Understanding ultra-wide-band (UWB) propagation channels is a prerequisite for UWB system design as well as communication-theoretic and information-theoretic investigations. This paper surveys the fundamental properties of UWB channels, pointing out the differences to conventional channels. If the relative bandwidth is large, the propagation processes, and therefore path loss and shadowing, become frequency-dependent, and the well-known wide-sense stationary uncorrelated scattering model is not applicable anymore. If the absolute bandwidth is large, the shape of the impulse responses as well as the fading statistics change. This paper also describes methods for measuring UWB channels and extracing channel parameters. Throughout this paper, the relationship between channel properties and other areas of UWB research are pointed out.

Ultra-Wide-Band Propagation Channels

A very compact ultrawideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation is presented in this letter. The proposed antenna, consisting of two UWB slot antennas, has a very compact size of $22 \times 26~\hbox{mm}^{2}$ , which is smaller than most of UWB antennas only with single antenna element. A T-shaped slot is etched on the ground to improve the impedance matching characteristic in the low-frequency and reduce the mutual coupling for the frequencies $ \geq 4~\hbox{GHz}$ . By etching a line slot to cancel out original coupling, isolation enhancement at the 3–4 GHz band is achieved. The antenna possesses a low mutual coupling of less than $ - 18~\hbox{dB}$ over the operating band from 3.1–10.6 GHz. The performance of this antenna both by simulation and by experiment indicates that the proposed antenna is a good candidate for UWB applications.

Isolation Enhancement of a Very Compact UWB-MIMO Slot Antenna With Two Defected Ground Structures

This letter presents an ultrawideband multiple-input-multiple-output (MIMO) antenna that covers the WCDMA (1.92-2.17 GHz), WiMAX (2.3, 2.5 GHz), WLAN (2.4 GHz), and UWB (3.1-10.6 GHz) bands for wireless device applications. The proposed antenna consists of a printed folded monopole antenna coupled with a parasitic inverted-L element, with an open stub inserted in the antenna to reject the WLAN (5.15-5.85 GHz) band that interferes with the UWB band. These two antennas are symmetrically arranged on a mobile device substrate. The -10-dB bandwidth of the designed antenna is 1.85-11.9 GHz without the WLAN band 5.15-5.85 GHz. S21 and the envelope correlation coefficient are lower than -17.2 dB and 0.18 in the operating bands, respectively. The size of the antenna is 55 ×13.5 × mm2.

A Compact Ultrawideband MIMO Antenna With WLAN Band-Rejected Operation for Mobile Devices

A compact multiple-input–multiple-output (MIMO) antenna is presented for ultrawideband (UWB) applications with band-notched function. The proposed antenna is composed of two offset microstrip-fed antenna elements with UWB performance. To achieve high isolation and polarization diversity, the antenna elements are placed perpendicular to each other. A parasitic T-shaped strip between the radiating elements is employed as a decoupling structure to further suppress the mutual coupling. In addition, the notched band at 5.5 GHz is realized by etching a pair of L-shaped slits on the ground. The antenna prototype with a compact size of $38.5 \times38.5~\hbox{mm}^{2}$ has been fabricated and measured. Experimental results show that the antenna has an impedance bandwidth of 3.08-11.8 GHz with reflection coefficient less than $-10~\hbox{dB}$ , except the rejection band of 5.03-5.97 GHz. Besides, port isolation, envelope correlation coefficient and radiation characteristics are also investigated. The results indicate that the MIMO antenna is suitable for band-notched UWB applications.

Compact Offset Microstrip-Fed MIMO Antenna for Band-Notched UWB Applications

A new technique to achieve both good isolation and dual band-notched functions for ultrawideband (UWB) multiple-input–multiple-output (MIMO) antennas was developed. The proposed antenna consists of the radiation patch connected through a via with the strip placed beneath the patch. The strip not only provides another coupling path, but also serves as the impedance transformer, resulting in good isolation ( $S_{21} dB) and dual band rejection at WiMAX (3.4–3.7 GHz) and WLAN (5.15–5.35 and 5.725–5.825 GHz) over the UWB system operation (3.1–10.6 GHz). Without decoupling element or resonator, which is often placed between the antennas to acquire good isolation or band rejection, the proposed UWB MIMO antenna requires an individual antenna element size of only 11.2 $\,\times\,$ 12 mm $^{2}\ (0.12 \lambda_{0}\times 0.11 \lambda_{0})$ and overall MIMO antenna size of 30 $\,\times\,$ 40 mm $^{2}\ (0.31 \lambda_{0}\times 0.41\lambda_{0})$ . The edge-to-edge separation between antennas is $0.052\lambda_{0}$ , and separation between feeds is $0.175 \lambda_{0}$ at 3.1 GHz. Detailed investigations of the parameters were performed, and the experimental results agree closely with the simulation results, demonstrating the feasibility of the proposed method.

An Ultrawideband MIMO Antenna With Dual Band-Notched Function

Ultra-wide-band (UWB) technology combined with multiple transmit and receive antennas (MIMO) is a viable way to achieve data rates of more than 1 Gb/s for wireless communications. UWB is typically applied to short-range and therefore mainly indoor communications in environments characterized usually by dense multipath propagation. For this type of environment, MIMO systems allow for a substantial increase of spectral efficiency by exploiting the inherent array gain and spatial multiplexing gain of the systems. In this paper, we provide a brief overview for UWB-MIMO wireless technol- ogy. The overview covers channel capacity, space-time coding (STC), and beamforming. It is shown that the spectral efficiency is increased logarithmically and linearly, respectively, for single transmit and multiple receive antennas (SIMO) and MIMO systems. For multiple transmit and single receive antenna (MISO) systems, a threshold for the data transmission rate exists such that the spatial multiplexing gain can be obtained if the data rate is lower than this threshold, but it is not beneficial to deploy multiple transmit antennas if the required data rate is higher than the threshold. Two STC schemes for UWB-MIMO are briefly discussed, and their performance comparison is presented. A discussion about antenna selection is also presented, and the performance comparison between antenna selection and equal gain com- biner is provided showing the diversity gain for some scenarios. For the beamforming, it is shown that the optimal beamformer is obtained if all the weighting filters in each antenna branch are identical. About the optimal beamformer, it is found that the amplitude of the side lobe is independent of the ray incidence angle, and the amplitude of the main lobe is increased by a fold of the element number in the array. Three kinds of beam patterns are defined, and the beamwidth of the main lobe is given. Experimental results based on an offline testbed are provided to verify some analytical results pre- sented in this paper. Since UWB-MIMO is still in its research infancy, the aim of this paper is to present some first results on spatial multiplexing, STC, and beamforming to illustrate the potential of UWB-MIMO.

https://ieeexplore.ieee.org/iel5/5/4802183/04796281.pdf

An Overview of Ultra-Wide-Band Systems With MIMO Multiple input and output antennas used in ultrawide band systems can provide increased data rates, or they can make increased range available through beamforming.

Emil Dimitrov

Papers

An Overview of Ultra-Wide-Band Systems With MIMO Multiple input and output antennas used in ultrawide band systems can provide increased data rates, or they can make increased range available through beamforming.