Seastema SpA, a company owned by Fincantieri (Genova, Italy), designs, develops, and supplies integrated automation systems for different areas of the marine industry. The company established an Innovation Division in Rome to verify the feasibility of an unconventional radar system by means of a demonstrator built as much as possible with commercial off-the-shelf (COTS) devices.
The Need for Ubiquitous Radar
Currently, multifunctional phased array radars (MPARs) are centered around a monostatic architecture based on planar antennas that form a high-resolution single beam in transmission and in reception. Modern MPARs employ Active Electronically Steerable Arrays (AESA) that allow each radar antenna in the system to act as a small computer, giving the radar system a wider range of simultaneously operational frequencies, which makes it harder for opposing systems to detect. Conventional AESA radars normally scan ±45° so that the entire round angle is covered by means of four faces, or by a rotating single face. This implies that the different tasks assigned to them are sequentially fulfilled, leaving a limited amount of time to accomplish dedicated tasks such as low-angle surveillance and tracking of very fast and very small targets. The first type of target needs a rapid formation of the track to be counteracted in time; both types require long observations to be properly extracted from the surrounding clutter. These operational needs require a continuous observation of the interested area, which only staring beams can obtain.
Omega 360 2D radar instead utilizes a “rose” of simultaneous staring beams on receive, with a single omnidirectional beam on transmit (Figure 1). This solution recalls the concept of “ubiquitous radar” that looks everywhere all the time. The architecture is then bistatic in the sense that transmission and reception use different antenna beams. The receiving beams are formed by digitally combining the signal received from radiating columns distributed over a frustum of a cone.
Scientists have realized and assembled a demonstrator of this architecture (Figure 2) called a Digital Antenna Evaluator (D.Ant.E) in the laboratory of Seastema Rome, where a radar station has allowed full characterization of the staring antenna beam's features after DBF and pulse compression. D.Ant.E was designed with an overall requirement of rapid and reliable detection of small moving targets at low altitude, from extremely high to very slow speed, in severe clutter. Typical targets include sea skimmer missiles, small boats, periscopes, and drones. The surveillance feature was enabled by of a group of staring antenna beams formed around a cone. This solution offers very long times on target, so the radar needed to be capable of selective Doppler filtering with consequent fine separation between real targets and clutter.
D.Ant.E comprises 216 columns of radiating elements evenly distributed along the surface of a frustum of a cone. Each column connects to a receiving channel through which the received RF signal is amplified, filtered, downconverted, and digitally sampled. The receiving channels are grouped by four into 54 modules called Q-Packs. The sampled digital signals in baseband transfer in real time to a central processing unit that applies eight sets of coefficients to obtain eight simultaneous beams.
A PXIe-1085 chassis from National Instruments (Austin, TX) was used that includes a host computer and a number of specialized modules (Figure 3) to implement the radar signals and timings. Modules used include a controller to command and control modules in the chassis, one to generate the IF signal, one to generate the sampling and system clocks and route all radar timings, a device to generate all radar timings, a module to generate the Stable Local Oscillator (STALO) signal, and a module to acquire the beams after digital beam-forming, perform pulse compression, and transmit the data to the PC processor by means of optical fiber.
The IF signal is upconverted to the X band (in the frequency range of 9-10 GHz) using an upconversion unit amplified by a solid-state power amplifier module, and then transmitted. The sampling clock by Q-Packs was used to sample the received signal, and by DBF to synchronize Q-Pack data links. The system clock constitutes the time base of the entire demonstrator. The unit is locked by a 10-MHz reference oscillator.
The chassis can be controlled remotely with a radar management computer (RMC) that allows the user to choose all the operative parameters of the test to be done. The RMC also controls the radar processor, console, and tracker units.
During the experimental validation in the laboratory in Rome, the DBF output, after pulse compression, was presented in real time on a display, and recorded for analysis. The beams were obtained through a digital combination of the signals received by the columns when an RF chirp waveform is transmitted by a horn, and the antenna platform is mechanically rotating in a sector from -180 to 180 degrees with a sampling step of 0.2 degrees.
On the outdoor test range, attention was focused on the verification of the detection capabilities of standard targets immersed in the sea clutter. This required the identification of a dedicated setting of all the radar variables pertaining to the detection thresholds, to plot extraction and the tracking algorithms. Because the radar is almost completely digital, the adopted COTS hardware and software solutions have demonstrated their efficacy as far as the possibility of monitoring the signal flow along the processing chain, and the ease of use of the variable setting.
The experimental results confirm that the innovative nature of the Omega 360 architecture powers the implementation of algorithms capable of exploiting the advantages of the multiple simultaneous beams and their inherent benefits, such as a long time on target and a seamless surveillance. This affects reduction in reaction time after the first target detection, the filtering capability of all types of clutter, and the cancellation of passive and active interferences.
The results obtained with the D.Ant.E demonstrator first in the laboratory and then in a real environment, confirm the validity of this “ubiquitous” approach. Based on this, the company configured a product called Sea Omega 360 that supports the anti-sea skimmer missile defense of modern vessels.
The Sea Omega 360 configuration, unlike D.Ant.E, concentrates the antenna gain on the horizon to maximize the rapidity and reliability of the detection of small moving targets at low altitude, from extremely high to very slow speed, and in severe clutter typical of the naval environment. These include sea skimmer missiles, small boats, periscopes, and drones. This has required the modification of the solid of rotation from a frustum of cone to a cylinder (Figure 4). The system can be installed on the top of a mast at a height that can permit sufficient optical visibility on the horizon, and provide a stabilization mechanism for pitch and roll compensation. A spherical radome fulfils the dual need of protecting the hardware from atmospheric injuries and creation of an ambient suitable for on-the-mast maintenance. The Sea Omega 360 system can integrate the surveillance capabilities of a modern ship with outstanding performance against surface and low-angle threats at a competitive price with other existing systems.
This article was contributed by National Instruments, Austin, TX. For more information, visit here .