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高阻抗表面的设计与测量
资料介绍
The design process of High Impedance Surface (HIS) is a challenge in realizing low-profile antenna. To carry out properly this process, a 3D-electromagnetic simulator is required. This paper shows an overview of the different numerical techniques which can be applied to simulate the behaviour of an HIS
using CST Microwave Studio (CST MWS). The considered HIS is composed of a metallic square patches array printed on the top of a metal backed substrate. To demonstrate the validity of the different solvers used, some measurements of the dedicated structure have been performed in a waveguide simulator.
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（完整内容请下载后查看）Design and Measurement of High Impedance
Surface
F. Linot∗†, R. Cousin‡, X. Begaud∗, M. Soiron†
Institut Telecom - Telecom ParisTech - LTCI - CNRS - UMR 5141
∗
46 Rue Barrault, 75634 Paris, France
,
‡
CST AG
Bad Nauheimer Str. 19, D - 64289 Darmstadt, Germany
†
THALES Airborne Systems
78852 Elancourt Cedex France
Abstract—The design process of High Impedance Surface
(HIS) is a challenge in realizing low-profile antenna. To carry out
properly this process, a 3D-electromagnetic simulator is required.
This paper shows an overview of the different numerical tech-
niques which can be applied to simulate the behaviour of an HIS
R
using CST Microwave Studio ꢀ (CST MWS). The considered
HIS is composed of a metallic square patches array printed on
the top of a metal backed substrate. To demonstrate the validity
of the different solvers used, some measurements of the dedicated
structure have been performed in a waveguide simulator.
I. INTRODUCTION
(a)
This research is in the framework of collaboration between
Telecom ParisTech and Thales Airborne Systems to design
low-profile antenna considering high impedance surface (HIS).
To develop tools to simulate HIS, a partnership with CST
R
AG ꢀ has been done. These surfaces can exhibit surface
wave band gaps where the propagation of electromagnetic
waves is prohibited [1]. High impedance surfaces can exhibit
frequency band where the propogation of electromagnetic
wave is prohibited. Moreover these structures can imitate
the interesting phase behaviour of a hypothetically perfect
magnetic conductor (PMC) at resonance: the high-impedance
surface reflects all of the power just like a perfect electric
conductor (PEC), but it reflects in-phase, rather than out-of-
phase, allowing the radiating element to be directly adjacent
to the surface. High impedance surface consists on a periodic
(b)
Fig. 1. (a) Part view of the infinite HIS analyzed, (b) View of the lattice
considered
metallic arrangement printed on a metal-backed substrate. To this paper the Finite Integration Technique (FIT) is used as
design HIS easily and quickly, several analytical models based a generalization of the FDTD approach. The FIT approach
on an equivalent transmission line model have been proposed which has been developed at CST is using the Perfect Bound-
[2]. However all the geometry’s dimensions must be smaller ary Approximation (PBA) as a better geometry discretization
than the wavelength in order to consider a quasi-static model without increasing the memory consumption. As the previous
[3], and a Computational Electromagnetic (CEM) simulation methods mentioned, the accuracy of the results depends on the
is required to demonstrate the validity of designing complex volume mesh computed. To demonstrate the validity of this
3D-HIS structures. Several ”full-wave” methods namely the computational code in the high impedance surfaces domain,
Finite Difference Time Domain method (FDTD) [4], and a HIS consisting of a metallic square patches array printed
the Finite Element Method (FEM) [5], are widely used to on the top of a metal backed substrate is studied. The goal
plot the reflection coefficient of the artificial structure. These of this paper is to describe several approaches to validate
numerical methods consist on a volume discretization to solve the reflection coefficient of an HIS using CST MICROWAVE
R
the Maxwell’s equations using different mesh techniques. In STUDIO ꢀ (CST MWS) in order to predict the behaviour of
such devices. In this paper, only the phase relection property hexahedral mesh discretization. This technique reveals to be a
is considered but all these approaches can be used to predict highly efficient method as it combines easy-to-use cartesian
the absorption coefficient [6]. All the results are compared and grids without any approximation of the structure geometry
validated to measurement done in a waveguide simulator [7]. [8]. The PBA can improve the geometry description without
increasing the memory. As illustrated in Fig. 2, the hexahedral
mesh grid is applied to the structure with a denser mesh near
II. OVERVIEW OF THE DIFFERENT APPROACHES
The reflection property of high impedance surfaces is gen-
erally described by the reflection coefficient which is the ratio
of the reflected field on the incident field at the top of the
structure.
