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MODERN ANTENNA
HANDBOOK
by CONSTANTINE A.BALANIS
ch. 4.1 – 4.3.1.5
Min Byeong Hyeok
Hanyang University
2/31
Contents
• 4.1 INTRODUCTION
• 4.2 TECHNICAL BACKGROUND
- 4.2.1 Features of the Microstrip
Antenna
- 4.2.2 Advantage and Disadvantage
Trade-offs
- 4.2.3 Material Consideration
• 4.3 ANALYSIS AND DESIGN
- 4.3.1 Analysis Techniques
- 4.3.1.1 Transmission-Line Circuit
Model
- 4.3.1.2 Multimode Cavity Model
- 4.3.1.3 Moment Method
- 4.3.1.4 Finite-Difference Time-Domain
(FDTD) Method
- 4.3.1.5 Finite-Element Method (FEM)
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4.1 INTRODUCTION
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• Properties of the microstrip antenna
- low profile / light weight / compact and conformable to mounting
structure / easy fabrication and integratable with solid-state devices.
• The purpose of this chapter
- microstrip antenna’s technical features
- its advantages and disadvantages
- substrate material considerations
- excitation techniques
- polarization behaviors
- bandwidth characteristics
- miniaturization techniques
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4.2 TECHNICAL BACKGROUND
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4.2.1 Features of the Microstrip Antenna
• The metallic patch
- is made of thin copper foil or is copper-foil plated with a corrosion resistive
metal, such as gold, tin, or nickel.
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4.2 TECHNICAL BACKGROUND
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4.2.1 Features of the Microstrip Antenna
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4.2 TECHNICAL BACKGROUND
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4.2.2 Advantage and Disadvantage Trade-offs
• Advantages of microstrip antennas
- The extremely low profile makes it lightweight and it occupies very little
volume
- conformally mounted onto a curved surface
- aesthetically appealing and aerodynamically sound
- when produced in large quantities, can be fabricated with a simple etching
process, which can lead to greatly reduced fabrication cost
- low antenna RCS when conformally mounted on aircraft or missiles
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4.2 TECHNICAL BACKGROUND
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4.2.2 Advantage and Disadvantage Trade-offs
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4.2 TECHNICAL BACKGROUND
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4.2.3 Material Consideration
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4.2 TECHNICAL BACKGROUND
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4.2.3 Material Consideration
• Selection of appropriate material based on
- desired patch size, bandwidth, insertion loss, thermal stability, cost, etc
• For space application, its substrate material must survive three major effects
related to space environment : radiation exposure, material outgassing, and
temperature change.
- Cosmic radiations such as beta, gamma, and X-ray can damage materials
after the prolonged exposure typical of a long space mission
- Outgassing will cause a material to lose its mass in the form of gases or
volatile condensable matter when subject to a vacuum
- The effect of temperature in space on electrical and physical properties of
the substrate material must be taken into consideration when designing
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
• The main reason for developing an analytic model for the microstrip antenna
is to provide a means of designing the antenna without costly and tedious
experimental iteration.
• Also, it may allow the designer to discover the physical mechanisms of how
the microstrip antenna operates.
• With an analysis technique, the engineer should be able to predict the antenna
performance qualities, such as the input impedance, resonant frequency,
bandwidth, radiation patterns, and efficiency.
• The most popular ones can be separated into five groups
: transmission-line circuit model, multi-mode cavity model, moment method,
finite-difference time-domain(FDTD) method, and finite-element method
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.1 Transmission-Line Circuit Model
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.1 Transmission-Line Circuit Model
• Can be represented by and equivalent circuit network
• This transmission-line model is simple, intuitively appealing, and
computationally fast
• But, suffers from limited accuracy
- lacks the radiation from the non-radiating edges of the patch, and it has no
mutual coupling between the two radiating slots.
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
• Any microstrip radiator can be thought of as an open cavity bounded by the
patch and its ground plane
• The open edges can also be represented by radiating magnetic walls
(4.1)
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
• These figures indicate that, along the central line orthogonal to the resonant
direction (x-direction), it is a null field region underneath the patch
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
• The radiating fringing fields are shown in below Figure
• The left- and right-edge fringing fields do not contribute much to far fields
due to their oscillatory behavior and, hence, cancel each other in the far field
• The top- and bottom-edge fringing fields are the primary contributors to the
far-field radiation of a patch
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
• The top- and bottom-edge fringing
fields contribute to the co
polarization radiation in both the E
and H-planes, while the left- and
right-edge fringing fields yield the
cross polarization radiation only in
the H-plane pattern
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.2 Multimode Cavity Model
• By knowing the total fields at the edges of the patch from all modes, the
equivalent edge magnetic currents can be determined and integrated to find
the total far-field radiation patterns
• By knowing the total radiated power and the input power, one can also
determine the input impedance
• However, because it assumes the field has no z-variation, its solution is not
very accurate
• Also, the calculation of mutual coupling between patches in an array
environment is very tedious and inaccurate
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.3 Moment Method
• The radiated fields of a microstrip antenna can be determined by integrating
all the electrical currents on its metallic surfaces via the integral equation
approach whose solution is obtained by the so-called moment method.
in the dielectric (region Ⅰ) (4.2)
in free space (region Ⅱ) (4.3)
then the vector potential may be given as
(4.4)
where is the dyadic Green’s function for regions I and II.
