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Microwave Theory & Techniques
(MTT)
Society The Microwave Theory & Techniques Society (MTT-17) provides a networking environment for LI technical professionals involved in the development and application of microwave/RF hardware.
For upcoming MTT Society lectures and meetings, please
visit the calendar page. |
Application Notes > Generation of Standard Fields > HF Resistor Application Guide > PIN Diode Bias for High Power > Quartz Crystal Res & Oscillators > RF/Microwave PCB Fundamentals LI Microwave/RF Firms > ATC > ATM > Comtech > L3 > Miteq > Rodelco LI Microwave/RF Reps > Astrorep > ERA > RF Sales > Superior Technical Solutions Organizations > CEWIT > iNARTE Publications Reference > Falstad > Open EMS > RF Café |
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Past Lectures |
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Magnetic Resonance Imaging (MRI) scanners are an important diagnostic tool for the medical practitioner. MRI provides a non-invasive means of obtaining high contrast images of soft tissues and to obtain real-time images of the cardiovascular system and other dynamic changes in the human body. MRI scanners rely heavily on a number of topical areas of interest to Electrical Engineers: image processing, high speed computing and RF (radio frequency) systems and components. This presentation focuses on some of the RF aspects of the MR process and MR scanners. A primer on the physical phenomenon behind magnetic resonance starts the presentation and includes a discussion of the origin of the MR signal. The need for the high static magnetic field (B0), the use of gradient coils for MR signal spatial encoding, simple RF pulse sequences and how they are used in image construction are also covered.
Infrared (IR) Thermography has been widely used as a tool for thermal mapping and characterization of devices and systems. This technique conveniently provides non-contact measurement and the resulting 2-D thermal map provides a global view of the thermal characteristics of the target device. However, there are some major limitations with this technique in terms of spatial and temporal resolution, especially for photonic or high power MMIC device applcations. The thermo-reflectance thermal imaging provides a solution that addresses these challenges. How the hotspots in MMIC gate structure can be measured instead of the more average heat distribution measurement with IR scanners. In contrast to typical InGaAs or InSb sensor array for IR Thermography, visible CCD sensors are mass produced and can provide a greater number of pixels. Microsanj demonstrated how the Thermo-reflectance Imaging Analyzer can be used to detect static and dynamic hot spots on a sub-micron scale with a temperature resolution of 0.1 °C and a time resolution of 800 picoseconds.
Differential devices have moved into the RF and microwave world. However, some key attributes of active differential devices are extremely difficult to measure. These include harmonics and IMD measurements. I/Q mixers and modulators are also moving into the RF and microwave range and even making basic measurements, such as Conversion Gain, LO suppression, Image Rejection is difficult and advance measurements such as spurious and harmonics are even more difficult. Traditional measurements require the use of 180 degree hybrids (in the case of differential devices) or 90 degree hybrids (in the case of I/Q mixers) and these devices are difficult to create and to characterize especially over broad bandwidths and at microwave frequency. Take mixers with I/Q inputs and differential outputs, and you find that characterization is extremely difficult. However, utilizing a new control mechanism, differential devices and I/Q mixers are simply and quickly characterized with speed and accuracy that was never available before.
This lecture introduces the GaN transistor,
its properties, various structures, including the latest GaN power
amplifier (PA) design techniques. The advantages of using GaN devices over
GaAs and Si is presented. GaN HEMT transistors will be shown delineating
the various geometries, semiconductor processes and structures with
associated performance. Guidelines for reliable operation will be
presented considering device junction temperature including thermal
management techniques. The nonlinear models of GaN HEMT devices necessary
for the CAD of PAs will be presented. Design considerations for both
constant amplitude envelope signals as
The technique of paralleling amplifiers to increase a systems output power has been used successfully for many years. Modeling the parallel devices for a chain analysis in performing a systems dynamic range calculation is not a straight forward task. Often the analysis gives erroneous results due to models used that are not corrected for anomalies as a result of the parallel paths. This seminar discusses the factors in determining a systems dynamic range, the pertinent characteristics of the devices used to divide and combine the parallel amplifiers, the noise and linearity of the devices and the techniques used to model the parallel combination too successfully. From a physical signal and noise point of view issues are the treatment of coherent and non-coherent signals through the dividing and combining process. These techniques apply to modeling all parallel topologies i.e. mixers, parallel filters, etc. even when as with the case of passive components linearity is assumed ideal and the additive noise is assumed to be zero.
