Radio frequency (RF) devices transmit an information signal from one point to another by moving the information signal to a higher frequency range. Radio communication networks have become increasingly popular over the years. Radio communication networks have rapidly expanded into several new coverage areas. Many portable electronic devices in use today rely on radio communications to receive and transmit information. Examples of such devices include pagers, cellular phones, cordless telephones, GPS (global positioning satellite) receivers, portable terminals, personal computers, walkie talkies, and baby monitors. Microwave is a type of electromagnetic wave with a frequency generally between 0.3-30 GHz. Microwave can be transmitted in many ways, for example, via a coaxial cable, waveguide or dielectric, wherein the waveguide is required for high-energy microwave. Microwave communication systems are widely used to provide networks for supporting communications across geographic regions. Analog microwave communication systems have been used to support private networks for voice and data communication. Digital microwave communication systems are used to support voice and data traffic and are being used, for example, to implement digital personal communication services (PCS). A microwave device generally uses an electron tube named magnetron as a microwave source. Wireless communication devices use power amplifiers to amplify and transmit radio frequency (RF) signals. Devices that use radio or microwave communications require antenna systems in order to couple their circuitry to the free space around them in order to receive and transmit information. Recently, low power RF systems have been used for providing communications between a plurality of transceivers through a short-range communications link. One such short-range RF technology is referred to as "bluetooth".
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Wednesday, 31 January 2007 |
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Antennas are used to radiate and/or receive typically electromagnetic signals, preferably with antenna gain, directivity, and efficiency. A microstrip antenna is used for the transmission and reception of electromagnetic energy. Microstrip patch antennas are resonant radiating structures that can be printed on circuit boards. Microstrip antennas comprise a radiator element commonly referred to as a patch. Microstrip patch antennas usually comprise just one square or circular metal antenna element attached to a low-loss dielectric substrate. Patch antennas are small, low profile, lightweight antennas that are mechanically robust, simple to manufacture and inexpensive. Accordingly, the patch antenna has many applications in mobile communication systems which require very small, low cost antennas. |
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Saturday, 20 January 2007 |
Dielectric resonators are useful in RF communication equipment in connection with filters, low noise oscillators, and other circuits. Dielectric ceramics are widely used as dielectric resonators and dielectric filters which are mounted to electronic devices such as in mobile phones, personal radios and satellite receivers. Dielectric resonators and resonator filters have multiple modes of electrical fields and magnetic fields concentrated at different center frequencies. Dielectric resonators are used in microwave circuits for concentrating electric fields. They can be used to form filters, oscillators, triplexers and other circuits. Dielectric resonator oscillators are commonly used in high precision RF and microwave systems to generate high-frequency signals of extremely good spectral purity.
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Thursday, 18 January 2007 |
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In mobile communication systems such as cellular and satellite phone communications systems, data is transmitted by means of a modulation method so that a desired communication quality can be obtained. The function of a radio frequency transmitter is to modulate, upconvert, and amplify signals for transmission into free space. An RF transmitter includes a modulator that modulates an input signal and a radio frequency power amplifier that is coupled to the modulator to amplify the modulated input signal. A transmitter for transmitting an analog signal or digital data is composed of active elements to increase power efficiency and spectrum efficiency. RF transmitters used in mobile phones typically include a power amplifier which amplifies the signals being transmitted from the phone's antenna. |
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Saturday, 13 January 2007 |
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Phase shifters are used to introduce a shift in phase of an electrical signal. A phase shift circuit is designed to shift the phase of an input signal on the basis of the phase shift characteristics of the circuit and output the resultant signal. Phase-shifting circuits are used in many electronic applications, such as in oscillators, phase-locked loops, and filters for modern communication systems including satellite receivers and cell phones. Phase-shifters are elementary components that generally associate heterogeneous technologies to obtain microwave and control functions. RF and microwave frequency phase shifters play key role in antenna array systems. In a phased array antenna, a variable phase shifter is used to introduce a fixed amount of phase shift to signals carried on a transmission line. |
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Saturday, 06 January 2007 |
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An RF coupler is a passive device that may be used to control the amplitude and direction of radio frequency signals in a transmission path between circuit modules. The most well-known coupler for radio frequency equipment is a directional coupler which is a four port circuit element which is adapted to provide an output which is proportional only to the incident power from a source. A directional coupler separates signals based on the direction of signal propagation. Directional couplers are placed in RF systems at locations where a determination of the amplitude of a signal is desired. A directional coupler measures the power in a wave traveling in a particular direction in a transmission line. A directional coupler is capable of sampling signals propagating in two different directions. |
