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This paper presents an experimental and analytical investigation of ultra-wideband (3–8 GHz) body-to-body (B-to-B) channel characterization. The channel parameters obtained are compared with off-body (off-B) and no-body (no-B) links. Measurements have been carried out considering different body positions and orientation of the Tx–Rx pair. The type of channel link and position of the wearable antenna lead to significant changes in the radio link channel. Path loss (PL) computed shows the increase in magnitude for non line of sight (NLOS) in comparison to line of sight (LOS), though the variation over a distance of 5 m is more significant for LOS (10 dB) than NLOS links (4–5 dB). For total NLOS links, B-to-B channels have slightly higher PL and delay spread parameters in comparison to off-B channel. The B-to-B LOS channels have least PL (44–56 dB), rms delay spread (0.5–4 ns), and multipath components (3–20) which can be attributed to the directional radiation pattern due to the presence of the human body for both Tx and Rx nodes. For back-to-back antenna orientation of the B-to-B channel, maximum signal strength degradation and multipath are observed. It can be concluded that for certain links, the B-to-B channel shows a significant change in channel behavior in comparison to off-B/no-B scenario. [ABSTRACT FROM AUTHOR]

A novel localization framework is presented based on ultra-wideband (UWB) channel sounding, employing a triangulation method using the geometrical properties of propagation paths, such as time delay of arrival, angle of departure, angle of arrival, and their estimated variances. In order to extract these parameters from the UWB sounding data, an extension to the high-resolution RiMAX algorithm was developed, facilitating the analysis of these frequency-dependent multipath parameters. This framework was then tested by performing indoor measurements with a vector network analyzer and virtual antenna arrays.The estimated means and variances of these geometrical parameters were utilized to generate multiple sample sets of input values for our localization framework. Next to that, we consider the existence of multiple possible target locations, which were subsequently clustered using a Kim–Parks algorithm, resulting in a more robust estimation of each target node. Measurements reveal that our newly proposed technique achieves an average accuracy of 0.26, 0.28, and 0.90 m in line-of-sight (LoS), obstructed-LoS, and non-LoS scenarios, respectively, and this with only one single beacon node. Moreover, utilizing the estimated variances of the multipath parameters proved to enhance the location estimation significantly compared to only utilizing their estimated mean values. [ABSTRACT FROM PUBLISHER]

An ultra-wideband, lossless cavity-backed Vivaldi antenna array for flush-mounting applications is proposed. Eigenmode analysis, used to investigate antenna-cavity interaction, has shown that the entire structure may resonate within the band of interest resulting in a significant degradation of antenna performance. A simple approach based on connecting the array’s edge elements in E-plane to the cavity walls is utilized to eliminate the deleterious impact of these cavity resonances. The proposed antenna is a $3\times 4$ array with three elements in E-plane and four elements in H-plane, fabricated using stacked all-metal printed circuit board technique. Resonant-free behavior with gain better than 5 dBi and VSWR <2 from 1.5 to 7.5 GHz is obtained. High-quality radiation patterns with sidelobe levels lower than 20 dB over the same bandwidth are also demonstrated. Scan performance of the proposed cavity-backed antenna is investigated in two principal planes and is shown to have similar performance compared to its free-standing counterpart. [ABSTRACT FROM AUTHOR]

This paper presents a clustering and tracking method that exploits the geometry of the scattering points (SPs) obtained from the measurement-based ray tracer. The multipath components (MPCs) were categorized into clusters by applying the KPowerMeans (KPM) framework to those SPs. The clusters were tracked by comparing the cluster-centroid SPs of the adjacent snapshots. The clusters were estimated based on the indoor environment geometry at 11 GHz, and their physical mechanisms were interpreted. The complexity and performance of this method was assessed and compared with that of conventional KPM by comparing the number of floating point operations (FLOPS) and the channel eigenvalues obtained from the reconstructed channel matrices, which were calculated by superposing the MPCs randomly generated from intracluster parameters. The verification of this method showed that most clusters were estimated and tracked according to the physical location of the scatterers in the environment with acceptable error. Moreover, the eigenvalues reconstructed from the proposed method were closer to the measured ones with less number of FLOPS, which indicates both accuracy and complexity improvement. The results also imply that multiple-input multiple-output performance is highly dependent on the radio propagation channel; therefore, it is imperative that clusters in the channel be determined accurately. [ABSTRACT FROM AUTHOR]