The characterization of modern Radar systems presents significant challenges to even the most experienced RF designer. Modern Radar systems employ advanced complex features including pulse compression, modulation, stagger, frequency/phase hopping, frequency agility, etc. Traditional tools can address some, but often not all, of these capabilities. As a result, Radar test systems are typically composed of a complex integration of many instruments. Today, modern real-time spectrum and signal analysis techniques can be employed to simplify the characterization and testing of these complex Radar systems. The sophisticated real-time capabilities make it easy to discover transient problems and issues, as well as being able to trigger on specific aspects of the complex Radar signal patterns. These new tools also include many advanced measurement features, such as the ability to perform time sidelobe (impulse response) measurements of chirped Radar pulses.
Temperature Compensated Crystal Oscillators (TCXOs) are widely used and well known frequency control products. Their performance has improved over the decades due to the advent of superior technologies. Evolution of the TCXO from resistor thermistor networks to modern polynomial generators has pushed TCXO temperature stabilities to nearly +/-100 ppb deviation over the industrial temperature range of -40 to +85 °C. Even with these advances, users still have a need for tighter stabilities. This discussion focuses on a new temperature compensation technique for crystal oscillators. Through the use of an artificial neural network (ANN), temperature compensation of AT cut crystal oscillators can be achieved that have better than +/-10 ppb stability over the industrial temperature range (-40 to +85 °C) - a more than 10 fold improvement over polynomial function generator compensation. In addition, the adaptive nature of the ANN technology allows for the compensation of other crystal oscillator environmental effects. These include trim effect, thermal hysteresis, warm-up drift, and aging.
Today’s modern communication systems face conflicting requirements. They operate with signals that have high peak-to-average power ratios (PAPR), such as multi-carrier WCDMA and OFDM based LTE, since these signals inherently possess good spectral efficiency. At the same time, modern communication systems need to have high power added efficiency (PAE) in order to minimize DC power consumption. Unfortunately, operating the PA in a region where it achieves high PAE increases signal distortion. Without corrections, the drive level of the PA needs to be backed off to reduce distortion to acceptable limits, thus compromising PAE. The problem is further compounded by the fact that high PAE design typically relies on techniques that result in PA nonlinearities with memory. The most popular techniques for reducing distortion when the PA is operated at high efficiency operating points uses PA linearization with digital predistortion (DPD). The performance that the DSP engineer can achieve using the DPD technique depends heavily on the PA model. This presentation provides an overview of popular DPD techniques and some unique approaches for PA modeling.
The semiconductor industry continues to develop higher frequency and higher power device technologies and geometries which enable the fabrication of MMICs with multi-watt performance at microwave and mm-wave frequencies. The efficient and novel combining of these devices enables the promise of high power, solid state power amplifier (SSPA) solutions capable of supplant traveling wave tube amplifiers (TWTAs) in many applications. This presentation discusses the merits and challenges, as well as the disadvantages of replacing tubes with SSPAs. Several architectures, including traditional printed circuit board, non-traditional three dimensional circuit board, waveguide, and spatial combining are presented along with the specific strengths and weaknesses of each approach. Performance results of several non-traditional combining methods are also presented.
Amplifiers employed in microwave systems are a major determinant of performance. Meeting stringent requirements depends not only on the selected device (the core of the amplifier) but also on the supporting circuitry and the design topology. The lecture highlights relevant characteristics of microwave devices and their suitability for various applications. Device noise figure, output power and frequency characteristics are compared and their limitations discussed. Several amplifier architecture configurations are discussed along with performance limitations and tradeoffs of MESFET, HEMT, HBT and GaN devices. Finally, practical implementation and test results for several amplifiers classified by critical requirements are presented.
