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

More documents

Recommendations

Info

A resonator can be modelled as a parallel resonance circuit, as shown in figure 2.10. Figure 2.10. Parallel resonance circuit. The total energy stored in the resonance structure, is the average energy stored in the capacitance C added with the average energy stored in the inductance L. These definitions give the following formula to calculate the resonance frequency [24]. f r 1 = (2.9) 2π LC 2.3.4 Quality Factor The quality factor describes the ratio between energy stored and energy lost in a resonator circuit per unit time. There are numerous definitions of Q, but the most fundamental one is Maximum energy stored in the network Q = 2π * (2.10) energy dissipated per cycle Note that the Q is dimensionless and that it is fundamental because it does not care about what stores or dissipates the energy. For that reason it applies perfectly well to both resonant and non-resonant systems. Therefore it is appropriate to characterise a RC circuit, or even a single component, by the Q [25]. The quality factor for the circuit in figure 2.10, according to formula 2.2 is ωrW ωrC 1 Q = = = (2.11) P G G * ω * L l r Where ω r is the angular resonant frequency, W is the energy stored and Pl is power loss in a resonator structure. The total loss can be divided into several load components, where each of them can be described by different quality factors. The total quality factor is called loaded quality factor (Ql) and describes the total loss and can be divided into the 22
unloaded quality factor (Q0) and the external quality factor (Qe). The unloaded quality factor describes the internal losses, which can be further divided into radiation, conductor and dielectric losses. The unloaded and radiation (Qrad) quality factors are in an ideal case equal but in practise there are losses in dielectrics and conductors, which are included in the dielectric (Qd) and conductor (Qc) quality factors. The relation between all different quality factors is shown in equation (2.12) [26]. 1 Q 2.3.5 Bandwidth l 1 1 1 1 1 1 = + = + + + (2.12) Q Q Q Q Q Q 0 e rad c d e The useful bandwidth is limited by a number of factors, for example impedance, gain, polarization or beamwidth. The impedance matching is the main factor limiting the bandwidth of a resonator. The input impedance of a small antenna for handheld devices varies quickly with frequency, which limits the frequency range over that the antenna can be matched to its feed line. The unloaded quality factor is very important because it determines the bandwidth of the antenna. The relatively Bandwidth and the unloaded has the connection shown in equation (2.13). B r = 1 Q 0 ( TS −1)( S − T ) S 23 (2.13) Where VSWR = S over the impedance bandwidth and T = Y0/G, where G is the conductance seen at the input of a resonator at the resonance frequency and Y0 is the characteristic admittance of the transmission line [26]. 2.3.5.1 Impedance matching A basic task in radio engineering is to match the antenna load to the characteristic impedance of the feed line to prevent voltage reflection (see figure 2.11). A matching circuit can be realized by lumped elements (capacitor and inductor), distributed elements (stub or quarter-wavelength transformer) or by resistive matching. It is always possible to make a matching circuit as long as the Ra(f) of the input impedance is not zero. To design a matching circuit, formulas or Smith chart can be used. Resistive matching is not recommended because of the losses it results in. Matching network by lumped elements is close to ideal as long as the physical lengths of the components are clearly smaller than the free-space length and the
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: Figure 2.9. Impedance bandwidth def
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 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
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?