Showing papers in "IEEE Microwave Magazine in 2009"

Behavioral modeling and predistortion

Abstract: In this article, a thorough overview of behavioral modeling and predistortion of dynamic nonlinearities in RF PAs and transmitters was presented. The sensitivity of the DUT behavior to the characteristics of the stimulus was reviewed to ensure appropriate conditions for accurate observation. Nearly all state-of-the-art behavioral models were described and their relative performance and complexity discussed. Similarities and specifics of behavioral modeling and digital predistortion were presented. Thereby, digital predistortion can be seen as a behavioral modeling problem for which performance assessment is much more straightforward. For DUT behavioral modeling, there is no comprehensive metric that allows the model performance evaluation while taking into account the model accuracy in predicting all the three components of the DUT behavior (in-band distortion, static nonlinearity and memory effects). Finally, a software digital predistortion solution that enables closed-loop wideband linearization was briefly presented with excellent linearization capabilities when amplifying a 12-carrier 60-MHZ wide WCDMA signal.

Faster than fiber: The future of multi-G/s wireless

Abstract: This article provides an introduction to a panel session at the 2009 International Microwave Symposium (IMS 2009) on enabling multi-gigabit per second (Gb/s) wireless communication links. Blasting beams of high-speed data through free space is not new. Terahertz spectrum near visible light has been used for ultrahigh-speed optical links for many years. Newly released millimeter-wave (mm-wave) bands provide a similar potential but with different operating characteristics. Advances in manufacturing are yielding high-reliability, high-frequency mm-wave devices, faster digital field programmable gate arrays (FPGA) processors, and superfast analog-to-digital (A/D) and digital-to-analog (D/A) converters that enable higher frequency transceivers, faster modems, and more cost-effective radio architectures that need to be reliably realized. This panel session will explore the technologies being developed within the industry to enable this new field of communications. The strengths and weakness of each technology will be debated, and the viability of each to provide a compelling alternative to fiber will be determined. The panel will bring together leading device engineers with system providers to provide a complete overview of the state-of-the-art Gb/s communications and a road map for the future.

Tuning in to RF MEMS

Abstract: RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.

Frequency-reconfigurable antennas for multiradio wireless platforms

Abstract: Looking to increase the functionality of current wireless platforms and to improve their quality of service, we have explored the merits of using frequency-reconfigurable antennas as an alternative for multiband antennas. Our study included an analysis of various reconfigurable and multiband structures such as patches, wires, and combinations. Switches, such as radio-frequency microelectromechanical systems (RFMEMS) and p-i-n diodes, were also studied and directly incorporated onto antenna structures to successfully form frequency-reconfigurable antennas.

Radar remote monitoring of vital signs

Abstract: Medical technology has improved remarkably over the past few generations, becoming more sophisticated and less invasive as the years progress. Now, with microwave Doppler radar phase modulation, noncontact respiration and heartbeat monitoring offers an attractive alternative to commonly prescribed chest-strap monitors. Doppler radar uses double-sideband transmission for vital sign detection from four sides of a human body. An unmodulated radio-frequency signal is transmitted toward the human body, where it is phase-modulated by the periodic physiological movement and reflected back to the receiver. The radar receiver captures the reflected signal and demodulates it to extract the vital sign signal components.

The next challenge for cellular networks: backhaul

Abstract: Growth in the number of mobile users, coupled with the strong uptake of wireless broadband services, is driving high transport capacity requirements among cellular networks. However, revenues are not scaling linearly with increases in traffic. Demand for optimizing the cost efficiency of backhaul is becoming as critical as investment in the radio infrastructure. As a result, new transmission technologies, topologies, and network architectures are emerging in an attempt to ease the backhaul cost and capacity crunch.

Near-field direct antenna modulation

Abstract: NFDAM systems provide a unique solution for transmitting highly secured direction-dependent data and hence preventing eavesdroppers from properly demodulating the signal. A 60-GHz proof-of-concept chip was designed and measured.

