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1562 results in RF and microwave engineering

Page 23 of 79

  • 5 - Wearable Radar Tag Systems for Physiological Sensing/Monitoring

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 154-171

  • Summary

    Introduction

    One limitation with Doppler radar is that for vital sign monitoring, any torso movement by the subject will affect the measurements. Other limitations include interference from moving objects or people in the vicinity and an inability to detect multiple targets. These issues arise due to the fact that a continuous-wave (CW) radar motion-detecting system is not inherently selective and will detect any motion in its field of view. Various solutions have been proposed for this, such as the use of multiple antennas with blind source separation (BSS) techniques to identify multiple respiration signatures [2,36] and use of two and four radars to cancel body sway [12,38]. BSS techniques are very effective in identifying multiple motion signatures but cannot associate those signatures with a particular source, leading to ambiguity in the interpretation of results. A good solution still does not exist for identification of a subject from the environmental clutter and making the Doppler radar system selective.

    Bringing selectivity to the radar implies introducing ways to ensure that the motion signals obtained correspond to the desired source. By rejecting clutter motion and detecting the physiologic motion of a subject, we are implementing the first stage of selectivity. The only way to resolve targets without placing any circuit on them is by spatial resolution and range. Spatial resolution can be brought to the radar through coherent detection using pulse Doppler radar. This principle is used in synthetic aperture radars (SARs) and inverse synthetic aperture radars (ISARs) [33]. In order to achieve good resolution, we would have to use millimeter-wave signals and associated circuitry and would still have ambiguities in the range. Spatial resolution can also be obtained through multiple-input, multiple-output (MIMO) systems and BSS techniques, but the sources of motion would still remain ambiguous. Range can also be calculated using frequency-modulated continuous-wave (FMCW) radars, but then Doppler processing would become more challenging. The resolution provided by FMCW radar is also limited by the bandwidth of frequencies used.

    Introducing modulation at the source of motion may allow more flexible solutions compatible with the current Doppler radar system. The way to achieve selectivity would be to have some form of modulated backscatter from the subject and no modulated backscatter from other objects, similar to radiofrequency identification (RFID) systems. Although RFID technology is mature and easily available, it is difficult to apply to motion-sensing applications.

  • 8 - Biomedical Applications of UWB Technology

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 228-264

  • Summary

    Introduction

    Interest in ultra-wideband (UWB) technology has increased significantly since the Federal Communications Commission's (FCC's) inquiry in 1998 and approval of its use in 2002. The FCC opened up two bands, the 3.1- to 10.6- and 22- to 29-GHz frequency bands. UWB has been used for both communication and radar applications. The fundamental purpose of this chapter is to open up new areas of application for UWB technologies applied to medicine. This includes pushing the achievable limits in terms of high-accuracy indoor three-dimensional (3D) localization using UWB technology and to use this technology in a real-time location system that tracks multiple tags simultaneously with high 3D accuracy in the millimeter range. The application of this technology goes beyond localization to other areas such as breast cancer detection, human gait analysis, and vital signs monitoring, and the list goes on.

    Historically, Time Domain Corporation has pioneered real-time precise location of people and assets. Time Domain is the first company to unleash its full potential [1]. Their pulse-on system enables real-time localization in the most difficult environments – where GPS fails and where ad hoc or moving frames of reference are required. Multispectral Solutions, Inc., also used UWB for multiuser networking applications – more specifically, an ad hoc wireless UWB communications network for tactical voice and high-speed communications, a long-range UWB system for over-the-water and non-line-of-sight voice, data, and video communications, and a wireless UWB communications network for support of both tactical and strategic (long-haul) communications [2].

    In this chapter, we will focus on three areas: (1) indoor positioning, (2) human gait analysis and vital signs detection, and (3) early breast cancer detection.

    Overview of UWB Technology for Indoor Positioning Systems

    It is important to recognize that the use of UWB technology in a high-performance localization system requiring millimeter 3D accuracy has not been well researched, and far fewer systems have been developed compared with its use in cheaper but more widespread systems with lower accuracy requirements on the order of 10- to 15-cm 3D accuracy.

