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Disclosed herein is a design, simulation, and hardware build of a photonic compressed sensing Nyquist folding receiver that is able to directly undersample wideband RF signals and detect the original Nyquist zone and frequency information. According to an exemplary embodiment, this is achieved by generating a frequency modulated optical impulse train for directly undersampling the RF environment at the antenna. The impulse train undersamples the signals using an optical modulator configuration at 1550 nm and collects the detected samples in a low pass interpolation filter which is subsequently processed to extract the undersampled signals.

The invention automatically detects a gunshot at a plurality of detection and response nodes distributed in an area, determines the location of the active shooter, and deploys a suppression response to the location of the active shooter from each of the plurality of detection and response nodes to prevent the active shooter from firing further gunshots.

This thesis investigates the feasibility of using Costas frequency shift transmission waveforms to generate spotlight Synthetic Aperture Radar (SAR) images. A spotlight SAR image formation algorithm is used to evaluate the radar returns from scenes containing multiple point scatterers. Two-dimensional imagery is used to investigate the sidelobe effects. The peak sidelobe ratio (in dB) is determined from the one-dimensional slices in both the down-range and cross-range dimensions. Three unique Costas frequency shift sequence lengths are used in the investigation, N = 15, 100, and 150. Results of this investigation show that Costas frequency shift sequences are practical for the formation of spotlight SAR images. The autocorrelation sidelobe levels resulting from the Costas waveform are reduced with an increasing sequence length, providing an improved peak-to-sidelobe ratio. Image scenes with multiple neighboring scatterers are interrogated. Results show a spotlight SAR image peak-to-sidelobe ratio of – 20 dB, – 40 dB, and – 44 dB for N = 15, 100, and 150, respectively, thus offering the potential for producing high-quality spotlight SAR imagery while maintaining the strategic advantages of low probability of intercept., http://archive.org/details/investigationoff1094561295, Civilian, Raytheon, Approved for public release; distribution is unlimited.

Modern electronic warfare systems require increasingly larger bandwidth monitoring ability. Analog-to-information techniques increase bandwidth-monitoring capability without increasing the performance requirements placed on analog-to-digital converters. Two analog-to-information compressive sensing receiving methodologies capable of recovering signal information below the Nyquist sampling rate are considered. The designing and simulation of these receiving methodologies using photonic components in MATLAB and OptSim shows successful information recovery below the Nyquist rate. Finally, prototype receiver models were implemented using commercial off-the-shelf equipment, demonstrating rudimentary capability of recovering compressed radio frequency signal information using Mach-Zehnder interferometers as sampling devices., http://archive.org/details/photonicanalogto1094562229, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

Radar systems often use low power, continuous waveform radio frequency (RF) modulations and require high-speed adaptive signal processors to provide the necessary processing gain to detect small radar cross-section targets in clutter on range-Doppler maps. Counter-radar technologies include digital RF memories (DRFMs) that attempt to provide multiple, structured false targets with clutter, for example, using a pipelined, finite impulse response arrangement of complex range bin processors. This thesis investigates high-capacity field-programmable gate array (FPGA) technology to enable on-the-fly flexibility and reconfigurability for both radar signal processing and DRFM electronic attack using a Xilinx Virtex Ultrascale+. A three-stage range, Doppler, post-detection integration radar modulation compression circuit is designed and quantified. A range compression circuit with a peak power consumption of 6.100W and a post-implementation utilization of 11% was designed. The Doppler filter bank was designed at 400 MHz with a peak power consumption of 2.688W and a post-implementation utilization of 9%. A coherent integration processor at 400 MHz had a peak power consumption of 2.517W and a post-implementation utilization of 9%. In addition, a DRFM complex range bin processor was designed and quantified at 500 MHz and had a peak power 2.543W with a post-implementation utilization of 11%.

This thesis investigates the feasibility of using Costas frequency shift transmission waveforms to generate spotlight Synthetic Aperture Radar (SAR) images. A spotlight SAR image formation algorithm is used to evaluate the radar returns from scenes containing multiple point scatterers. Two-dimensional imagery is used to investigate the sidelobe effects. The peak sidelobe ratio (in dB) is determined from the one-dimensional slices in both the down-range and cross-range dimensions. Three unique Costas frequency shift sequence lengths are used in the investigation, N = 15, 100, and 150. Results of this investigation show that Costas frequency shift sequences are practical for the formation of spotlight SAR images. The autocorrelation sidelobe levels resulting from the Costas waveform are reduced with an increasing sequence length, providing an improved peak-to-sidelobe ratio. Image scenes with multiple neighboring scatterers are interrogated. Results show a spotlight SAR image peak-to-sidelobe ratio of – 20 dB, – 40 dB, and – 44 dB for N = 15, 100, and 150, respectively, thus offering the potential for producing high-quality spotlight SAR imagery while maintaining the strategic advantages of low probability of intercept.

