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Broadband Radar: By Kevin Poulter A quantum leap forward Mariners have always needed to know the quickest and safest route between where they are and where they want to be – and what obstacles might be encountered on the way. 12  Silicon Chip siliconchip.com.au This comparison of Broadband vs Pulse radar shows a line of mooring poles. In the Broadband image (left) there’s a boat moored between the fourth and fifth poles – a fact completely missed by the pulse radar. In fact, it’s having a hard time differentiating the poles! Just as important is the “blind spot” immediately around the pulse radar, masking close craft. R adar systems, first used during WWII, are commonplace on larger, ocean-going vessels but for quite a number of reasons – cost being a major one but also the inherent danger of traditional radar signals – they haven’t been found on too many smaller craft. With the exception of tall-masted vessels, keeping boat users and radar signals separated isn’t easy! The electronics age has revolutionised small boat use with accurate positioning guaranteed, collision avoidance systems, depth sounders, world-wide radio contact, AIS and much more. But now there’s a new player in the game: Broadband Radar, which promises to revolutionise navigation for vessels of all sizes – at a price that is significantly lower, bringing it into the range of the casual yachtsman or recreational fishing boat owner. Not only that, it’s dramatically safer to use than existing (pulse) radar systems. Broadband Radar utilises technology similar to that used in military and IMO-certified radar applications – unlike anything else on the recreational marine market. Designed from the ground up, Broadband Radar is not an improvement on old designs, rather its a completely new design. Consumer FMCW (Frequency- Modulated Continuous Wave) Broadband Radar technology was introduced during 2009. It came after more than five years of intensive research, development and testing, even when one manufacturer ‘threw in the towel’ as too hard/too expensive. It was developed by Navico, the world’s largest marine electronics company, which has five leading marine electronics brands: B&G, Eagle, Lowrance, Northstar and Simrad. Broadband Radar is available in three of their brands: N o r t h s t a r, Lowrance and Simrad. Broadband Radar systems clearly differentiate between docks, channel markers, pilings, moored vessels and other important targets. Target resolution is from <10m up to 13km (7 nautical miles), depending on the size of the object. Broadband Radar is far more than a minor upgrade. FMCW radar technology is not new – it’s existed for as long as traditional or “Pulse” radar systems (using the Inside the Navico Broadband Radar radome, along with the electronics which drives it. There is no physical connection between the transmit/receive antennas (at top) and the drive system – spinning toroids induce power and data is fed via an IR link. siliconchip.com.au November 2010  13 magnetron) have. It’s commonplace, especially in military radar where expense is not a constraint. But in the leisure market FMCW was not used at all until last year, as it was considered too expensive. Traditional radar Traditional “pulse” radars use high-powered magnetrons to generate microwave signals with very short pulses. Cavity magnetrons, which consist of a hot cathode with a high-pulsed negative potential activated by a high voltage, direct-current power supply, are one of the most common devices on earth – every microwave oven is based on one! Pulse Radar transmits an enormous pulse of microwave energy. Because it has a single antenna, Pulse Radar is ‘deaf’ for a brief period during and immediately after transmitting, as the receive circuitry must be turned off to prevent being overloaded by the transmitting pulse. Therefore it cannot ‘see’ at close range. After the RF Pulse, it turns off and goes to ‘listen’ mode. On a typical boat the resultant ‘blind spot’ is typically within about 10 – 15m of the vessel. Some units cannot even see within 30m. The high-power radar pulses, being microwave energy, are also dangerous at close range, so must be used away from where people are, or can go, on the vessel. This significantly reduces mounting options. Also, Pulse Radar emissions are particularly ‘dirty’, polluting the radio spectrum, with significant unwanted transmitted frequencies each side of the desired frequency. Another major disadvantage of Pulse Radar is its warm-up time – the magnetron filament must be heated for it to work, just like the vast majority of thermionic devices. This delay can be as much as 2-3 minutes – a significant safety consideration. Two minutes can be a long time when you’re worried about a collision. The alternative, leaving it on standby all the time, wastes a lot of power which is often unacceptable, especially on power-limited vessels such as yachts. Leaving the unit on also ages the magnetron’s filament. It has a finite life – typically around 3000-4000 hours – after which time it will either 14  Silicon Chip burn out or lose emission – either one of which will render the radar useless until the quite expensive Magnetron is replaced. FMCW radar is a whole new technology Unlike pulse radar, FMCW radar is instant-on and has no filament to burn out. Nothing beats Broadband Radar in the most vital navigation scenarios, such as coming into port at night, with possibly fog in the atmosphere too. The skipper may be navigating between boats, moorings and jetties, adding to the need to see at close range. FMCW can