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

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6 Results Now three final antenna prototypes have been designed and measured (foldedpatch, loop antenna and switched monopole 2). In this chapter they will be evaluated and compared to each other. 6.1 RF Performance 6.2 Design A big difference between these three prototypes is the bandwidth. The loop antenna covers only 1/30 of the DVB-H band, while the switched monopole 2 covers one fourth of the bandwidth and the folded-patch covers the whole band. Different bandwidths have different advantages. The narrowband loop antenna has the advantage of being interference tolerance against GSM 900. This is why the loop antenna has very bad performance for all frequencies except its resonance frequency. The antenna acts like a filter against all unwanted frequencies. Another feature that makes the loop antenna interference tolerant is that it is an antenna that responds to the magnetic field. The folded patch has no filter effect at all and therefore becomes very sensitive to interference. The switched monopole 2 has interference tolerance somewhere in between these. All three prototypes fulfil the gain specification well. The folded-patch differs from the other two in the sense that it has almost the same gain in the two ends of the band while the other two antennas gain increases with the frequency. Since the efficiency depends on the gain these two values have the same characteristic. The folded-patch has best efficiency in the lower part and in the middle of the band. The switched monopole 2 has the best efficiency in the higher part of the band while the loop antenna has a more even efficiency. The folded-patch has the radiation pattern closest to an isotropic antenna, with no distinct zero. In the radiation pattern for the loop antenna two zeros can be seen. The zeros for the switched monopole 2 are not as distinct as for the loop antenna. The folded-patch and the loop antenna cannot be placed above a ground plane. Therefore a mechanical solution has to be designed for these two antennas. This mechanical solution that includes the antenna has to be extractable, which reduces the design flexibility for this two antenna concepts. Both these antennas could be manufactured out of flexible film. The antenna element of switched monopole 2 is placed along the ground plane and can thereby be designed as an embedded antenna. This antenna element is preferably made of sheet metal. 72
6.3 Control signal 6.4 Cost The switched monopole 2 needs the most complex control signal to work properly. For the switches used in this prototype three digital control signals are needed to control the switches. To control the loop antenna an analogue DC voltage between 0.5 and 3.0 V is required. This DC voltage can be the same that controls the VCO in the tuner. A big advantage with the folded-patch antenna is that no control signal is required. The manufacturing cost varies a lot between the different prototypes. The most expensive antenna solution will probably be the switched monopole 2 since the two switches and the expander are expensive circuits. The switches we used from Peregrine can be bought for about $1 each and the expander costs $1.50. For this solution three inductors and four capacitances are also required. The inductors cost $0.02 each and the capacitors cost $0.005 a piece. Which adds up to about $3.60 for components only. Hopefully the DVB-H chipset will be able to deliver the needed control signal and then the expander is not needed. There are cheaper switches on the market that are possible to use in this concept, our time limit did not allow us to test these. The second in line is the loop antenna, mostly because the variable capacitance diodes are relatively expensive. One variable capacitance diode cost about $0.30. One capacitor and one inductor are also needed for this prototype so the total component cost adds up to about $0.60. The folded patch antenna does not need any components. However this prototype and the loop antenna will need a slightly more expensive mechanical solution than the switched monopole 2. All prices are approximations and apply when one component is bought, if the antennas were to be mass-produced the prices will be significantly lower. 73
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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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Page 33 and 34: losses should be avoided in handhel
Page 35 and 36: 3.3 Loop Figure 3.1. Yagi-Uda anten
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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
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Page 47 and 48: Figure 4.11. Loop antenna schematic
Page 49 and 50: Figure 4.15. Wire loop antenna retu
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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
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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: was received in all five channels.
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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