Multiport antenna systems can be regarded as $N$ -port networks, which can be analyzed using the theory of network characteristic modes (NCMs). Due to the profound physical insights provided by an NCM, a desired antenna performance can be achieved by properly manipulating the modes through reactive loading at specified ports. This paper presents a new matching technique for an $N$ -port internally loaded small antenna. By combining the NCM with the differential evolution algorithm, optimal reactive load values can be calculated. These loads can manipulate the NCMs to match the antenna in a desired bandwidth. Unlike other matching techniques based on the NCM, the desired bandwidth is achieved through internal reactive loading without the need for an input matching network. Two examples of electrically small monopole antennas are studies. In both examples, we study the possibility to match the antennas in the GSM 900 band, and we further investigate the possibility to achieve wider bandwidths by varying the number of ports and the loading topologies based on the interpretation of the characteristic modes. The loaded antennas are wideband with a relatively stable radiation pattern and an efficiency higher than 90%. To confirm the theoretical results, a prototype is fabricated and measured. [ABSTRACT FROM AUTHOR]

Detection of packages or storage containers relies heavily on the use of radio frequency identification (RFID) tagging, though such technology provides no means to determine the quantity of items within them. This paper presents a comprehensive study of ultra wideband (UWB) detection in the reactive near field as a low cost, low power way of detecting solid items within a package to complement RFID. For proof of concept, egg boxes within a smart fridge are used as a chosen test case. Simulations and measurements are carried out to evaluate the filtering of the UWB impulse response from which it can resolve the quantity of eggs in a box, using an array of sensors either attached to the package or placed underneath. Correlation coefficients are derived as a metric of this filtering in a reactive near field detection scenario. The robustness of the approach is further evaluated by considering other food cluttered around and above the egg box. The results show smart packages which detect an item directly above the sensor is not affected by surrounding clutter. [ABSTRACT FROM AUTHOR]

An optimization method for ultrawideband multiple-input-multiple-output (MIMO) planar array topology design, which can satisfy both uniformity and lower element shadowing principles, is proposed by extending our previous work. Two planar MIMO arrays, namely, the basic optimal array (BOA) and the extended optimal array (EOA) are optimized. The focusing and sidelobe-suppression properties of the BOA and the EOA are demonstrated to be superior to other two previous state-of-the-art planar MIMO arrays. The advantages of the two optimized arrays in 3-D imaging are further indicated by experimental results for different distributed targets. The validity of the proposed method is verified by the excellent performances of the BOA and the EOA. [ABSTRACT FROM PUBLISHER]

A subsection of the radiating spiral arm, placed in parallel, induces a bandstop response at a notch frequency proportional to the resonant length of the strip. Detailed parametric study on the effect of variation of design parameters for an Archimedean spiral antenna and the resonant parallel strip (RPS) is presented. Empirical analysis on phase velocity on the radiating spiral arms allows characterization of RPS in terms of its resonant length. Identified systematic relation between design parameters and filter response is applied to design an antenna for the 3.1–10.5 GHz operating band with the notch response over the IEEE 802.11a band, 5.15–5.95 GHz. Successful implementation is demonstrated through performance comparison between simulated and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a systematic design technique for quadruple-ridged flared horn antennas is presented, to enhance the radiation properties through the profiling of the ridge taper. The technique relies on control of the cutoff frequencies of specific modes inside the horn, instead of brute-force optimization. This is used to design a prototype antenna as a feed for an offset Gregorian reflector system, such as considered for the Square Kilometer Array (SKA) radio telescope, to achieve an optimized aperture efficiency from 2 to 12 GHz. The antenna is employed with a quadraxial feeding network that allows the excitation of the fundamental TE11 mode, while suppressing all other modes that causes phase errors in the aperture. Measured results confirm the validity of this approach, where good agreement is found with the simulated results. [ABSTRACT FROM PUBLISHER]