    These localization systems based on using UWB narrow pulses are typically comprised of a transmitter and numerous receivers. The transmitter (the tag) has a narrow-pulse generator (in the picosecond range) controlled by a clock, a power amplifier, and a wide-band omnidirectional antenna.

  • 1 - Implantable Wireless Medical Devices for Gastroesophageal Applications

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 1-39

  • Summary

    Introduction

    Advances in low-power-consumption radiofrequency integrated circuits (RFICs), multifunctional integrated circuits, high-sensitivity sensing electrodes, biocompatible materials, and packaging techniques have made implants with wireless communication functionality and/or wireless charging capability more feasible and practical. However, wireless communication or wireless powering has not been widely used in implants. There are several challenges. The implant applications are typically disease oriented and implementation focused. The designs of implants have to address specific needs in the disease diagnosis or treatment modalities, which are strongly related to both electronic and mechanical parameters. The sensing modalities or therapy methods determine the electrical specifications, while the biological environments often present serious design constrains. The implementation has to suit clinical settings for safe, cost-effective, and relatively easy implantation procedures and, most important, the needs and comfort of patients in daily life.

    It is obvious that integration of wireless communication functionality in implants can provide critical and increased capabilities in applications. The outbound communication brings sensor signals and device conditions to the reader outside the body. The sensors can monitor physiologic signals, such as blood pressure, intracranial pressure, core temperature, electrical signals of tissue or motility of organs, and biochemical conditions such as pH and certain protein or factor concentrations, of patients in vivo and in real time. In addition, the wireless communication can periodically report device conditions such as battery level, electrical resistance of electrodes, and current/voltage delivered to tissues. The inbound communication can be used for device reconfiguration, dosage setting, and condition probing. Bidirectional communication will be ideal for remote access of the implants, adding capabilities for real-time feedback as an integrated system between body and computer. The wireless closed-loop system also can provide real-time patient condition alerts, patient self-diagnosis using smart phones, and autonomous treatment-efficacy studies over a population of patients.

    From the perspectives of patients, wireless communication removes the discomfort and inconvenience of tethered wires coming out of the body. Currently, the wires either go through small surgical openings in the body, such as for the extension wire from the head in deep brain stimulation, or an orifice, such as the nostril for stomach stimulation and multichannel intraluminal impedance tests or the urethra for bladder monitoring. The tethered wires connecting to the external electronic device, either a reader or a pulse generator, obviously bring some inconvenience to patients and sometimes pain, and they often limit patient mobility, hindering quality of life.

  • 2 - Embedded Wireless Device for Intracranial Pressure Monitoring

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 40-88

  • Summary

    Introduction

    Intracranial pressure (ICP) monitoring is a significant tool that aids in the management of neurologic disorders such as hydrocephalus, head trauma, tumors, colloid cysts, and cerebral hematomas. ICP is the pressure exerted on the rigid, bony skull by its constituents, which are brain, cerebrospinal fluid (CSF), and cerebral blood. Increased ICP can lead to brain damage, disability, and death. Various modalities have been developed for monitoring ICP in hospitals and in ambulatory conditions. Currently, only catheter-based systems have made it to clinical practice. The catheter-based systems can only be used in a hospital setting and have a limited useful life owing to drift and the risk of infection. The wired methods of patient monitoring are cumbersome, cause patient discomfort, and can potentially introduce motion artifacts in the measured quantity. The contemporary medical world is witnessing a transition from a wired to a wireless healthcare domain.

