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Lò vi sóng rf

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  • Wireless Communication Systems The RF and microwave wireless communication systems include radiolinks, troposcatter=diffraction, satellite systems, cellular=cordless=personal communication systems (PCSs)=personal communication networks (PCNs), and wireless localarea networks (WLANs). The microwave line-of-sight (LOS) point-to-point radiolinks were widely used during and after World War II. The LOS means the signals travel in a straight line. The LOS link (or hop) typically covers a range up to 40 miles....

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  • Review of Waves and Transmission Lines At low RF, a wire or a line on a printed circuit board can be used to connect two electronic components. At higher frequencies, the current tends to concentrate on the surface of the wire due to the skin effect.

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  • BRIEF HISTORY OF RF AND MICROWAVE WIRELESS SYSTEMS The wireless era was started by two European scientists, James Clerk Maxwell and Heinrich Rudolf Hertz. In 1864, Maxwell presented Maxwell's equations by unifying the works of Lorentz, Faraday, Ampere, and Gauss. He predicted the propagation of electromagnetic waves in free space at the speed of light. He postulated that light was an electromagnetic phenomenon of a particular wavelength and predicted that radiation would occur at other wavelengths as well.

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  • Receiver System Parameters A receiver picks up the modulated carrier signal from its antenna. The carrier signal is downconverted, and the modulating signal (information) is recovered. Figure 5.1 shows a diagram of typical radio receivers using a double-conversion scheme. The receiver consists of a monopole antenna, an RF amplifier, a synthesizer for LO signals, an audio amplifier, and various mixers, IF amplifiers, and filters.

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  • Various Components and Their System Parameters An RF and microwave system consists of many different components connected by transmission lines. In general, the components are classified as passive components and active (or solid-state) components. The passive components include resistors, capacitors, inductors, connectors, transitions, transformers, tapers, tuners, matching networks, couplers, hybrids, power dividers=combiners, baluns, resonators, filters, multiplexers, isolators, circulators, delay lines, and antennas. ...

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  • Antenna Systems The study of antennas is very extensive and would need several texts to cover adequately. In this chapter, however, a brief description of relevant performances and design parameters will be given for introductory purposes. An antenna is a component that radiates and receives the RF or microwave power. It is a reciprocal device, and the same antenna can serve as a receiving or transmitting device. Antennas are structures that provide transitions between guided and free-space waves. ...

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  • Other Wireless Systems The two major applications of RF and microwave technologies are in communications and radar=sensor systems. Radar and communication systems have been discussed in Chapters 7 and 8, respectively. There are many other applications such as navigation and global positioning systems, automobile and highway applications, direct broadcast systems, remote sensing, RF identi®cation, surveillance systems, industrial sensors, heating, environmental, and medical applications. Some of these systems will be discussed brie¯y in this chapter....

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  • Network Analysis Filter networks are essential building elements in many areas of RF/microwave engineering. Such networks are used to select/reject or separate/combine signals at different frequencies in a host of RF/microwave systems and equipment. Although the physical realization of filters at RF/microwave frequencies may vary, the circuit network topology is common to all. At microwave frequencies, voltmeters and ammeters for the direct measurement of voltages and currents do not exist.

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  • Basic Concepts and Theories of Filters This chapter describes basic concepts and theories that form the foundation for design of general RF/microwave filters, including microstrip filters. The topics will cover filter transfer functions, lowpass prototype filters and elements, frequency and element transformations, immittance inverters, Richards’ transformation, and Kuroda identities for distributed elements. Dissipation and unloaded quality factor of filter elements will also be discussed.

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  • Lowpass and Bandpass Filters Conventional microstrip lowpass and bandpass filters such as stepped-impedance filters, open-stub filters, semilumped element filters, end- and parallel-coupled half-wavelength resonator filters, hairpin-line filters, interdigital and combline filters, pseudocombline filters, and stub-line filters are widely used in many RF/microwave applications. It is the purpose of this chapter to present the designs of these filters with instructive design examples.

