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Spectrally Efficient Radar Systems

How will they help?

In the frequency band between 1GHz and 3 GHz around 30% of the spectrum is primarily allocated to radar systems and is largely unavailable to other users of the spectrum. These frequency bands have very desirable propagation properties, and could be used to support other communication services, such as cellular telephony, messaging and wireless local area networks. Potentially large amounts of spectrum could be freed up for commercial purposes if radar systems can be improved in terms of their spectral efficiency, moved to a different frequency band in lower demand, or can share the spectrum with commercial users.

Ofcom is researching this area to:

demonstrate the practicality of techniques which will
- improving the spectral efficiency of radar systems
- allow radar systems to operate in different bands
establish a cost benefit analysis, determining the costs of modifying and re-certifying existing radar systems or deploying new systems, and comparing them to the value of the spectrum released for other commercial applications.

How does a radar system operate?

Radar systems send out radio pulses in a given direction to detect targets. The angle of the target is determined from the antenna pointing direction. The range of the target is measured from the time taken by the transmitted pulse to be reflected back from the target and received as an echo at the antenna.

Figure 1 A typical air traffic control radar system

Signals returned from distant targets such as aircraft can be extremely small due to the distance of the target and dispersion of the transmitted energy. To compound this, the signal must complete with that from other interfering signals such as reflections from the land and weather, termed ‘clutter’.

Ofcom has conducted previous work in this area. An earlier SES study considering radar systems within the 1-16GHz band identified techniques that could potentially improve the spectrum utilisation of radar systems considerably. Short term solutions identified include:

improving the interference emissions of systems for example through the use of sharper cut-off filters in existing radars
improving the spectral re-use between systems through the use of waveform coding

In a longer time frame, the work estimated that the use of continuous wave (CW) and long pulse length radar systems could reduce the spectrum used in certain applications by up to 90%.

Further work has been commissioned to follow up on these findings. The work will investigate the practical issues remaining which must be addressed to implement these recommendations and use the expertise of radar manufacturers to establish the indicative costs of implementing the solutions, for example system redesign costs and re-certification costs for ATC modifications.

Initial work in this area has covered the following topics, which are discussed below:

A study into the practical problems of generating high power coded waveforms using travelling wave tube or alternative devices, in order to increase radar frequency reuse.
Analysis of the practical issues in deploying a CW radar system, for example investigating the susceptibility of such systems to deliberate or accidental jamming and investigating techniques that could be employed to recover range information from CW radar.

Project status

The continuing work in this area will estimate costs of the various system enhancements and new deployments. These will determine the feasibility of measures to improve the spectrum utilisation of these radar systems and provide an assessment of the increased value and services that could be made.

The project is now complete and you can download the final report below.

The main report has been broken up into sections for ease of download.