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

More documents

Recommendations

Info

There will be no reflection only when the impedance of the antenna and the characteristic impedance of the transmission line are equal, then the antenna is perfectly matched. To achieve good antenna performance in a wide frequency range a slight mismatch in the whole band is the best solution. The reflection is unwanted because a part of the power is not delivered into the antenna, in the transmission case and vice versa in the receiving case. The impedance matching is an important task in the antenna design. Some basic methods for matching are presented later [25]. The voltage at a point on a transmission line is in the general case the sum of two waves travelling opposite directions. This scenario is known to create a standingwave pattern along the transmission line. The ratio between the maximum and the minimum value of this sum is termed the voltage standing-wave ratio and can be calculated from the reflection coefficient with equation 2.4. 1+ Γ VSWR = (2.4) 1− Γ Power loss due to reflection, called reflection loss Lrefl, can be calculated from 1 L refl = 10 log (2.5) 2 1 − Γ Return loss describes the ratio between the propagated and the reflected power and can be calculated from 1 L retn = 10log (2.6) 2 Γ VSWR, Lrefl and Lretn are all calculated from the reflection coefficient and they are normally used to define the impedance bandwidth. In figure 2.9, the bandwidth BWabs is defined by the absolute value of the reflection coefficient Γ ≤ 0. 501, which corresponds to the return loss criterion of Lretn ≥ 6dB or the VSWR criterion of S ≤ 3. 01. This limit has to be set in each case separately. Nowadays Lretn ≥ 6dB is an acceptable upper limit on the bandwidth criterion for built-in antennas [24]. 20
Figure 2.9. Impedance bandwidth defined according to the absolute value of the reflection coefficient ⎟Γ⎜ = ⎟S11⎜ = -6 dB. BWabs is the absolute frequency bandwidth. From the absolute bandwidth the relative bandwidth can be defined according to the following equation. BWabs Br = (2.7) CF Where BWabs is the absolute frequency bandwidth and CF is the arithmetic center frequency of the impedance band. 2.3.3 Resonance Circuit The small antennas studied in this thesis are resonators. Input impedance of such antennas consists of one resistive part and one reactive part according to the following formula ( f ) R ( f ) + jX ( f ) Za a a = . (2.8) The resistance Ra(f) represents the radiation and ohmic loss. Xa(f) represents the reactive, non-radiating energies of the antenna structure that consists of inductive and capacitive components. Resonance in the antenna structure is achieved when the inductive part and the capacitive part cancel each other, which results in the best efficiency for the antenna. This can be achieved by a self-resonant structure, but only inside a narrow bandwidth, or by a matching circuit. A short-circuited λ / 4 or an open λ / 2 antenna normally achieves the self-resonance, where λ is the wavelength at the used frequency in the used medium. 21
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: 2.3 Antenna theory This section des
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 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

Create successful ePaper yourself

Delete template?

Save as template?