MODERN ANTENNA HANDBOOK - Hanyang

Hanyang University

1/31 Antennas & RF Devices Lab.

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


• 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


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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4.2.1 Features of the Microstrip Antenna

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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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4.2.2 Advantage and Disadvantage Trade-offs

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4.2.3 Material Consideration

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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


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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4.3.1.1 Transmission-Line Circuit Model

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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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4.3.1.2 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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• 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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• 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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• 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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• 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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4.3.1.3 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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• 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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4.3.1.4 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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* 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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4.3.1.4 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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4.3.1.5 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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• 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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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


• 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


• 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


Thank you for your attention

MODERN ANTENNA HANDBOOK - Hanyang

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