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Direct path interference and clutter suppression removal algorithms are a necessity in the processing chain of a passive radar. Most echoes originating from targets of interests are many orders of magnitude weaker than the clutter. However, targets with a high radar cross-section, or close to a transmitter, or to a receiver, may contribute significant power to the recorded signal. If such a target approaches the zero-Doppler line on a range-Doppler plot, it could affect a clutter cancellation algorithm and produce significant, non-removable sidelobes. In this paper, the effects of such processing are presented for an Extensive Cancellation Algorithm. An off-grid method of estimation and removal of an endoclutter target is presented. The effectiveness of the algorithm is presented on both simulated and measured data sets.

This paper reports on two measurement campaigns aimed at investigating the importance of atmospheric variability in several applications, including passive radar. First, UHF wide-band spectrometry analyses seek to quantify diurnal statistics, power series correlation, and signal reliability. Second, long-term radar detection data further enhances the understanding of how this variability affects both clutter and moving targets. Results demonstrate the dynamic nature of the illumination environment as well as enhancement of clutter and targets. Beyond ducting enhancement, phenomena seen in the data include station dropout, unexpected illuminators, rainstorms echoes, and other unexplained diurnal features.

This paper proposes an alternative form of the Keystone Transform (KT), which is known for mitigating range walk in radar returns. While traditionally applied as an interpolation to the cross ambiguity function (CAF), the present work shows that the KT can be implemented prior to, and agnostic of, the cross correlation operation. The new time-domain KT algorithm is derived as a time-variant filter and demonstrated against simulated data. The computational cost, and architectural flexibility offered by the filter, are each examined.

With the growing demand on radio frequency interference mitigation techniques in radio astronomy, better testing tools are required. This paper presents the signal oriented simulator developed at Embry-Riddle Aeronautical University. The modular simulator is capable of simulating ground based, satellite and celestial sources with a variety of transmit IQ signals. The concept, basic modes, and a configuration of the simulator are presented. The simulator is written in class-oriented MATLAB language.

This paper reports on a simulation-based study estimating illuminator usage statistics in passive radar systems with mobile receivers. A metric termed illuminator survivability is proposed to describe the size of a geographic region, with respect to the receiver location, in which a transmitter facilitates near-optimal localization capability. We attempt to relate along-track survivability to the maximum operating region of a circling receiver using a static illuminator set. In each case, the radar's coverage is optimized using a greedy algorithm based on the multistatic range CRLB. Results suggest individual illuminator sets might provide useful localization capability over receiver flight paths of 100 km or more.

This paper presents results from model-based work investigating the influence of atmospheric refractivity on the performance of UHF passive radars, using parabolic-equation (PE)-based propagation techniques. It is shown that, since PE-based models are monochromatic, modeling the illuminator bandwidth can smooth their usual multipath power variations; this smoothing can affect the maximum predicted range of the radar. Further, it is shown that changing atmospheric conditions (refractivities) can impart meaningful variations in illumination and path loss at a variety of ranges and altitudes, ultimately affecting the radar's coverage. Finally, it is shown that, although specific refractivities do affect the realized radar performance, they do not appear to strongly influence the selection of optimal illuminators in channel-constrained passive radars.

This paper discusses the development of a testbed for real-time experimental studies of time-modulated arrays. The proposed architectural design will be described, and the current state of progress will be presented through simulation and over-the-air tests conducted in a lab. The TMA antennas and radios are designed to operate at about 2.3 GHz for a target application of passive radar using XM Radio, in which the TMA capabilities will be targeted at multibeaming and interference suppression.

This paper presents techniques for predicting the resolution of the radar imaging point spread function (PSF). These techniques are useful for predicting the performance of multistatic passive synthetic aperture radars (P-SARs), and passive inverse SARs (P-ISARs), for which the PSF depends on a multitude of factors. Greedy algorithms are used in combination with the fast techniques to optimize the PSF resolution for both incoherent and coherent multistatic imaging scenarios, subject to constraints on combining methods, sparsity, and target isotropy.

