arXiv subjects

Jeffrey A. Nanzer

Publications and source records attributed to Jeffrey A. Nanzer.

At least 19 recordsLinked to original sources

arXiv2026

Fourier Domain Synthesis Imaging Using A Wirelessly Coordinated Distributed Antenna Array

In this work we present an experimental demonstration of one-dimensional Fourier-domain imaging using a fully-digital wirelessly coordinated coherent distributed antenna array (CDA) receiver. The nodes consist of two software-defined radios (SDRs) operating with independent system clocks performing wireless time, frequency, and phase coordination without a shared reference such as the global navigation satellite system (GNSS). Two spatially separated noise sources transmit independent noise waveforms with a bandwidth of 25 MHz and a carrier frequency of 915 MHz. Two sources were positioned at angles of $-6.28°$ and $12.95°$ off broadside and imaging was performed. The two sources are clearly resolved to within $3°$ of their expected locations in both the individual and combined source measurements and demonstrating the Fourier-domain image reconstruction principle using a fully-digitally coordinated distributed antenna array.

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arXiv2026

Multi-Objective Adaptive Beamforming Using Partial Knowledge of Dynamic Dielectric Media for Non-Invasive Microwave Hyperthermia

We investigate multi-objective adaptive beamformer design strategies for non-invasive microwave hyperthermia. Our focus is to address the challenges of maintaining focused power deposition in desired locations while reducing unwanted heating elsewhere under conditions of changing dielectric properties. The process of heating the media causes changes in the dielectric properties of the media, which can degrade the effectiveness beamformers with static weights. Typical hyperthermic beamformer designs calculate antenna beamforming weights using patient-specific high resolution dielectric maps obtained by MRI or microwave tomography, however this process is time consuming and difficult to perform in real-time. In this work, we explore the efficacy of microwave hyperthermia in various inhomogeneous media under changing dielectric conditions, with the goal of informing the design of future adaptive real-time microwave hyperthermia techniques. We aim to achieve cell apoptosis by obtaining temperatures of $\sim$ 45 $^\circ\text{C}$ through selective absorption of electromagnetic wave focusing at a 2.5 GHz carrier frequency with little to no knowledge of the changes in the dielectric media and simultaneously place nulls to avoid unwanted heating outside of the treatment zone. We investigate the effectiveness of the linear constrained minimum power (LCMP) algorithm for near-field multi-objective beamforming and examine the power density obtained from finite-difference time-domain (FDTD) simulations on simple analytical models and anatomically realistic numerical breast phantoms. To gain a comprehensive knowledge of the efficacy of the beamformer we evaluate the resulting thermal maps of the models in simple homogeneous cases, heterogeneous cases and MRI-derived phantom breast models.

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arXiv2026

A Compact Cross-Structured Dynamic Antenna for Reconfigurable Directional Modulation

A compact cross-structured dynamic antenna is presented for antenna-level physical-layer security using reconfigurable information-beam control rather than conventional radiation beam steering. The antenna uses four printed meander-line monopoles in a planar cross structure and a switching network that realizes two complementary excitation states for each dynamic mode. By switching between opposite or diagonal port groups, the aperture introduces apparent two-dimensional phase center displacement and supports four information-beam directions: $φ=0^\circ$, $45^\circ$, $90^\circ$, and $135^\circ$. An average--differential array factor formulation shows that the average component preserves broad omnidirectional coverage, while the odd-symmetric differential component creates angle-dependent magnitude and phase distortion that determines where the constellation remains recoverable. The recoverable information region is therefore reconfigured without phased-array beamforming, multiple RF chains, or mechanical motion. A 5.05-GHz prototype on Rogers RO4350B is fabricated with an electrical footprint of $0.57 \times 0.47λ_0^2$. Measured 16-QAM results show that low bit error rate is confined to the intended E-plane information-beam sectors, while off-beam angles exhibit large magnitude and phase errors, elevated BER, or unrecoverable constellations despite high received SNR. The measured H-plane cuts maintain low BER over nearly the full angular range, confirming omnidirectional information recovery in the orthogonal plane.

