A simple approach is presented for designing an antipodal Vivaldi antenna in this paper. A new and better estimation of the low frequency end of the operational range is shown. Final dimensions of the antenna parameters are determined by using the High Frequency Structure Simulator (HFSS). The proposed antenna has a simple configuration but exhibits low return loss, good radiation characteristics, and high and flat gain in the operating ultra wideband frequency range (3.1-10.6 GHz). Lastly, the fabrication has been done along with the specification to confirm the properties by measurements.

A use of ultra wideband (UWB) technology within spacecrafts has been proposed with a view to partially replacing wired interface buses with wireless connections. Adoption of wireless technologies within the spacecrafts could contribute to reduction in cable weight (and launching cost as a result), reduction in the cost of manufacture, more flexibility in layout of spacecraft subsystems, and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. In this paper, UWB and narrowband propagation were measured in a UWB frequency band (from 3.1 to 10.6 GHz, the full-band UWB approved in the United States) within a small spacecrafts and a shield box of the same size. While narrowband propagation resulted in considerable spatial variations in propagation gain due to interferences caused by multipath environments, UWB yielded none. This implies that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Throughputs exceeding 80 Mb/s were obtained by means of commercially-available UWB devices in the spacecraft. Path gains and throughputs were also measured for various antenna settings and polarizations. Polarization configurations were found to produce almost no effect on average power delay profiles and substantially small effects on the throughputs. Significantly long delay spreads and thus limited link performance are caused by a conductive enclosure (the shield box) without apertures on the surfaces. Even in such an environment, it was found that delay spreads can be suppressed by partially paneling a radio absorber on the inner surfaces. More than 96 Mb/s throughputs were attained when the absorber panel covered typically 4% of the total inner surface area.

The paper presents capability of signal detection for realizing coexistence between broadband wireless access (BWA) systems and ultra wideband (UWB) devices. The capability is experimentally evaluated for baseband signals of downlink (DL) in both mobile WiMAX and 3GPP LTE. An UWB receiver based on fast Fourier transform (FFT) compliant with MB-OFDM standard is implemented as a detector of the BWA signals. The capability is evaluated in terms of elapsed time required to achieve signal detection with probability of 99% by the implemented FFT-based UWB receiver at different conditions of the receiver. Decisions on the signal detection are made by the simplest method which is by setting a threshold which is determined by noise floor of the receiver as reference. The experiments have been conducted though baseband signals for both AWGN and multipath fading channels without any synchronization between the DL signals and UWB receiver. In AWGN environment, results show that the elapsed time depends on the duty ratio of the DL signal to be detected, however, the correlation between the required time and duty ratio is not linear since their envelopes of the DL signals are not constant. In multipath fading environments based on channel models commonly employed as mobile radio environments, the required time for the signal detection becomes as 17 times longer than that in AWGN due to its signal attenuation. For robust signal detection in multipath fading environments, it has been revealed that the number of quantization bits at ADC is crucial through the experiments.

A time-reversal (TR) approach with multiple signal classification (MUSIC) provides super-resolution for detection and localization using multistatic data collected from an array antenna system. The theory of TR-MUSIC assumes that the number of antenna elements is greater than that of scatterers (targets). Furthermore, it requires many sets of frequency-domain data (snapshots) in seriously noisy environments. Unfortunately, these conditions are not practical for real environments due to the restriction of a reasonable antenna structure as well as limited measurement time. We propose an approach that treats both noise reduction and relaxation of the transceiver restriction by using a time-domain gating technique accompanied with the Fourier transform before applying the TR-MUSIC imaging algorithm. Instead of utilizing the conventional multistatic data matrix (MDM), we employ a modified MDM obtained from the gating technique. The resulting imaging functions yield more reliable images with only a few snapshots regardless of the limitation of the antenna arrays.

