Electronic Warfare Applications Research Articles

Design of a Compact Log Periodic Dipole Array Antenna for Broadband and High-Power Beam Synthesis Using Superposition

This paper investigates various array beam shapes for high-power electronic warfare applications using an actual broadband array antenna. For use in a limited mounting space, a compact printed log periodic dipole array (LPDA) operating over a wide bandwidth is designed. The LPDA is then extended to an 8 × 1 array, with active element patterns (AEPs) obtained through simulation and measurement. Beam synthesis is performed by the superposition of several array patterns, which involves adjusting the weight of each AEP. To derive a synthesized array beam shape that is similar to the guided mask, the Taylor window weighting method is applied to each array pattern. Finally, beam synthesis for the flat-top beam, cosecant-squared beam, and iso-flux beam is performed using Taylor window-weighted AEPs, and the results are compared with those of beam shapes using ideal isotropic patterns. The results demonstrate that various beam shapes can be achieved for high-power electronic warfare applications using the AEPs of an actual array antenna.

Microwave Photonics Broadband Doppler Velocity Simulator with High Spurious Suppression Ratio by Using Serrodyne Modulation

A Doppler velocity simulation method based on serrodyne modulation is proposed to achieve the frequency shift from hundred hertz to megahertz. One sub-phase modulation (PM) in a dual-parallel dual-drive Mach–Zehnder modulator loads a sawtooth signal to achieve a small frequency shift of the optical carrier. The other three sub-PMs implement carrier-suppressed double-band modulation of the RF signal. The RF signal is directly coupled from the receiving antenna to the modulator’s RF port without any electrical devices like a 90° hybrid, which ensures a broad operational bandwidth of the system. After filtering out one of the RF modulation sidebands by an optical filter, Doppler frequency shifting (DFS) is realized through frequency beating. The half-wave voltage of modulators rapidly decreases at low frequency shifts, leading to an increase in spurious signals. In order to improve the spurious suppression ratio (SSR) of DFS, a digital pre-distortion compensation based on the measured half-wave voltage is implemented in the frequency domain. Experimental results show that SSRs are larger than 35 dB when frequency shifts range from 0.1 kHz to 1 MHz. The RF operation bandwidth covers 2–40 GHz. The effectiveness of a Doppler velocity simulator is evaluated, and the simulation velocity error is less than 0.06 km/h. The proposed method has potential applications in both broadband electronic warfare and traffic metering applications.

Dual TOA and Signal Type Prediction for Electronic Warfare Applications

Dual TOA and Signal Type Prediction for Electronic Warfare Applications

High-resolution photonic-assisted microwave frequency identification based on an ultrahigh-Q hybrid optical filter

Photonic-assisted microwave frequency identification has been extensively studied in civil and defense applications due to its distinct features including wide frequency coverage, large instantaneous bandwidth, high frequency resolution, and immunity to electromagnetic interference. In this paper, we propose and experimentally demonstrate an approach for high-resolution frequency identification of wideband microwave signals by linearly mapping the microwave frequencies to the time delays of the optical pulses. In the proposed system, an ultrahigh-Q hybrid optical filter is a key component, which consists of a fiber ring resonator (FRR) and a silicon photonic racetrack micro-ring resonator (MRR). The FRR has an ultra-narrow bandwidth of 7.6 MHz and a small free spectral range (FSR) of 292.5 MHz, while the MRR has a bandwidth of 167.5 MHz and a large FSR of 73.8 GHz. By precisely matching the resonance wavelengths of the FRR and the MRR, a hybrid optical filter with an ultrahigh Q-factor and a large FSR is realized, which is much preferred to realizing a high resolution and a wide measurement range for microwave frequency identification. An experiment is performed and different types of microwave signals are identified. A frequency measurement range as broad as 33 GHz from 2 to 35 GHz, a frequency resolution as high as 15 MHz and a measurement accuracy as high as 5.6 MHz are experimentally demonstrated. The proposed frequency identification system holds great advantages including high frequency resolution, high measurement accuracy, and wide frequency coverage, which can find extensive applications in next-generation electronic warfare and cognitive radio systems.