A radio-frequency (RF) amplifier-integrated ultra-wideband (UWB) multiple-input–multiple-output (MIMO) antenna system is presented. Instead of designing both the antenna and the amplifier separately based on $50-\Omega $ interfaces, they are codesigned without this impedance requirement so that improved wideband antenna matching and total radiation efficiency are achieved. The design is implemented with a two-element semi-ring UWB MIMO antenna integrated with a commercially available UWB amplifier. The antenna has the size of $0.01\lambda_0^2 $ where $\lambda_0 $ is the free-space wavelength at 1.8 GHz. The integrated antenna shows minimum realized gain and efficiency of 14.1 dBi and 60%, respectively, over the 1.8–5.5-GHz band. Diversity parameters of the integrated MIMO antenna are evaluated. Detailed design and measurement procedures are presented with simulation and experimental results. [ABSTRACT FROM AUTHOR]

A monostatic ultra-wideband simultaneous transmit and receive (STAR) antenna subsystem is introduced. An inherent geometrical symmetry of a four-arm spiral antenna and feeding rearrangement are exploited to achieve the simultaneous transmit (TX) and receive (RX) functionalities without any time, polarization, or frequency multiplexing. The antenna is configured such that one arm-pair is used for TX and the other for RX. Thus, even though the two antennas are spatially separated by 90°, they still share the same aperture and the system is considered monostatic. Theoretical and computational studies are conducted to demonstrate the feasibility of the proposed approach under ideal conditions as well as in the presence of feed network non-idealities. The experimental data indicate that isolation levels greater than 39.6–50 dB over multiple octaves are achievable with realistic components. To improve the TX and RX far-field patterns, the planar four-arm spiral aperture is grounded via resistor-loaded quadrifilar helix with the two-arm TX/two-arm RX feed arrangement preserved. Furthermore, to simplify the feed network and reduce the impact of hybrid imbalances, an impedance-transforming microstrip feed is integrated with each arm pair. Isolation > 37\;\text dB and similar with high-quality measured and simulated TX/RX radiation patterns are obtained over the operating bandwidth. [ABSTRACT FROM AUTHOR]

A polarization-reconfigurable low-profile ultra-wideband VHF/UHF antenna array is presented in this paper. The design is based on resistively loaded planar dipole antenna elements backed with a ground plane. The antenna array has two mechanically field-switchable polarization configurations which are designed to measure the crystal orientation of ice sheets. The nominal operating mode of the array is in the vertically polarized configuration with operating frequency ranges from 150 to 550 MHz. The planar dimension of the array is 3.6\;\textm \times 0.8\;\textm with a ground plane height of 16 cm (0.08\lambda low,{{\text f}low} = 150\,\text{MHz}). Anechoic chamber measurements show that the array performance is in very good agreement with simulated results, for both VSWR and array radiation pattern. It is also shown that the array is capable of handling 1-kW peak power per transmit channel. The antenna array is housed within a flight-qualified composite S2-glass/epoxy fairing and can readily be mounted on airborne platforms, such as Basler BT-67 and Twin Otter, for radar sounding of polar ice sheets and glaciers. [ABSTRACT FROM PUBLISHER]

This communication presents a bandwidth-enhanced, compact, monopole antenna with modified ground plane for modern automotive ultra wide-band (UWB) applications. The proposed antenna has hybrid geometry and is constructed using half circular ring and half square ring. The ground plane of the fundamental radiator is curved and defected to improve the VSWR bandwidth. An extended ground stub is added to further enhance the bandwidth to suit the modern automotive requirements. The designed antenna covers 3.1–10.9 GHz frequency spectrum with \mathrm VSWR \leq 2. This antenna can be conveniently placed inside the shark fin housing or it can be printed along with the existing print circuit board (PCB) electronics nullifying the need for dedicated location for in-car communications. Furthermore, a simple two-port multiple input multiple output (MIMO) antenna is constructed and its diversity performance is estimated. The prototype is fabricated and tested for impedance and radiation characteristics. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel formalism to improve the performance of an off-body system by deploying multiple ultra wideband (UWB) antennas, positioned strategically on the body. A methodology is presented for determining the optimal positions of UWB antennas on the body, necessary to provide a reliable multiband orthogonal frequency division multiplexing (MB-OFDM) UWB diversity antenna system operating in the Federal Communications Commission frequency band between 3.1 and 10.6 GHz. By evaluating the diversity metric, using simulation and measurement data, it is shown that the performance of such a system is stable throughout the entire investigated frequency band for both indoor and outdoor environments. There is a good agreement between the simulated and measured diversity values with a deviation of less than 9%. Therefore, the proposed technique optimizes the antennas’ positions for maximum diversity performance within a very broad frequency band, independent of the used wireless communication standard. Thus, the obtained diversity system might be used in any kind of wireless communication link within that frequency band, e.g., UWB-OFDM, UWB MB-OFDM, UWB, or even narrowband transmission. [ABSTRACT FROM PUBLISHER]

Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer (\bf55\;\upmu\mathrmm) with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit–patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented. [ABSTRACT FROM PUBLISHER]

Recent telecommunication systems exploit the degrees of freedom of the radio propagation channel more and more. Deeper investigations of system performance require realistic channel models. For this purpose, a new MIMO UWB channel sounder is introduced. The novelty is its capacity to estimate simultaneously direction of arrival and departure in 3D, including polarization state information. The second novelty is a modified SIC algorithm which speeds up the search of the multipath properties of the propagation channel. An extensive measurement campaign is performed in different residential environments and statistical results are provided. [ABSTRACT FROM PUBLISHER]

The paper presents a new approach to time-domain modeling of ultra-wideband (UWB) channels with multiple convex obstacles. Rational approximation exploiting the vector fitting algorithm (VF) is used for deriving the closed-form impulse response of a multiple diffraction ray creeping on a cascade of convex obstacles. The VF algorithm is performed with respect to new generalized variables proportional to frequency but also taking into account geometrical parameters of the obstacles. The limits of the approximation domain for the VF algorithm reflect the range of UWB channel parameters that can be met in practical UWB channel scenarios. The results of VF approximation have the form of a finite series of partial fractions in the frequency domain, which then is easily transformed to the time domain. Obtained in this way, impulse response is a sum of exponential functions. As a consequence, in simulations of electromagnetic (EM) wave propagation, we can implement very fast and effective convolution algorithms with any input signal or perform simulations implementing SPICE-like programs. [ABSTRACT FROM PUBLISHER]

The physical motivation and interpretation of the stochastic propagation channel model of Saleh and Valenzuela are discussed in detail. This motivation mainly relies on assumptions on the stochastic properties of the positions of transmitter, receiver and scatterers in the propagation environment, and on the frequency range that is covered by the model. Some of these assumptions break down when the application of the model is extended from wideband to ultra-wideband propagation channels. Another important difference between these application contexts is the spatial scale over which the stochastic properties of the channel fluctuate when the transmitter or receiver is moved. This is further illustrated by analyzing the average power delay profile and some other channel properties for different levels of ensemble averaging, and discussing the relation between the ensemble averaging levels and the spatial variation scales. The notion of the averaging levels is essential for correct interpretation of the model, and hence for appropriate channel characterization and system design. [ABSTRACT FROM PUBLISHER]

We present a dual-polarized self-grounded bowtie antenna. The antenna is mechanically simple and wideband. One of the characteristics is its flexibility: it can be used either as a 4-port antenna in multiple-input–multiple-output (MIMO) systems or as a directional 2-port dual-polarized antenna in radar or sensor systems. The latter application requires a balun. The 4-petal geometry of the antenna has been optimized for the best matching to 50 \Omega coax over 1.5–3 GHz. Both simulated and measured results are presented to verify the design. The antenna radiates over parts of the bandwidth similar to four Huygens source, one from each petal, each having directivity close to 4.8 dBi. [ABSTRACT FROM PUBLISHER]

A compact ultra wideband antenna with strong notch-band rejections up to VSWR= 26, that is tunable over a wide frequency range from 3.55 GHz to 6.8 GHz, is presented. It has wide radiation patterns and yields a measured 10 dB return-loss bandwidth from 3 GHz to 10.5 GHz. [ABSTRACT FROM PUBLISHER]