Ultra wideband (UWB) radar is considered a promising technology to complement existing camera-based surveillance systems because, unlike cameras, it provides excellent range resolution. Many of the UWB radar imaging algorithms are based on large-scale antenna arrays that are not necessarily practical because of their complexity and high cost. To resolve this issue, we previously developed a two-dimensional radar imaging algorithm that estimates unknown target shapes and motion using only three antennas. In this paper, we extend this method to obtain three-dimensional images by estimating three-dimensional motions from the outputs of five antennas. Numerical simulations confirm that the proposed method can estimate accurately the target shape under various conditions.

Power patterns in the frequency domain are usually used to describe the antenna performance in narrowband communication systems; however, they are not sufficient for ultra wideband (UWB) antennas in wideband communication systems. In this paper, energy pattern and energy gain are introduced to describe the performance of UWB antennas. Numerical simulations and measurements are used to demonstrate the difference between power patterns and energy patterns for narrowband Yagi-Uda antenna, UWB CPW–fed bow-tie slot antenna, and UWB comb taper slot antenna. The results of simulations and measurements are agreement not only in energy pattern, but also in received voltage at various observation angles. For narrowband antennas, the energy patterns are similar to that of the power patterns in the main beam region. However, there are quite differences between power pattern in frequency domain and energy pattern in time domain for UWB antennas.

This study aims how to contain the environment reflection in a dynamic on-body ultra wideband (UWB) channel model. Based on a measurement approach, it is demonstrated that a complete body area channel model can be regarded as a combination of the on-body propagation characteristic and additional components from the environment. Based on such a channel model, the effect of environment reflection on the average bit error rate performance was investigated for a typical impulse radio UWB system.

In this work, an ultra-wideband impulse radio (UWB-IR) transceiver with accurate time-of-arrival (TOA) estimation for a ranging/positioning system was developed for wireless sensor network applications. The system uses an impulse radio characterized by a low duty cycle and direct-sequence spreading, which enable very precise ranging and good receiver sensitivity. An algorithm enabling the TOA of the first-path signal to be measured accurately in a multi-path environment with simple, low-power and low cost implementations was proposed. UWB chips with CMOS 0.18-µm technology and UWB transceiver modules performed that the accuracy of the proposed ranging system is 18.5 cm in a closed space.

The objective of this study is to investigate the feasibility of an ultra wideband (UWB) impulse radio system for in-body to off-body wireless communication for biomedical applications. At first, a UWB antenna is designed in the UWB low band for implant use in the chest. Then the channel model is extracted and established based on the finite difference time domain (FDTD) simulation with an anatomical human body model. The established channel model consists of a small set of parameters for generating discrete time impulse responses. The generated model shows good agreement with the FDTD-calculated result in terms of key communication metrics. For effective communication over the multipath-affected channel, the pulse position modulation is employed and a 2-finger RAKE structure with a constant temporal delay is proposed in the receiver. The bit error rate performance has shown the validity of the system in the in-body to off-body chest channel.

This paper describes ultra wideband (UWB) radio propagation measurements and modeling for wireless body area network (WBAN) applications in different environments. Several propagation measurement campaigns and associated modelings were carried out in either a radio anechoic chamber or a specific room type; however, dependence of the radio propagation on surrounding environments was not studied. Multipaths (mainly reflected from floor, ceiling, and walls) highly depend on the environment. To address this problem, radio propagation around the human body was measured in a radio anechoic chamber and four different-sized rooms. Parameters in a conventional loss model derived from the measurements were found to significantly diverge and depend on room volume and line-of-sight (LOS)/non-LOS (NLOS) cases. A modified model considering the impact of room volume has been proposed for the LOS/NLOS cases. Different propagation mechanisms were discussed along with parameter derivation. Probability distributions for the UWB propagation losses were also examined.