This paper develops methods for using frequency shift keying (FSK) Costas-coded transmission waveforms in order to generate synthetic aperture radar (SAR) imagery. This analysis examines the use of a specific Costas sequence waveform in order to generate FSK modulation. A matched correlation receiver is used to form SAR imagery corresponding to the transmitted Costas-coded waveforms. This investigation demonstrates the ability to generate SAR images via simulated radar measurement data collected by a notional radar platform that transmits and receives Costas-coded waveforms. This analysis examines the resulting spotlight-mode SAR imagery that are generated through the use of the Costas-coded transmission waveforms.

In this thesis, we investigate two critical components of a digital-image synthesizer electronic warfare architecture that can be used to infuse false targets into high-range resolution profiling radars. The first investigation encompasses the design of an in-phase and quadrature (I/Q) converter based on a CORDIC (Coordinate Rotation Digital Computer) algorithm. Mathematical modeling is used to examine the accuracy of converting a digitized radar signal I/Q sample into a corresponding five-bit binary phase angle. Results obtained from MATLAB show that 18 CORDIC iterations are required to achieve accuracy at 5.625˚. The resulting design was implemented using the Verilog hardware description language. The second investigation concerns generating sea clutter to impose on the false target. The mean-power return of the sea clutter is calculated using the average power of the radar-cross section derived from the Naval Research Laboratory sea clutter model. The modulation coefficients for the sea clutter were generated using the fluctuating power returns and Doppler spectra generated using a random KA distribution. The coefficients for several sea states were generated using MATLAB. Results show that the correct sea clutter model can effectively add realism to the false target image.

The use of integrated optical components and how they can be used to implement a compressed sensing microwave photonic receiver are investigated in this thesis. The scope of this research covers the design, simulation, and hardware build of a photonic compressed sensing Nyquist folding receiver that is able to directly undersample wideband RF signals and detect the original Nyquist zone and frequency information. This is achieved by generating a frequency modulated optical impulse train for directly undersampling the RF environment at the antenna. The impulse train undersamples the signals using an optical modulator configuration at 1550 nm and collects the detected samples in a low pass interpolation filter. Two independent photonic receiver architectures are designed and analyzed over the course of this research. Both receiver designs are simulated in the OPTSIM photonic design suite and are able to successfully extract the undersampled signals. The first receiver design proved more effective at representing the signal environment and was constructed using electro-optical hardware. Using off-the-shelf components in a proof-of-concept hardware prototype, we confirmed the simulation results by correctly identifying input test frequencies up to an order of magnitude higher than the sampling frequency.

The combination of Wigner-Ville distribution (WVD) and Hough transform (HT) has been successfully used in detection and parameter extraction of frequency modulated continuous waveform (FMCW) signals. In this paper, a combination of Cross-Wigner-Ville and HT [(Cross Wigner-Hough transform (XWHT)] is proposed for detection and parameter extraction of FMCW signals with a novel methodology. The XWHT method makes use of the cross-terms created by WVD instead of trying to suppress them. Utilization of the properties of the cross-terms to detect and unveil the parameters of FMCW signals on HT space is a new approach. The performance of the method is compared with other Wigner-Hough transform-based methods in terms of transform speed, parameter extraction, and detection performance. As a result, this study proposes that the XWHT is a candidate method to be used in digital electronic support receivers' automatic signal detection and analysis capabilities due to its speed and performance.

ESM systems need to use sophisticated signal processing, such as time-frequency representation techniques, for the interception of nonstationary LPI radar signals. In this study, an adaptive filtering technique using an ambiguity-domain elliptical Gaussian kernel is proposed to increase the readability of pseudo-Wigner-Ville distribution based representations for LPI waveform parameter extraction purposes. The complexity and information content of the outputs obtained by the proposed method are evaluated by objective criteria, such as ratio of norms, Rényi entropy, and Jubisa measure. The results quantify efficient filtering performance under severe SNR conditions with lower computational complexity.