The transmission line characteristics of balanced interconnect networks used in RF and high-speed digital systems have a major impact on signal quality or integrity. The traditional instruments used for characterizing transmission lines are Vector Network Analyzers (VNAs) and Time Domain Reflectometers (TDRs). However, most commercial test equipment have single-ended ports, therefore a single-ended to differential conversion must be performed. Various techniques to accomplish this are explored and compared. Time Domain Reflectometers can be used to measure transmission-line impedance, attenuation and delay, and can also be used to locate discontinuities. The Vector Network Analyzer on the other hand, is inherently a frequency-domain instrument. However, through the use of Inverse Fourier Transforms (IFT), the VNA can be used to make timedomain measurements. The advantages and limitations of both the TDR and VNA approaches are analyzed and compared. Lastly, the creation of custom adapters that do not perturb integrity measurements is also addressed.
The accurate and efficient electromagnetic simulation of antenna elements poses a substantial challenge due to the wide variation present in antenna topologies and operating specifications. Variations in installation environments can further complicate matters. This presentation provides an overview of several of the most robust numerical techniques currently employed by commercial simulation packages, including transient, finite element and integral equation based methods. The details of each algorithm are discussed, and their relative strengths and weaknesses are compared. Several antenna examples are presented to demonstrate where each solver technology is most applicable.
Noise is the ever-present foe of good RF & Microwave measurements, limiting dynamic range and the accuracy of small-signal measurements. This presentation covers measurement techniques and signal analyzer features, both old and new, which can dramatically reduce the effects of noise while improving both accuracy and speed. RF and microwave measurements are discussed, along with the extra challenges associated with near-noise analysis.
The fundamentals and design of a highly integrated Ka-band antenna array is presented. The integration and packaging techniques employed to fabricate the antenna, RF circuitry and cooling system as one functional block in LTCC technology is discussed in detail. Also explained is the full-wave EM simulation software utilized in the design. It is also shown that this system concept can be applied to large antenna arrays as needed to fulfill link budget requirements for satellite communication (in this instance) as well as for other phased array applications.
Frequency converters need to be characterized not only in terms of amplitude transmission but also in terms of phase transmission or group delay, especially with the transition to digital modulation schemes. A very accurate technique has been developed using a Vector Network Analyzer to measure group delay of mixers and frequency converters without access to their internal local oscillators. The key aspect of this new technique is that the network analyzer utilizes a two-tone signal. By measuring the phase differences between the two tones at the input and output, the VNA readily calculates group delay and the relative phase.
Microwave designers choose multilayer construction approaches over double sided techniques for numerous reasons. These include the need for densification, reduced crosstalk amongst multiple channels, and reduced propensity for inter-cavity oscillation. In addition, the EM field distribution of strip-line structures is more symmetrical than micro-strip and strip-line offers improved control over even and odd mode impedances. On the other hand, the ease with which micro-strip circuits can be tuned offers a significant advantage over a strip-line design. A strip-line design therefore must be more tolerant to fabrication, material, and component variations. A multilayer board design is influenced by many variables. These include etch tolerances, pre-preg thickness control tolerances, pre-preg bonding temperatures, dimensional stability of the dielectric core at the pre-preg bonding temperatures, and via drill registration. The choice of pre-pregs and cores will influence thermal stability, thermal expansion, mechanical stiffness, and defects in fabrication that affect the performance of embedded circuits. Furthermore, the sensitivity of loss tangent and dielectric constant to frequency and thermal exposure varies amongst materials.
This presentation focuses on Nonlinear Vector Network Analyzer (NVNA) measurements and X-parameters for the design and analysis of active components. NVNA enables designers to accurately measure and model nonlinear device characteristics. Measurements of complex stimulus/response component behavior as well as measurement and calibration configurations are discussed. Details on the applications of measured X-parameters in design and validation of active components, including the simulation/optimization of complex stimulus/response behavior in ADS, are also explored.