AlGaN/GaN HFET reliability

Abstract: High-voltage AlGaN/GaN HFETs can produce high RF output power with nearly ideal power-added efficiency. But widespread adoption of these HFETs has been limited by a lack of acceptable reliability data for practical communications and radar applications. Device problems that have been observed include dc current and RF output power degradation as a function of time when the device is operating. Sudden and permanent degradation shifts in device performance have also been observed under certain operating conditions. Identified causes of the reliability problems include the quantum mechanical tunneling of electrons on the gate electrode to the surface of the semiconductor adjacent to the gate on the drain side, and a defect generation mechanism that occurs at a high, critical electric field. The gate leakage phenomenon described in this article produces electrons on the surface of the AlGaN layer adjacent to the gate electrode, and this creates a negative charge layer that partially depletes the conducting channel, thereby producing a degradation in dc current and RF output power. The gate leakage current is present when the device is biased and driven with an RF signal, and therefore the charge accumulation increases as a function of operation time. The gate tunnel current is a very sensitive function of surface state density, particularly near the gate edge, and of the magnitude of the electric field at this location. In addition, at a critical magnitude of the electric field defects in the AlGaN layer are created due to mechanical stress on the crystal structure, and these defects act as charge trapping centers. This mechanism is not well understood at this time and is currently the subject of research and investigation. Parameters that affect reliability are a function of device design and surface processing. Improvements in device reliability have been achieved through design modifications to produce improved surface passivation layers that reduce the gate and surface leakage currents and further modifications to reduce the magnitude of the electric field internal to the device. Continuing reliability study is required to fully elucidate the link between observed degradation behavior and physical failure mechanisms in a statistically significant manner.

High-data-rate millimeter-wave radios

Abstract: This article discusses millimeter-wave Gigabit-class radio systems operating at 1-10-Gb data rates, i.e., at fiberoptic speeds. Yet, we need to talk first about fiber optics. There has been stunning progress in high-speed fiber optic technology during the past 10-15 years. Systems operate 50-100 channels per fiber and with 50-100 fibers per communications bundle. Each wavelength channel operates at 10-40 Gb/s per channel. Cost for hardware is decreasing rapidly, particularly for Ethernet optical equipment. Companies have begun transmitting radio signals over free-space optics links. There is also an industry growing around the technology of transmitting radio signals over fiber optics. As noted, the developments are absolutely stunning.

Reconfigurable planar filters

Abstract: Electronically reconfigurable or tunable microwave filters are attracting more attention for research and development because of their increasing importance in improving the capability of current and future wireless systems. For instance, emerging ultrawideband (UWB) technology requires the use of a wide radio spectrum. However, the frequency spectrum as a resource is valuable and limited, so the spectrum is always being used for several purposes, which means it is full of unwanted signals when an operation such as a UWB wireless system is concerned. In this case, existing undesired narrowband radio signals, which vary from place to place and from time to time, may interfere with the UWB system's range. A solution for this is to introduce an electronically switchable or tunable narrow rejection band (notch) within the passband of a UWB bandpass filter. Such an electronically reconfigurable filter is also desired for wideband radar or electronic warfare systems. This paper discusses the development of electronically reconfigurable filter types.

Practical waveform engineering

Abstract: RF I-V waveform measurement and engineering systems are now finally enabling practical waveform engineering to be directly undertaken with systems capable of supporting continuous wave stimulus reaching a high level of maturity. On-going research and development activities are presently addressing the multitone requirement. The availability of RF I-V measurement and engineering capability extends the characterization opportunities for both high-frequency/speed transistor technology developers and circuit/system designers; terminal waveforms are the unifying theoretical link between transistor technology, circuit design, and system performance. Design support can involve the direct utilization of such a measurement system in the design investigation/evaluation loop of either power transistor technology or PAs. This eliminates the black box design processes and allows for the development of new intelligent design processes that are completely founded on theoretical waveform analysis. Alternatively, it can also indirectly support the amplifier investigation/evaluation loop by supporting the development or improving the accuracy of nonlinear transistor models or by providing CAD-accessible behavioral or behavioral model parameter datasets. W can now only hope that, triggered by the availability of RF waveform measurement and engineering systems, we will see a renaissance in theoretical waveform mathematical analysis addressing not only power and efficiency but also design sensitivity and linearity.