A four-element wideband photonic DF system with robust symmetrical number system preprocessing utilizes dual electrode Mach-Zehnder modulators (DE-MZMs) to conduct phase detection for direct wideband direction finding (DF) of RF signals, such as microwave signals, in which the normalized magnitude of the output signal phase detector circuit is equal to lsin(cp/2)1 where cjJ is the phase difference between the plane waves arriving at the reference and measurement antennas of a linear DF array. The method and system allow fine angular resolution using a much smaller array size than is typically required for linear arrays employing super-resolution signal processing techniques.

Direction finding (DF) systems are critical components in electronic warfare intercept receivers. Many existing radio frequency DF techniques use a non-linear frequency down-conversion process that generates spurious frequencies that can hide the signals-of-interest. In addition, these systems suffer from a limited bandwidth and poor resolution (e.g., > 2°). To overcome these limitations, a miniature microwave-photonic phase-sampling DF technique is investigated in this thesis. This front-end design uses a combination of integrated optical Mach-Zehnder phase detectors to measure the emitter's phase difference with the largest baseline being 23 cm. The front-end components were characterized to ensure accuracy in the resolved angle-of-arrival (AOA). The front-end design was constructed to be modular in order to facilitate testing and verification of analog components accuracy. Signal processing with a class IV laser required particular attention to ensure that any stray radiation or leakage was isolated. Testing with low probability of intercept (LPI) waveform modulation consisted of using a linear frequency-modulated continuous wave (FMCW) and a phase coded P4 modulation, both at 2.4 GHz, in an anechoic chamber. Measurements were taken to quantify the DF receiver sensitivity was Ȣʀ = 62.96 dBm. It was demonstrated that the system was capable of estimating the AOA for the FMCW signal with a root-mean square (RMS) error of 0.29° at < 1° resolution and a P4 modulation RMS error of 0.32° at <1° resolution.

Direction finding (DF) systems are fundamental electronic support measures for electronic warfare. A number of DF techniques have been developed over the years; however, these systems are limited in bandwidth and resolution and suffer from a complex design for frequency down-conversion. An innovative design of a microwave-photonic direction finding technique for the detection and direction finding of low probability of intercept (LPI) signals is investigated in this thesis. Key advantages of this design include a small baseline, wide bandwidth, high resolution, and minimal space, weight, and power requirement. A unique phase encoding method is used to resolve the ambiguities over the entire field-of-view with high accuracy. Experimental tests using frequency-modulated continuous wave (FMCW) and continuous wave (CW) P4 modulated signals were conducted in an anechoic chamber to verify the system design. Test results showed that the microwave-photonic DF system has a sensitivity of –62.96 dBm and is capable of measuring the angle-of-arrival (AOA) of the LPI signals with <1° resolution over a 180° field-of- view. For an FMCW signal, it was demonstrated that the system is capable of estimating the AOA with a root-mean-square (RMS) error of 0.29° at <1° resolution. For a P4 coded signal, the RMS error in estimating the AOA is 0.32° at 1° resolution.

Wireless propagation modeling is a necessary task in the design of countless applications. Wireless signals attenuate at different rates according to the propagation environment. Given that vegetation is an unavoidable feature for most outdoor wireless channels, propagation models in forested environments are in high demand. The characterization of radio waves propagating through foliage is particularly complex due to the random characteristics of the channel. This research is focused on the development of three radiowave propagation models in forested environments. Field tests were performed at 2.4 GHz for the case where both the transmitting and receiving antennas are immersed in foliage. The propagation loss added by the forest component was estimated from the sets of measurement data, and an empirical model was created to forecast it. Also, electromagnetic properties of the medium were estimated and used in the investigation of a two-layered homogeneous model (ground and foliage). A dielectric slab representing the forest was modeled using an electromagnetic field simulation application. Results from the empirical and analytical model show good agreement with the measured data. These findings bear direct relevance on radiowave propagation through foliage and provide useful information for accurate design of the link budget for similar scenarios.

