=0.017 and tan(δ)∥=0.004.The power pattern measurements shown in Figure14 were
performed at 77.2 GHz, this is being the frequency where the maximum adjustable
phase range of the unit cells was recorded.Figure 14
Three
recorded E-plane patterns for three different voltage configurations, with the
main beam pointing at different angles:−10°,0°, and +25° (at 77.2 GHz).In order to illustrate the beam steering capability in
the E-plane of the reflectarray, three selected patterns are presented: the
main beam directed toward−10°,0°, and 25°, respectively. The main beam of the
reflectarray can be continuously scanned between −25° and +25° with a side lobe
level of 8 dB for the main beam steered to 0°. Nevertheless, it can be observed
that the pattern for the main beam directed to −10° is deteriorated in
comparison to the other two. This can be caused by the beam-focusing algorithm,
which evaluates only a very limited number of phase/amplitude distributions
from the totality of all possible combinations [10]. It is thus not guaranteed
that the obtained pattern is the best in terms of gain or side lobe level.


## 7. Summary

In this contribution, recent results of
frequency agile components based on LC are presented. The first section of this
contribution deals with tunable phase shifters which are the key component of tunable-phased
arrays. Special attention has been paid to develop a technique for the
fabrication of an LC-compatible LTCC material system. The phase shifters
presented in this work reached a tunable phase shift of138° at 30 GHz with a
FoM of 16. It should be noted that these first measuring results can be
considerable improved by using an LC which is optimized for microwave
applications as shown in [1].In the second part of the paper, a
demonstrator of a tunable reflectarray antenna has been presented. With this
topology, it is possible to realize tunable high-gain antennas. The realized
demonstrator has been designed to operate at 77 GHz and is able to steer the
main beam continuously in between±25° by applying bias voltages below 15 V.
Its performance could be improved by employing LCs with better microwave
features as employed in [14] and by improving the configuration algorithm
calculating the bias voltages.As there are at least some LC mixtures available
which prove to be stable in the exposure of protons, tunable devices based on
LC seem to be suited to be used in space applications, especially as for this
concept no moving mechanical parts are needed.



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*Source: 876989-2009-03-30.xml*