see within metres of the boat – the very objects that pose the greatest threat of collision – plus smaller targets, like a pole or fibreglass canoe. There’s a saying: ‘All collisions happen at zero metres’. Dramatically lower power Despite the high-definition improvements, Broadband Radar transmits a minuscule 100mW continuous – around 1/20,000 the power of typical pulse radars! To put that in some form of perspective, that’s around a tenth of the peak power a mobile phone radiates. Therefore the Broadband Radar radome (antenna) is safe to mount almost anywhere, in locations never before possible. You can even hug the radome during transmission! Lower power equals lower battery drain. With such low transmit power, the unit is easy on the battery, with only siliconchip.com.au about 14W consumption. Achieving the lowest DC power drain of any Xband marine radar makes Broadband Radar ideally suited for vessels with limited power, like sailboats. The beauty of being solid state is the unit can be turned right off and activated only when you want to make a sweep. Lower range – but clearer! Looking at the average power of a 2kW Pulse Radar, it’s sending out 2,000 pulses per second – average that out and it’s about 80 to 120 watts. The pulse radar has a range of about 44km (24 nautical miles). Broadband Radar does not cover such a range – it’s limited to about 5 to 7km – however, images are in highdefinition and as mentioned, they are down to very close to the vessel, where it really matters. Interference Because other boat’s FMCW Radars have the same technology, two antennas ‘looking’ at the same data at the same time could cause interference. However, in practice, this is almost unheard of. At worst, you see a single line across the screen, radiating from the centre out, which would only last for a short time. Sea clutter Sea clutter, or unwanted reflections The ethernet junction box which allows the system to accept a range of other inputs, such as sonar, audio, side-scan radar and so on. from waves, is a major problem in conventional radar for areas close to the boat. Traditionally, pulse radar has been detuned slight to eliminate sea clutter but this potentially causes legitimate targets to be missed. Highly improved range discrimination in FMCW radar allows it to scan smaller areas of the sea and so receive less unwanted reflection from waves in that area. Any small target amongst those waves will show up more clearly. Expansion The display unit is a modular type system, utilising ethernet in the antenna/scanner, expanding functionality through an ethernet junction-box. There are three ethernet connections across the back of the junction-box, enabling other devices to be attached, such as audio, engine management, autopilot control, AIS transceiver and much more can be connected. How it works Navico’s first-generation Broadband solid-state X-band radar technology utilises Frequency Modulated Continuous Wave (FMCW) techniques, by sending a continuous transmission wave with linearly increasing frequency. If those transmitted waves intercept an object, some are reflected back to the radar’s receiver. The difference between the currently transmitted and received frequencies, coupled with the known rate of frequency increase, is the basis for precisely calculating a “time of flight” and target distance. This system provides target detail superior to pulse radars, while transmitting at far lower energy levels. No slip rings The multi-pupose visual display has broadband radar on the left and Navico’s Sonar on the right. Highlighted is a shipwreck, clearly indentified on the screen. siliconchip.com.au In the scanner/antennas, there are two rotating toroids creating a transformer effect, transferring power from the bottom to the top. In the middle of the two toroids there’s a high-speed November 2010  15 infrared data link. The installation height is a balance between the ‘line of sight’ advantage of being high up and the benefit of seeing close targets, achieved best by a lower installation height. So oceangoing vessels generally have a higher installation while for inshore, lower height is best. This offers more flexibility – because it’s safe, the unit can be installed lower, with no adverse affect from radiation. On a Maritimo boat, for example, the Transponder is mounted quite low on the flybridge, on the arches. This would definitely not be safe for a Pulse Radar installation. Interface box To make it installation as easy as possible, even for the home boat handyman, Navico developed a unique interface box for their Broadband Radar. With standard radar, there’s connections such as the power cable, heading information to the radar plus ethernet cable. Installers like Broadband Radar with its plug’n’play installation. Other advantages are a lightweight design, low electromagnetic interference due to low emissions (which keep regulatory authorities happy) and of course a longer life. Narrow band, wide frequency sweep Broadband Radar operates in the 9GHz Marine X-Band. Specifically, the transmit frequency is swept over Simrad’s NSE12 visual display here shows the Broadband Radar but can display a wide range of data that will extend its capabilities – for example, an echosounder/fishfinder, AIS transceiver, autopilot control, engine performance display and much more – all accessible from a single screen. a bandwidth of 65MHz between 9.30GHz to 9.38GHz. That’s intended to keep clear of X-Band Pulse Radars and their ‘dirty big bangs’ of about 10-20MHz bandwidth. One of the key performance measures of any radar is its ‘range discrimination’ – the