    Wireless Technology in Medical Use

    The application of wireless technology in healthcare is becoming ubiquitous, if it is not already so. The therapeutic and diagnostic applications of radiofrequency (RF) and microwave technologies in medicine have been the subject of extensive study in the past [1–3]. Medical implants for the transfer of information at these nonionizing frequencies have been developed [4]. Research accomplishments using data communication links at microwave frequencies between a medical implant and an external unit have been reported by many researchers. The resonance characteristics of implanted antennas operating at a frequency band of 402 to 405 MHz and their radiation pattern outside the body have been shown to be favorable for short-range medical implants [5]. Poon et al. [6] demonstrated that the optimal frequency for power transmission in biologic media is in the gigahertz range. Gosalia et al. [7] demonstrated a novel approach of establishing a data telemetry link between an implant and an external unit in the 1.45 and 2.45 GHz band for retinal prostheses. Such medical implants are basic components for the success of telemedicine, which refers to the use of telecommunication technologies in healthcare. Telemedicine not only facilitates medical treatment and care but is also gaining popularity in posthospital patient care [8]. It provides expert consultation in remote understaffed locations and advanced emergency care via modern telecommunication techniques [9]. Mobile patient monitoring systems using wireless implants have been developed to maintain records of patient vital signs and history [10,11].

  • 4 - Microwave Biosensors for Noninvasive Molecular and Cellular Investigations

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 124-153

  • Summary

    This chapter will give a status on the current possibilities of analysis at the molecular and cellular levels enabled by the convergence of microwave dielectric spectroscopy and the use of microtechnologies. Highlights of the technique will be addressed, such as its noninvasivity, its specificity in terms of high-frequency signature, its compatibility with high ionic and nutrient contents classically encountered with cell culture media, and its suitability and sufficient sensitivity for cell probing, even down to single-cell investigations. These particularities notably will be performed in the context of cancer studies in order to offer complementary noninvasive analyzing tools to the biologists and physicians for living cells in their typical liquid microenvironment.

    Introduction

    There are plenty of physical ways to identify and characterize (bio-)matter physically and/or chemically. Whereas humans exploit their traditional senses (sight, hearing, taste, smell, and touch) to probe the environment, (artificial) sensors – especially biosensors, which are the topic of this chapter – also rely on such sensing mechanisms, for example, mechanical (touch) and optical (sight), but also on other types of interactions, for example, electromagnetic. Such techniques feature a key characteristic: the frequency of the electromagnetic waves can be varied over a range (narrow or broad) to get a rich set of data from spectra, and consequently, the technique is called spectroscopy. Combined with the massive progress in micro- and nanotechnology, miniature biosensors based on dielectric spectroscopy have been in use for several decades, first initiated in direct current (dc) and low frequencies (kilohertz and megahertz) and now reaching microwave and millimeter-wave ranges.

    This chapter aims at showing the status of the current possibilities of analysis at the molecular and cellular levels enabled by the convergence of microwave dielectric spectroscopy and the use of microtechnologies. To understand the interests of developing microwave-based and miniature biosensors for molecular and cellular investigations, examples of the main and current cellular analyzing techniques that are available in biolabs will be given, followed by an introduction to microwave dielectric spectroscopy. Highlights of such a technique will then be addressed in terms of noninvasivity, specificity, compatibility with the high ionic and nutrient contents classically encountered in cell culture media, and suitability and sufficient sensitivity for cell probing, even down to single-cell investigations.

  • 6 - Physiological Radar Sensor Chip Development

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 172-201

  • Summary

    Theory and Recent Advancements

    Using radar to detect small physiologic signals such as respiration and heartbeat dates back to the 1970s [1]. It was realized by detecting the change in carrier phase or the round-trip time of flight (RTOF) in the received radar signals that is caused by the physiologic motion of the human body. The fundamental principle is similar to that in the radar guns that detect the speed of vehicles. Based on the format of transmit signal, there are two basic types of radars: continuous-wave (CW) radar and pulse radar. CW radar falls into two subcategories: single tone, which is mostly operated in interferometry mode, and frequency-modulated CW (FMCW), which sends out a chirp signal with the carrier frequency dynamically changing in time domain. Each category of radar has its specific advantages. Single-tone CW radar has a simple system architecture that allows high-level chip integration. It can also easily achieve high accuracy (submillimeter) in relative displacement measurement. FMCW radar is able to detect the absolute distance between the radar source and the subject, which is referred to as range information. Researchers also have successfully integrated FMCW radar on a chip. Recently, a hybrid radar system combining the advantages of single-tone and FMCW radar was reported by Wang et al. [2]. Pulse radar, which is usually accompanied by ultra-wideband (UWB) characteristics, has very high special resolution due to its large-wideband nature [3]. The integration of UWB radar is also reported for noncontact physiologic sensing.