This paper compares results of a simulation study and experimental measurement campaign designed to evaluate the performance of a DTV-based passive radar. The simulations considered a tower-mounted receiver in Springfield, Ohio, and predicted the accuracy of localizing airborne targets using the illuminations of regional transmitters. The predicted coverage area was found to vary with the selection of the propagation loss model used by the simulator. Supporting experiments at the site did not favor any particular model, but showed 10 dB variations in both the direct path and clutter over several hours. These results illustrate the need to accurately model tropospheric radio propagation in passive radar performance predictions.

This paper describes the design and fabrication of an 8-element wideband Vivaldi antenna array with an integrated feed network. This array was created for use in an X/Ku-band measurement system for characterizing dynamic rocket plasma, extending previous measurements of this phenomenon. The array is instrumented to help distinguish plume-induced mechanical changes from electrical ones.

The formulation of multibeaming in time modulated arrays (TMAs) is generalized for nonsinusoidal basis functions. This can overcome ambiguities between angle and frequency present in TMA harmonic beams and detrimental to radars and spectrometers. This concept is used to analyze the Doppler VHF Omni Range (DVOR), and it is shown that the DVOR is a TMA using a single-tone frequency-modulated basis function.

This paper presents results of a simulation study quantifying the expected importance of cochannel interference (CCI) in a passive radar using Advanced Television Systems Committee (ATSC) illuminators. CCI stations broadcasting on the same frequency as the illuminator are modeled as additional direct path interference. It is found that spatial nulls alone can be insufficient to suppress CCI in small airborne radars, which might observe up to 10 significant CCIs for each illuminator. A proposed hybrid algorithm uses remodulation to suppress the strongest CCI and nulls only CCI that cannot be decoded. This method improves predicted coverage as compared to nulls alone.

This paper reports on analytical and simulation-based investigations of the Keystone transform (KT), which is used to remove range walk in radar systems. The KT modifies the cross ambiguity function to fix a radar target at its initial range, allowing longer integration times and higher SNRs. Limits on the useful length of integration time are explored, demonstrated, and found to depend on residual range migration caused by the acceleration of the target. A second order double-Keystone transform is then presented as an alternative that corrects for both velocity-based and acceleration-based range walk and enables chirp detection of an accelerating target.

Accurately predicting propagation loss is critical to determining if an area can support passive bistatic radars (PBRs), which must rely on illuminators of opportunity and might operate near the threshold of detection for weak targets. Models available to calculate propagation loss vary in their complexity and might include factors such as terrain, refraction, clutter, and multipath. This paper reports on work comparing two such models, the Advanced Refractive Effects Prediction System (AREPS) and the Irregular Terrain Model (ITM). An interface between AREPS, ITM, and MATLAB was developed to enable model comparisons for similar configurations. Results were incorporated into a PBR simulator to examine how the model differences affect localization performance predictions.

The affinity of lightning to a charged rocket plume depends on the plume's electrical properties, many of which are poorly characterized in theoretical models. The vulnerability of rockets to lightning-induced vehicle failure motivates study of this phenomenon. This paper describes experimental efforts to determine the plasma frequency and electron number density of plumes from static firings of amateur high power rocket motors, by analysis of the microwave transmission characteristics. Two new techniques presented include time delay measurements and using reflectors to sample multiple paths in the plume.

This paper presents a design for a passive tag to be used as a transponder for unmanned aircraft systems. The tag is designed to scatter digital television signals with an imposed modulation, negating the need for an onboard transmitter. The ground station processes the backscattered signal using passive coherent location techniques. Results suggest the feasibility of communication between a ground station and aerial vehicle with relatively high data rate, long range, and minimal power consumption without further congesting existing bands such as 1030/1090 or 978 MHz.

A case study of the trade off between fidelity and complexity is presented for a passive radar simulator. Although it is possible to accurately model the underlying physics, signal processing, and environment of a radar, the resulting model might be both too complex and too costly to evaluate. Instead, simplifications of various model attributes reduce the complexity and permit fast evaluation of performance metrics over large areas, such as the United States. Several model simplifications and their impact on the results are discussed.