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arXiv2026

A Miniaturized Dynamic Array for Antenna-Level Physical Layer Security

A compact dynamic omnidirectional array is proposed for antenna-level physical-layer security through directional modulation. Unlike conventional directional-modulation transmitters based on phased-array beam synthesis or multiple RF chains, the proposed architecture uses a single RF input and a switching-controlled four-element printed meander-line monopole array operating at 5.05 GHz. The state-dependent excitation introduces controllable magnitude and phase perturbations in the radiated field, producing angle-dependent constellation distortion and bit error rate behavior. Reliable information recovery is confined to a narrow broadside region in the E-plane, whereas the H-plane remains quasi-static and omnidirectional, providing a full 360-degree information-recoverable region. The antenna is implemented on a single-layer Rogers RO4350B substrate with a compact footprint of 0.57 x 1.11 lambda_0^2. A four-path switching network based on commercial RF components is used for experimental validation. Communication measurements using 16-QAM at 5.05 GHz demonstrate BER-defined E-plane information beamwidths of 30 to 36 degrees for calibrated switching modes under a BER <= 10^-3 criterion, while no bit errors are observed in the measured H-plane and the SNR remains above approximately 33 dB. Feed-phase offsets are also used to steer the BER-defined information-recoverable sector, demonstrating information-beam steering with the same antenna-level switching mechanism. These results show that compact antenna-level directional modulation can provide angularly selective information recovery in one principal plane while preserving omnidirectional coverage in the orthogonal plane.

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arXiv2026

A Compact Omnidirectional Meanderline Antenna Array for Wireless Security Using Dynamic Magnitude and Phase Pattern Modulation

A compact dynamic four-element array with omnidirectional H-plane coverage is presented for planar physical-layer security using antenna-level directional modulation. The proposed approach achieves angularly selective information transmission without phased-array beamforming or multiple RF chains by dynamically switching the excitation paths of a four-element array. The antenna comprises four printed meander-line monopole elements operating at 5.05 GHz with independently controlled differential power excitation, which introduces magnitude and phase pattern modulation and dynamic motion of the apparent element spacing, resulting in strongly angle-dependent signal distortion and bit error rate (BER) performance. Reliable information recovery is confined to a narrow broadside region in the E-plane, while significantly elevated BER is observed at off-broadside angles. In contrast, the H-plane radiation remains static and omnidirectional, enabling full 360-degree information-recoverable coverage in the orthogonal plane. The antenna is fabricated on a single-layer Rogers RO4350B substrate with a compact footprint of 0.55 x 1.73 lambda_0^2. A four-path switching network implemented using commercial RF components validates the concept experimentally. Communication measurements under high-SNR conditions above 19 dB using 16-QAM demonstrate a planar information beamwidth below 24 degrees, confirming effective antenna-level directional modulation with angle-dependent BER characteristics and omnidirectional H-plane coverage.

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arXiv2026

Spatial-Spectral Modeling of the Array Pattern of a Two-Element Dynamic Antenna Array with Differential Amplitude Modulation

We present a theoretical model for a two-element dynamic phased array and characterize the transfer of information as a function of angle. The array is based on a two-state switched structure with phase shifting to support beamsteering. Dynamic motion of the phase center of antenna arrays generates time-varying radiation patterns that, when appropriately designed, support directional modulation, or the transfer of information to regions of space that are narrower than that covered by the energy radiated by the array. We evaluate the impact of switching frequency and steering on the spatial width of the information beam, which is the region of space where information is recoverable. The concepts are evaluated through simulation and experiment using a 0.75$λ$ two-element array operating at 2.5 GHz.

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arXiv2026

Array Layout Optimization in a 24-Element 38-GHz Active Incoherent Millimeter-Wave Imaging System

Active incoherent millimeter-wave (AIM) imaging is a recently developed technique that has been shown to generate fast millimeter-wave imaging using sparse apertures and Fourier domain sampling. In these systems, spatial frequency sampling is determined by cross-correlation between antenna pairs, making array geometry an important aspect that dictates the field of view (FOV) and image quality. This work investigates the impact of array redundancy and spatial sampling diversity on AIM image reconstruction performance. We present a comparative study of three receive array configurations, including one simple circular design and two arrays obtained through optimization strategies designed to maximize unique spatial samples while preserving system resolution and FOV. Performance is evaluated using the image-domain metrics of structural similarity index (SSIM) and peak sidelobe level (PSL), enabling a quantitative assessment of reconstruction fidelity and artifact suppression. We perform experimental validation using a 38-GHz AIM imaging system, implementing a 24-element receive array within a 48-position reconfigurable aperture. Results demonstrate that optimized array configurations improve spatial sampling efficiency and yield measurable gains in reconstruction quality compared to a conventional circular array, highlighting the importance of array design for AIM imaging systems.