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Tuesday, 19 December 2006 |
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Remote keyless entry (RKE) systems are used in vehicles to provide a convenient way to lock and unlock vehicle doors. RKE systems utilize an RF transmitter contained in a key fob to broadcast remote entry commands to a vehicle receiver to allow a user to remotely lock and unlock doors and perform other convenience functions. The receiver is typically provided in the vehicle for receiving the vehicle device function signals. The RKE transmitter positioned in a key fob for communication with an antenna in the vehicle. It is activated by the driver to send out a modulated signal including an ID code unique to the transmitter and an operation command code. The keyless entry receiver which receives a radio signal demodulates the signal to determine whether it is from the paired transmitter. |
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Thursday, 14 December 2006 |
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Low noise amplifiers (LNAs) are used in many systems where low-level signals must be sensed and amplified. Low noise amplifiers are used in wireless communication systems to amplify received signals, which tend to be very weak in signal strength. An LNA is installed in an input stage of the signal receiving apparatus and amplifies the input RF signal so that an amplified signal has a required gain and noise figure. An LNA is capable of decreasing most of the incoming noise and amplifying a desired signal within a certain frequency range to increase the signal to noise ratio of the communication system and improve the quality of received signal. Low noise amplifiers are used in conjunction with numerous radio frequency functions such as mixers, voltage controlled oscillators, limiters, and filters. |
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Friday, 17 November 2006 |
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Surface acoustical wave (SAW) filters are constructed from interdigital transducers, which are electroacoustical transducers formed on a piezoelectric material. The interdigital transducer (IDT) excites a surface acoustic wave on a piezoelectric substrate. The interdigital transducer can be designed to give the SAW device various characteristics and functions. A transversal SAW filter has two interdigital transducers arranged on a piezoelectric substrate with a predetermined distance therebetween. SAW filters are widely used as bandpass filters in portable telephones and other communication devices. The ladder-type filter has an excellent characteristic of the attenuation near the pass band. However, its attenuation characteristic in a higher frequency region is rapidly deteriorated. |
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Thursday, 16 November 2006 |
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A radio frequency (RF) switch is a device that controls the flow of an RF signal. An RF switch selectively switches the RF path from the integral antenna to the RF accessory port. In communications applications, switches are often designed with semiconductor elements such as transistors or pin diodes. PIN diodes and GaAs field effect transistors (FETs) switches typically require a bias current and have a limited frequency response. In order to reduce the size and weight of such RF switches, micro-electromechanical system (MEMS) technology has been known to be used to fabricate such switches. MEMS switches use electrostatic actuation to create movement of a beam or membrane that results in an ohmic contact or by a change in capacitance by which the flow of signal is interrupted. |
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Friday, 10 November 2006 |
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Radio frequency identification (RFID) systems are used to detect and prevent inventory shrinkage and to perform inventory management functions. Radio frequency identification devices (RFID) are becoming increasingly popular for a variety of industrial, retail, transportation, and other applications. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. A typical RFID system includes RFID tags, at least one RFID reader or detection system having an antenna for communication with the RFID tags, and a computing device to control the RFID reader. An RFID transponder generally includes a semiconductor memory in which digital information may be stored. |
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Wednesday, 25 October 2006 |
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A device for dividing or combining the wireless signals is called a power divider/combiner. A power divider is an interdependent device calculating a vector sum total of at least two signals. Powder dividers take a signal at a common terminal and divide the signal among a series of signal paths while maintaining desired impedances at the common terminal and at all output terminals. Power divider circuits are used in radio frequency applications to split an input signal over two or more outputs so that the input signal can be processed in parallel in subsequent stages. Power dividers are used in a transmitter for combining signals from a plurality of lower power devices to form a high power signal for transmission through an antenna. Optical power dividers are used in optical communications networks. |
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Wednesday, 18 October 2006 |
