
- •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

7.2 Design and practice of ESA |
203 |
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S11 (dB)
0 |
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−10 |
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−20 |
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−30 |
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−40 |
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Measurement DEA |
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4 |
5 |
6 |
7 |
8 |
9 |
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Simulation DEA |
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−50 |
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Measurement SEA 2 |
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860 |
880 |
900 |
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800 |
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820 |
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840 |
Frequency (MHz)
Figure 7.180 Return loss of DEA and SEA2 [87].
7.2.4Increase of excitation mode
By increasing the number of excitation modes (for instance, addition of a TM mode to a TE mode) enhancement or improvement of antenna performances such as gain, efficiency, bandwidth, and radiation pattern, can be expected. Composing an antenna with both TE and TM modes is one of the simplest ways. Examples are combination of a dipole with a loop, and a monopole with that of a dual slot that constitutes a selfcomplementary structure. Other types are a combination of an inductive element with a capacitive element in an antenna system that makes a conjugate structure. With the conjugate structure, the self-resonance condition can easily be achieved, even though the antenna has very small dimensions. A combination of an electric source with a magnetic source will bring out a conjugate structure as well as a complementary structure. A composite antenna system constituted with different types of antennas having different excitation modes is also used to create a conjugate antenna structure.
These means facilitate enhancement of the bandwidth, addition of functions such as multiband and multiple polarization, and so forth, in small-antenna design.
7.2.4.1Self-complementary structure
The self-complementary structure can be implemented by combining two antennas, having complementary properties of each other. There are two types; one type has rotationally symmetric structure while another type has axially symmetric structure. In a planar structure, for example, a rotationally symmetric type is constituted from one arbitrary generating structure by rotating it 180 degrees with respect to the feed point. An example was shown previously in Figure 6.35. In contrast, an axially symmetric type is fabricated by combining an arbitrary structure on a half-infinite space with a structure complementary to it on the other half-infinite space, with axial symmetry to each other (Figure 6.35). In a practical fabrication, a half structure divided by the axis of symmetry is formed on a half-infinite PEC (perfect electric conductor) plate, while another half is formed with the same structure, but as spaces on another half-infinite PEC plate. Figure 6.34 illustrated this example, showing a monopole combined with a complementary slot on the ground plane.

204 |
Design and practice of small antennas I |
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l
w
w
h
h
w
l
H
L
Figure 7.181 L-shaped self-complementary antenna [from 87].
The self-complementary structure has an inherent frequency independent property, which is infinite bandwidth, when it is constituted with an infinite structure. Unfortunately, practical antennas can never be realized in an infinite structure, as a truncation can never be evaded, thus bandwidth must always be finite. Although the bandwidth would be limited, antennas with complementary structure may still have wide enough bandwidth for practical applications; that is, an antenna is practically useful when the bandwidth is reasonably wide to satisfy the requirement. Hence, the complementary concept, even with truncation in the antenna structure – always encountered in small antennas – is adapted as a useful means to attain an appreciable bandwidth for an antenna of very small size.
7.2.4.1.1 L-shaped quasi-self-complementary antenna
One of the most simple self-complementary antennas is a monopole combined with a dual slot (Figure 6.34) introduced in [88, 89], in which wideband performance was demonstrated, even with an antenna of small size. Since a practical antenna can never be composed with infinite structure, it should be referred to as quasi self-complementary. Instead of a monopole, an Inverted-L antenna is combined with a dual L-slot to compose a quasi self-complementary structure (Figure 7.181) [89, 90]. The input impedance of the antenna with dimensions of l = 15 mm, h = 15 mm, and w = 4 mm, shows broad frequency characteristics covering about 2 GHz to 10 GHz for VSWR less than two (Figure 7.182(a)). However, the ground plane size (X × Y) was 46 mm × 60 mm, much smaller than one wavelength at the lowest frequency. Efficiency is sacrificed to a certain measure by using a load resistance 188 at the side opposite of the feed