Photonics for ultrawideband communications

Abstract: This paper discussed the applications of ultrawideband frequency technology especially in broadband indoor wireless communication. The concept of UWB-over-fiber was briefly introduced, and the different techniques for generating and encoding impulse UWB signals in the optical domain was discussed. The challenges of implementing UWB-over-fiber system was also examined. The approaches for generating impulse UWB signal in optical domain was classified as UWB pulse generation based on first- or second-order differentiation of a Gaussian pulse, based on differencing of Gaussian pulse, based on optical spectral shaping and frequency-to-time mapping, and based on photonic microwave delay-line filter. Photonic UWB codings using fiber Bragg grating array, multichannel fiber Bragg grating, and polarisation modulator were also discussed.

Vacuum tube amplifiers

Abstract: This article gives a brief overview of the common vacuum electronic tube amplifiers used in high-power transmitters. Only three types of devices [travelling wave tubes (TWTs) including helix and coupled-cavity types, microwave power modules (MPMs), and klystrons] are covered, with emphasis on the recent advance in the millimeter-wave band.

High-Q tunable dielectric resonator filters

Abstract: Tunable dielectric resonator filters can potentially address wireless and satellite applications that require very high Q values (4,000 and up) with a limited tuning range (less than 15%). Such high Q requirements cannot be met by any other known non-superconductor tunable filter technology at the present time. The intent of this paper is to provide newcomers and end users with the current status and prospective of using dielectric resonators for tunable filters. It is an enabling technology for high-Q tunable filter applications. A key challenge, however, is to increase the tuning range without degrading the Q value. While several techniques have been reported to demonstrate the feasibility of tuning dielectric resonators, the tunable dielectric resonator filter technology is still in its infancy. Very limited research effort has been dedicated to explore the potential for improving the tuning range. Most of the work reported thus far has focused on the use of TE01delta modes and standard shape resonators demonstrating a narrow tuning range. We believe that the tuning range can be increased while maintaining reasonably high Q values by exploring the use of other modes and by the use of non-standard-shape dielectric resonators.

Electronically Tunable Filters

Abstract: In this article, a brief introduction to the development of tunable filters was given. A classical design technique based on a combline filter approach was shown, where minimum degradation in passband performance could be obtained across a broad-tuning range. The fundamental disadvantages associated with the conventional resonator tuning approaches were also discussed, recognizing the importance of developing new techniques for realizing tunable microwave filters. It was shown that there is a possibility in realizing an electronically reconfigurable microwave filter based on parallel- coupled switched-delay lines, which possesses the important property of maintaining constant absolute bandwidth over almost an octave of tuning bandwidth. Furthermore, the filter has the ability to incorporate active switching elements in the filter circuit, without sacrificing its loss and linearity performance. With the exceptional linearity performance and power handling capability, the filter is readily adapted to poor environments. Although the use of p-i-n diodes as switching elements would result in large dc consumption, the approach could also be readily adapted for use with any switches, such as pHEMT or RF MEMS switches, to achieve extremely low power consumption. The integration of switchable couplings to enable both bandwidth and center frequency to be reconfigurable would be an enhancement.

Multiple-resonator-based bandpass filters

Abstract: This article describes a class of recently developed multiple-mode-resonator-based bandpass filters for ultra-wide-band (UWB) transmission systems. These filters have many attractive features, including a simple design, compact size, low loss and good linearity in the UWB, enhanced out-of-band rejection, and easy integration with other circuits/antennas. In this article, we present a variety of multiple-mode resonators with stepped-impedance or stub-loaded nonuniform configurations and analyze their properties based on the transmission line theory. Along with the frequency dispersion of parallel-coupled transmission lines, we design and implement various filter structures on planar, uniplanar, and hybrid transmission line geometries.

Digitized RF transmission over fiber

Abstract: Our studies have shown that a digitized radio- over-fiber system based on bandpass sampling with an analog-to-digital converter having a resolution of 8 b is sufficient to construct a high-performance, cost-effective link that can allow easy integration of wireless backhaul with optical communication infrastructure. We also show that the performance of the digitized system is predominantly limited by the performance of the analog-to-digital converter used, with its quantization noise limiting the performance for the lower values of resolution ( 7 b).