A fully textile microstrip topology with ultra wideband (UWB) characteristics useful in wireless body area networks (WBAN) is proposed. The antenna is operable within the full UWB band and incorporates a full textile shielding ground plane. The full ground plane is shown to be crucial in maintaining the performance when worn on-body. It successfully reduces any on-body performance degradation, resulting in a very robust structure. A detailed numerical and experimental evaluation of the antenna is performed in free space and on body. [ABSTRACT FROM AUTHOR]

In order to correctly identify a remote target, an efficient and robust target signature identification technique is required. Radar target identification based on complex natural resonances (CNRs) has drawn the interest of many researchers following the development of the singularity expansion method (SEM). As evident from the literature, statistical techniques such as the generalized likelihood ratio test (GLRT) have produced a better identification result, in the presence of noise, compared to some other SEM-based identification methods such as the extinction pulse (E-pulse) technique. However, one of the issues related to a resonance based target classifier is that it requires the commencement of the late time period for the unknown target response to be determined accurately in order to avoid false alarms during target classification process. For automatic target recognition (ATR) applications, usually such information is not known a priori. In view of this problem, a modified GLRT technique that utilizes time–frequency analysis is presented in this paper. The improved GLRT method does not require prior knowledge of the beginning of the late time period for the transient response of the unknown target. Simulation results using various targets show that our method is comparable to the original GLRT technique when the commencement of the late time period for the unknown target response is correctly determined and outperforming the original GLRT technique when the commencement of the late time period for the unknown target response is incorrectly determined. [ABSTRACT FROM AUTHOR]

The Allen Telescope Array (ATA) is a cm-wave interferometer in California, comprising 42 antenna elements with 6-m diameter dishes. We characterize the antenna optical accuracy using two-antenna interferometry and radio holography. The distortion of each telescope relative to the average is small, with RMS differences of 1% of beam peak value. Holography provides images of dish illumination, characterizing as-built mirror surfaces. Maximal distortions across ~ 2 meter lengths appear to result from mounting stresses or solar radiation. Experimental RMS errors are 0.7 mm at night and 3 mm under worst-case solar illumination. For frequencies 4, 10, and 15 GHz, the nighttime values indicate sensitivity losses of 1, 10 and 20%, respectively. ATA's wide-bandwidth receiver permits observations over a continuous range 0.5-11.2 GHz. We probe the antenna optical gain and beam pattern stability as a function of focus position and observation frequency, concluding that ATA can produce high fidelity images over a decade of simultaneous observation frequencies. We quantify solar heating effects on antenna sensitivity and pointing accuracy. We find that during the day, observations >;5 GHz will suffer some sensitivity loss and it may be necessary to make antenna pointing corrections on a 1-2 hourly basis. [ABSTRACT FROM AUTHOR]

Next generation of instruments for radio astronomy will benefit greatly from reflector antenna feeds that demonstrate very wide instantaneous bandwidth and exhibit low noise behavior. Our study focuses on design and measurement of an ultra-wideband inverted conical sinuous antenna and its integration with a low noise pseudo differential amplifier. The self-complementary, frequency independent nature of the planar sinuous geometry results in a nearly constant beam pattern and fixed phase center over more than a 10:1 operating frequency range. In order to eliminate the back-lobe response over such a wide frequency range, we have projected the sinuous pattern onto a cone, and a ground plane is placed directly behind the cone's apex. This inverted, conical geometry assures wide bandwidth operation by locating each sinuous resonator a quarter wavelength above the ground plane. The presence of a ground plane near a self complementary antenna destroys the self complementary nature of the composite structure resulting in frequency dependent impedance variations. We demonstrate, using simulations and measurements, how the return loss can be improved by modifying the sinuous geometry. A physically smaller, laboratory version of the 0.3 to 3 GHz antenna that is truncated to operate from 1 to 3 GHz was fabricated to verify proper LNA-feed integration through careful modeling and measurements. Over this range, a return loss of better than 9 dB is measured while simulations indicate a nearly constant beam pattern. A full decade bandwidth, low noise amplifier was specially designed for noise match to the higher terminal impedance encountered by this antenna yielding an improved sensitivity over what is possible with conventional 50 Ω amplifiers. A measured system noise temperature of less than 100 K is reported. Based on these results, we will increase the bandwidth of the system to 10:1 by simply attaching additional resonators to the sinuous arms. [ABSTRACT FROM AUTHOR]