An efficient and flexible hardware implementation of a Volterra-based digital pre-distortion linearizer is presented. This adaptive digital pre-distortion provides efficiency enhancements for high-power RF amplifiers, while extending its linear range. This is accomplished through crest factor reduction which enables the RF power amplifier to be driven harder and more efficiently, while meeting spectral efficiency and modulation accuracy requirements.
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Applications of a new solid-state silicon-based high-power technology, the High Voltage Vertical Field Effect Transistor or HVVFET, are explored. The first generation of HVVFET products which debuted in 2008, use a single positive operating voltage (48V). The high operating voltage facilitates higher impedance devices that ease the design process by reducing the impedance ratio in the input and output matching networks. The vertical structure gives rise to unique thermal characteristics achieving high power density and high ruggedness. These advantages make HVVFET devices ideally suited for pulsed power applications such as RADAR, ATC, IFF, TCAS and DME systems especially where size and weight are at a premium.
The success of simulation-based design of circuits for wireless communications is limited by the accuracy of the models that are used to represent the circuit elements. Transistors are an important fundamental building block of any active circuit, such as amplifiers, mixers and oscillators, and they can also be the source of performance limiting noise, non-linear impairments, and frequency roll-off that need to be properly predicted prior to committing to an expensive wafer or circuit fabrication. This lecture provides an overview of measurement-based modeling for a range of transistor technologies used in RF and microwave applications. Established methods as well as some on-going research areas are outlined, with several modeling examples given for MOSFET, HEMT, and HBT transistors. A discussion is also provided relative to behavioral modeling of RFIC/MMIC amplifiers.
Phase noise levels establish critical performance parameters of radar, radios, navigation systems, space interferometry, and measurement systems. Vibration induced noise can significantly degrade system performance. As improvements have been achieved in reducing oscillator phase noise, increased awareness of the effects of vibration on phase noise performance has developed. This presentation describes special custom crystals, vibration isolation systems, and phase locking techniques for high system integrity under extreme environments.
Advanced OFDM (Orthogonal Frequency Division Multiplex) technologies impose challenges for testing new wireless communication devices and systems. This presentation compares traditional single-carrier modulation schemes with multi-carrier OFDM schemes to help highlight the test equipment and measurement considerations. Topics covered include spectrum, power, and modulation quality measurements in both R&D and production test applications. Also covered is the testing of SISO (Single-Input, Single-Output) and MIMO (Multiple-Input, Multiple-Output) communications systems used in 802.11n WLAN, and 802.16e mobile-WiMAX Wave 2, which are also applicable to future LTE and UMB cellular standards.
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Viewgraphs (1.7
MB)
Filter design is often considered a black art. As more and more engineers specialize in digital engineering, RF filter design expertise is becoming scarce. The lecture centers around Dionysus, a tool that allows engineers with limited filter expertise to design and analyze complex filter circuits. The seminar discusses rudimentary background information on filter design, and then demonstrates how Dionysus can be used to design complex filter circuits using multiple transfer functions, and generate predicted performance data. Also discussed are transferring simulation data as S-parameters into higher-level system simulators.
The approach of utilizing statistical techniques in RF design is explored. Topics covered include yield prediction, yield optimization, design robustness (i.e. insensitivity to process variations) and improving time-to-market. Specific RF design examples are used to illustrate the project steps; generating a first-cut design for simulation; optimizing the design to meet the electrical specifications; performing a yield analysis based on manufacturing variations; generating yield sensitivity histograms to identify the components or process parameters that have the greatest negative effect on manufacturing yield; performing design-of-experiments (DOE) analysis, to replace the most sensitive design topologies with less sensitive topologies; and performing yield optimization (sometimes called design centering) to choose the values for manufacturing that provide the highest yield.
James Clerk Maxwell stands shoulder to shoulder with Newton and Einstein, yet even those of us who have spent decades working with Maxwell's equations are almost totally unfamiliar with his life and times. This presentation, from the viewpoint of a microwave engineer, draws on many sources in providing an understanding of James Maxwell himself. What was Maxwell like as an infant? What was the tragedy at eight years old that profoundly influenced his life? What unique means of transportation did young Maxwell use to escape a cruel tutor? What memorable event occurred on his first day of school? When did he publish his first papers, and what were they about? What did Maxwell have to do with the rings of Saturn? Why did he lose his job as a professor? Why did he have a hard time getting another job? What was his wife like? What is Maxwell's legacy to us? The answers to these questions provide insight into Maxwell the person and add an extra dimension to those four simple equations we have studied ever since.