    A generalized setup of radar noncontact physiologic sensing is shown in Figure 6.1. To detect physiologic signals, the system usually consists of a waveform generator, a radiofrequency (RF) front end, baseband signal conditioning blocks, an analog-to-digital convertor (ADC), and a signal-processing unit. The radar-generated signal is transmitted toward the human subject, where it is modulated by the physiologic motion and partially reflected. The radar receiver captures the received signal, down-converts it into baseband, and sends the digitized signal to the signal-processing unit to extract physiologic motion information, from which important vital signs such as heartbeat, respiration, or even blood pressure can be derived.

    Operation of CW Physiologic-Sensing Radar

    The basic CW radar configuration normally transmits a single-tone RF signal (f 0) toward the human subject, as shown in Figure 6.2. The received signal will maintain the same frequency of f 0, but with a phase shift accumulated along the signal path.

Microwave Electronics
  • Giovanni Ghione, Marco Pirola
  • Published online:
    10 November 2017
    Print publication:
    09 November 2017
  • Drawing on over twenty years of teaching experience, this comprehensive yet self-contained text provides an in-depth introduction to the field of integrated microwave electronics. Ideal for a first course on the subject, it covers essential topics such as passive components and transistors, linear, low-noise and power amplifiers, and microwave measurements. An entire chapter is devoted to CAD techniques for analysis and design, covering examples of easy-to-medium difficulty for both linear and non-linear subsystems, and supported online by ADS and AWR project files. More advanced topics are also covered, providing an up-to-date overview of compound semiconductor technologies and treatment of electromagnetic issues and models. Readers can test their knowledge with end-of-chapter questions and numerical problems, and solutions and lecture slides are available online for instructors. This is essential reading for graduate and senior undergraduate students taking courses in microwave, radio-frequency and high-frequency electronics, as well as professional microwave engineers.

  • 3 - CAD Techniques

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 87-128

  • Summary

    Modeling of Linear and Nonlinear Blocks

    In an integrated microwave circuit, passive devices (such as resistors, inductors, capacitors, transformers, simple and coupled transmission lines) are linear blocks, and can therefore be characterized by linear models. Transistors (field effect or bipolar) and diodes are, instead, nonlinear components also in DC or quasi-static conditions, although they can behave in an approximately linear way under small-signal operation. Linear passive reactive components (such as linear inductors and capacitors) are with memory in the (v, i) port variables; nonlinear reactive elements, like the capacitances of pn or metal-semiconductor junctions, on the other hand are also associated with active components, such as transistors. Thus, MMICs generally include linear and nonlinear elements, memoryless or with memory.

    The small-signal approximation, where the transistor characteristics are linearized in the neighborhood of the DC operating point, is well suited to the design of high-gain or low-noise amplifiers; in small signal conditions the active device is approximated as a linear block with memory. The simulation of distortion and power saturation occurring in power amplifiers (but also in low-noise and high-gain amplifiers in the upper limit of their spurious free dynamic range, see Sec. 8.2.3) require instead a nonlinear transistor model, often including linear and nonlinear memory effects.

    In analog circuits, linear n-ports are conveniently modeled in the frequency domain, selecting conventional variables (such as voltages and currents) as the component input and output, or exploiting circuit variables that are more suited to the analysis and characterization of microwave circuits, such as the power waves, see Sec. 3.2. A linear n-port can be represented through a linear relationship between input and output variables; if we identify the component status in terms of the Fourier transforms of port voltages and currents, according to the choice of the input and output variable sets we obtain wellknown frequency-domain models such as the series (or current-driven, or impedance) representation and the parallel (or voltage-driven, or admittance) representation [1].