Dual-band tunable microwave pulse signals generation based on a time domain mode locked optoelectronic oscillator

We propose and experimentally demonstrate a dual-band tunable microwave pulse signals generation method based on a time domain mode locked optoelectronic oscillator (TDML-OEO). The dual-band radio frequency (RF) combs are generated via injecting two single-tone signals and a low frequency signal. The two single-tone signals are injected to optimize the aimed center frequencies gain, while the low frequency signal is used to accomplish the multi-mode oscillation mode locking process. Furthermore, the dual-band RF combs with variable repetition rates of 3.69 MHz, 9.22 MHz, and 18.45 MHz are obtained with an over 72 dB ultra-high suppression of super mode noise as the TDML-OEO operates in the varied harmonic multiples mode locking state. Besides, by adjusting the amplitude and central frequency of the two injected local oscillator signals (LOs), a controllable output power and frequency tunability ranged from 11.1 GHz to 13.8 GHz are achieved for the generated dual-band RF combs. The proposed dual-band tunable microwave pulse generation method has great potential applications in multiband radars and electronic warfare.© 2023 Optica Publishing Group under the terms of the Optica Publishing Group Open Access Publishing Agreement.

Quantization error for weak RF simultaneous signal estimation

In a congested signal environment, it is difficult to obtain estimates of weak RF signal parameters. Determining signal parameter estimates in real time is a challenge for electronic warfare receivers that aim to receive multiple simultaneous signals. Prior work provided estimates of weak signal parameters (weak signal frequency and weak signal amplitude) without taking into account any error introduced by analog-to-digital converters that are inherently part of digital signal processing systems. In order to obtain realistic estimates, we need to take error introduced by an ADC into account. The primary aim of this paper is to quantify error introduced by a single ideal ADC as a function of angle. This paper presents a method to estimate angle resolution and quantization levels in N-bit analog-to-digital converters (ADCs) for use in a weak radiofrequency (RF) simultaneous signal estimation process. The paper quantifies the error in the angle quantization of an N-bit ADC for an input complex signal that is the instantaneous frequency obtained for the situation in which there are two simultaneous signals (with one strong signal and one weak signal) in a weak RF simultaneous signal estimation process. The presented method describes the process to determine the angle quantization range, angle quantization uncertainty, and angle quantization error. This approach has potential applications in electronic warfare (EW) systems. The approach also has potential for assessing ADC performance for measurements that approach the quantum limit. Results are presented for 1-bit, 2-bit, 3-bit, and 10-bit ADCs.

High-frequency electric field intensity measurement based on frequency shift with high gain and wide frequency range

For the safe operation of equipment and personal safety protection in high-voltage environments, the precise measurement of the high-frequency electric field is of paramount importance. Optical electric field sensor (OES) is a current research trend for high-frequency electric field measurement but is generally limited by low sensitivity and the need for high-speed acquisition modules. Here, we propose a high-frequency electric field intensity measurement approach based on frequency shift with a high gain and a wide frequency range. We used two different frequency shift methods, i.e., stimulated Brillouin scattering and down-conversion. Based on the former method, an amplification module is designed to enhance the OES signal with a frequency range from 11 GHz to 20 GHz and a noise-suppressed gain of up to 63 dB, and based on the latter one, the high-frequency OES signal is down-converted to a sub-MHz intermediate frequency signal. The frequency shift approach shows the potential to detect and analyze high-frequency electric fields with low cost and a small footprint, which is valuable for their applications in electronic warfare, high-voltage engineering, space exploration, etc.

An 800-W Four-Level Supply Modulator for Efficient Envelope Tracking of RF Transmitters

Modern RF communication and electronic warfare applications require systems capable of amplifying signals with high bandwidths and high peak to average power ratios (PAPR). One technique used to meet these demands is supply modulation also known as envelope tracking where the drain voltage of the power amplifier (PA) is dynamically changed according to the signal envelope. The limiting factor with supply modulation is typically the efficiency and switching speed of the power converter. The power converter must also be capable of producing high power levels when supplying an array of PA units or a single high power transmitter. This paper demonstrates the design and characterization of a four-level discrete supply modulator with a peak output power of 800W operating at a maximum switching frequency of 10MHz. The modulator switches between four discrete voltages from 10 to 20V. GaN on silicon HEMT power transistors are selected for the switching devices after conducting a survey of commercially available silicon MOSFET, silicon-carbide MOSFET, and GaN on silicon power transistors. Trace interconnect models are developed to achieve accurate predictions of the time domain waveforms, including ringing at the switching edges. These interconnects are first analyzed using full-wave electromagnetic simulations, and then modeled with RLC networks suitable for time domain simulations. For a test signal with equal duty cycle between the four levels, an efficiency greater than 94.0% is demonstrated for average output powers exceeding 91.6W. When tracking the envelope of an 8MHz 64-QAM signal, an average efficiency of 93.5% is achieved providing a peak power of 800W.

