- •Contents
- •Preface
- •Chapter 1 Introduction (K. Fujimoto)
- •Chapter 2 Small antennas (K. Fujimoto)
- •Chapter 3 Properties of small antennas (K. Fujimoto and Y. Kim)
- •Chapter 4 Fundamental limitation of small antennas (K. Fujimoto)
- •Chapter 5 Subjects related with small antennas (K. Fujimoto)
- •Chapter 6 Principles and techniques for making antennas small (H. Morishita and K. Fujimoto)
- •Chapter 7 Design and practice of small antennas I (K. Fujimoto)
- •Chapter 8 Design and practice of small antennas II (K. Fujimoto)
- •Chapter 9 Evaluation of small antenna performance (H. Morishita)
- •Chapter 10 Electromagnetic simulation (H. Morishita and Y. Kim)
- •Chapter 11 Glossary (K. Fujimoto and N. T. Hung)
- •Acknowledgements
- •1 Introduction
- •2 Small antennas
- •3 Properties of small antennas
- •3.1 Performance of small antennas
- •3.1.1 Input impedance
- •3.1.4 Gain
- •3.2 Importance of impedance matching in small antennas
- •3.3 Problems of environmental effect in small antennas
- •4 Fundamental limitations of small antennas
- •4.1 Fundamental limitations
- •4.2 Brief review of some typical work on small antennas
- •5 Subjects related with small antennas
- •5.1 Major subjects and topics
- •5.1.1 Investigation of fundamentals of small antennas
- •5.1.2 Realization of small antennas
- •5.2 Practical design problems
- •5.3 General topics
- •6 Principles and techniques for making antennas small
- •6.1 Principles for making antennas small
- •6.2 Techniques and methods for producing ESA
- •6.2.1 Lowering the antenna resonance frequency
- •6.2.1.1 SW structure
- •6.2.1.1.1 Periodic structures
- •6.2.1.1.3 Material loading on an antenna structure
- •6.2.2 Full use of volume/space circumscribing antenna
- •6.2.3 Arrangement of current distributions uniformly
- •6.2.4 Increase of radiation modes
- •6.2.4.2 Use of conjugate structure
- •6.2.4.3 Compose with different types of antennas
- •6.2.5 Applications of metamaterials to make antennas small
- •6.2.5.1 Application of SNG to small antennas
- •6.2.5.1.1 Matching in space
- •6.2.5.1.2 Matching at the load terminals
- •6.2.5.2 DNG applications
- •6.3 Techniques and methods to produce FSA
- •6.3.1 FSA composed by integration of components
- •6.3.2 FSA composed by integration of functions
- •6.3.3 FSA of composite structure
- •6.4 Techniques and methods for producing PCSA
- •6.4.2 PCSA employing a high impedance surface
- •6.5 Techniques and methods for making PSA
- •6.5.2 Simple PSA
- •6.6 Optimization techniques
- •6.6.1 Genetic algorithm
- •6.6.2 Particle swarm optimization
- •6.6.3 Topology optimization
- •6.6.4 Volumetric material optimization
- •6.6.5 Practice of optimization
- •6.6.5.1 Outline of particle swarm optimization
- •6.6.5.2 PSO application method and result
- •7 Design and practice of small antennas I
- •7.1 Design and practice
- •7.2 Design and practice of ESA
- •7.2.1 Lowering the resonance frequency
- •7.2.1.1 Use of slow wave structure
- •7.2.1.1.1 Periodic structure
- •7.2.1.1.1.1 Meander line antennas (MLA)
- •7.2.1.1.1.1.1 Dipole-type meander line antenna
- •7.2.1.1.1.1.2 Monopole-type meander line antenna