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.3 Moment Method
• The electric field E everywhere is given by
(4.5)
• Using the proper basis and testing functions for the unknown current, the
integral equation is then discretized and reduced to a matrix equation:
(4.6)
where the impedance matrix element has the form
(4.7)
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.3 Moment Method
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4.3.1 Analysis Techniques
4.3.1.4 Finite-Difference Time-Domain (FDTD) Method
• Can solve more complex problems with 3D interfaces and connections
• Suffer from laborious computation time
• Not suitable for solving large microstrip array problems
• Uses Yee’s algorithm to discretize Maxwell’s equation in 3D space and in time
• The volume space → discretized into many cubic cells
• E- and H-fields are then solved through Maxwell Equation with given
boundary conditions from cell to adjacent cells.
(4.8)
(4.9)
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4.3.1 Analysis Techniques
* The YEE Algorithm
In 1966, Kane Yee originated a set of finite-difference equations for the
time-dependent Maxwell’s curl equation system for the lossless materials
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.4 Finite-Difference Time-Domain (FDTD) Method
• With time and space discretized, the E- and H-fields are interlaced within the
spatial 3D grid. For example, Eq. (4.9) can be discretized for the x-directed E-
field :
(4.9)
• One significant advantage of the FDTD method is that, by discretizing time,
one is able to see on a computer screen how the field is actually traveling and
radiating in time sequence in a complicated antenna/circuit configuration.
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.5 Finite-Element Method (FEM)
• First, one should define the electromagnetic boundary-value problem by an
appropriate partial differential equation (PDE)
• Second, one obtains a variational formulation for the PDE in terms of an
energy-related functional or weighted residual expressions
• Third, one subdivides the field regions into discrete subregions (finite
elements), such as triangles and quadrilaterals
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.5 Finite-Element Method (FEM)
• Fourth, one chooses a trial or approximate solution (polynomial) defined in
terms of nodal values (boundary points between elements) of the solution yet
to be determined for each element
• Fifth, one minimizes the functional (set function derivative to zero) with
respect to the nodal value potentials
• Finally, the resulting set of algebraic equations is solved and the required
field problem solution is obtained
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4.3 ANALYSIS AND DESIGN
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4.3.1 Analysis Techniques
4.3.1.5 Finite-Element Method (FEM)
FDTD FEM
Time Domain Solution Frequency Domain Solution
From cell to cell Each entire element
Cell size must be small Geometry or field variation
Less computing time with
more cells
Spend more time but with
fewer elements
More versatile and flexible
Stable, accurate
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• Vehicle Antenna
- 내장 안테나
: 차량의 윈도우 열선에 안테나 기능이 내장되어 AM 혹은 FM 등의 방송
신호를 수신할 수 있는 글래스 안테나
- 외장 안테나
: λ/4의 수직도선을 동축 케이블에 접속하고 차체를 접지로 사용하는 휩 안테나
길이가 신장되는 텔레스코픽 안테나
막대형의 폴 안테나
- DMB 등의 방송 신호를 수신하기 위해 외부에 별도로 설치하는 샤크 안테나
HOMEWORK
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* HOMEWORK
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• Vehicle Antenna
• 샤크 안테나의 내부
- 케이스, 베이스, 인쇄회로기판, 칩 안테나,
헬리컬 안테나
- 케이스는 하부가 개방된 상어 지느러미 형상
- 내부가 비어 있어 인쇄회로기판, 칩 안테나 및
헬리컬 안테나를 수용
- 칩 안테나 : GPS나 CDMA 신호를 수신
- 헬리컬 안테나 : DMB 신호를 수신
- 칩 안테나와 헬리컬 안테나는 각각
인쇄회로기판에 전기적으로 연결
- 인쇄회로기판에는 도전성 패턴이 형성되어 있어
각 안테나에 수신한 신호를 연결된
동축케이블로 전달
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* HOMEWORK
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• Vehicle Antenna
미래 자동차 안테나 기술
- 미래에는 차량에 적용된 인공위성을 기반으로
운행중인 차들끼리 데이터를 주고 받아,
병목현상과 같은 교통정체를 완화하는데 큰
도움을 줄 것
- 소프트웨어와 액상 크리스탈 기술로 평평한
형태의 인공위성을 만들어내어 차량 지붕에
탑재하는 형식의 안테나가 개발될 것으로 예상됨
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Thank you for your attention