New Concepts of Transmitting Antennas for DMB and DVB-H

Transcription

1 New Concepts of Transmitting Antennas for DMB and DVB-H Hermann Zehetner Head of Broadcast Antenna Development with the support of: Dr. Norbert Ephan Senior Manager New Technology 1

2 Overview Broadcast antenna basics Omni-directional antennas Pattern synthesis with sector antennas Quasi-omni-directional antennas 2

3 Antenna Prinziples The Antenna matches the electromagnetic wave of a line to the free space Parameters, that define the design of an antenna: Gain, Pattern (coverage) Frequency (size) Polarization (linear, circular) Bandwidth (Pattern, Impedance) Power Handling Capability Environment (wind, ice, temperature) Optical Appearance 3

4 Broadcast means mainly omni-directional antennas 1x Backbone 1x Transmitter 1x Site Acquisition Infrastructure costs divided by many users Large cell broadcast high power antenna mainly omni-directional one large height site Revenue per Mbyte Revenue per MHz SMS Mobile Voice Fixed Broadband Broadcast Throughput Small cell broadcast low power antenna mainly directional antenna many low height sites gap filler, transposer, repeater... 4

5 Omni-directional antennas Top mount: Vertical pattern 470 MHz) 1 λ/2 dipol ideal pattern Side mount: 2 λ/2 dipols (1150 mm) 4 λ/2 dipols (2300 mm) other solutions are necessary... 8 λ/2 dipols (4600 mm) 5

6 Sector antenna as a component for omni-directional antennas Dipole array as basic element for various pattern: - broadband - high power handling - optimized for smooth group pattern shaping ϕ 6 db = 90 Antenna pattern of a sector antenna for DVB-H at 600 MHz covering a 90 sector 6

7 Omni-directional antennas consisting of 4 sector antennas r r = 280 mm r/λ = 0.56 r = 500 mm r/λ = 1 r E res = 0.74 minima < -6 db for r >λ 7

8 Omnidirectional Antennas on a mast with large diameter r = 1000 mm r = 1000 mm r/λ = 2 r r/λ = 2 r minima < -10 db for r > 2λ 14 Panels needed for minima < -2 db 8

9 Omni-directional antennas with sector-antennas in skew arrangement Tangential radiation r + only 4 antennas necessary + cost effective - sensitive to mechanical tolerances (not possible for L-Band) - small band (only for 1-2 channels) - very careful installation required r = 1100 mm r = 2540 mm 9

10 Omni-directional antenna examples (DMB L-Band) 2 bays of 4 antennas round a mast 2 bays of 8 antennas round a mast in a GRP Zylinder (Radom, 1.6 m) 10

11 Omni-directional antenna exampes 16 panels /bay Skew Antenna 11

12 Try to live with interference - Two point sources - Quasi Omni Increase Distance between elements > decrease angle for first zero (phase difference ϕ = 180 ) Nulls: φ = arcsin [± (2k+1)λ/2d] Maxima: φ = arcsin [± kλ/d] k = 0, 1, 2,... d =10λ = 20 * λ/2 ->40 lobes φ > increase number of lobes and zeros ϕ d d = 20λ 12

13 Quasi omni-directional antennas with sector-antennas 4 sector antennas round a mast of large diameter r = 50 λ, f.e. 10 m for DBM L- Band Nulls: 1 / 90 m in 5 km interference region filled up with reflections r mean value of field strength 6 db less 13

14 Omnidirectional Antennas build with 2 x 180 secto r-antennas mean value of field strength more constant Antenne with HPBW = 180 r = 5 m (25 λ) 2 x 180 Sector Antennas 14

15 Optimised design by using dual polarized antennas 4 sector antennas round a mast r = 100 λ, f.e. 20 m for DBM L- Band r

16 Adjacent antennas with dual polarization r = 10 λ 16

17 Adjacent antennas with dual polarisation maximum of the horizontal polarized E-Field minimum of the vertical polarized E-Field Antenna system radiates two orthogonal polarisation: linear: vertical, horizontal slant 45, slant -45 circular: left, right Resulting polarization at coverage zone: elliptical changing in space and frequency Polarization diversity for maximum receiving signal (car) Handy - how polarized? Rooftop antennas 17

18 Comparison dual-polarisation / vertical polarisation small variation of field-strength if dual polarization is used intereferenc causes nulls in urban area filling up due reflexions 18

19 Results of L-Band DMB-System Frankfurt Route: Frankfurter Kreuz A5 Ausfahrt Friedberg TX: vertical polarized RX: vertical polarized Fahrtstrecke in km Route: Frankfurter Kreuz A5 Ausfahrt Friedberg TX: dual polarized RX: vertical polarized Fahrtstrecke in km 19

20 Dual polarized antennas for GAP-Fillers (SFN analog repeater)... another scope of application... main transmitter polarizations-decoupling between receiving and transmitting antenna increases system performance Ch33 H-Pol V-Pol RX TX Ch33 overlap zone: orthogonal polarization will reduce interference problems 20

21 Summary Single polarized quasi-omni antennas only for: urban areas (reflections of buildings) distance from transmitting station not too far distance of adjacent antennas >> λ Dual polarized quasi-omni antennas can be used: in urban and suburban areas distance of adjacent antennas >= λ receiving antenna should receive every polarisation Dual polarized antenna for SFN gap-filler and shadow network: polarizations-decoupling between overlapping areas of transmitter and repeater cell reduces interference problems of coverage polarizations-decoupling between receiving and transmitting antenna increases system performance 21

22 Every Antenna, which fits in frequency and power can be used... DVB-H MHz DMB L-Band 22

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