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arXiv2025

Secure Wireless Communication Using Coherent Distributed Transmission and Spatial Signal Decomposition

We present a new approach to secure wireless communications using coherent distributed transmission of signals that are spatially decomposed between a two-element distributed antenna array. High-accuracy distributed coordination of microwave wireless systems supports the ability to transmit different parts of a signal from separate transmitters such that they combine coherently at a designated destination. In this paper we explore this concept using a two-element coherent distributed phased array where each of the two transmitters sends a separate component of a communication signal where each symbol is decomposed into a sum of two pseudo-random signal vectors, the coherent summation of which yields the intended symbol. By directing the transmission to an intended receiver using distributed beamforming, the summation of the two vector components is largely confined to a spatial region at the destination receiver. We implement the technique in a 50 wavelength array operating at 3 GHz. We evaluate the symbol error ratio. (SER) in two-dimensional space through simulation and measurement, showing the approach yields a spatially confined secure region where the information is recoverable(i.e., the received signal has low SER), and outside of which the information is unrecoverable (high SER). The proposed system is also compared against a traditional beamforming system where each node sends the same data. We validate experimentally that our approach achieves a low SER of 0.0082 at broadside and a SER above 0.25 at all other locations compared to a traditional beamforming approach that achieves a SER of 0 at all locations measured.

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arXiv2025

Real-Time High-Accuracy Digital Wireless Time, Frequency, and Phase Calibration For Coherent Distributed Antenna Arrays

This work presents a fully-digital high-accuracy real-time calibration procedure for frequency and time alignment of open-loop wirelessly coordinated coherent distributed antenna array (CDA) modems, enabling radio frequency (RF) phase coherence of spatially separated commercial off-the-shelf (COTS) software-defined radios (SDRs) without cables or external references such as global navigation satellite system (GNSS). Building on previous work using high-accuracy spectrally-sparse time of arrival (ToA) waveforms and a multi-step ToA refinement process, a high-accuracy two-way time transfer (TWTT)-based timefrequency coordination approach is demonstrated. Due to the two-way nature of the high-accuracy TWTT approach, the time and frequency estimates are Doppler and multi-path tolerant, so long as the channel is reciprocal over the synchronization epoch. This technique is experimentally verified using COTS SDRs in a lab environment in static and dynamic scenarios and with significant multipath scatterers. Time, frequency, and phase stability were evaluated by beamforming over coaxial cables to an oscilloscope which achieved time and phase precisions of ~60 ps-70 ps, with median coherent gains above 99 % using optimized coordination parameters, and a beamforming frequency root-mean-square error (RMSE) of 3.73 ppb in a dynamic scenario. Finally, experiments were conducted to compare the performance of this technique with previous works using an analog continuous-wave two-tone (CWTT) frequency reference technique in both static and dynamic settings.

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arXiv2025

Passive Microwave Tag Classification Using RF Fingerprinting and Machine Learning

We present an approach to identifying wireless microwave tags using radio frequency (RF) fingerprinting and machine learning. The tags are designed for low cost and simplicity, consisting of only two antennas and a single nonlinear element (a diode). An interrogating transceiver transmits a signal consisting of a set of individual frequency tones that is captured by the tag. The signal response of the diode is nonlinear, and can be represented by an infinite power series, the coefficients of which are similar but not identical for different physical diodes due to small manufacturing perturbations. The small differences in the signal responses manifest in the spectral signal response of the tag, which is retransmitted back to the interrogating transceiver. Input into machine learning algorithms, the slight differences in the spectral responses of the diodes can be used to uniquely identify devices. To demonstrate the concept, we designed 2.0 GHz tags consisting of patch antennas and a single diode, along with a bi-static radar system operating at the 2.0 GHz 802.11 Wi-Fi band transmitting multi-tone continuous wave signals representing common 802.11 training fields. The received signals were processed using a set of algorithms for comparison purposes. A real-time classification accuracy of 95% between two tags was achieved.