Instantaneous Frequency Measurement with Reasonable Resolution and Simple Structure

Microwave signals carry important intelligence information in electronic warfare. Hence, the measurement of microwave signals plays a very important role. Traditional electronic microwave measurement systems are not appropriate for the instantaneous frequency measurement (IFM) of high-speed signals. A simple and low-cost photonic approach to the IFM based on frequency-to-power mapping is proposed and demonstrated with a reasonable resolution. The measurement is performed on account of a double Mach–Zehnder modulator (MZM), single-mode fiber (SMF), photodetector (PD), and signal processing. The scheme using four wavelengths achieves resolutions of ±0.1 and ±0.09 GHz respectively for the 15.8–18.4 and 18.4−21.2 GHz frequency measurement ranges. Therefore, the scheme is a broad prospects method for high-resolution IFM. Moreover, it is of great importance for applications in electronic warfare and high-resolution sensor systems.

Multi-delay photonic correlator for wideband RF signal processing

Correlation of radio-frequency (RF) signals is a fundamental operation in many fields such as information processing, detection, and imaging techniques at large. Because of the intrinsic limitations of electronic techniques, standard digital correlators, which rely on the acquisition of signals and their processing, become very complex to implement for the real-time analysis of signals whose bandwidth exceeds a few hundred MHz. On the other hand, analog correlators are limited by the performances of RF components. In this paper, we report the proof-of-concept of a correlator architecture based on a simple photonic platform, suitable for analog wideband RF signal processing. The concept, based on multi-heterodyne interferometry, gives access in real time to the entire correlation function of two signals by computing the cross correlation coefficients for 200 values of their relative delay simultaneously. The time-delay step can be adjusted from a few ns down to a few ps, enabling us to process signals with MHz to multi-GHz bandwidth. We have applied this architecture to the localization of RF transmitters by time difference of arrival (TDoA) and obtained a precision close to 10 ps for a 100 ms integration time. This concept is expected to find practical applications in various domains, from radar and electronic warfare to telecommunications, imaging, and radio-astronomy.

Dual-Conversion Microwave Down Converter for Nanosatellite Electronic Warfare Systems

In this work, a microwave down converter is proposed for nanosatellite electronic warfare applications. It provides high spurious suppression by exploiting a dual-conversion architecture and premium performance in terms of noise figure and linear dynamic range. The system design takes advantage of commercial off-the-shelf components, thus allowing for both fast and cost-effective prototyping, which are key requirements particularly concerning CubeSat systems. Since different military, commercial, radar and communication systems operate in the 2–18 GHz frequency band, the capability to integrate such kinds of receivers in CubeSats represents the new frontier of the electronic warfare systems. Moreover, due to the wide operating bandwidth, it can be successfully exploited as the receiver for different applications, e.g., satellite communication, radars, etc.

Modelling and Optimisation of UHF band EW Based WTA Problem within the Scope of Threat Assessment

The classical weapon target allocation (WTA) problem has been evaluated within the scope of electronic warfare (EW) threat assessment with an electromagnetic effect-based jammer- tactical radio engagement approach. As different from the literature, optimum allocation of non-directional jammers operating at different operating UHF frequencies under constraints to RF emitters is aimed in this study. The values of the targets are modelled using an original threat assessment algorithm developed that takes into account operating frequencies, jamming distance, and weather conditions. The computed jammer-target effect matrix has been solved under different scenarios according to the efficiency and cost constraints. It is seen at the end of the simulations that the allocation results for EW applications largely depend on the effect ratio used. The better results are taken in the case of under 0.5 effect ratio. Finally, jammer-radio allocation problem specified at the suggested model is solved successfully and effectively.

