Multi-Emitter Scenario Generator, Reference Solution

Keysight Technologies

Multi-Emitter Scenario Generator, Reference Solution

Solution Brochure

• Simulate realistic and dynamic radar threat-emitter signal environments consisting of thousands of emitters and millions of pulses-per-second
• Make Angle of Arrival (AoA) measurements in changing signal environments for real-time radar threat-emitter sorting and direction finding
• Quickly and easily set up complex AoA signal scenarios with Signal Studio software

Challenges of Simulating Multi-Emitter Environments

The modern spectral environment contains thousands of emitters—radios, wireless devices, and tens to hundreds of radar threats — producing millions of radar pulses per second amidst background signals and noise. In EW design, the multiplicity, density, and bandwidth, make it impractical to use a single source or a small number of sources to simulate a single emitter or a small number of emitters. Cost, space, and complexity considerations rule out these approaches. The most practical solution is to simulate many emitters with a single source, and to employ multiple sources — each typically simulating many emitters — when required to produce the needed signal density or to simulate specific phenomena such as angle-of arrival (AoA). The ability to simulate multiple emitters at multiple frequencies depends on the pulse repetition frequency, duty cycle and number of emitters, and ability of the source to switch between frequency, amplitude, and modulation quickly.

In addition to creating emitters with the desired fidelity and density, it is also important to match the geometry and kinematics of EW scenarios since the AoA of a radar threat to the EW system changes slowly compared to other parameters such as center frequency and pulse repetition frequency. EW systems measure AoA and estimate distance using amplitude comparison, differential Doppler, interferometry (phase difference), and time difference of arrival (TDOA). Precise AoA measurements enable precise localization of radar threats. New stand-off jamming systems use active electronically-scanned arrays capable of precise beam forming to minimize loss of jamming power due to beam spreading towards a threat. Moreoever, EW receivers with better AoA capability reduce the need for pulse de-interleaving and sorting. Consequently, AoA is an increasingly important test requirement.

Angle of Arrival Methodologies

Three common angle of arrival (AoA) or direction finding (DF) methods for EW receivers include: amplitude comparison, time difference of arrival (TDOA), and interferometry. These are all passive monopulse methods which require no cooperation from the threat radar (active homing) and each measures RF pulses from the threat to calculate an AoA.

Amplitude comparison method

Amplitude comparison monopulse, the most common direction finding method used in radar warning receivers, relies on the ratio signal (P2/P1 in Figure 2) of two displaced radiation patterns originating from a single phase center that overlaps in the far field. The antenna boresights are oriented (physically squinted) 90 degrees from one another so that the same pulse incident on both patterns has a measureable power difference in each channel. The power difference gives a meaningful arctangent calculation shown in the equation in Figure 2. If the two antenna beams were pointed in the same direction such that P1 and P2 were the same, the arctangent would almost always give 45 degrees.

Amplitude-comparison monopulse gives 10-15 degree direction finding accuracy because measured cross-channel power levels vary due to aircraft motion and amplitude attenuation or shadowing by the aircraft. For example, the receive power in one channel may be inaccurate because the power was attenuated by the airplane. Often, AoA resolution is more important than the accuracy. The resolution is the ability to distinguish co-located threats such as different radars within the same SAM site.

Time difference of arrival and interferometry methods

Less commonly used are the time difference of arrival (TDOA) and interferometry AoA methods. TDOA (Figure 3) derives AoA based on the delta time difference an RF pulse is seen at two antennas. Knowing that a signal will travel at the speed of light (c) over a distance equal to the distance between the two antennas, we can take the arcsine of the ratio (TDOA x c)/d to determine the AoA. Although this method does not depend directly on wavelength, it does require precise knowledge of delays through each receive channel, which vary with frequency.

Like TDOA, interferometry (Figure 4) is calculated using the arcsine of a ratio. With interferometry, the EW receiver is measuring the phase difference between apertures, φ. Wavelength, λ, is measured by the EW receiver using an instantaneous frequency measurement receiver (IFM) which gives the frequency of a pulse to ±1 to 3 MHz. The distance between apertures, called a baseline, is known with some uncertainty level. In general, longer baselines are used since this provides better accuracy and less sensitivity to uncertainties. However, at long distances, the phase difference will wrap, leaving ambiguities in this measurement. This is why most modern systems use more than one baseline or a shorter baseline to resolve ambiguities.

Cost, size and procurement time benefits

Beyond realistic AoA simulations, the reference solution provides other advantages including size, cost and procurement time. Traditional EW systems have been developed using large, expensive proprietary test systems that have long lead times and provide limited support for ongoing end user customization. The reference solution hardware, small enough to fit on an engineer’s desk (Figure 5), is configured with COTS test equipment at a fraction of the cost of typical EW test systems. Because it incorporates COTS hardware and software, it can be delivered in months instead of years.