Generating millimeter and terahertz waves

Abstract: Research on millimeter waves and/or terahertz waves, which cover the frequency range from 30 GHz to 10 THz, has lately increased since the nature of these electromagnetic waves is well suited to spectroscopic sensing as well as ultrabroadband wireless communications. One of the obstacles to developing applications of millimeter waves and terahertz waves is a lack of solid-sate signal sources, rather than detectors. In fact, the frequency band in this region is often referred to as the terahertz gap.

Is microwave backhaul up to the 4G task

Abstract: With the evolution toward the fourth generation of mobile networks, the backhaul network that portion of the network infrastructure that provides interconnectivity between the base stations and the core network is expected to come under intense pressure as capacity requirements increase to support new mobile broadband services. As a key technology used in backhaul networks around the world, point-to-point microwave is rapidly evolving to support this increasing capacity demand, improve network efficiency, and allow operators to reduce network operational costs. This article details how recent developments in the microwave industry support both the lowest cost per Mb/s transport and also the maximum Mb/s/MHz. These developments embrace the dramatic shift to support Internet protocol (IP) network convergence, including the key features to enable link capacities not previously seen in the industry, and the new methods developed to enable every last drop to be squeezed out of the finite resource that is the available frequency spectrum.

RF MEMS on the radar

Abstract: This article gives an overview of applications of radio frequency (RF) microelectromechanical system (MEMS) technology in radio detection and ranging (radar). RF MEMS components for radar include attenuators, limiters, (true-time-delay) phase shifters, transmit/receive (T/R) switches and tunable matching networks. Radar subsystems that benefit from RF MEMS technology include active electronically scanned arrays (T/R modules), passive electronically scanned arrays (lenses, reflect arrays, subarrays, and switched beamformers), and radomes. Using a bottom-up approach, the figures of merit for RF MEMS technology are related to the figures of merit for radar subsystems. The article also discusses ultrawideband RF MEMS reflect array and T/R module design as examples. First, electronically scanned array, radar and RF MEMS fundamentals are briefly introduced.

MMICs in the millimeter-wave regime

Abstract: On the basis of the current status of silicon based MMICs, it is possible to implement millimeter-wave SOC in silicon-based technologies that include the antenna, a medium-power amplifier, a transceiver, an LO (frequency synthesizer), and baseband circuits in a single chip. With certain interconnection schemes, such as flip-chip, to connect the chip to the substrate, it is also possible to integrate the best possible chips for a millimeter-wave communication system. Currently, CMOS is the best choice for the baseband circuits, while GaAs and InP MMICs can provide the best noise/power performance in the transceiver. High-efficiency antennas can be implemented directly on the packaging substrate. The SIP approach has the optimal combinations of the components for the best performance in a particular system. For example, a system in a package including CMOS baseband circuits, GaAs/InP-based transceiver, high-efficiency antenna, and high-power amplifier can achieve the best system characteristics. As we have discussed, the scope of SOC can be expanded along with more advanced MMIC fabrication technology and design techniques.

Silicon RFICs for phased arrays

Abstract: Phased arrays allow electronic scanning of the antenna beam. However, these phased arrays are not widely used due to a high implementation cost. This article discusses the advantages of the RF architecture and the implementation of silicon RFICs for phased-array transmitters/receivers. In addition, this work also demonstrates how silicon RFICs can play a vital role in lowering the cost of phased arrays.

The case for free space

Abstract: This article discusses the prospect of free- space optical links (FSOLs) in relation to backhaul applications as well as its technology trend, including the recent development of radio on free-space optical links (RoFSOLs). Here, we consider how FSOLs act as useful transport media, focusing on practical experience in mobile backhaul networks. We refer to studies on FSOL conducted by the International Telecommunications Union (ITU) from the viewpoint of the possible exploitation of the frequency bands above 3,000 GHz, which are outside the scope of the current Radio Regulations.