RF self-interference canceller prototype for 100-W full-duplex operation at 225–400 MHz

Military applications require more and different characteristics from in-band full-duplex radio technology than what the research prototypes developed for civil/commercial applications can offer. While the challenge of cancelling the strong transmit–receive coupling, i.e., self-interference (SI), in a full-duplex radio has been largely resolved at higher ultra high frequency (UHF) bands for low-power transmission, tactical communication and electronic warfare applications require major research efforts toward supporting lower military-relevant frequencies and significantly higher transmission power levels. In this paper, we present a prototype of a radio-frequency SI cancellation circuit for the lower UHF band at 225–400 MHz and transmit power of up to 100–200 W. The experimental results demonstrate that the canceller can suppress SI by 40–50 dB depending on the operation frequency within the band. It is targeted for the military application of simultaneous full-duplex jamming and interception of communications, where we can estimate that a 5-W signal-of-interest could be intercepted from 10 km away when simultaneously jamming with 100 W power.

Broadband Instantaneous Multi-Frequency Measurement Based on a Fourier Domain Mode-Locked Laser

Broadband instantaneous multi-frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked (FDML) laser source is proposed and experimentally demonstrated. An electrically controlled silicon microdisk resonator (MDR) with an ultra-narrow linewidth of 60 pm (~7.5 GHz) functioning as a fast tunable optical filter is used to implement the FDML to generate a linearly chirped optical waveform (LCOW) with a wide frequency-sweeping range of 0.5 nm. The LCOW is then mixed at a modulator with a microwave signal with its frequency to be measured, detected at a low-speed photodetector (PD) and sent to a narrow bandpass filter (BPF). When the difference between the instantaneous frequency of the LCOW and that of the signal to be measured is equal to the center frequency of the BPF, a short-duration temporal signal is produced, and the time location of the temporal signal represents the frequency of the signal to be measured. A proof-of-concept experiment is carried out. Both single and multi-tone microwave frequency measurements are experimentally demonstrated. The measurement range is as large as 20 GHz with a measurement resolution of 200 MHz and an accuracy better than ±100 MHz. The proposed method showcases a new method for instantaneous frequency measurement (IFM) with high performance in terms of multi-frequency identification, real-time measurement, and high measurement speed compared with traditional approaches, which is attractive for applications in modern radar, electronic warfare, communication, and cognitive radio systems.

Design of a High-Power UWB Antenna Incorporating a Solid Dielectric for Electronic Warfare Applications

In this paper, a high-power ultrawideband antenna is presented for the purpose of remotely neutralizing improvised explosive devices. The developed antenna has a bandwidth between 230 MHz and 2 GHz, as well as a maximum realized gain of 18.7 dB. The antenna structure incorporates a solid dielectric (HDPE 1000) so that it can be powered, without risk of a possible breakdown voltage, by a Marx generator which delivers a bipolar pulse with a peak amplitude of +/−250 kV, a rise time of 170 ps, and a duration of 1 ns. The radiated electric field obtained in simulation is, respectively, 1 MV/m peak and 126 kV/m peak at a distance of 1 m and 10 m.

Low-Complexity Aggregation Techniques for DOA Estimation over Wide-RF Bandwidths

Accurate direction of arrival (DOA) estimation of wideband, low-power nonstationary signals is important in many radio frequency (RF) applications. This article analyses the performance of two incoherent aggregation techniques for the DOA estimation of high chirp-rate linear frequency modulated (LFM) signals used in modern radar and electronic warfare (EW) applications. The aim is to determine suitable aggregation techniques for blind DOA estimation for real-time implementation with a frequency channelised signal. The first technique calculates a single pseudospectrum by directly combining the spatial covariance matrices from each of the frequency bins. The second technique first calculates the spatial pseudospectra from the spatial covariance matrix (SCM) from each frequency bin and then combines the spatial pseudospectra into one single estimate. Firstly, for single and multiple signal emitters, we compare the DOA estimation performance of incoherent SCM-based aggregation with that of the incoherent spatial pseudospectra-based aggregation using the root mean-squared error (RMSE). Secondly, we determine the types of signals and conditions for which these incoherent aggregation techniques are more suited. We demonstrate that the low-complexity SCM-based aggregation technique can achieve relatively good estimation performance compared to the pseudospectra-based aggregation technique for multiple narrowband signal detection. However, pseudospectra aggregation is better suited for single wideband emitter detection. Both the incoherent aggregation techniques presented in this article offer a computational advantage over the coherent processing techniques and hence are better suited for real-time implementation.