    Although a linear element is completely described by a proper set of parameters conveniently sampled over the frequency band of interest, in many cases an equivalent circuit approach is preferred. The equivalent circuit is an approximate model of the component, whose topology and element parameters have to be fitted on measured (or physically simulated) characteristics.

  • 10 - CAD Projects

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 522-565

  • Summary

    Introduction

    The present chapter describes a set of simulation or design exercises meant to apply, within a microwave Computer-Aided Design CAD environment, the concepts developed in the rest of the book. Each example is, potentially, a CAD laboratory trace. To allow the reader to replicate the examples, additional material is made available online in the form of a project in its specific CAD environment. We chose to develop the project on two well-known and widely used platforms, Microwave Office (MWO) [1] and ADS (Advanced Design Systems) [2]. To keep the presentation within reasonable limits (and also to avoid fast obsolescence due to the evolution of the CAD tool interfaces), for each example only a synthesis is provided with the main results in graphical form.

    The examples closely follow the evolution of the text and are intended as short and tutorial in nature. Rather than reporting on full real-word designs, leading to a ready-togo layout, they concentrate on specific aspects that are dealt with in the text on a more theoretical equation-based level. All figures are directly copied (sometimes with minor changes and a conversion to black and white) from the CAD tool user interface, their graphical format being in a way a part of the design experience of the user. Some of the CAD projects actually provide a CAD implementation of numerical examples presented throughout the text.

    Microstrip Line and Stub Matching of a Complex Load

    The project proposes a CAD implementation of Example 2.5. A line plus stub section (the stub in short circuit) is set up to match to the impedance. The design frequency is chosen as 10 GHz. The electrical line length at 10 GHz is initially set equal to the approximate values found in Example 2.5, and a further optimization is carried out, obtaining slightly different values. Fig. 10.1 shows the resulting input impedance compared to the goal,.

  • 2 - Passive Elements and Circuit Layout

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 28-86

  • Summary

    Transmission Lines

    Transmission lines (TXLs), simple or multiconductor, are a key distributed element in microwave circuits. They operate as signal transducers between components but are also the building block for passive distributed elements such as couplers, filters, matching sections, power dividers. In hybrid and monolithic microwave circuits the preferred guiding structures are the so-called TEM or quasi-TEM lines, characterized by broadband behavior and by the absence of a cutoff frequency, that is found in metal waveguides.

    From a theoretical standpoint, N metal conductors with a ground plane support N TEM or quasi-TEM propagation modes. In TEM (Transverse ElectroMagnetic) modes, the electric and magnetic fields are transverse with respect to the propagation direction, i.e., orthogonal to the line axis. A purely TEM mode propagates in a line without conductor losses and with a homogeneous cross section, while lossy metal lines and lines with a non-homogeneous cross section support quasi-TEM modes with small longitudinal field components. An example of quasi-TEM line is the microstrip, where the cross section is partly filled by a dielectric, and partly by air. TEM and quasi-TEM lines may also support upper propagation modes with a cutoff frequency; however, the excitation of those modes is to be avoided because they contribute to radiation losses and coupling.

    Transmission Line Theory

    Transmission lines are a simple but convenient model for one-dimensional wave propagation, serving as a bridge between circuit theory and electromagnetics. Suppose first that the line is made of two lossless parallel conductors, one acting as the signal conductor, the other as the return or ground conductor, surrounded by a homogeneous, lossless medium. Such a structure supports a TEM propagation mode in which the electric and the magnetic fields lie in the line cross section and are orthogonal to the line axis and wave propagation direction; see Fig. 2.1 (a). In a TEM mode the transverse electric field can be derived from a potential function satisfying, in the line cross section, the Laplace equation. This is uniquely determined by the potential of the signal line v(z, t) with respect to the ground line, where the coordinate z is parallel to the line axis and propagation direction. The transverse magnetic field is in turn related to the total current i(z, t) flowing in the signal conductor; −i(z, t) flows instead in the return conductor.

