is obtained with ⌬L ϭ Ϫ1.5 mm. Figure 7 shows the results of the adjustments. CONCLUSIONInvestigations on two-segment DRAs have been presented in this paper. The resonant frequency was predicted by a new method. An optimum lower-segment design was introduced. A fast and efficient design algorithm which prevents a futile time-consuming trial-and-error process was demonstrated using these methods. Impedance bandwidths of up to 30% were achieved with the optimum design. Two numerical methods were used to examine the performance of the methods. The simulation results are in good agreement and confirm the proposed methods. Wide impedance bandwidth, compact size, and lack of metal in the antenna structure (for high radiation efficiency) contribute to make TSDRA a useful element in high-frequency fixed-broadband wireless applications such as LMDS. Recently, the number of dual-band handset phones capable of operating at two different cellular systems has increased. A handset phone available for dual-frequency bands requires the antenna to operate equally well at both frequency bands. Also, the antenna is required to have small size, light weight, high radiation efficiency, and wide bandwidth. In order to satisfy these requirements for each band, PIFAs have limitations in both bandwidth and antenna height (6 -8 mm from the substrate) [1]. Those structures cannot provide easy placement of the antenna on the substrate in a practical mobile phone. However, planar-type antennas are relatively easy to manufacture in a very accurately repeatable way. Therefore, the planar-type antenna can be considered one of the best candidates to meet these criteria. For the planar-monopole antenna, a variety of designs has been also reported [2,3]. This paper presents an internal dual-band antenna with a modified ground plane. This antenna is very suitable to be integrated on the circuit board of a communication device, leading to the attrac- tive feature of occupying very small volume in the system. In addition, with the use of this kind of printed monopole antenna, a concealed antenna for the system can be obtained. Thus, no protruding portions of the antenna appear [4,5]. In this paper, the measured data are compared with the simulation results in order to validate the proposed design methods. The descriptions and design considerations of the proposed antenna are presented in detail. ANTENNA CONFIGURATIONThe geometry of the proposed internal dual-band antenna for CDMA/PCS applications is shown in Figure 1(a). This novel antenna is mounted on FR-4 substrate whose permittivity is 4.6 and dimensions are 80 ϫ 40 mm. In Figures 1(b) and 1(c), segment[A] is a ground part of the antenna top plane, which is electrically shorted with bottom ground segment [E] through the via hole. Part [B] is a feeding point where the inner conductor of the feeding coaxial cable is directly connected. The outer conductor of the feeding coaxial cable is connected through segment [A]. In order to expand the bandwidth, part [C] of signal line is fabricated as a righ...
Surveys for land snails of several bush patches on or near the Manukau Peninsula, southwest of Auckland, restrlted in finding up to 60 species (only 3 introduced) in a single 4 ha patch of bush. Analysis of I'e!oords from all bush patches suggests that an essentially sympatric communi,ty of about n native species is a probable reality, whereas in most areas of the world the sympatric existence of more than 15 land snail species is highly unusual. A first attempt at indicating the moisture, space, and foraging preferences of the 89 land snail species recorded from the Manukau Peninsula is presented, and an attempt is made to indicate broad categories of species association or habit;!t preference within this area. Many species occur throughout litter types (40-757< of all species in one bush patch would be in a 20 X 30 cm bag of litter from one spot), and it is hypothesised that the qualities of moisture retention and air space are more significant to the snails than the species of plant that provided the litter. This sympatric land snail diversity is norm;!l from the central North Island up into Northland. but diversity levels drop sharply in the far north and southward from Mt EgmontfEast C.lpe. Most of the South Island has 15-20 sympatric land snail species, with even grea.ter reduction on Stewart I'siand and the subantarctic islands. It is hypothesised that the high sympatric diversity level reached in the Manukau area results from equability of the moisture regime. This diversi'ty is based in accumulation of phyletically unrelated taxa, not localised speciation. The land snail population here has the aspect ofa mature communi,ty. Even few-hectare patches of bush can hold ne:u--maximum land snail communities, if they are protected against burning, clearing, and trampling of the litter by stock. The preservation of such patche3 is urged, for the conservation not only of the land snails but of the other soil micro-organisms that coexist.
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