Machine learning-based radar waveform classification for cognitive EW

In this paper, we propose a waveform classification approach for cognitive electronic warfare applications in which a supervised classification method is presented in an efficient framework. In this manner, we introduce an end-to-end framework for detection and classification of radar pulses. Our approach is complete, i.e., we provide raw radar signal at the input side and produce categorical output in the end. We use short-time Fourier transform to obtain time–frequency image (TFI) of the signal. Hough transform is used to detect pulses in TFIs. Convolutional neural networks (CNN) are used for intra-pulse modulation classification. In experiments, we provide supervised classification results at different signal-to-noise ratio (SNR) levels and achieve 98.08% classification accuracy for 10 dB SNR on a diverse set of both frequency- and phase-modulated signals. The method sustains high classification accuracy levels as [93.9%;85.83%] for 0 and $$-10$$ dB SNR, respectively, that signifies the robustness of the method against noise for low-power intercepted signals. Simulation results also show that CNN outperforms artificial neural networks in intra-pulse modulation classification task.

Review on Ultra-Wideband Phased Array Antennas

Ultra-wideband (UWB) phased array antennas are essential for radar, communication, and Electronic Warfare (EW) applications. Systems can operate over wide-band coverage. The high gain systems require wide-band, wide-angle scanning, good radiation pattern, and return loss over a multi-octave bandwidth. This review discusses the problems present in the UWB phased array system, which include mutual coupling, grating lobe rejection, active return loss, gain fluctuation with scanning, and multiple beam generation. In this, the aperture size of the array is limited by the overall gain requirement of the system. On the other hand, low gain systems require a wide-band with a good radiation pattern and axial ratio. Here the matching over wide-band is simpler as it depends on broadband balun configuration. This system has limited bandwidth over scan angles. These antennas are more preferred as wearable antennas in communication applications. This paper mainly discusses the existing UWB phased array antennas such as Vivaldi Arrays, All-metal Arrays, Spiral Arrays, Sinuous Arrays, and Coupled Arrays. This review paper presents a correct direction for selecting the type of antenna in terms of impedance bandwidth, gain, and materials influencing antenna performance, suited for different applications.

Miniaturized ultra‐wideband printed dipole array for electronic warfare applications in unmanned aerial vehicle systems

AbstractThe advances in unmanned aerial vehicles (UAV) and their applications in various areas of military, communications made the researchers focus on the design of compact, wide beam, lightweight antennas. In this article, a novel miniaturized printed dipole antenna with quasi rhombus shape exhibiting an Impedance bandwidth of 113% (within 2:1 VSWR for the frequency range from 6.3 to 23 GHz) is presented. The length and width of the antenna element in terms of λ6.5 considered at the resonant frequency of 6.5 GHz is 0.347λ6.5 × 0.369λ6.5 (16 mm × 17 mm). Design equations are included to carefully match the impedance at every segment of the antenna. The optimized element is fabricated to confirm the finding from the analysis. The wideband characteristics of the antenna with good cross‐polarization levels, stable radiation patterns and matching performance of element makes it suitable for various EW applications in UAV systems. The optimized linear antenna array with eight elements is fabricated and tested to evaluate its suitability for broadband applications. Various antenna parameters such as reflection coefficients, bandwidth, radiation patterns are measured and compared with computed results to validate its suitability for EW applications. Miniaturization of antenna size finds the suitability of antenna to be used for smaller platforms having smaller surface similar to UAV. The wideband performance from a single antenna/array is useful for multitude applications. Some of the areas of application are shared aperture; communication support measure; SATCOM; data link; electronic support measure; radar warning receiver applications.

Approximate analysis of DF ambiguity probabilities for an interferometer direction‐finding system using gamma distributions

To obtain high direction-finding (DF) accuracy in electronic warfare applications, it is necessary to maximise the number of effective data points with a small angle-of-arrival error. Thus, a method to obtain the DF ambiguity probability for the selected set of array spacing is required. In this Letter, a novel method to obtain DF ambiguity probabilities for four- and five-element arrays by using gamma distributions is presented. The DF ambiguity probability obtained by the proposed method for the five-element array was in good agreement with the results of simulations. For the four-element array, the proposed method produced data that showed approximate agreement with the results of simulations. Thus, the proposed method should be useful for future applications.