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Introduction and Overview 1. To meet the miniaturization requirement, the antennas employed in mobile terminals must have their dimensions reduced accordingly. Planar antennas, such as microstrip and printed antennas, have the attractive features of low profile, small size, and conformability to mounting hosts and are very promising candidates for satisfying this design consideration.
For this reason, compact and broadband design techniques for planar antennas have attracted much attention from antenna researchers. Very recently, especially after the year , many novel planar antenna designs to satisfy specific bandwidth specifications of present-day mobile cellular communication systems, including the global system for mobile communication GSM; MHz , the digital communication system DCS; MHz , the personal communication system PCS; MHz , and the universal mobile telecommunication system UMTS; MHz , have been developed and published in the open literature.
This book organizes those novel designs for applications as internal mobile phone antennas and base station antennas, and detailed design considerations and experimental results are presented. Planar antennas are also veryattractive for applications in communication devices for wireless local area network WLAN systems in the 2. Novel planar antenna designs for achieving broadband circular polarization CP and dual-polarized radiation in the WLAN band for overcoming multipath fading problem to enhance system performance have been demonstrated recently.
In addition, surface-mountable antennas that can be easily integrated on the circuit board of a communication device to reduce the packaging cost have also received much attention, and related new designs for WLAN operations have been reported recently. These newly developed WLAN antennas are presented and discussed. Dielectric resonator antennas also have the features of low profile and small size, like the microstrip and printed antennas, and in addition, there is no metallic loss, leading to low loss for operating at higher frequencies.
Furthermore, when the DR element with a very high relative permittivity is used for example, larger than 80 , the antenna can have a very low profile less than 2mm for operating in the 5. Some related promising designs are introduced in this book. Finally, the integration of antennas for different operating bands, such as the GPS antenna, the WLAN antenna, and the DCS antenna, is discussed and details of some practical integration designs and experimental results are shown. Owing to their compact size the designs of PIFAs have attracted much attention, and a variety of dual-band or multiband PIFAs suitable for applications in mobile phones have been demonstrated recently.
Figure 1. These PIFA designs usually occupy a compact volume and can be integrated within the mobile phone housing, leading to concealed or internal mobile phone antennas. Because this kind of internal antenna can avoid the damages caused by catching on things and will not break, compared with the conventional protruded whip or rod antennas used for mobile phones, it is now becoming one of the major design considerations for mobile phones.
In addition, in comparison to the conventional whip antennas showing omnidirectional radiation, such PIFAs have the advantage of relatively smaller backward radiation toward the mobile phone user. These advantageous characteristics have led many novel PIFA designs, most of them capable of dual-band operation, to be applied in mobile phones in the market.
In the former case, the design techniques include the use of an inserted L-shaped slit or a folded slit Fig. To achieve this goal, the techniques of using a branch-line slit to achieve a lengthened resonant path Fig. To include the WLAN operation in the 2. The techniques of using a parasitic shorted patch placed coplanar with the driven patch or stacked on top of the driven patch to enhance the operating bandwidth of the PIFA have also been reported.
Recently, it was reported that, by using an L-shaped ground plane see two possible designs shown in Fig. These recently reported results for the applications of PIFAs as internal mobile phones antennas are presented in Chapter 2.
Because of this large antenna height, it is impossible to integrate such monopole antennas within the mobile phone housing. To reduce the monopole height, which makes the antenna less prone to breaking off, monopoles in the form of a helix or wound coil or a folded loop for mobile phone applications have been used.
Many related designs for achieving MHz dual-frequency operations have been reported. A typical dual-frequency design is shown in Figure 1. The second design uses a straight rod for MHz operation placed inside a uniform helix having the MHz resonance. The design technique of configuring a folded loop to achieve two desired separate resonant frequencies for the and MHz operations has also been used.
To further reduce antenna height, a variety of novel dual-frequency monopole designs have been reported very recently. These designs are mainly associated with bending, folding, or wrapping two-dimensional planar monopoles into three-dimensional structures. This technique greatly reduces the total antenna height from the ground plane of a mobile phone. Such antennas are very promising for placement within the mobile phone housing, that is, a concealed antenna for the mobile phone can be obtained.
This kind of very-low-profile monopole designs for dual-frequency internal mobile phone antennas are described in detail in Chapter 3.
In Figure 1. Because of the meandering, the antenna height from the mobile phone ground plane can be greatly reduced.
Furthermore, it has been shown that, by wrapping a similar branch-line planar monopole into a rectangular boxlike structure as shown in Figure 1. It should be noted that, in this design example, there are three branch lines. Dual-frequency operation obtained by loading a meandered wire, which is for generating the MHz resonance, to an inverted-L wire having the MHz resonance, has also been reported, and a typical configuration of the design is shown in Figure 1.
Note that, in Figures 1. This design concept has also been used in the designs shown in References 38 and In Reference 38 a branch-line slit is inserted within a planar monopole to create two desired different resonant paths for the and MHz resonances, and in Reference 41 a planar monopole comprising two subpatches of different sizes is wrapped into a rectangular boxlike structure to achieve and MHz operations with a much reduced antenna height.
A typical design using a rectangular spiral strip monopole is presented in Figure 1. The rectangular spiral strip monopole printed on a microwave substrate is mounted on the top portion of a mobile phone circuit board and positioned in perpendicular to the circuit board. With this arrangement, the distance of the rectangular spiral strip monopole from the mobile phone ground plane is greatly reduced; that is, a much reduced antenna height for the mobile phone is obtained.
By utilizing this characteristic, the desired dual-frequency operation at and MHz can be obtained by tuning the widths in different sections. This kind of dual-frequency rectangular spiral strip can also be folded onto a plastic chip as a surface-mountable antenna, as demonstrated in Reference The planar inverted-F antenna can also be directly printed on a mobile phone circuit board to operate as an integrated or on-board monopole antenna.
A typical design has been recently reported, and its geometry is shown in Figure 1. These newly reported designs are discussed in detail in Chapter 3.
To achieve a broadband operation, conventional designs using a thick air-substrate patch antenna incorporating a U-slotted patch, an E-shaped patch, a wedge-shaped patch, an L-shaped probe feed, a three-dimensional transition feed, and so on, have been used. To satisfy the specific operating bands, defined by 1.
To achieve single-band operation, a variety of designs using the slot-coupled feed, probe feed, coplanar probe feed, microstrip-line feed, and capacitively coupled feed have been used. Among these designs, many interesting novel design techniques are applied; for example, to avoid the large probe pin inductance introduced by a long probe pin required for a thick air-layer substrate, a very effective method of using a coplanar probe feed has been developed, in which the vertical ground plane added is for accommodating the coplanar probe feed see Fig.
This design has a simple geometry, and good broadside radiation characteristics have also been obtained. Other successful methods of using a conducting cylinder transition, a triangular transition patch, a ground plane with a small elevated portion, a W-shaped ground plane, an E-shaped patch incorporating a U-shaped ground plane, and so on, have also been reported.
In addition to the obtained wide impedance bandwidths covering the required bandwidths of the GSM, DCS, PCS, or UMTS systems, excellent radiation characteristics with much reduced cross-polarization radiation have been obtained in the designs shown in References 57 and Moreover, enhanced antenna gain for the design with a W-shaped ground plane has been observed.
The peak antenna gain can reach about 10 dBi for a single-patch case in the DCS band. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher. Excerpts are provided by Dial-A-Book Inc.
KIN LU WONG PLANAR ANTENNAS FOR WIRELESS COMMUNICATIONS PDF
Planar Antennas for Wireless Communications / Edition 1
Planar Antennas for Wireless Communications