A waveform of an ultra wideband impulse radio (UWB-IR) system can be extremely distorted through a channel even for free-space transmission because of antenna dispersion. This highly degrades the link budget performance. Therefore, the understand of antenna characteristics, which effects on waveform distortion, is necessary. This paper studies the waveform distortion due to antenna in free space transmission in UWB-IR system. The link budget is usually evaluated by using the Friis' transmission formula. However, it is not directly applicable to the UWB-IR transmission system. The link budget evaluation formula attended from conventional Friis' transmission formula that takes into account the transmitted waveform, its distortion due to the antennas, the channel and the correlation receiver is proposed. Since the antenna is significant pulse-shaping filters in UWB-IR system, the example kind of the log-periodic dipole antenna (LPDA) is experimentally examined, especially focused on the effect of the template waveforms.

This letter proposes an Ultra WideBand (UWB) channel gain estimation algorithm that is based on frequency response correlation. From data measured in indoor and outdoor environments, the frequency correlation statistics of the UWB channel are characterized by correlation coefficients, which are represented as functions of the frequency separation according to the propagation environments. We use empirically established correlation coefficient models to develop the proposed channel gain estimation algorithm. In this algorithm, unknown channel gains of intermediate frequencies are estimated from known channel gains of neighboring reference frequencies. The performance of the proposed algorithm is evaluated against various configurations of reference frequencies and compared with that of a conventional estimation algorithm using a linear interpolation scheme.

This letter proposes a high-performance single-sided horn-shaped tapered bowtie antenna which is compact and covers more than the whole UWB frequency band. This design implements a bowtie radiating element and tapered strip-line feeder element on a single-sided dielectric substrate, which offers a measured return loss of less than -10 dB over the whole UWB frequency band of 3.0-10.8 GHz. The measured radiation pattern is bi-directional with consistent gain over the above frequency band. This compact-size design shows much enhanced performance, compared to the previously reported antenna, which is useful for UWB radar and communication applications.

Synchronization poses a major challenge in ultra wideband (UWB) systems due to low signal duty cycles in UWB. This study develops an effective synchronization scheme for frame-differential IR-UWB receivers to improve the synchronization speed. The proposed parallel search mechanism reduces the search region of the symbol boundaries to only a single frame duration. Moreover, only one delay element is needed in each branch, since a shared looped delay-line (SLD) is also proposed to lower the implementation complexity of the parallel search mechanism. Simulations and performance analysis show that the proposed scheme achieves a lower mean square error and a higher probability of detection than other alternatives.

In this paper, we study the capacity and performance of nonorthogonal pulse position modulation (NPPM) for Ultra-Wideband (UWB) communication systems over both AWGN and IEEE802.15.3a channels. The channel capacity of NPPM is determined for a time-hopping multiple access UWB communication system. The error probability and performance bounds are derived for a multiuser environment. It is shown that with proper selection of the pulse waveform and modulation index, NPPM can achieve a higher capacity than orthogonal PPM, and also provide better performance than orthogonal PPM with the same throughput.

Wireless communication devices in the field of medical implant, such as cardiac pacemakers and capsule endoscopes, have been studied and developed to improve healthcare systems. Especially it is very important to know the range and position of each device because it will contribute to an optimization of the transmission power. We adopt the time-based approach of position estimation using ultra wideband signals. However, the propagation velocity inside the human body differs in each tissue and each frequency. Furthermore, the human body is formed of various tissues with complex structures. For this reason, propagation velocity is different at a different point inside human body and the received signal so distorted through the channel inside human body. In this paper, we apply an adaptive template synthesis method in multipath channel for calculate the propagation time accurately based on the output of the correlator between the transmitter and the receiver. Furthermore, we propose a position estimation method using an estimation of the propagation velocity inside the human body. In addition, we show by computer simulation that the proposal method can perform accurate positioning with a size of medical implanted devices such as a medicine capsule.

Ultra wideband (UWB) technologies are expected to be used in ultra-high-speed wireless personal area networks (WPAN) and wireless body area networks (WBAN). UWB human electromagnetic phantoms are useful for performance evaluation of antennas mounted in the vicinity of a human body and channel assessment when a human body blocks a propagation path. Publications on UWB phantoms, however, have been limited so far. This paper describes the development of liquid UWB phantom material (aqueous solution of sucrose) and UWB arm and torso phantoms. The UWB phantoms are not intended to evaluate a specific absorption rate (SAR) in a human body, because UWB devices are supposed to transmit at very low power and thus should pose no human hazard.