- •7.2.1.1.1.1.3 Folded-type meander line antenna
- •7.2.1.1.1.1.4 Meander line antenna mounted on a rectangular conducting box
- •7.2.1.1.1.1.5 Small meander line antennas of less than 0.1 wavelength [13]
- •7.2.1.1.1.1.6 MLAs of length L = 0.05 λ [13, 14]
- •7.2.1.1.1.2 Zigzag antennas
- •7.2.1.1.1.3 Normal mode helical antennas (NMHA)
- •7.2.1.1.1.4 Discussions on small NMHA and meander line antennas pertaining to the antenna performances
- •7.2.1.2 Extension of current path
- •7.2.2 Full use of volume/space
- •7.2.2.1.1 Meander line
- •7.2.2.1.4 Spiral antennas
- •7.2.2.1.4.1 Equiangular spiral antenna
- •7.2.2.1.4.2 Archimedean spiral antenna
- •7.2.2.1.4.3.2 Gain
- •7.2.2.1.4.4 Radiation patterns
- •7.2.2.1.4.5 Unidirectional pattern
- •7.2.2.1.4.6 Miniaturization of spiral antenna
- •7.2.2.1.4.6.1 Slot spiral antenna
- •7.2.2.1.4.6.2 Spiral antenna loaded with capacitance
- •7.2.2.1.4.6.3 Archimedean spiral antennas
- •7.2.2.1.4.6.4 Spiral antenna loaded with inductance
- •7.2.2.2 Three-dimensional (3D) structure
- •7.2.2.2.1 Koch trees
- •7.2.2.2.2 3D spiral antenna
- •7.2.2.2.3 Spherical helix
- •7.2.2.2.3.1 Folded semi-spherical monopole antennas
- •7.2.2.2.3.2 Spherical dipole antenna
- •7.2.2.2.3.3 Spherical wire antenna
- •7.2.2.2.3.4 Spherical magnetic (TE mode) dipoles
- •7.2.2.2.3.5 Hemispherical helical antenna
- •7.2.3 Uniform current distribution
- •7.2.3.1 Loading techniques
- •7.2.3.1.1 Monopole with top loading
- •7.2.3.1.2 Cross-T-wire top-loaded monopole with four open sleeves
- •7.2.3.1.3 Slot loaded with spiral
- •7.2.4 Increase of excitation mode
- •7.2.4.1.1 L-shaped quasi-self-complementary antenna
- •7.2.4.1.2 H-shaped quasi-self-complementary antenna
- •7.2.4.1.3 A half-circular disk quasi-self-complementary antenna
- •7.2.4.1.4 Sinuous spiral antenna
- •7.2.4.2 Conjugate structure
- •7.2.4.2.1 Electrically small complementary paired antenna
- •7.2.4.2.2 A combined electric-magnetic type antenna
- •7.2.4.3 Composite structure
- •7.2.4.3.1 Slot-monopole hybrid antenna
- •7.2.4.3.2 Spiral-slots loaded with inductive element
- •7.2.5 Applications of metamaterials
- •7.2.5.1 Applications of SNG (Single Negative) materials
- •7.2.5.1.1.2 Elliptical patch antenna
- •7.2.5.1.1.3 Small loop loaded with CLL
- •7.2.5.1.2 Epsilon-Negative Metamaterials (ENG MM)
- •7.2.5.2 Applications of DNG (Double Negative Materials)
- •7.2.5.2.1 Leaky wave antenna [116]
- •7.2.5.2.3 NRI (Negative Refractive Index) TL MM antennas
- •7.2.6 Active circuit applications to impedance matching
- •7.2.6.1 Antenna matching in transmitter/receiver
- •7.2.6.2 Monopole antenna
- •7.2.6.3 Loop and planar antenna
- •7.2.6.4 Microstrip antenna
- •8 Design and practice of small antennas II
- •8.1 FSA (Functionally Small Antennas)
- •8.1.1 Introduction
- •8.1.2 Integration technique
- •8.1.2.1 Enhancement/improvement of antenna performances
- •8.1.2.1.1 Bandwidth enhancement and multiband operation
- •8.1.2.1.1.1.1 E-shaped microstrip antenna
- •8.1.2.1.1.1.2 -shaped microstrip antenna
- •8.1.2.1.1.1.3 H-shaped microstrip antenna
- •8.1.2.1.1.1.4 S-shaped-slot patch antenna
