Radar Detection of Small Targets for Improved Security

Easat is a wholly owned subsidiary of the family-controlled UK engineering group, Goodwin PLC. Goodwin PLC traces it’s origins to 1883, and today has annual sales of about £65millions, and some 650 employees.

To date, Easat has supplied antennas or complete radar sensor equipment to over 160 separate radar installations, in over 40 counties worldwide.

Easat operates a Quality Management System complying with ISO/EN 9001:2000, being audited by the British Standards Institution.

Radar Application

The company’s core products of antennas and turning units are designed and manufactured in-house; transmitter/receivers and other electronic equipment and software is selected from world-leading specialist manufacturers.

The company provides long range coastal radar surveillance systems for EEZ security and law enforcement, with emphasis on the detection of small and large vessels in adverse weather. Detection of small targets is good weather in itself is not challenging but in poor weather (heavy rainfall and rough seas) the situation changes dramatically. In these conditions radar detection of small targets requires very high gain antennas with narrow beamwidth to reduce rainfall and sea clutter return. Additional features of Easat radar antennas include the ability of polarisation switching in X band to improved performance in heavy rainfall, frequency diversity and a combined dual X and S band antenna for the most demanding weather conditions.

Typically radar targets may be 1m² or 2m² Radar Cross Section, such as Rigid Inflatable Boats, wooden or glass fibre fishing boats or high speed launches. These targets are detected and tracked simultaneously with the largest of maritime targets, based on achieving the maximum available dynamic range. Easat radars may combine low altitude detection of aircraft, with the detection of sea surface targets. For these reasons, Easat radar sensor systems generally provide better detection performance than its competitors, particularly in adverse weather conditions.

Easat activities include radar performance predictions, site surveys, installation and commissioning of antennas, turning units, towers and foundations, radomes where necessary, transmitter/receivers, target trackers, data fusion, data base management, operator workstations, and all related ancillary equipment to provide the complete radar sensor installation. Easat provides operator and maintainer training, and is particularly proud of its excellent reputation for long term support.

Easat equipment is commercial off-the-shelf (COTS) and at the planning stage careful consideration is to the end user requirements. In the initial phase, Easat will study in detail what are the customer needs in terms of radar detection and tracking and this will include the following points:-

• What type of target is required to be detected
• What are the minimum and maximum ranges of detection
• Antenna height
• Worst weather conditions expected
  
• Local topography and the effect this will have on false echoes and blind area
  
• Sector blanking
  

Easat core philosophy is provide a radar system that will be guaranteed to fully comply with the customer contractual detection requirements.

Radar Options for VTS Applications

From the beginning, Easat coastal radar antennas and systems have been rugged, COTS designs, developed in response to a small but growing market for long range surveillance radar for VTS, border security and law enforcement; mainly in applications where the use of high cost military or defence equipment was inappropriate or could not be justified.

For this market, radar engineers in various organisations had concluded that the most important factors limiting the radar performance of conventional VTS radars was the low gain and limited resolution of the standard antennas used. Mostly the antennas were slotted wave guide (SWG) antennas, derived from shipboard navigational radars. That is, by replacing the standard low gain VTS antenna with a shaped beam, high gain high resolution antenna, having low side lobes and preferably with additional facilities such as polarisation control and dual band operation, so the overall radar performance would be greatly improved. This conclusion is valid irrespective of the type of radar transmitter and receiver, and is especially true for the low power marine magnetron systems on which most VTS systems are based.

Modern advances in signal processing can greatly improve the radar performance in rain or in rough seas, i.e. in clutter; signal processing techniques can do little to improve clear weather radar performance. All such improvements can do is to reduce the degradation of radar performance due to clutter.

A cost effective route is to continue the development of reflector antenna technology by optimising well-proven RF engineering principles with the latest numerical analysis and modelling methods; and to employ the best available magnetron radar transmitter/receivers derived from those supplied for marine navigational use, but with additional RF techniques such as the use of frequency diversity, switchable polarisation, and dual band operation.

This is the Easat COTS approach, which to-day includes specially developed magnetron transceivers incorporating frequency diversity, together with unique advanced anti-clutter processing techniques.

The Easat philosophy is that for coastal radar surveillance each end user has a unique set of operational requirements, unique topography, and unique constraints. This is in contrast to most military, naval, air surveillance requirements.

Therefore, each coastal surveillance project requires an individual, customised system solution. A standard “catalogue “solution will be sub-optimum.

Easat has the ability to create teaming of proven specialist suppliers, to provide a complete surveillance system.

Radar Options For Coastal Radar

For sea surface surveillance in clear weather, X band microwave systems are preferred due to the longer range that can be achieved, with better resolution, as compared to S band systems having similar size of antenna and similar transceivers. In heavy rain, and rough seas, the rain and sea clutter reverses this situation as regards target detection, with S band giving the better radar performance; as the rainfall rate increases the detection performance of the S-band remains unaffected whilst X-band starts to degrade, but with lower resolution. When air targets are to be detected, S band will generally be used to reduce the clutter from rain clouds and due to lower propagation losses.

Due to the curvature of the earth, conventional microwave radar is capable of reliable surveillance covering only the radar “line-line-of-sight”. This approximates to 15 nautical miles for a small boat, detected by radar at 30 metres height to 80 nautical miles for a large ship, detected by radar at 1000 metres height. Air targets can be detected at longer ranges depending on target size and altitude.

Summary

A low cost, high performance radar surveillance system for VTS and coastal applications should consist of:-

1. High gain reflector antenna, with dual polarisation switching and narrow azimuth beam width.
2. Purpose designed frequency diverse magnetron transceivers.
3. Target and track extractors and local displays, including specially developed anti-clutter processing
4. Operator display, data processing and control suites chosen to meet user's requirements.
5. Additional sensors such as Radio Direction Finding, A.I.S transponders, CCTV.
6. Voice and data communications.

Easat Antennas offer a complete design and supply service for all elements of a VTS or coastal surveillance systems, backed by our extensive experience in the design and supply of high performance radar system products.