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arXiv2025

A Compact Dynamic Antenna for Physical Layer Wireless Security

We propose a novel omnidirectional antenna design incorporating directional modulation for secure narrow planar information transmission. The proposed antenna features a compact size and stable omnidirectional radiation performance by employing two tightly spaced, printed meander line monopole antennas, acting as a single radiating element. To achieve a narrow information secure region, the proposed antenna is fed by differential power excitation of two ports with real-time dynamic switching. This leads to phase pattern modulation only along the electrical polarization, resulting in directionally confined information recoverable region in the E-plane, while maintaining highly constant or static omnidirectional H-plane pattern, inducing a $360^\circ$ information recoverable region. The dynamic antenna is designed and fabricated on a single layer of Rogers RO4350B which provides a miniaturized planar size of $0.36 \times 0.5 , λ_0^2$ at 2.7 GHz and easy integration. To validate the wireless communication performance, the fabricated antenna is directly fed with a 10 dB power ratio by a radio frequency (RF) switching system and evaluated for 16-QAM and 256-QAM transmission in a high signal-to-noise ratio (SNR) environment. Experimental results demonstrate that for 16-QAM transmission, a narrow E-plane information beam (IB) of approximately $34^\circ$ and omnidirectional H-plane IB are obtained, and a narrower E-plane IB is achieved around $15^\circ$ for 256-QAM. These results confirm that the proposed antenna offers a simple yet effective approach to enhance planar physical information security with a compact dynamic antenna system.

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arXiv2025

Three-Dimensional Millimeter-Wave Imaging Using Active Incoherent Fourier Processing and Pulse Compression

We present a novel three-dimensional (3D) imaging approach that combines two-dimensional spatial Fourier-domain imaging techniques with traditional radar pulse compression to recover both cross-range and down-range scene information. The imaging system employs four transmitters, three of which emit spatially and temporally incoherent noise signals, while the fourth transmits a known linear frequency modulated (LFM) pulsed signal. The spatial incoherence of the noise signals enables sampling of the 2D spatial Fourier spectrum of the scene from which two-dimensional cross-range (azimuth and elevation) images can be formed via interferometric processing. Simultaneously, the LFM signal enables high-resolution downrange imaging through matched filtering. The received signals consist of a superposition of the noise sources and the known pulse allowing for joint recovery of all three dimensions. We describe the system architecture and waveform design, and demonstrate the imaging technique using both simulations with a linear array and experimental data from a 38 GHz active incoherent millimeter-wave imaging system with 23-element randomized array. Results show the reconstruction of targets in three dimensions.

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arXiv2025

Collaborative Beamforming for Communication Applications Using a Two-Element Fully-Wireless Open-Loop Coherent Distributed Array

In this work we demonstrate a proof of concept of a fully-wireless two-node open-loop coherent distributed communication system and evaluate its performance by transmitting QPSK , 64-, and 256-QAM constellations at a symbol rate of 2 MBd over a 58 m link in an urban environment. The system is implemented in a distributed manner with on-node processing using software-defined radios (SDRs) and wireless internode communication to share coordination information and does not rely on external time or frequency references such as the global navigation satellite system (GNSS). In each experiment ~100 messages were transmitted and a mean coherent gain of 0.936 was achieved across all measurements with a mean symbol error ratio of below $1.4\times 10^{-4}$ achieved up to 64-QAM, demonstrating a reliable bandwidth of up to 12 Mbps.

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arXiv2025

Distributed Beamforming Using Decentralized Time Synchronization in a Six-Element Array

We demonstrate a distributed beamforming and beamsteering from a six-node distributed phased array using fully wireless coordination with decentralized time synchronization. In wireless applications such as distributed beamforming, high-accuracy time synchronization across the array is crucial for high coherent gain. The decentralized time synchronization method employed is based on the average consensus algorithm and the two-way time transfer method presented in our previous work, which achieved picosecond time synchronization with a cabled frequency reference. The system presented in this paper utilizes a centralized wireless frequency transfer method to achieve wireless frequency syntonization in a fully wireless coordination and a distributed computing system architecture. We experimentally evaluate system performance through beamforming and beamsteering to a receiver 16.3 m away from the six-node non-uniformly distributed antenna array, achieving an average coherent gain of 98% of the ideal gain at a carrier frequency of 1.05 GHz. The average time synchronization accuracy achieved was less than 36 ps.