ability of the radar to discriminate between two close targets in range. Range discrimination for any radar is proportional to the bandwidth of the transmit/receive signal. A narrow bandwidth signal produces poor range discrimination, while conversely, FMCW’s wider bandwidth produces best range discrimination. In some operation modes Broadband Radar does transmit a narrower band signal. In these cases Navico uses “frequency-hopping”, a spreadspectrum technique, to spread the energy transmitting across the entire Another view mmm inside the Radome, this mmm this time showing rear (left) and front (right) views. Of particular interest is the double antenna seen clearly from the front, one section for transmitting and one for receiving. The signal processing is all achieved within the Radome and is fed to the display via an Ethernet connection. 16  Silicon Chip siliconchip.com.au available band. This reduces interference between radars. Broadband Radar picks up surfboard riders The receiver Conceptually the receiver is quite simple. It mixes the transmitted signal with the received signal that has bounced off a target. This received signal will be a delayed, producing a ‘difference’ or ‘beat’ frequency that’s proportional to the delay (and therefore also proportional to the distance to the target). The Broadband Radar unit then performs “Fourier analysis” of the ‘beat’ signal (using an FFT) to identify target responses in the signal. While conceptually the principle of FMCW radar is quite simple, the implementation can be quite involved. Since the radar is transmitting at the same time as it’s receiving, the transmitter has to be extremely low noise, so weak returns from distant targets are not obscured by noise from the radar’s own transmitter. Also a very high dynamic range is vital, so the receiver can process the large signals from close targets while at the same time processing the weak signals from very distant targets. The system design for the radar is quite different to a conventional radar. A conventional radar uses only one antenna, however because Broadband Radar transmits at the same time as receiving, two antennas are grouped in the one housing, one for transmit and one for receive. With a single conventional antenna, it’s relatively easy to couple the transmit/receive signal (in the base of the radar) to the rotating antenna through a rotary joint using a waveguide. With two antennas, Navico mounted the transmitter and receiver on the back of the rotating antenna. Navico does this because the aim is to detect the very faint returns from distant targets at the same time as transmitting. The receiver circuitry has no problem in removing the transmitted signal but the distant echos are so faint that they can get swamped by noise from the transmitter. By using separate antennas, the coupling of the noise from transmitter to receiver is reduced, making this problem significantly easier to overcome. Nevertheless, the RF transmitter has exceedingly low noise characteristics to meet the performance goals. siliconchip.com.au Every waterway has hazards particular to it – and the passage out to the open sea from the Gold Coast Broadwater, known as the Seaway, is no exception. In addition to fast-moving tides, Gold Coast boaties making their way out to sea know they have to keep a sharp look-out for surfers paddling across the Seaway to and from a popular break on South Stradbroke Island. The surfers are particularly hard to see when the swell’s up – which is unfortunate, given that’s when surfers are most likely to be out searching for waves! Last year, the Navico Australia team was heading out to sea to continue trials on its new Broadband Radar, the BR24. To everyone’s amazement, the radar picked up an image long before those on board spotted it: a group of surfers paddling across from South Stradbroke Island – even though the surfers were flat on their boards and had radar profiles of no more than about 30cm above the sea! Clearly, Navico’s BR24 Broadband Radar takes precision radar to a whole new level. The ‘beat’ frequency signal is sampled by a 16-bit ADC. This digitised signal is then processed by a signalprocessing chain implemented in an FPGA (Field Programmable Gate Array). The signal-processing chain performs Fourier analysis plus a number of other signal processing operations including interference suppression and rejection, sea and rain clutter filtering, equalisation for range, targettracking and conversion to a 4-bit-perpixel protocol for transmission on an Ethernet network. The display reads the radar data off the Ethernet network, applies a colour palette and performs a Cartesian-topolar conversion to generate the standard radar PPI (Plan Position Indicator) that most people associate with radar. The price? Compared to pulse radar, Broadband Radar is exceptional value for money, even disregarding the clear operational advantages. First you buy the multi-pupose visual display screen and then add on what you need – including Broadband Radar of course! The entry-level 5-inch HDS screen, intended for smaller craft, is $1000 and the BR-24 radar is currently $1999 RRP, or $3,000 for a full system. For larger boats, the system with 12inch NSE Screen plus BSM-1 (Sounder Module) and BR-24 is $8299 RRP. Acknowledgement Our thanks for assistance in the prepartion of this feature to: Kevin Soole, Program Manager, Navico Auckland Andrew Corbett, R&D Manager, Navico Asia Pacific Estelle Baldry and Damien Weber, Navico Australia and Ben Sandman. SC Further information: Contact Marine Dealers, or Navico at www.navico.com November 2010  17