Microwave Transmission Basics Microwave Transmission Basics Table of Contents • MW Advantages • MW Frequency bands • MW Link elements • Antenna Radiation Pattern • MW Alarms Microwave Transmission Basics Features Advantages ? Rapid Deployment – A microwave link can be installed in as little as one day No right-of-way issues – Radio ps all obstacles such as roads, railways, etc. , avoiding any requirement to seek permissions that inevitably are costly and introduce time delays. Flexibility – The capacity of a microwave link can be easily increased at minimal or even no cost.
Radios can also be redeployed if network needs change or as a result of customer churn. Losing customers does not mean assets are lost like in the case of fiber build. ? ? Microwave Transmission Basics Features Advantages • • • • Easily crosses city terrain – In many metropolitan and city authorities, street digging to install fiber is either extremely restricted, prohibitively expensive or is even banned outright. Operator-owned infrastructure – no reliance on competitors. Low start-up capital costs, which are independent of the link distance.
Minimal recurring operational costs. • • Radio infrastructure already exists for many networks in the form of rooftops, cellular masts and existing radio transmission towers. Microwave radio is not susceptible to common catastrophic failure of cable systems caused by cable cuts, and can be repaired in minutes instead of hours or days. • Limitations • • • Transmission Capacity Limits (i. e. PDH, STM-1) Competitive Transmission Media Optical Fiber (i. e. STM-1 up to STM-N) Microwave Transmission Basics Common M/W Frequency Bands According to ITU-R recommendations ? ? ? ? ? ? ? ? 7 GHz 8 GHz 11 GHz 13 GHz 15 GHz 18 GHz 23 GHz 28 GHz 38 GHz Note: Hop distance is depending on frequency. High frequency coincides with shorter transmission hop distance. Systems on 23 – 38 GHz are prone to rain attenuation. Microwave Transmission Basics M/W Channel Arrangement Lower Band F0 Upper Band F1 F2 F3 F4 F5 F6 F1’ F2’ F3’ F4’ F5’ F6’ RF channel arrangement acc. ITU-R Microwave Transmission Basics Table of Contents M/W Link Elements? ? ? ? ? ? ? ? IDU ODU Antenna— Functions Specifications Types Pressurization Equipments
Microwave Transmission Basics Elements of a MW link Antenna ODU Free Space Antenna ODU IDU IF Cable IF Cable IDU Microwave Transmission Basics Spur Link (Low Capacity Link) 7 – 38GHz Systems, generally used for PDH Spur Links Outdoor Unit (ODU, consists of RF-transmitter and antenna) IF-interconnection cable Indoor Unit (IDU) ? ? ? ? IDU Functions: Multiplexing /Demulteplexing of Tributaries. Modulation/Demodulation with the Carrier. IF conversion. Microwave Transmission Basics IDU BLOCK DIAGRAM: Power Supply 155Mbps
Main Channel MUX/ DEMUX Modulator IF Card Cable Combi-ner 2 Mbps Wayside Channel 64 Kbps User Channel Demodulator Coax Cable NMS/Ethernet External Alarms IDU Controller Microwave Transmission Basics • ODU BLOCK DIAGRAM: Power Supply AGC Voltage Reading 350MHz TX Converter 3-4GHz Coax Cable AGC Cable Combiner X Band Synthesizer RX Converter Trans receiver Converter Amplifier 140 MHz 3-4GHz IDU Controller Microwave Transmission Basics ? • • Antenna Functions: Works as an amplifier to overcome the fade margin and give desired AGC levels.
Antennas: Wire carrying HF Current is surrounded by Electric and Magnetic Fields Voltage Standing Wave radiation 2 Microwave Transmission Basics ? Antennas: Voltage Standing Wave radiation Microwave Transmission Main Specification Basics Antenna Radiation Pattern Omni Antenna Lobe Point-to-Multipoint Directional Antenna Lobe Point-to-Point Microwave Transmission Basics Antenna Gain: Directive Gain ? Power Density radiated by antenna ? Power Density Radiated by Isotropic Antenna ? ? ? * Power Density measured at same distance * Both Antenna radiate radiate the same total power Bandwidth: — Operating Frequency bands — Possible to tune antenna for slightly different frequency range while retaining the same characteristics • VSWR: Is the Guaranteed peak Voltage Standing wave ratio within the operating band Microwave Transmission Basics Antenna Specifications: Gain: Stated in dBi( Decibels over an isotropic radiator). Primirarly a function of antenna size ? Front to back Ratio: In dB. Denotes highest radiation relative to main beam at 180+/-40 degree across the band. ? Half Power Beam Width: Nominal total width of the main beam at -3dB points ?
Polarization: Can be single or dual polarised ? ? ? Isolation: For Dual polarised antennas. Refers to isolation between each polarised beam Microwave Transmission Basics Antenna Polarization ? Two main Types of Polarization: ? Vertical Polarization ? Horizontal Polarization Microwave Transmission Basics Antenna Polarization Vertical Polarization Horizontal Polarization Gridpak Low Back Lobe Focal Plane High Performance Dual Beam Angle Diversity Microwave Transmission Basics Antenna Feeder Types Air Dielectric Antenna Cables require Pressurization when used outdoors