LPI radar is a class of radar systems possessing certain performance characteristics that make them nearly undetectable by today's digital intercept receivers. This presents a significant tactical problem in the battle space. To detect these types of radar, new digital receivers that use sophisticated signal processing techniques are required. This thesis investigates the use of cyclostationary processing to extract the modulation parameters from a variety of continuous-wave (CW) low-probability-of-intercept (LPI) radar waveforms. The cyclostationary detection techniques described exploit the fact that digital signals vary in time with single or multiple periodicity, owing to their spectral correlation, namely non-zero correlation between certain frequency components, at certain frequency shifts. The use of cyclostationary signal processing in a non-cooperative intercept receiver can help identify the particular emitter and aid in the development of electronic attack signals. LPI CW waveforms examined include Frank codes, P1 through P4, Frequency Modulated CW (FMCW), Costas frequencies as well as several frequency-shift-keying/phase-shift-keying (FSK/PSK) waveforms. This thesis show that for signal-to-noise ratios of 0 dB and -6 dB, the cyclostationary signal processing can extract the modulation parameters necessary in order to distinguish between the various types of LPI modulations.

This thesis investigated five specific phase-shift keyed (PSK) modulated signals for usage in Spotlight Synthetic Aperture Radars (SAR) and the effects each of the individual PSK signals sidelobe structure has on SAR imagery. The specific PSK codes studied were the Frank code, P1 code, P2 code, P3 code and P4 code. A mathematical approach was used to define SAR limitations from signal parameters, and simulations were used to investigate an individual signal parameter’s effects on the sidelobe structure in SAR images. Simulations were used to generate spatially diverse targets, collect each target’s unique echo and apply cross-correlation match filtering and pulse integration to detect each returned echo from the targeted area. Results show the P1 and Frank codes to be the most promising based on the selected parameter presented in this thesis. The P4 code may be better given additional processing to remove range ambiguities, enhancing its unambiguous range.

This paper investigates techniques for using low probability of intercept (LPI) modulation techniques for forming synthetic aperture radar (SAR) imagery. This analysis considers a speci c waveform type based upon Frank codes in providing for the LPI capability via phase shift keying (PSK) modulation. A correlation receiver that is matched to the transmitted waveform is utilized to generate a set of SAR data. This analysis demonstrates the ability to form SAR images based upon simulated radar measurements collected by a notional radar sensor that has ability to transmit and receive Frank-coded waveforms and to form SAR images based upon the results of a correlation receiver. Spotlight-mode SAR images are generated using the Frank-coded waveforms and their properties are analyzed and discussed.

The robust symmetrical number system (RSNS) is a number theoretic transform based on N = 2 sequences that can extract the maximum amount of information from symmetrical folding waveforms. The sequences, based on coprime moduli, exhibit an integer Gray code property making the RSNS well-suited for many applications that benefit from an inherent error detection and correction capability such as analog-to-digital converters, direction finding arrays and radar waveform design. To use the RSNS, it is necessary to know the greatest length of combined sequences without ambiguities, called the dynamic range M, for which only a few closed-form expressions currently exist. In this paper, an efficient algorithm for computing M and its position within the combined set of sequences is presented and shown to be independent of the size of the moduli. The algorithm is used to generate the equations for several groups of additional moduli arrangements. Closed form expressions for M are conjectured and proved using the obtained congruence equations that define the ambiguity locations., Published in IEEE Transactions on Information Theory, v60 n3 p1-11, 2014.

This report is divided into two sections. Section One profiles a range of Low Probability of Intercept radars organized by function that are currently marketed to be commercially available. Included are naval navigation and surveillance radar systems, ground surveillance radar systems, radar motion detector sensor chips, and modular radar systems developed for use in training and research applications. The profile for each radar system includes a picture, description of the radar system's major features and applications, and a table of unclassified technical parameters. Most of the systems included are low power systems that operate using frequency modulated continuous wave waveforms, although several also include frequency shift keying capabilities. Section Two of this report presents modern ES/ELINT systems and their sensitivities. It is organized based on the platforms these systems are deployed on, including airborne, submarine/surface ship and ground mobile systems. The profile for each system includes a picture, description of the system's major features and applications and a table of technical available parameters., The original document contains color images.

An increasingly dynamic battlefield requires increasingly faster software development. Cyber threats and Information Assurance certifications induce significant delays in software operational deployment designed to meet these emerging battlefield requirements. An alternative software development methodology for Department of Defense (DOD) acquisitions was proposed. The proposed software development methodology uses tailoring of commercial pre-approved applications such as Microsoft Office and Adobe currently available on most DOD networks. The application developed to test the validity of this approach is called the electronic attack platform placement optimization (EAPPO) algorithm. Given digital terrain data, a user inputted strike route, and an enemy order-of-battle (EOB) with their respective jammer techniques as inputs, the application output includes terrain and radar impacted threat range rings, aircraft strike routes, and an optimized flight path for the jamming platform (EA-18G). Successful development of the application validates the potential of using pre-approved, non-compiled software to develop military specific applications, a process that could significantly decrease software development time and cost for the DOD.