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  • CAD for Low-Cost and High-Volume Production There have been extraordinary recent advances in computer-aided design (CAD) of RF/microwave circuits, particularly in full-wave electromagnetic (EM) simulations. They have been implemented both in commercial and specific in-house software and are being applied to microwave filter simulation, modeling, design, and validation [1]. The developments in this area are certainly stimulated by increasing computer power. In the past decade, computer speed and memory have doubled about every 2 years [2]....

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  • Case Study for Mobile Communications Applications Microstrip filters play various roles in wireless or mobile communication systems. This chapter is particularly concerned with a case study of high-temperature superconducting (HTS) microstrip filters for the cellular base station applications. The study starts with a brief discussion of typical HTS subsystems and RF modules, including HTS microstrip filters for cellular base stations.

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  • Highpass and Bandstop Filters In this chapter, we will discuss some typical microstrip highpass and bandstop filters. These include quasilumped element and optimum distributed highpass filters, narrow-band and wide-band bandstop filters, as well as filters for RF chokes. Design equations, tables, and examples are presented for easy reference.

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  • Coupled Resonator Circuits Coupled resonator circuits are of importance for design of RF/microwave filters, in particular the narrow-band bandpass filters that play a significant role in many applications. There is a general technique for designing coupled resonator filters in the sense that it can be applied to any type of resonator despite its physical structure. It has been applied to the design of waveguide filters [1–2], dielectric resonator filters [3], ceramic combline filters [4], microstrip filters [5–7], superconducting filters [8], and micromachined filters [9]. ...

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  • Advanced RF/Microwave Filters There have been increasing demands for advanced RF/microwave filters other than conventional Chebyshev filters in order to meet stringent requirements from RF/microwave systems, particularly from wireless communications systems. In this chapter, we will discuss the designs of some advanced filters.

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  • The term microwaves may be used to describe electromagnetic (EM) waves with frequencies ranging from 300 MHz to 300 GHz, which correspond to wavelengths (in free space) from 1 m to 1 mm. The EM waves with frequencies above 30 GHz and up to 300 GHz are also called millimeter waves because their wavelengths are in the millimeter range (1–10 mm). Above the millimeter wave spectrum is the infrared, which comprises electromagnetic waves with wavelengths between 1 m (10–6 m) and 1 mm. Beyond the infrared spectrum is the visible optical spectrum, the ultraviolet spectrum, and x-rays.

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  • Radar and Sensor Systems Radar stands for radio detection and ranging. It operates by radiating electromagnetic waves and detecting the echo returned from the targets. The nature of an echo signal provides information about the target—range, direction, and velocity. Although radar cannot reorganize the color of the object and resolve the detailed features of the target like the human eye, it can see through darkness, fog and rain, and over a much longer range.

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  • Multiple-Access Techniques Three commonly used techniques for accommodating multiple users in wireless communications are frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Frequency division multiple access and TDMA are old technologies and have been used for quite a while. Code division multiple access is the emerging technology for many new cellular phone systems. This chapter will brie¯y discuss these techniques.

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  • Transmitter and Oscillator Systems A transmitter is an important subsystem in a wireless system. In any active wireless system, a signal will be generated and transmitted through an antenna. The signal’s generating system is called a transmitter. The specifications for a transmitter depend on the applications. For long-distance transmission, high power and low noise are important. For space or battery operating systems, high efficiency is essential. For communication systems, low noise and good stability are required....

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  • Advanced Materials and Technologies High-temperature superconductors (HTS), ferroelectrics, micromachining or microelectromechanical systems (MEMS), hybrid or monolithic microwave integrated circuits (MMIC), active filters, photonic bandgap (PBG) materials/structures, and low-temperature cofired ceramics (LTCC) are among recent advanced materials and technologies that have stimulated the rapid development of new microstrip and other filters.

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