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Maxwell's Legacy
(2.9 MB)
Oscillators are fundamental components in most system designs, and are often the least understood. Sometimes creating an oscillation is easier to achieve than most engineers would desire. Yet, controlling an oscillation, i.e. selecting the frequency of oscillation, stabilizing the frequency, stabilizing the amplitude, insuring the signal is spectrally pure, and minimizing the outside-world effects, is a difficult and complex problem. This lecture examines the conditions for creating an oscillation and relates it to various parameters of the oscillator and its effect on the system design. Understanding this cause-and-effect relationship is critical to both designing the oscillator and understanding the impact on system performance. Topics discussed are frequency accuracy, frequency stability, oscillation amplitude, spurious and parasitic oscillations, pulling effects, and phase noise. Particular attention is paid to phase noise, a parameter many times misunderstood in terms of its effect on communications and RADAR systems performance.
Accurate RF power management is a hot topic for modern wireless communications, offering a variety of benefits ranging from power amplifier protection in base-stations to battery conservation in mobile phones. Applications requiring high power transmission are dramatically affected by even small errors in RF power detection. Several different technologies are available to measure and control the power levels of RF signals. Monolithic logarithmic amplifiers (log amps) can detect RF power over dynamic ranges of 60 dB or more. TruPWR RMS-responding detectors offer an alternative with insensitivity to changes in the peak-to-average ratio. RF power measurement applications, RF power detector fundamentals, and the pros & cons of various measurement technologies are explored. In addition, calibration and temperature-compensation techniques are also reviewed.
New configurations for RF/microwave filters are presented using a folded-transmission line methodology. This new approach yields interesting advantages over conventional stub-loaded designs, which include greatly reduced real estate requirements and more practical aspect (trace width to height) ratios. The design approach of the folder filters is reviewed. Several design examples are presented to highlight the advantages of the folded topology over the conventional method. S-parameter comparisons are also presented which illustrate the performance similarity of the two approaches. For completeness, the comparison data is derived from the theoretical response, and validated by full-wave EM simulation, as well as with measured data.
The inherent architecture of traditional swept spectrum analyzers, offer only a limited real-time view in the frequency domain. Newly available Real-Time Spectrum Analyzers overcome this limitation by performing an FFT over the entire frequency range of interest, allowing the instrument to display the band without the delay associated with swept measurements. These Real-time Spectrum Analyzers provide a new dimension in the ability to characterize, test and measure PPLs. The basic theory of Phase Locked Loops is presented and subtleties regarding their linear and non-linear behavior are discussed. In addition, the operation and limitations of swept spectrum measurements are explored, followed by the operation and advantages of real-time spectrum analysis. Through live PLL measurements, the benefits of real-time analysis are demonstrated - revealing PLL characteristics that were not before viewable using conventional swept measurements. During this interactive demonstration, settling times, damping factors and other time-related measurements are made.
Noise, ever-present in all receiver systems and in their component parts, acts to limit available signal sensitivity. Noise Figure, as elegantly defined by Friis, gathers all the critical factors and succinctly characterizes the resultant degradation in system sensitivity. The Noise Figure concept is shown to easily extend to complex cascades of components and is applicable to both active and passive devices having gain or loss. Select (and in some cases, surprising) examples are illustrated to provide insight into Noise Figure and Noise Temperature. > Viewgraphs, Second Revision (0.5 MB)
The fundamentals of RF power amplifiers are reviewed, including amplifier class designation, a summary of RF power transistor construction techniques and the definitions of RF transistor parameters. An in-depth discussion of LDMOS devices is then presented along with an exploration of their advantages over other technologies, especially in L-band applications. Matching structures, both internal and external to the power transistor are explored in addition to amplifier design considerations involving stability, efficiency and signal fidelity. Amplifier characterization methods, using various signal conditions, are discussed. Thermal considerations, and their associated impact on reliability, are also covered. While the topics discussed are applicable to a wide range of products, a cellular base-station design is used as a reference throughout the presentation.