the edges of the PEC sheet for a better ElectroMagnetic (EM)
field discretization. In CST MWS, several methods can be used
to simulate the reflection phase in normal incidence. Firstly
the analytical expression (1) can be computed in a Visual
Basic language for Application (VBA) which requires three
simulations in that case: one for extracting the incident field
components without any parasitic reflection in the calculation
domain, the second one to take into account the modified E-
field components reflected at an equivalent PEC reference and
the last one to deduce the phase shift created by the real case.
An Electric Probe is required to record the time signals for all
the three simulations. This method can be used to simulate
the reflection phase diagram of finite structure. However,
this method requires few minutes to simulate the reflection
coefficient of the real structure [9]. Another method is used,
consisting in defining the appropriate boundary conditions to
introduce a crossed-E and H-field such that a TEM wave is
applied similar to a plane wave considering one single element
as infinitely periodic in the x and y directions. The reflection
phase diagram is then computed for normal incidence of the
ElectroMagnetic (EM) field propagation. The phase reference
Zs − Z0
Γ =
(1)
Zs + Z0
Where Zs and Z0 are respectively the surface impedance
of the structure and the free space impedance. For a perfect
electric ground plane, the reflected E-field and the incident E-
field have opposite signs, resulting in a coefficient reflection
equal to -1. In the case of a hypothetically PMC surface,
the reflection phase is null corresponding to a coefficient
reflection equal to +1. However, HIS reveals that they can
realize the PMC condition in a certain frequency band. At very
low frequency, the HIS behaves like a PEC. At the resonant
frequency, the impedance of the structure tends to infinity,
resulting in a zero reflection phase. To calculate the reflection
phase of an high impedance surface, a plane wave illuminating
the structure where a PEC surface is set as a reference leads
to a normalization of the reflected phase of the HIS (ΦHIS
from the PEC surface (ΦP EC):
)
Φ = ΦHIS − ΦP EC + π
(2)
A surface impedance is comprised of metallic square
patches printed on the top of a metal backed dielectric sub-
strate without vias (see Fig.1a). According to Fig. 1a, the
parameters of the high impedance surface analyzed are: P =
4mm, g = 0.4mm, h = 1mm and ꢀr = 10.2. Where P is the
periodicity of the patch array, g is the gap between adjacent
patches, h the height of the dielectric substrate and ꢀr the
relative permittivity of the host medium. As the HIS is a
periodic structure, only one lattice is needed to discribe the
behaviour of the whole structure. With the periodic boundary
conditions used, the structure can be modelled as an infinite
surface (see Fig. 1b).
(a)
A. The Time Domain
All time domain ”Full-Wave” methods such as FIT, FDTD
and TLM techniques use a conformal cartesian grid. Whereas
the FDTD approach uses the hexahedral mesh grid, this dis-
cretization has some limitations when complex 3D-structures
have to be simulated at higher frequency range for which the
level of accuracy has to be enhanced. For a better geometry
discretization, mainly thin structures, rounded solids and shell
objects, the PBA was implemented in connection with the FIT
to reduce the global number of mesh cells of an equivalent
FDTD simulation for a considerable enhanced level of ac-
curacy. For instance, that means that a mesh cell can take
(b)
Fig. 2. Hexahedral discretization of the lattice: (a) Front view, (b) Perspective
into account two different material properties in the global view
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