Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

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7 Conclusion During this project the different measurements have been the major problem, and already during our first measurement we ran into trouble. No DVB-T signal was detected when measurements with the spectrum analyzer was done. The reason for this is that the walls and windows attenuate the signal. The windows at Perlos laboratory have a thin metal layer on the glass. This means that there is no indoor coverage in Perlos laboratory in Lund and probably not in larger parts of Skåne. For the DVB-H system to be successful coverage inside cars, busses, trains and buildings has to be achieved. The base stations operating today only provide full indoor coverage in the near of the base stations. If the DVB-H system is successful more base stations are planed and full indoor coverage will be achieved. As you all now by now the frequencies used for the DVB-H system are 470-862 MHz. This frequency range is good in aspect of getting good coverage with few base stations. The only drawback with these low frequencies is that the antennas become electrically very small, and thereby inefficient. If higher frequencies had been used more base stations had been required since higher frequencies have a higher propagation loss. DVB-H system can use all existing DVB-T base stations and only a handful new base stations have to be built in the future. This is a huge economical advantage against competing systems. Another big advantage is that it is a broadcasting system, which means that it is spectrum efficient. That it is a broadcasting system means that an infinite number of users can watch the same show without occupying more bandwidth. This could be compared to the technique used today in the 3G network where smaller shows are streamed to each user separately. One of the reasons why shows are streamed separately is that in this way the operators can easily control how long time each user has watched and thereby be charged. Another reason is that the operators have a lot of unused capacity in the 3G network and want to use this to stream TV shows in. A big difference between DVB-H and DVB-T is time slicing. This has been added in the DVB-H standard to decrease the power consumption to a level suitable for handheld devices. This technique has a couple of drawbacks. The first one is that when the user likes to change channel it might take up to five seconds before the next burst are transmitted. This means that no picture can be shown until the burst for the chosen channel has been received. The second one is if the terminal has bad reception during the burst time, then the terminal will not have any video to play until the next burst is received. When this technique is used live shows will 74
not be possible, there will always be some delay. This is for instance not wanted when a live football match is transmitted. Other notable differences between DVB-H and DVB-T are MPE-FEC and 4kmode. These features are added to DVB-H to make the system more robust and to make the network design more flexible. They have no major drawbacks but when MPE-FEC is used more bits have to be sent per data bit. The DVB-H system suits handheld terminals very well in all ways except that a normal sized antenna for the frequencies used would be larger than the terminal itself. The large bandwidth that the antenna has to cover is a hard problem to solve. We have solved this problem in three different ways, with one wideband, one switched and one tunable narrowband antenna. The different solutions fit different kinds of terminals. Since the wideband antenna, folded-patch, is sensitive to interference this solution fits best in devices without GSM 900, like Ipod and other terminals with screens suitable for watching TV. From this point of view the loop antenna is the most suitable antenna for GSM 900 terminals. Theoretically the isolation between an H-field and an E-field antenna is much higher than for two E-field antennas. This theory and its narrowband characteristic are two things that make the loop antenna interference tolerant. No tests have been done to find out which of these things that contributes most to the interference tolerance. A lot of discussions with senior antenna designers about the H- and Efield theory have been conducted. None of these designers could say for sure that this theory has any effect in the real case. If the folded patch should be used in a GSM 900 terminal a good filter on the DVB-H chipset is required. As an example, if the maximum allowed input level of the DVB-H chipset is –28 dBm the total attenuation (isolation + filter) must be at least 61 dB (since a GSM 900 terminal transmits with a peak value of 33 dBm). The requirement of the filter depends on the antenna used since the isolation between the GSM 900 antenna and the DVB- H antenna will differ. If the mobile manufacturers desire an embedded antenna the only suitable solution would be the switched monopole 2.This is the major advantage with this solution compared to the other two that needs an extension. Customers today are used to embedded antennas and do not prefer an external solution that easily breaks. If an external solution is chosen anyway it could be combined as a support for the terminal to be able to stand on a table or another smart mechanical solution. Regardless of which antenna that is selected an important thing is the placement of the antenna element. It has to be placed so that the antenna characteristics are changed as little as possible when the user holds the terminal in different ways. 75
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Design of Antennas for Handheld DVB
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Acknowledgements This master thesis
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4 DESIGN AND TESTING OF ANTENNA SOL
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Figure 5.2. Reference dipole antenn
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1 Introduction The passed decade th
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2 Background This chapter provides
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is simultaneously modulated into 10
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2.1.3 Reed-Solomon Codes 2.1.4 DVB-
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2.1.5 DVB-H DVB-H is the latest dev
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2.1.5.2 Time slicing A large proble
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figure 2.5). All three elements tog
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symbols or four 2K OFDM symbols. Th
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2.2 Competing standards The DVB-H s
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2.3 Antenna theory This section des
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Figure 2.9. Impedance bandwidth def
Page 31 and 32: unloaded quality factor (Q0) and th
Page 33 and 34: losses should be avoided in handhel
Page 35 and 36: 3.3 Loop Figure 3.1. Yagi-Uda anten
Page 37 and 38: PIFA Figure 3.2. Four different con
Page 39 and 40: The size of the antenna is another
Page 41 and 42: 4.4 PIFA To verify the balun a resi
Page 43 and 44: 4.5 Folded-Patch With the PIFA-ante
Page 45 and 46: Figure 4.9a. Folded-patch 2, front
Page 47 and 48: Figure 4.11. Loop antenna schematic
Page 49 and 50: Figure 4.15. Wire loop antenna retu
Page 51 and 52: using an H-field antenna together w
Page 53 and 54: antenna. The dimension of the anten
Page 55 and 56: The result of the return loss measu
Page 57 and 58: Figure 4.24. Return loss graph for
Page 59 and 60: The result of the measurement of th
Page 61 and 62: Figure 4.31. Return loss graph for
Page 63 and 64: frequency band, the first from 470
Page 65 and 66: Figure 5.6. Radiation pattern for R
Page 67 and 68: 5.1.3 Measurement result In this ch
Page 69 and 70: Figure 5.10. Radiation pattern for
Page 73 and 74: Table 5.4. Switched monopole 1, gai
Page 75 and 76: Power gain / dB 2 0 -2 -4 -6 -8 -10
Page 79 and 80: was received in all five channels.
Page 81: 6.3 Control signal 6.4 Cost The swi
Page 85 and 86: There are many advantages with tuna
Page 87 and 88: 8 References [1] Schiller, Jochen -
Page 89: [29] Gardiol, Fred - Microstrip cir
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Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

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