The analysis and design of a state-of-the-art, user equipment grade, all digital gain control, direct conversion radio receiver is presented. The receiver employs a logarithmic amplifier in the analog baseband to compress the signal dynamic range before the analog-to-digital converter. As a result, the receiver is able to deliver a large instantaneous dynamic range. Two implementations of the receiver are presented. The enhanced performance implementation employs a digital anti-log function matched to the logarithmic amplifier characteristics over the expected input signal range. The reduced complexity implementation omits the digital anti-log function. The performance of the digital receivers is compared to that of a traditional direct conversion AGC receiver, using parameters such as the 3rd order intercept point (IP3) and spurious free dynamic range (SFDR).
RF system design often begins with a spreadsheet analysis of gain, noise and intermodulation characteristics. This approach is error prone because only the expected signal paths are analyzed, filtering effects on noise and intermodulation are difficult to consider, and data must be transferred among tools. Although time domain analysis is well proven, certain RF system characteristics are poorly managed using this approach. This lecture describes a spectral domain approach to RF system analysis that accurately estimates noise and intermodulation products, and identifies all spurious signals generated by conducted paths within the system. This technique is applicable in a variety of RF systems including receivers, transmitters, communication links, phase-locked loops, multiple-loop synthesizers, feed-forward amplifiers, non-linear amplifiers and signal control devices. The integration of spectral domain methods with circuit synthesis, circuit analysis and measured data is also illustrated.
The presentation will provide a tutorial on the technology for achieving high precision frequency sources using quartz crystals and atomic materials, such as Rubidium. The vibration effects on clock stabilities will also be presented, and breakthrough technology in the field of vibration insensitive oscillators will be explored. The lecture will then move into broadband compensation techniques - a new technology that greatly improves acquisition of targets in RADARs installed on moving/vibrating platforms such as helicopters, fixed wing aircrafts, unmanned aerial vehicles and ships. This technology is also ideal for missile guidance systems, SATCOM, and other applications where motion and vibration severely limit accuracy.
The basic definition of electrical noise is reviewed and common applications are explored - with a focus on gaussian white noise. Fundamentals of noise measurement are also covered, including the creation of a noise standard, errors in noise measurements, Noise Figure measurements, Y factor measurements, and twice power measurements. Noise amplification and the concerns in maintaining low noise when amplifying, are also reviewed.
With the internet revolution and bandwidth consumption of recent days, wireless and wireline products need to operate at much higher frequencies than in prior years. With increasing frequency, transmission line effects and parasitic effects need to be considered in almost every aspect of the product design. This also includes the effects of packaging on the RFIC. This lecture will explore some of the capabilities of Agilent's Advanced Design System and Momentum RF to provide the necessary understanding of these effects during the design cycle.
System engineers rely on different techniques for generating sinusoidal waveforms with varying parameters, usually with exacting standards on the phase, amplitude, frequency or some combination thereof. Often, either precision or agility (sometimes both) are difficult to achieve satisfactorily. Direct Digital Synthesis (DDS) is a method, which incorporates digital synthesis to digitally manipulate the phase, frequency and amplitude of a sinusoid and provide a digitally controlled analog sine wave. This discussion will focus on the DDS architecture: what it is, what the relative advantages/disadvantages are, and what sort of performance criteria are important to consider when using this technology. The discussion will then address DDS circuit implementation, in a variety of applications such as chirp generators, quadrature digital upconverters (QDUCs) and clocking circuits. |
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Interested in presenting an IEEE MTT lecture for Long Island? |
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Providing a lecture for the Long Island IEEE MTT society is an excellent method for reaching out to the microwave/RF community in this area. If your company or organization is interested in presenting an MTT lecture, please review the following guidelines. |
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2020-06-20 |
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Chair
Vice
Chair
RF Aspects of MRI
Robert H. Caverly
- Villanova University