To realize the compact ultra-wideband (UWB) bandpass filters, a novel filter prototype with two short-circuited stubs loaded at both sides of a stepped-impedance resonator (SIR) via the parallel coupled lines is proposed based on a distributed filter synthesis theory. The equivalent circuit of this filter is established, while the corresponding 7-pole Chebyshev-type transfer function is derived for filter synthesis. Then, a distributed-circuit-based technique was presented to synthesize the elements' values of this filter. As an example, a FCC UWB filter with the fractional bandwidth (FWB) @ -10 dB up to 110% was designed using the proposed prototype and then re-modeled by commercial microwave circuit simulator to verify the correctness and accuracy of the synthesis theory. Furthermore, in terms of EM simulator, the filter was further-optimized and experimentally-realized by using microstrip line. Good agreements between the measurement results and theoretical ones validate the effectiveness of our technique. In addition, compared with the conventional SIR-type UWB filter without short-circuited stubs, the new one significantly improves the selectivity and out-of-band characteristics (especially in lower one -45 dB@1-2 GHz) to satisfy the FCC's spectrum mask. The designed filter also exhibits very compact size, quite low insertion loss, steep skirts, flat group delay and the easily-fabricatable structure (the coupling gap dimension in this filter is 0.15 mm) as well. Moreover, it should be noted that, in terms of the presented design technique, the proposed filter prototype can be also used to easily realize the UWB filters with other FBW even greater than 110%.

Ultra wideband (UWB) radar cross sections (RCSs) of several targets have been measured using various combinations of transmitting and receiving linear polarizations (V-V, H-H, and +45- -45) with a view to obtaining information on the design of vehicular short-range radars. This paper reports the UWB RCSs (σLR and σLL) of a typical passenger automobile using two circular polarization combinations (L and R denote left and right circular polarizations). The wideband measurements were carried out with use of a vector network analyzer by sweeping the frequency from 24.5 to 28.8 GHz in a radio anechoic chamber. The UWB RCSs were derived by integrating the received power in the frequency domain. Similar to the linear polarization results, fluctuations of the RCSs were smaller in the UWB than in narrowband for both L-R and L-L, because the ultra-wide bandwidth cancels out RCS plunges caused by narrowband interference among reflected waves from various facets of the target. The median of (σLR- σLL) was 2 dB, while the median of (σHH - σ+45 - -45) or (σVV-σ+45- -45) was 6 dB. This is because the body of the automobile comprises a number of smaller scattering objects yielding σ LL, either similar to the corner reflectors or asymmetrical to the radar boresight. Frequency-domain responses showed a number of notches caused by the interference between numerous reflecting waves having power levels of a similar order and different round-trip path lengths. Some representative reflective parts of the automobile were identified through analyses of time-domain responses.

This paper proposes a combination of novel Received Response (RR) sequence at the transmitter and Matched Filter-Equalizer-RAKE (MF-EQZ-RAKE) combining scheme receiver system for Direct Sequence-Ultra Wideband (DS-UWB) multipath channel model. When binary code sequence such as M sequence is used, there is a possibility of generating extra Inter-Symbol Interference (ISI) in the UWB system. Therefore, it is quite a challenging task to collect the energy efficiently although RAKE reception method is applied at the receiver. The main purpose of the proposed system is to overcome the performance degradation for UWB transmission due to the occurrence of Inter-Symbol Interference (ISI) during high speed transmission of ultra short pulses in a multipath channel. The proposed system improves the system performance by improving the RAKE reception performance using RR sequence and suppressing the ISI effect with the equalizer. Simulation results verify that significant improvement can be obtained by the proposed system especially in UWB multipath channel models such as channel CM4 that suffered severe ISI effect.