- •8.1.2.1.1.2.1 Microstrip slot antennas
- •8.1.2.1.1.2.2.2 Rectangular patch with square slot
- •8.1.2.1.2.1.1 A printed λ/8 PIFA operating at penta-band
- •8.1.2.1.2.1.2 Bent-monopole penta-band antenna
- •8.1.2.1.2.1.3 Loop antenna with a U-shaped tuning element for hepta-band operation
- •8.1.2.1.2.1.4 Planar printed strip monopole for eight-band operation
- •8.1.2.1.2.2.2 Folded loop antenna
- •8.1.2.1.2.3.2 Monopole UWB antennas
- •8.1.2.1.2.3.2.1 Binomial-curved patch antenna
- •8.1.2.1.2.3.2.2 Spline-shaped antenna
- •8.1.2.1.2.3.3 UWB antennas with slot/slit embedded on the patch surface
- •8.1.2.1.2.3.3.1 A beveled square monopole patch with U-slot
- •8.1.2.1.2.3.3.2 Circular/Elliptical slot UWB antennas
- •8.1.2.1.2.3.3.3 A rectangular monopole patch with a notch and a strip
- •8.1.2.1.2.3.4.1 Pentagon-shape microstrip slot antenna
- •8.1.2.1.2.3.4.2 Sectorial loop antenna (SLA)
- •8.1.3 Integration of functions into antenna
- •8.2 Design and practice of PCSA (Physically Constrained Small Antennas)
- •8.2.2 Application of HIS (High Impedance Surface)
- •8.2.3 Applications of EBG (Electromagnetic Band Gap)
- •8.2.3.1 Miniaturization
- •8.2.3.2 Enhancement of gain
- •8.2.3.3 Enhancement of bandwidth
- •8.2.3.4 Reduction of mutual coupling
- •8.2.4 Application of DGS (Defected Ground Surface)
- •8.2.4.2 Multiband circular disk monopole patch antenna
- •8.2.5 Application of DBE (Degenerated Band Edge) structure
- •8.3 Design and practice of PSA (Physically Small Antennas)
- •8.3.1 Small antennas for radio watch/clock systems
- •8.3.2 Small antennas for RFID
- •8.3.2.1 Dipole and monopole types
- •8.3.2.3 Slot type antennas
- •8.3.2.4 Loop antenna
- •Appendix I
- •Appendix II
- •References
- •9 Evaluation of small antenna performance
- •9.1 General
- •9.2 Practical method of measurement
- •9.2.1 Measurement by using a coaxial cable
- •9.2.2 Method of measurement by using small oscillator
- •9.2.3 Method of measurement by using optical system
- •9.3 Practice of measurement
- •9.3.1 Input impedance and bandwidth
- •9.3.2 Radiation patterns and gain
- •10 Electromagnetic simulation
- •10.1 Concept of electromagnetic simulation
- •10.2 Typical electromagnetic simulators for small antennas
- •10.3 Example (balanced antennas for mobile handsets)
- •10.3.2 Antenna structure
- •10.3.3 Analytical results
- •10.3.4 Simulation for characteristics of a folded loop antenna in the vicinity of human head and hand
- •10.3.4.1 Structure of human head and hand
- •10.3.4.2 Analytical results
- •11 Glossary
- •11.1 Catalog of small antennas
- •11.2 List of small antennas
- •Index
400 |
Electromagnetic simulation |
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0 dB -2 dB -4 dB -6 dB -8 dB -10 dB -12 dB -14 dB -16 dB -18 dB -20 dB -22 dB -24 dB -26 dB -28 dB -30 dB -32 dB -34 dB -36 dB -38 dB -40 dB
(a) Unbalanced-fed
(b) Balanced-fed
Figure 10.7 Measured current distribution on a ground plane: (a) unbalanced feed and
(b) balanced feed.
and FIM simulators, respectively. In all cases, the current on the GP is reduced by the balanced feeding method, which is the same result as the MoM simulator.
