Why do we need UWB? (2)


There are many potential applications for the UWB new emerging technology that can be used in recent personal and commercial communication systems, vehicular radar systems, and imaging systems such as ground-penetrating radar, wall-imaging systems, medical systems, and surveillance systems.

Why do we need UWB (2)

Current Trends in RF and Microwave Integrated Circuits Research (2)

Example of UWB Beamforming systems

Beamforming techniques can be generally classified into two main categories: conventional (fixed) beamforming techniques and modern (adaptive) techniques. The fixed beamforming technique is considered to be a simple technique to improve the system performance. Switched-beam antenna (SBA) systems are defined as antenna array systems that can generate multiple fixed beams with increased performance. Many different structures of multi-beam network beamformers have been proposed such as the Blass matrix, the Nolen matrix, the Rotman lens, and the Butler matrix. Butler matrix is considered to be the popular network among these beamformers. This is because of its simple design and ease of implementation and testing as shown in Fig. 5 (a). A Butler matrix consists of a passive N X N phased antenna array network that has the ability to steer the main beam in the desired direction and/or to form nulls in the direction of strong interference or jamming. Practically, it consists of a combination of both hybrid couplers and phase shifters. The type of hybrid couplers used in its implementation determines the type of Butler matrix which can be either symmetrical or asymmetrical network. If the Butler matrix uses quadrature or 90°hybrids, the network becomes symmetrical while the asymmetric one uses out-of-phase or 180° hybrids. Fig. 5(b) shows the developed 4×4 butterfly-shaped UWB Butler beamforming system using 3dB/90° hybrid couplers and 45° phase shifters of butterfly shapes on microstrip PCB multi-layered technology.

Fig. 5 (a) Schematic block diagram of Butler beamforming system (b) photograph of the developed 4×4 UWB Butler beamforming system [11]


Example of RF Transceiver for IR-UWB systems

An example of a fully integrated impulse response-ultra-wideband (IR-UWB) transceiver is presented in [12]. The small size of UWB transmitters is a requirement for inclusion in today’s consumer electronics. The main arguments for the small size of UWB transmitters and receivers are due to the reduction of passive components. However, antenna size and shape is another factor that needs to be considered. Ultra-wideband antennas are considered in the next article. Among the most important advantages of UWB technology are those of low system complexity and low cost. Ultra-wideband systems can be made nearly “all-digital”, with minimal RF or microwave electronics. The low component count leads to reduced cost, and smaller chip sizes invariably lead to low-cost systems. The simplest UWB transmitter could be assumed to be a pulse generator, a timing circuit, and an antenna.

Fig. 6 An example of a IR-UWB Transceiver Chipset Using Self-Synchronizing on off keying (OOK) Modulation (90nm CMOS) [13]

Example of 60 GHz UWB Transceiver systems

The use of microwave frequencies (3.1–10.6 GHz) for ultra-wideband (UWB) systems is actually subject of intensively research. According to the definition of Federal Communications Commission (FCC), UWB is not limited to the frequency range 3.1–10.6 GHz. The FCC defines UWB as “any radio technique that has a bandwidth exceeding 500 MHz or greater than 25% of its center frequency”. In recent years, an on-going research is carried out to use this special technology into millimeter-wave (MMW) frequencies (frequencies between 30 GHz and 300 GHz) for the development of wireless communications: unlicensed short-range (57 – 64 GHz), outdoor semi-unlicensed point to point links (71 – 76 GHz, 81 – 86 GHz, and 92 – 95 GHz), automotive radar (76 – 77 GHz), and imaging sensor (84 – 89 GHz and 94 GHz) systems.

Fig. 7 shows an example of a UWB wireless transceiver system working in V-band (60 GHz) [14]. The system parameters’ are as follows: transmitted LO power = -25 dBm, amplifier gain (A) = +20 dB, and an antenna transmitting gain (GT) = 10 dBi. These values are been intentionally chosen in order to obtain a transmitted signal power equal to 10 dBm (allowed by FCC for V-band communications system). The antenna receiving gain is +10 dBi, the low noise amplifier (LNA) gain is +20 dB, so the six-port input signal power has a value of -38 dBm.

The six port model used here consists of four 90° hybrid couplers interconnected by transmission lines and four power detectors, as shown in Fig. 8(a) [15]. This circuit is integrated on a 125 μm alumina substrate having a relative permittivity of 9.9, using a Miniature Hybrid Microwave Integrated Circuit (MHMIC) technology. Fig. 8(b) shows several microphotographs of the MHMIC 90º hybrid couplers. The diameter of the coupler is around 700 μm and the 50 Ω line width is nearly equal to the thickness of the alumina substrate. In order to characterize these circuits, on-wafer measurements are performed using a Microtech probe station connected to a millimeter-wave precision network analyzer (PNA).

Fig. 7 An example of a 60 GHz UWB transceiver system [14]

Fig. 8 (a) Six-Port block diagram (b) MHMIC 90º hybrid coupler [15]


UWB Applications

There are many potential applications for the UWB new emerging technology that can be used in recent personal and commercial communication systems, vehicular radar systems, and imaging systems such as ground-penetrating radar, wall-imaging systems, medical systems, and surveillance systems. UWB systems have shown a number of noticeable features compared to other existing conventional NB systems. One of those features is less complexity of UWB systems compared to conventional NB systems. Another feature is their low cost which becomes very attractive for commercial communications applications. Because the available power level for UWB systems is very low for FCC legal operation, this enables them to work very close to the noise floor level and hence to have a noise-like signal spectrum which makes them good at mitigating severe multipath fading environments, strong interference and jamming. Some radar applications such as positioning, geo-location, localization and tracking objects require excellent time-domain resolution and high accuracy which can be achieved by using UWB systems rather than conventional NB systems. For Wireless Personal Area Networks (WPANs) environments, UWB technology is an excellent solution for the ultra high-speed data services up to 500 Mega bit per second (Mbps). These speeds can be greatly increased by using antenna arrays instead of single antenna element and different beamforming techniques.

1. Positioning, geo-Location, localization:

· Accurate positioning

· High multipath environments

· Obscured environments

2. Radar/sensor applications:

· Vehicular, marine, GPR

· Imaging, wall-imaging, STTW

· Surveillance systems

3. Communications:

· High multipath environments

· Send data at a very low power

· Short range communications

· High data rates > 500Mbps (very fast)


Dr. Osama Haraz,
Concordia University, Montreal, Canada

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