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

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ohmic losses are small enough. A complex load can always be matched by two lumped components. At higher frequencies, when the lumped components not are ideal, it is better to implement the matching circuit by using distributed elements like tuning stub. It is possible to use distributed elements even at RF frequencies but the lengths of the stubs may be to long for printed circuit board. A resistive attenuator can be placed between a load and a transmission line for giving resistive matching. If a 3-dB attenuator is used, the signal level and the total efficiency will be attenuated with 3 dB, while the reflection coefficient decreases 6 dB. Resistive matching can be used if power consumption is not a problem, but usually resistive matching is not acceptable, because valuable power cannot be wasted in the resistive matching circuit in handheld devices. 2.3.6 Bandwidth enhancement Figure 2.11. Matching circuit scheme. The matching networks described above give perfect matching at single frequency points. To achieve matching over certain impedance band the matching criterion must be loosen. Instead of a criterion with return loss, Lretn = -∞ dB, usually the return loss is chosen to be less than –6 dB for antennas in handheld devices. To make the bandwidth as wide as possible, there are two characteristics to choose to loosen, either to make the volume larger or lower the efficiency. Impedance, volume and efficiency are three antenna characteristics that depend on each other, so the best compromise to reach the specified performance must be found. Changing the volume for internal antennas for DVB-H to make them wideband is not easy because the small size of the terminal, and users do not want terminals in non-pocket-size. One method that makes it possible to enhance the bandwidth is to worsen the efficiency, which can be made in three ways, accepting mismatching, resistive matching with attenuator or adding resistive losses. As mentioned before, resistive 24
losses should be avoided in handheld devices, so accepting mismatching is the best choice to get wider bandwidth. Other possible, but more complicated methods to make the bandwidth as wide as possible is multiple resonant antennas and to split the frequency range into several frequency bands and design one matching circuit to each band and switch between these. An alternative to wideband antennas is a tuneable antenna that is narrowband but possible to tune in a large frequency band. It can be made by adjustable components in the matching network, in former time it was adjusted mechanical that is not possible with handheld devices. A possible solution for the DVB-H system is to use a control signal from the tuner to adjust the matching circuit [24, 25, 26]. 25
Page 1 and 2: Design of Antennas for Handheld DVB
Page 3 and 4: Acknowledgements This master thesis
Page 5 and 6: 4 DESIGN AND TESTING OF ANTENNA SOL
Page 7 and 8: Figure 5.2. Reference dipole antenn
Page 9 and 10: 1 Introduction The passed decade th
Page 11 and 12: 2 Background This chapter provides
Page 13 and 14: is simultaneously modulated into 10
Page 15 and 16: 2.1.3 Reed-Solomon Codes 2.1.4 DVB-
Page 17 and 18: 2.1.5 DVB-H DVB-H is the latest dev
Page 19 and 20: 2.1.5.2 Time slicing A large proble
Page 21 and 22: figure 2.5). All three elements tog
Page 23 and 24: symbols or four 2K OFDM symbols. Th
Page 25 and 26: 2.2 Competing standards The DVB-H s
Page 27 and 28: 2.3 Antenna theory This section des
Page 29 and 30: Figure 2.9. Impedance bandwidth def
Page 31: unloaded quality factor (Q0) and th
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 and 82: 6.3 Control signal 6.4 Cost The swi
Page 83 and 84:
not be possible, there will always
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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