Introduction
Radio systems enhance lives and create economic wealth. You most likely use mobile phones and watch TV whilst our emergency services rely on radio to keep us safe. The radio spectrum has to be managed to accommodate changes in demand and technology which leads to the reallocation of frequencies for new services.
We consider whether the reallocation of some S Band radar frequencies could affect the availability of radar mitigation solutions for wind farms.
Radar Frequency Bands
Radar frequency ranges are defined in bands as shown below:
| Band | Frequency Range | Radar Types |
| 1030MHz and 1090MHz | All Secondary Surveillance Radar (SSR) | |
| L Band | 1215MHz – 1400MHz | En-Route Primary Surveillance Radar (PSR) Air Defence Radar (PSR) Aveillant Holographic RadarMultistatic PSR |
| S Band | 2300MHz – 2500MHz and 2700MHz – 3600MHz |
Civil and Military Airport Approach PSR Air Defence Radar (PSR) C-Speed Lightwave Radar Meteorological Radar/ Multistatic PSR |
| C Band | 5250MHz – 5925MHz | Meteorological Radar |
| X Band | 8500MHz – 10550MHz | Terma Scanter 4002 Radar Marine Radar |
S-Band Spectrum Release Programme
The UK government is seeking to release radio spectrum for new commercial services including mobile telecommunications, data and broadband before 2020.
This requirement is being driven by the Department for Culture Media and Sport which has identified spectrum currently used by S-Band radar for reallocation – specifically frequencies between 2700MHz and 3100MHz.
The Civil Aviation Authority (CAA) has undertaken an initial study that has concluded that some of the S-Band can in fact be released for other uses.
It is not yet known exactly which frequencies are to be released when, but it is fairly certain that some S-Band frequencies are to be reallocated meaning that the availability of S-Band spectrum for new users could be limited.
Wind Farm Radar Interference
Wind turbines can affect radar when their rotating blades are within radar line of sight. Impacts can include clutter and desensitization.
It is sometimes necessary to find a technical or operational solution to deal with these effects. This can involve the provision of a new radar which would need its own allocated frequency.
Wind Turbine Radar Mitigation Technologies
There are many technologies and processes that have been considered for mitigating the effects of wind turbines on radar systems. Those that have enabled – or are considered likely to enable – the construction of wind farms are listed in the table below:
| Mitigation | Description | Radar Spectrum Implications |
| Markers | An electronic marker showing wind farm location is added to radar display | None |
| Blanking | The radar or system is blanked at the wind farm location | None |
| Non Auto Initiation Zone (NAIZ) | The radar is configured not to initiate tracks in the vicinity of the wind farm | None |
| Transponder Mandatory Zone (TMZ) | Aircraft flying in the vicinity of the wind farm must have operational SSR transponders | None |
| Operational | Operational measures are taken to ensure wind turbine impacts are managed safely | None |
| Thruput MIDAS III | Hardware clutter processing system connected to air traffic control display | None |
| NERL System RM | NATS En-Route radar modifications to eliminate wind farm clutter. | None |
| In-fill with existing conventional radar | The affected radar is blanked in the area of the wind farm. Data from an existing radar is substituted. | None |
| In-fill with new conventional radar | The affected radar is blanked in the area of the wind farm. A new conventional radar is commissioned. Data from the new radar is substituted. | A radar frequency has to be allocated. This is likely to be an S Band frequency. |
| C-Speed Lightwave Radar | This is a replacement radar designed to provide radar data from above the wind farm whilst not detecting the wind farm. | An S-Band radar frequency has to be allocated. |
| Aveillant Holographic Radar | This is a replacement 3D solid state radar designed to provide radar data from above the wind farm whilst not detecting the wind farm. | An L-Band radar frequency has to be allocated |
| Terma Scanter 4002 Radar | This is a replacement radar designed to provide radar data from aircraft whilst filtering out wind turbines. | An X-Band radar frequency has to be allocated. |
| Multistatic PSR | This is a new distributed surveillance radar technology that is unlikely to be affected by wind turbines | Radio spectrum will be required in either L or S Bands. |
Conclusions
The spectrum release programme is likely to result in a reduction in the available S-Band frequencies between 2700MHz and 3100MHz. The majority of available wind farm radar mitigation solutions will not be affected. It is possible, but by no means certain, that three mitigation technologies could be affected. These are:
- In-fill with new conventional radar
- C-Speed Lightwave radar
- Multistatic PSR
- The wind industry should work with the CAA to ensure that spectrum is made available for wind farm mitigation.
Recommendations
Wind farm developers should ensure that radio spectrum is available for their own specific radar mitigation solutions.
Image accreditations: “motion rainbow slapzoom” by “Creativity103” / CCBY/ Resized from original.
Changed Priorities Ahead sign” by “R/DV/RS” / CCBY/ Resized from original.