Time modulation is explored as a tool for inexpensive sidelobe blanking in a digital beamformer. Rapid switching of the steering coefficients encodes acquisition and sidelobe suppression beams within a single output during beamforming so that they are separable by a synchronized decoder. The computational cost is the same as traditional beamforming, making this method advantageous versus other sidelobe blanking methods. Experimental results are shown using data from the Allen Telescope Array.

We provide performance information on the reduction of sidelobe levels in sparse linear phased arrays operating in the near-field. Iterative optimization techniques are used to choose inter-element spacings which reduce grating lobe magnitudes at select distances, and array configurations are generated with constraints on the minimum spacing between elements. The performance of these array configurations is then analyzed over a scan angle of 180 degrees. We show that it is possible to generate arrays which outperform the side-lobe level of far-field-optimized array configurations in the near-field by as much as 3 dB.

Time-modulation is applied to an array pattern by alternating a beamformer between two sets of beamforming coefficients. These are selected so signals arriving in the sidelobes are BPSK modulated by the beam-switching while signals in the main lobe are not. This technique enables sidelobe blanking using a single beamformer, which is simpler than other approaches.

This paper describes passive radar observations using the ATSC digital television signal as an illuminator. The system has two unique attributes. First, it recovers the reference signal by remodulation of the surveillance channel, a process which permits a compact single-antenna receiver. Second, it is shown that keystone formatting of the cross-ambiguity data mitigates range walk of moving targets and allows meaningful increases to the integration time and sensitivity.

A method of communications is presented based on the backscatter modulation of terrestrial digital television signals by low-complexity tags. The modulation is sensed by receivers implementing passive coherent detection algorithms similar to those used in passive radar. This method enables shared use of the UHF television band for low-data-rate applications. Analyses and experiments suggest the feasibility of this technique but also highlight the unique challenges for designing such a system.

Beamforming methods of maximal ratio combining (MRC) and equal gain combining (EGC) are compared in the presence of calibration errors. It is found that sufficient uncertainties in the antenna sensitivities make MRC less effective than EGC. Furthermore, the threshold noise temperature for including a new antenna in a time-limited survey is explored, and is found to be lower than previously-described results.

RF Tomography is a technique to reconstruct an image of the area of interest using distributed transmitters and receivers assumed to be cooperating. This paper explores the possibility of using RF tomography when the sources' locations and waveforms are not known. With this added complexity, the system must 1) sense the environment to detect radar waveforms of opportunity 2) estimate the source's locations 3) use a tomographic reconstruction based upon match-filtered data, where the phase information of targets is practically lost. This paper addresses these steps through a new formalization of the tomographic model and associated signal processing. Simulations and experimental results are shown.

This paper describes the simulation approach and model for a software tool used to analyze passive radar scenarios. A database of known transmitters includes more than 250,000 sources from FM radio, digital television, cellular, and aeronautical radio-navigation aids. Terrain is considered using digital elevation maps and the Irregular Terrain Model. The tool calculates the expected detection and localization performance for PBR receivers, and can be used to guide receiver design.

This paper reports on early observation results from the S-band Array for Bistatic Electromagnetic Ranging Technology Demonstrator Array. This system is a demonstration platform for a passive ground-based primary radar station for monitoring aircraft. This station is unique in that it utilizes existing satellite-based radio signals as transmitters rather than terrestrial signals. Using algorithms that enable long integration times, this system might provide accurate position and velocity measurements at ranges of tens of nautical miles from the ground station for most targets, and up to 100 nautical miles for larger targets. In these measurements, XM-Radio was used as the illuminator and the SABER-TDA station as the receiver. Different types of aircraft were observed in different scattering geometries. Comparison with truth data is in progress.

This paper presents a remote, human-controlled, immersive Unmanned Robotic System (URS) designed to assist in search and rescue operations. The system is being designed and constructed by the Embry-Riddle Aeronautical University Department of Electrical, Computer, Software, and Systems Engineering 2011/2012 Senior Design Team. Described in this paper are two different implementations of the URS - one is controlled using a handheld tablet and the other is controlled by way of a Human Robotic Interaction (HRI) head-mounted display. This paper outlines the architecture, implementation, and design considerations for each system.

