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

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The only thing that could be read out about the antenna performance from the specification is the power gain requirement for a handheld DVB-T antenna. Though the requirements of the DVB-H antennas certainly not will be higher than for DVB-T antennas, these are reasonable limits for our design. However the gain itself does not say much about the antenna performance for a handheld terminal since an isotropic radiation pattern is desired. This is why we have chosen to present both gain, efficiency and radiation pattern. When these three things are presented it is easier to draw conclusions about the antennas RF performance. The gain requirement is not very hard to achieve but to get good efficiency is hard. This is a consequence of electrically small antennas, which all DVB-H antennas must be to take place in a handheld device. For an electrically small antenna it is the ground plane that contributes most to the radiation. This means that it is easier to achieve good efficiency with a large terminal. Our prototypes fulfilled the gain specification with large margin. Therefore the antennas could not be separated in RF performance from the gain measurement. From the efficiency measurement it could be seen that the folded-patch has a bit higher values than the other prototypes but not so much that any solution can be excluded. From a gain and efficiency perspective the folded-patch is slightly better than the other two prototypes. In a report from EICTA it is claimed that generally no polarisation discrimination can be expected [31]. However, polarisation discrimination was found during our DVB-T box measurement, the most sensitive prototype was the loop antenna. When watching TV with the loop antenna the reception was good when the antenna was held in vertical led but when the antenna was turned to horizontal led the reception was bad. After some studies in the subject, the conclusion is that for these low frequencies the polarisation is not much changed when the signal is reflected. Therefore antenna designers cannot assume that the income signal has different polarisations. From the radiation patterns and the DVB-T box measurement it can be seen that the folded-patch is least sensitive to polarisation and the loop antenna most sensitive. Another important thing to discuss is the different control signals the antennas need. Today it is not common with tunable antennas, but we think that it will be more common in the near future. More and more antennas are included in the mobile phones that take up much space. A solution for this problem could be to use an antenna for more than one application, and then a controllable antenna could be used. An example is that the switched monopole 2, with one extra matching network can be used as FM antenna. The control signals available from the chipsets today are an I2C signal and the VCO voltage. In the future it might be possible to get more adapted signals to control the antenna. For an example it would be easier if the DVB-H chipset could deliver the three control signals needed to control the switches in switched monopole 2. 76
There are many advantages with tunable antennas, but one big drawback for the manufactures is the extra cost the circuits brings. The cost is one of the most important aspects whether the antenna is to be realized or not. It is up to the manufacturer to decide if the advantages a tunable antenna has is worth the extra cost. The three prototypes designed and measured in this thesis have very different characteristics. Here below the different prototypes will be summarized. Folded-patch Advantages • Good RF performance • Simple and cheap design • No control signal needed Disadvantages • Large antenna that has to be extended • Bad interference tolerance Loop antenna Advantages • Good RF performance • High interference tolerance (filter function) • Simple analogue control signal Disadvantages • Has to be extended • Expensive variable capacitance diodes needed • Polarisation sensitive Switched monopole 2 Advantages • Good RF performance • Embedded antenna • Possible to use same antenna for DVB-H and FM radio Disadvantages • Expensive components • Complex control signal • Losses in RF switches It is impossible to say that one antenna is better than another because they have different advantages and suit different terminals. If we were to choose a favourite it would be the switched monopole 2 because this is the only antenna that could be embedded and we are willing to pay the extra cost that this results in. Below follows a list of demands for a DVB-H antenna: 77
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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
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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 and 82: 6.3 Control signal 6.4 Cost The swi
Page 83: not be possible, there will always
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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