Figure 10.9 shows the measured and simulated return-loss characteristics. The simulated result of each simulator is similar to the measured results. For the results obtained by the MoM simulator, the frequency at the lowest return loss is low in the case of the number of cells per wavelength of 10, compared to other cases. For the results obtained by the FDTD simulator, it is apparent that the calculated results show wider bandwidth than the measured results. For the results of the FEM and FIM simulators, the frequency at the lowest return loss becomes higher as the number of the total cells increases, but remains lower than the measured one.
Figure 10.10 shows the simulated return-loss characteristics of unbalanced and balanced-fed models by using the optimized conditions in all the simulators as well as the measured results. All the simulated results agree very well with the measured results in both models.
Figure 10.11 shows the simulated and measured radiation patterns. All the simulated results agree very well with the measured results, and the patterns of the unbalancedfed model are almost the same as those of the balanced-fed model. This is because a folded loop antenna has the self-balance effect and the radiation from the GP is almost suppressed. The difference in the maximum gain is below 1 dB as shown in Table 10.2.
10.3.4Simulation for characteristics of a folded loop antenna in the vicinity of human head and hand
In this section, the antenna performances in the vicinity of the human head and hand will be investigated by means of simulation, in which the human head and hand are simulated in consideration of the practical situation of an operator using a handset, and equivalent phantom models are used for the verification.
10.3 Example (balanced antennas for mobile handsets) |
401 |
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0 dB −2 dB −4 dB −6 dB −8 dB −10 dB −12 dB −14 dB −16 dB −18 dB −20 dB −22 dB −24 dB −26 dB −28 dB −30 dB −32 dB −34 dB −36 dB −38 dB −40 dB
Jsurf[A/m] 1,0000e+001
9,0452e+000 8, 4422e+000 7, 8392e+000 7, 2362e+000 6, 6332e+000 6, 0302e+000 5, 4271e+000 4, 8241e+000 4, 2211e+000 3, 6181e+000 3, 0151e+000 2, 4121e+000 1, 8090e+000 1, 2060e+000 6, 0302e+000 0, 0000e+000
A/n
10
9.69
9.06
8.44
7.81
7.19
6.56
5.94
5.31
4.69
4.06
3.44
2.81
2.19
1.56
0.938
0.313
0
(a) FDTD Method
(b) Finite Element Method
(c) Finite Integration Method
Figure 10.8 Current distribution on a ground plane simulated by each electromagnetic simulator (unbalanced-fed model): (a) FDTD Method, (b) Finite Element Method, and (c) Finite Integration Method.
10.3.4.1Structure of human head and hand
Figure 10.12 illustrates a folded loop antenna in the vicinity of the human body, where
(a)is the spherical head model, and (b) are the spherical head and hand models. The spherical head model has dielectric properties of relative permittivity of 43.37 and conductivity of 1.204 S/m at 1.9 GHz. The diameter of the head is 200 mm and the distance between the human head model and the antenna is 10 mm. The human hand model has dielectric properties of relative permittivity of 54 and conductivity of 1.45 S/m at 1.9 GHz. There is 4 mm spacing between the inner surface of hand model
402 |
Electromagnetic simulation |
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Return loss (dB)
Return loss (dB)
0
−5
−10
−15 −20
−25
−30 1.6
0
−5
−10
−15 −20
−25
−30 1.6
Mea. 10 cells 15 cells 20 cells 30 cells
1.7 1.8 1.9 2.0 2.1 Frequency (GHz)
(a) Method of Moments
Mea. 27563 cells 38873 cells 55411 cells
1.7 1.8 1.9 2.0 2.1 Frequency (GHz)
(c) Finite Element Method
Return loss (dB)
Return loss (dB)
0
−5
−10
−15 −20
−25
−30 1.6
0
−5
−10
−15 −20
−25
−30 1.6
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Mea. |
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0.1-4 mm |
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0.1-2 mm |
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0.1-1 mm |
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1.7 |
1.8 |
1.9 |
2.0 |
2.1 |
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Frequency (GHz) |
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(b) FDTD Method |
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Mea. 10 cells 20 cells 30 cells 40 cells
1.7 1.8 1.9 2.0 2.1 Frequency (GHz)
(d) Finite Integration Method
Figure 10.9 Return-loss characteristics (unbalanced-fed model): (a) Method of Moments,
(b) FDTD Method (c) Finite Element Method, and (c) Finite Integration Method.