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An antenna is a device to radiate and detect an electronic wave efficiently. Television broadcast antennas typically radiate horizontally polarized signals. Antennas for transmitting TV signals typically transmit in the VHF frequency range or the UHF frequency range. The satellite television system employs a dish antenna to collect satellite signals, and the signals are then reflected to low noise block down converters (LNB) for amplifying the signals and reducing its frequency. A dish antenna constructed to receive satellite signals comprises a dish-shaped reflector that has a support arm protruding outward from the front surface of the reflector. Digital television is a new type of broadcasting technology. DTV antenna systems transmit the information used to make television pictures and sounds by data bits. |
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Sunday, 08 October 2006 |
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Bandpass filters provide transmission at frequencies within the passband of the filter and attenuation of other frequencies outside of the band. Microwave bandpass filters are two port devices which allow the reception of a predetermined band of frequencies and suppress all other frequencies. Optical bandpass filers transmit light over a predetermined band of wavelengths while rejecting, by absorption, radiation or scattering, all other wavelengths. Most bandpass filters include a plurality of reactively coupled resonators which are coupled at a center frequency. Bandpass filters are used extensively in radio communication equipment fo the rejection of spurious response frequencies in superhet receivers, suppression of unwanted radiation from oscillators, and impedance transformation. |
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Thursday, 21 September 2006 |
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Radio frequency modulation techniques are used for transmitting information on a carrier signal. Frequency modulated (FM) signals are widely used in many communication devices for communicating messages and other types of information. In frequency modulation, the frequency of a carrier is changed in response to the amplitude of the modulating signal. The information signal may be an analog signal such as an audio signal or it may be a digital signal. Frequency modulators normally comprise an oscillator responsive to an amplitude variable signal for producing a corresponding frequency variable signal. To modulate the frequency being generated by the frequency resonator tank circuit, a modulation signal is routed via resistor to inductor, capacitor and modulation varactor. |
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Wednesday, 13 September 2006 |
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Amplifiers produce from an input signal, an output signal having an increased magnitude. Amplifiers are used in a variety of applications requiring small signal amplification. Modern wireless communication base stations transmit and receive radio frequency signals through the use of RF power amplifiers. An RF power amplifier is required to have linearity over the range of power operation and efficiency. Linearity is the ability to amplify without distortion while efficiency is the ability to convert DC to RF energy with minimal wasted power and heat generation. Amplifier output efficiency is defined as the ratio between the RF output power and the input (DC) power. RF power amplifiers are generally designed to provide maximum efficiency at the maximal output power. |
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Saturday, 02 September 2006 |
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A frequency converter device is used to convert a signal in one frequency range to a signal in another frequency range. Frequency converters are capable of attenuating image signals without using a narrow band-pass filter in a receiver which receives signals of a UHF band or signals of a microwave band. A typical frequency converter device uses a mixer to down-convert or up-convert an input signal to an output signal. A frequency converter is also used to generate an adjustable alternating voltage by using a constant-frequency voltage. By steplessly changing the frequency of a motor, the rotation speed of a controlled motor can be changed correspondingly. Such frequency converter is typically used for controlling electric motors for pumps, blowers, elevators, hoists, conveyors etc. |
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Tuesday, 29 August 2006 |
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An attenuator is a device passing an input signal while operating to attenuate the signal by a precise amount. An attenuator attenuates electromagnetic energy. Attenuators are used in applications that require signal level control. There are many applications for attenuators. A microwave attenuator may be implemented as a fixed attenuator or a variable attenuator. A variable attenuator allows the level of attenuation to be adjusted. Variable waveguide attenuators are commonly used to attenuate microwave signals propagating within a waveguide. In broadband microwave amplifiers, microwave attenuators are indispensable for temperature compensation of gain variation. Voltage-controlled variable attenuators have been widely used for automatic gain control circuits. |
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Tuesday, 15 August 2006 |
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Wireless modems are used to permit remotely located computers to communicate with other computers, usually as part of a computer network. With the advent of wireless modems, portable computer users are no longer dependent on land-line based phone systems and are able to communicate electronically wherever there is a wireless transmitter within range. Wireless modems enable mobile computer devices to communicate with other computer devices without requiring physical access to a land line communication port. Wireless modems using radio frequency technology have been developed to reduce the need for wired computer connections. Wireless technology allows people to access electronic mail (email), the internet, and other web applications while they are using the handheld device. Wireless modems generally modulate an RF carrier with a stream of data packets, and then amplify the modulated carrier for transmission from an internal antenna. |
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RF/Microwave Electronics