7.2 Design and practice of ESA |
205 |
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VSWR
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100 |
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2 |
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80 |
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(%) |
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60 |
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Efficiency |
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1.5 |
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40 |
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20 |
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1 |
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0 |
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10 |
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10 |
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Frequency (GHz) |
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Frequency (GHz) |
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(a) |
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(b) |
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Figure 7.182 (a) VSWR characteristics of L-shaped self-complementary antenna and (b) efficiency of L-shaped self-complementary antenna ([88], copyright C 2002 IEEE).
40 |
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20 |
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0 |
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y (mm) |
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–20 |
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–20 |
x (mm) |
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–40 |
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–40 |
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Figure 7.183 Self-complementary H-shaped antenna ([91], copyright C 2007 IEEE).
as needed to maintain the complementary condition [89]. However, with this size of antenna, efficiency was observed as high as 70% almost over the frequency range of 2 GHz to 10 GHz (Figure 7.182(b)). The load resistance may be omitted to improve efficiency, if some amount of sacrifice in the bandwidth is allowed. If a smaller ground plane is used, as in practical applications to small mobile terminals, the bandwidth will become narrower, but still wide enough for practical applications.
7.2.4.1.2 H-shaped quasi-self-complementary antenna
The antenna geometry is illustrated in Figure 7.183, in which a short-circuited microstrip line used for feeding the antenna and dimensions of antenna with the scale are shown [91]. A dielectric substrate used has εr = 2.2 and the thickness is 0.787 mm. Measured and simulated return loss and gain, respectively, are shown in Figure 7.184 and Figure 7.185. The figure demonstrates a wide bandwidth covering about 1.35 GHz to 3.2 GHz for the

206 |
Design and practice of small antennas I |
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S11 (dB)
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−5 |
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−10 |
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−15 |
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−20 |
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−25 |
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−30 |
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Measurement εr = 2.2 |
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Simulation εr = 2.2 |
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−35 |
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Simulation εr = 1.0 |
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1.5 |
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3.5 |
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4.5 |
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Frequency (GHz)
Figure 7.184 Measured and simulated return loss of H-shaped antenna ([91], copyright C 2007 IEEE).
4
2
(dBi)gain |
0 |
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Antenna |
–2 |
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–4 |
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–6 |
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Measurement |
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–8 |
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Simulation |
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1.5 |
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2.5 |
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3.5 |
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1 |
Frequency (GHz)
Figure 7.185 Comparison of measured and simulated gain ([90], copyright C 2003 IEEE).
return loss below –10 dB with the substrate εr = 2.2, whereas when εr = 1, meaning no dielectric substrate, a considerably wider bandwidth (1.3–3.9 GHz) is obtained. The gain obtained is about 1 dBi over the frequency range of 1.3 GHz to 3.5 GHz.
7.2.4.1.3 A half-circular disk quasi-self-complementary antenna
Antenna geometry with dimensional parameters is illustrated in Figure 7.186 [92], showing that a printed semi-circular disk on a dielectric substrate is combined with its

7.2 Design and practice of ESA |
207 |
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r |
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L |
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L2 |
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L1 |
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Microstrip line |
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wf |
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Ground plane |
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ws |
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in back |
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y |
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substrate |
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εr |
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Figure 7.186 Geometry of half-disk shaped quasi self-complementary antenna ([92], copyrightC 2009 IEEE).
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Simulated |
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−5 |
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Measured |
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(dB)loss |
−10 |
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−15 |
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Return |
−20 |
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−25 |
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−30 |
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−35 |
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−40 |
1 |
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Frequency (GHz)
Figure 7.187 Simulated and measured return loss ([92], copyright C 2009 IEEE).
dual slot to construct a quasi-self-complementary structure. A triangular notch is adopted at the feed point on the ground plane to improve the impedance matching. The substrate has thickness H = 1.6 mm and the relative permittivity εr = 3.0. Measured and simulated return loss are shown in Figure 7.187, which indicates fairly wide bandwidth, covering 3 GHz to 10.7 GHz for the return loss less than –10 dB. Simulated gain is depicted in Figure 7.188, in which a gain of 3 dB over the wide frequency range is observed.