Return loss (dB)
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−10 |
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−15 |
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−20 |
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Mea. |
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MoM |
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−25 |
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FDTD |
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FEM |
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−30 |
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FIM |
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1.6 |
1.7 |
1.8 |
1.9 |
2.0 |
2.1 |
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Frequency (GHz)
(a) Unbalanced-fed
Return loss (dB)
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−10 |
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Mea. |
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MoM |
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−25 |
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FDTD |
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FEM |
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−30 |
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FIM |
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1.6 |
1.7 |
1.8 |
1.9 |
2.0 |
2.1 |
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Frequency (GHz)
(b) Balanced-fed
Figure 10.10 Return-loss characteristics: (a) unbalanced feed and (b) balanced feed.
10.3 Example (balanced antennas for mobile handsets) |
403 |
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30°
60°
90°
120°
150°
30°
60°
90°
120°
150°
120°
150°
180°
210°
240°
0° z
5
0
−5
−10 −15
20
−15 −10
−5
0
5
180°
0° z
5
0
−5
−10 −15
20
−15 −10
−5
0
5
180°
90° y
5
0
−5
−10 −15
20
−15 −10
−5
0
5
270°
Eθ (Mea.) |
Eθ (FDTD) |
Eϕ (Mea.) |
Eϕ (FDTD) |
Eθ (MoM) |
Eθ (FEM) |
Eϕ (MoM) |
Eϕ (FEM) |
30° |
30° |
60° |
60° |
x |
90° |
90° |
|
120° |
120° |
150° |
150° |
30° |
30° |
60° |
60° |
y |
90° |
90° |
|
120° |
120° |
150° |
150° |
60° |
120° |
30° |
150° |
x |
180° |
0° |
330° 210°
300° |
240° |
Eθ (FIM) Eϕ (FIM)
0° z
5
0
−5
−10 −15
20
−15 −10
−5 0
5
180°
0° z
5
0
−5
−10 −15
20 −15 −10
−5
0
5
180°
90° y
5
0
−5
−10 −15
20
−15 −10
−5
0
5
270°
30°
60°
x
90°
120°
150°
30°
60°
y
90°
120°
150°
60°
30°
x
0°
330°
300°
(a) Unbalanced-fed |
(b) Balanced-fed |
Figure 10.11 Radiation patterns in free space: (a) unbalanced feed and (b) balanced feed.
Table 10.2 Gain of a folded loop antenna (f0 = 1860 MHz)
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Gain [dBi] |
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Method of Moments |
1.43 |
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FDTD Method |
1.36 |
Unbalanced-fed |
Finite Element Method |
1.37 |
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Finite Integration Method |
2.2 |
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Measured gain |
1.02 |
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Method of Moments |
1.34 |
|
FDTD Method |
1.76 |
Balanced-fed |
Finite Element Method |
2.05 |
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Finite Integration Method |
2.2 |
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Measured gain |
1.11 |
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z
x
y
Head model (Sphere)
Feed point
Loop element
D
Ground plane
h
(a)
z
x
y
Head model (Sphere)
D
l |
Hand model |
(b)
Figure 10.12 Antenna in the vicinity of a human model: (a) antenna in the vicinity of a spherical head model and (b) antenna in the vicinity of a spherical head model and hand model.