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arXiv2025

A Compact Narrowband Antenna Design for RF Fingerprinting Applications

Radio frequency (RF) fingerprinting is widely used for supporting physical layer security in various wireless applications. In this paper, we present the design and implementation of a small antenna with low-cost fabrication that can be directly integrated with nonlinear passive devices, forming a passive RF tag providing unique nonlinear signatures for RF fingerprinting. We first propose a miniaturized meander line dipole, achieved by two folded arms on two sides of the substrate. This leads to antenna with a simple feeding structure and compact size, making it ideal for planar integration. Two antennas on Rogers 4350B and ultra-thin flexible Panasonic Felios are fabricated, achieving small size at $0.21 \times 0.06 \times 0.004 λ_0^3$ and $0.14 \times 0.1 \times 0.0008 λ_0^3$ with realized gain of 1.87 dBi and 1.46 dBi. The passive tag consists of the proposed antenna structure and an integrated RF diode, and is further developed on both substrates, aiming to generate inter-modulation products (IMP) due to the nonlinearity of the diode, which can be used for device identification through classification algorithms. We investigate the nonlinearity of the designed tags for transmission at 15 dBm using two-tone signals. All tags produce a significant increased power at IMP frequencies at a range of 0.4 m. The tags on Rogers substrate provide around 23 dB IMP power increase and tags on flexible substrate embedded in lossy material provide around 16 dB power increase. These findings confirm that the proposed solution offers a simple passive tag design to support unique nonlinear signatures for RF fingerprinting applications in a simple, low-cost device.

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arXiv2025

Additive Frequency Diverse Active Incoherent Millimeter-Wave Imaging

We present an approach for improving spatial frequency sampling in active incoherent millimeter-wave (AIM) imaging systems using frequency diversity. AIM imaging relies on active transmission of spatio-temporally incoherent signals to illuminate a scene, from which interferometric Fourier-domain imaging can be implemented using a sparse receiving antenna array. One of the benefits of Fourier domain imaging is the sparsity of the receiving array, which can form images with equivalent resolution to traditional filled beamsteering arrays, but with a small fraction of the elements. The hardware reduction afforded by the sparse array often leads to an undersampled Fourier space, where even though image formation is possible, the image reconstruction may be degraded when viewing complex objects. To address this challenge without requiring additional receiver channels, we explore the use of frequency diversity in the illuminating and receiving systems. Fourier domain spatial frequency samples are determined by the electrical spacing and rotation of the receiving elements, thus by changing the frequency the sampled spatial frequencies also change. We implement an additive technique where the spatial frequency samples are summed prior to Fourier transform image formation. Importantly, because the system is active, a consistent signal-to-noise ratio is maintained across all frequencies, which may not be possible in traditional passive Fourier-domain imagers.

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arXiv2024

A Dipole Antenna with a Dynamic Balun for Wireless Security via Amplitude Based Directional Modulation

We present a new approach to secure wireless operations using a simple dipole antenna with a dynamic unbalanced feeding structure. By rapidly switching between two states, a dynamic radiation pattern is generated, resulting in directional modulation. The current distribution on the arms of the dipole antenna are made asymmetric by the balun, which changes the relative phase between the feed currents. By rapidly switching between two mirrored states, the relative phase shift changes sign, causing the current distribution to manifest asymmetrically on the arms of the dipole antenna. The resultant far field radiation pattern is therefore asymmetric in both states, but mirrored between the two states. Rapid switching between the two states results in a far-field pattern that is dynamic in amplitude at all angles except for a narrow region of space, which is referred to as the information beam. The dynamic radiation pattern causes additional modulation on any transmitted or received signals, thereby obscuring the information at all angles outside the information beam. The proposed directional modulation technique is separate from both the antenna and the rest of the wireless system, and can thus be implemented in a black box form in wireless communications or sensing systems. We demonstrate the concept in a 1.86 GHz printed dipole antenna, demonstrating the transmission of 256-QAM signals.

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arXiv2024

Decentralized Localization of Distributed Antenna Array Elements Using an Evolutionary Algorithm

Distributed phased arrays have recently garnered interest in applications such as satellite communications and high-resolution remote sensing. High-performance coherent distributed operations such as distributed beamforming are dependent on the ability to synchronize the spatio-electrical states of the elements in the array to the order of the operational wavelength, so that coherent signal summation can be achieved at any arbitrary target destination. In this paper, we address the fundamental challenge of precise distributed array element localization to enable coherent operation, even in complex environments where the array may not be capable of directly estimating all nodal link distances. We employ a two-way time transfer technique to synchronize the nodes of the array and perform internode ranging. We implement the classical multidimensional scaling algorithm to recover a decentralized array geometry from a set of range estimates. We also establish the incomplete set of range estimates as a multivariable non-convex optimization problem, and define the differential evolution algorithm which searches the solution space to complete the set of ranges. We experimentally demonstrate wireless localization using a spectrally-sparse pulsed two-tone waveform with 40 MHz tone separation in a laboratory environment, achieving a mean localization error vector magnitude of 0.82 mm in an environment with an average link SNR of 34 dB, theoretically supporting distributed beamforming operation up to 24.3 GHz.

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