The LPISimNet software tool provides the capability to quantify the performance of sensor network configurations by combining the information and physical domains. To combine the sensor network’s performance in a coherent context with a decision-maker, Boyd’s observe, orient, decide, act (OODA) loop is included along with its operational tempo. This thesis develops a new version of LPISimNet (LPISimNet(V)3) by correcting a code error and including a network comparison file. Additionally, this thesis evaluates the effects of different network configurations and size on the maximum operational tempo. Simulation results for a static network indicate that as the network size increases the rate at which decisions can be made declines. A prediction for further decline is presented based on the simulations. Also, dynamic network simulation results for a three-, four-, five-, and six-node network display the importance of node placement and network geometry to help offset network degradation due to range fluctuation between nodes. By surrounding the dynamic nodes of the network with static nodes, the maximum operational tempo can be bounded between an upper and lower limit, stabilizing the decision-making speed. Finally, the effect of electronic attack on the operational tempo is presented to display the robustness of a network.

Propagation models used in wireless communication system design play an important role in overall link performance. Propagation models in a forested environment, in particular, are especially valuable and complex due to the randomly distributed leaves, twigs, trunks, and trees. This has been an area of interest due to the operational needs of military and non-military domains. Applications in both domains require communication devices and sensors to be operated in forested environments. Various methods have been employed to model propagation loss. There are experimental measurements, empirical models, analytical, and computational electromagnetic methods. Each method has its applicability and limitations. In this thesis, investigation of a three-layer homogenous medium model (air, forest, and ground) by a ray tracing method was carried out. Both transmitting antenna and observation point are within the forest layer. The results from the ray tracing model showed good agreement with the available measurement data up to 100 MHz. Further, better approximation of the transmission loss was observed at separation distances greater than 1 km. Values of the effective electrical properties of the forest played an important role in transmission loss estimation within the forest. After adjustment, the deviation in propagation loss using the ray tracing model achieved an error of 1 dB.

Linear Frequency Modulated Continuous Waveform (LFMCW) is one of the most common waveforms used in low probability of intercept (LPI) radars. The Wigner- Hough transform (WHT) is a powerful technique for detection and parameter extraction of LFMCW waveforms that can be employed by Electronic Support Receivers. For a fast detection and a timely response to the adversary emitter, the selection of the pseudo Wigner-Ville distribution (PWVD) window length is critical. In this work we analyze the relation between PWVD window length, WHT span angle and span resolution. It is shown that faster correct detections can be achieved by decreasing the PWVD window length and consequently decreasing the WHT plane. A rapid detection and apiori estimation of target emitter signal chirp rate will allow enough time for a fine tuned post- processing which can be applied specifically to the a priori estimates.

This paper develops methods for using low probability of intercept (LPI) transmission waveforms in order to generate synthetic aperture radar (SAR) imagery. This analysis considers a specific transmission waveform based upon P3 codes in order to give phase shift keying (PSK) modulation. A matched correlation receiver is used to form SAR imagery corresponding to the transmitted P3-modulated waveforms. This analysis demonstrates the ability to generate SAR images based upon simulated radar measurements collected by a notional radar platform that can transmit and receive P3 waveforms. This work analyzes the resulting spotlight-mode SAR images that are generated using the P3 transmission waveforms.

The robust symmetrical number system (RSNS) is a number theoretic transform based on N > 2 sequences that can extract the maximum amount of information from symmetrical folding waveforms. The sequences, based on coprime moduli, exhibit an integer Gray code property making the RSNS well-suited for many applications that benefit from an inherent error detection and correction capability such as analog-to-digital converters, direction fnding arrays and radar waveform design. To use the RSNS, it is necessary to know the greatest length of combined sequences without ambiguities, called the dynamics range, M, for which only a few closed-form expresions currently exist. In this paper, an efficient algorithm for computing M and its position within the combined set of sequences is presented and shown to be independent of the size of the moduli. The algortihm is used to generate the equations for several groups of additional moduli arrangements. Closed form expressions for M are conjectured and proved using the obtained congruence equations that define the ambiguity locations.