  • 1 - A System Introduction to Microwave Electronics

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 1-27

  • Summary

    Radio Frequencies, Microwaves, Millimeter Waves

    The meaning of high-speed and high-frequency electronics has changed in a century of technological evolution; see [1]. Radio-frequencies (RF) were at first introduced within the framework of radio broadcasting and point-to-point transmission at the beginning of the twentieth century; however, new applications (such as TV broadcasting and above all the radar around 1940), fostered in turn by the availability of RF signal generators at increasing frequency, caused a gradual explosion of new application fields in the RF, microwave and millimeter wave frequency bands. Before 1970, high-frequency systems were based on vacuum tube generators; in the following decades, solid-state semiconductor devices able to operate above 1 GHz, based both on Silicon and on compound semiconductor technologies, were gradually introduced, leading to a new paradigm, the hybrid and then monolithic Microwave Integrated Circuit, (M)MIC, see, e.g., [1, Ch. 16]. Integration and the resulting downsizing of RF and microwave systems ultimately made microwave electronics, at least in high-volume applications, a low-cost commodity well suited to the consumer market.

    For the sake of clarity, let us focus on the meaning of the terms RF, microwaves and millimeter waves and on some of the significant applications in each frequency band:

  • • The RF band includes frequencies between a few MHz and 1 GHz, with free space wavelengths of the order of 1 m (30 cm at 1 GHz); the applications include analog radio broadcasting through frequency modulation (FM), and also many other systems, like TV broadcasting, point-to-point communications (for instance, the lowest band in European GSM systems), long-range radar systems, industrial applications like RF heating and RF drying.

  • • The microwave frequency band includes frequencies between 1 GHz and 30 GHz, with free space wavelengths between 30 cm and 1 cm. In the microwave range, several applications exist: below 10 GHz we have all mobile phone systems up to the LTE (Long-Term Evolution, commonly known as 4G LTE) standard, many Wireless Local Area Network (WLAN) applications, terrestrial and satellite radio links, radar systems, positioning systems. Also the electronic part of long-haul optical communication systems operates in this band, although in this case many of the exploited circuit architectures are digital rather than analog.

  • 9 - Microwave Measurements

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 489-521

  • Summary

    Introduction

    This chapter aims at providing an overview of the experimental characterization techniques of linear and nonlinear one- and two-ports. After a short review of some basic instrumentation tools (the power meter, the vectorial voltmeter, the spectrum analyzer) in Sec. 9.2, the characterization of linear one- and two-ports, such as passive circuits and linear amplifiers, based on the measurement of power waves (see Sec. 3.2.2) and the related circuit-oriented parameters are discussed. As a first example, one-port measurements are introduced, whose fundamental tool is the so-called reflectometer (Sec. 9.3). The analysis of the reflectometer already allows the main issues involved in microwave measurement set-ups to be discussed, such as: the use of directional couplers to separate incident and reflected waves at the port where the Device Under Test (DUT) is connected; the need to perform measurements at a suitably low Intermediate Frequency (IF) rather than at RF to improve accuracy; the need to calibrate the measurement system to correct for systematic errors in the instrumentation.

    In Sec. 9.4 the discussion is extended to the characterization of two-port linear devices adopting the two-port Vector Network Analyzer (VNA), the key instrument for high-frequency characterization first introduced by Hewlett Packard, around 1970 [2, 3]. Downconversion approaches are discussed in Sec. 9.4.1, while a number of calibration strategies are reported in Sec. 9.4.2.

    Large-signal rather than linear-only characterizations are fundamental in the experimental assessment of power amplifiers. In Sec. 9.5 the most important aspects related to load-pull measurements are discussed. Sec. 9.6 is devoted to system-level characterization of RF components under modulated signal excitation, with particular attention to power amplifiers. Finally, Sec. 9.7 presents an overview of noise measurement techniques.

    Basic Microwave Instrumentation Tools

    Microwave measurements exploit a number of tools that are also commonly found in low-frequency electronic or electrical characterizations. Their function and principle of operation will be briefly recalled here.

    Power meters are instruments able to measure the power dissipated by a resistive load being part of the meter.

Page 23 of 79