Advances in Linear Modeling of Microwave Transistors

Abstract: Heterojunction field effect transistors (HFET) based on gallium nitride (AlGaN/GaN) and metal semiconductor field effect transistors (MESFETs) based on silicon carbide (SiC) are the preferred transistors for high-power amplifier circuit designs rather than MESFETs, high electron mobility transistors (HEMTs) and pseudomorphic HEMTs based on gallium arsenide (GaAs) or indium phosphide (InP) semiconductor technology. While AlGaN/GaN and SiC are good candidates for high-power applications, GaAs and InP semiconductor technologies are the preferred transistors in low-power, low-voltage, and low-noise applications [1].

MM-wave long-range wireless systems

Abstract: Emerging technologies for long-range broadband wireless link systems were introduced. The common problem presented is how to construct a 10-Gb/s modem block with better performance at low cost. A single-carrier system with a simple modulation technique has the advantages of low cost and fast deployment. However, the drawback is poor spectral efficiency. A system using multiple carriers enables higher-order modulation; nevertheless, the hardware is presently very expensive. We described the circuit design and performance of ICs and their waveguide modules for 120-GHz, 10-Gb/s broadband wireless link systems. The demonstration results indicate that the IC modules using InP HEMTs enable us to construct viable 120-GHz millimeter-wave wireless link systems.

High speeds in a single chip

Abstract: This article reviews the development and breakthrough of SiGe technologies. SiGe HBTs with transit frequencies ft and maximum oscillation frequencies fmax above 300 GHz and monolithic integrated millimeter-wave circuits based on these HBTs have been developed by several groups. As this paper shows in the overview, the combination of active devices with passive planar structures, including antenna elements, allows single-chip realizations of complete millimeter-wave front-ends.

Truly wideband linearization

Abstract: This article shows that predistortion linearization can correct the distortion of high-power amplifiers over very wide bandwidths Examples of the linearization of both solid-state power amplifiers (SSPAs) and TWTAs over bandwidths greater than 10 GHz have been presented The ability to produce linearizers with desired nonlinear characteristics over continuous multioctave bandwidths was also shown Improvement in both intermodulation and harmonic distortion of more the 10 dB can be obtained using these techniques Combining multiple predistortors in a single package to correct wideband high-power amplifier distortion was also discussed In general, the narrower the bandwidth, the higher the improvement that can be obtained, but substantial improvement over large continuous bandwidths of more than an octave in width can be achieved

A reconfigurable bandpass-bandstop filter based on varactor-loaded closed-ring resonators [Technical Committee]

Abstract: In this article, a novel reconfigurable bandpass-bandstop filter based on the varactor-loaded closed-ring resonators is presented, where the bandpass and bandstop characteristics can be easily controlled by tuning the varactor bias voltage. This reconfigurability results from the perturbation effect on the degenerated even and odd modes of the closed-ring resonator. When the perturbation varactor is at the series resonance, its reactance vanishes, so a bandstop characteristic is formed. When the perturbation varactor is changed to be capacitive, the bandpass characteristic is generated. Additional varactors, incorporated at input and output ports, are tuned along with the perturbation varactors to maintain good return losses.

Agile microwave devices

Abstract: The current status of agile microwave technology is partly summarized in a book chapter and a book. The latter also gives a detailed review of applications of ferroelectrics in microwave technology and a forecast of possible future developments in the field. Several companies have started commercial development and marketing of ferroelectric varactors and devices based on them. This article highlights the advantages of ferroelectric varactors and gives a few examples of devices and system-level commercialization strategies.

Semiconductor technologies for higher frequencies

Abstract: An overview of the semiconductor active devices available for 100-GHz and 100-Gb/s applications is given, based on semiconductor properties and device requirements. The most widespread technologies are then described, and then the status of competing technologies is given in two different areas: frequency dividers, which illustrate the suitability of a technology for high-speed digital circuits, and oscillators, which illustrate their behavior in analog circuits applications. The aim of this presentation was to illustrate the variety and potential impact of these evolving technologies with consistently increasing frequency performance. While the improvement of device performance relied for a long time only on the reduction of dimensions permitted by progress in lithography, heterostructures and strain engineering are now powerful means by which to enhance performance, in both speed and power, to a level that opens a door to the 100-GHz and 100-Gb/s application arena.