The unknown radio propagation delay of the ionosphere is well-known as a potentially-limiting effect of microwave navigation systems such as GPS. We report on an analysis on the effects of the ionosphere on passive bistatic radar using non-cooperative satellite-based transmitters. Ionospheric data for a one-year period during 2010 are analyzed in the context of the bistatic geometry. Both geostationary (e.g., XM-Radio) and low Earth-orbiting spacecraft (e.g., Iridium) are considered. It is found that the worst-case effects of the ionosphere on a radar of this type might be meaningful for systems attempting to achieve the best accuracy at the longest range, but that the effect is small enough to be neglected for close-range measurements.

This research reports on the construction of a demonstration platform for a passive ground-based primary radar station for monitoring aircraft. The key to the system is the use of existing satellite transmitters as illuminators for the radar system. This proposed system can provide accurate position and velocity measurements of aircraft or small unmanned aircraft at ranges of tens to hundreds of nautical miles away from the ground station. This station is a light-weight, low-cost, portable, and field-deployable option to supplement deficiencies in the National Airspace System (NAS) and homeland security surveillance networks. Potential applications include providing coverage in remote mountainous regions, low-altitude en-route primary radar coverage throughout the continental United States, and low-altitude interdiction efforts in coastal areas. As a field-deployable system, this could also be used to quickly restore primary radar coverage in the event that a disaster or terrorist event disables existing primary radars. Additionally, the portable and non-emitting nature of the radar permits use in a wide range of applications where emitting radars are unacceptable. Previous research in the area of passive radar has used terrestrial sources as illuminators since satellite sources have been traditionally viewed as too weak. What makes this research unique is that it takes specialized signal processing techniques typically used to detect objects in deep space for radio astronomy applications and applies them to the domain of terrestrial bistatic radar. The system has been constructed and characterization of system performance is in process.

Using a generous grant from the IEEE Life Member Foundation, the IEEE Daytona Section has acquired, built, and operated a Small Radio Telescope as a tool to support Engineering Education in the Middle and High Schools, as well as Colleges and Universities. This paper describes the project and its educational goals and purposes.

The communication system presented in this paper, uses a directional antenna tracking system to minimize required power consumption on a remote system. The system utilizes the telemetry data from a remote system to determine the required azimuth and elevation angles necessary to track and maintain communications with the vehicle. The system is intended for fully mobile applications where the orientation of the ground tracking station is arbitrary and unknown. This paper describes a self-contained system integrating onboard sensors to automatically calibrate the antenna tracking station.

A genetic wire antenna is developed for a low-N phased array for use as a satellite-communications ground terminal. The radiation pattern of this antenna is optimized to compensate for the angularly-dependent path loss exhibited by a communications link with a low-earth-orbiting (LEO) earth-environmental satellite (EES).

To lower costs and reduce latency, a network of adaptive array ground stations, distributed across the United States, is considered for the downlink of a polar-orbiting low earth orbiting (LEO) satellite. Assuming the X-band 105 Mbps transmitter of NASA's Earth Observing 1 (EO-1) satellite with a simple line-of-sight propagation model, the average daily download capacity in bits for a network of adaptive array ground stations is compared to that of a single 11 m dish in Poker Flats, Alaska. Each adaptive array ground station is assumed to have multiple steerable antennas, either mechanically steered dishes or phased arrays that are mechanically steered in azimuth and electronically steered in elevation. Phased array technologies that are being developed for this application are the space-fed lens (SFL) and the reflectarray. Optimization of the different boresight directions of the phased arrays within a ground station is shown to significantly increase capacity; for example, this optimization quadruples the capacity for a ground station with eight SFLs. Several networks comprising only two to three ground stations are shown to meet or exceed the capacity of the big dish. Cutting the data rate by half, which saves modem costs and increases the coverage area of each ground station, is shown to increase the average daily capacity of the network for some configurations.

This paper presents numerical design models and predicted performance for a parasitic dipole antenna array tile that contains multiple feeds. This tile is designed for end-to-end concatenation with identical tiles to construct a phased array with a large number of feeds. The tile is optimized so that the radiation pattern of each feed is similar to the desired radiation pattern. The tile is simultaneously optimized so that the array exhibits low sidelobe levels for a range of scan angles.