Showing papers on "Radio frequency published in 1994"

Dual-channel RF power delivery system

Abstract: A dual-channel RF power delivery system for applying RF energy to dual electrodes of an RF ablation device with independent control of the power level, frequency, phase, and time duration of the RF energy applied to each electrode to more accurately control the ablation of a target tissue. The power delivery system supplies a first controlled RF signal having a first power level, frequency, phase, and time duration to the electrode of a first flexible stylet and a second controlled RF signal having a second power level frequency, phase, and time duration to the electrode of a second flexible stylet. The difference between the first and second power levels and the temperature of the tissue between the first and second stylers are monitored to control the ablation of the target tissue. The supply of the first RF signal is terminated when the monitored temperature of the first stylet exceeds a first predetermined value and the supply of the second RF signal is terminated when the monitored temperature of the second stylet exceeds a second predetermined value. By adjusting the frequency and/or phase of the first and second RF signals, the relative amounts of bipolar and monopolar ablation can be adjusted for accurate control of the lesion volume. The lesion volume can also be controlled by varying the deployment length of the electrodes.

The Gaseous Electronics Conference radio‐frequency reference cell: A defined parallel‐plate radio‐frequency system for experimental and theoretical studies of plasma‐processing discharges

Abstract: A “reference cell” for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

Numerical model for radio-frequency ablation of the endocardium and its experimental validation

Abstract: A theoretical model for the study of the radiofrequency (RF) ablation technique is presented. The model relies on a finite-element time-domain calculation of the temperature distribution in a block of tissue, resulting from the flow of RF ( >

Power control and delivery in plasma processing equipment

Abstract: The present invention relates to a system and method for control and delivery of radio frequency power in plasma process systems. The present invention monitors the power, voltage, current, phase, impedance, harmonic content and direct current bias of the radio frequency energy being delivered to the plasma chamber. In addition, the plasma mode of operation may be controlled by creating either a capacitively or inductively biased radio frequency source impedance. A radio frequency circulator prevents reflected power from the plasma chamber electrode to damage the power source and it further dissipates the reflected power in a termination resistor. The termination resistor connected to the circulator also effectively terminates harmonic energy caused by the plasma non-linearities. Multiple plasma chamber electrodes and radio frequency power sources may be similarly controlled.

Mobile communication system

Abstract: A cellular mobile communication system in which each of one or more cells is provided with a base radio station, and mobile terminals communicate with the base radio stations. Base radio stations (21, 22 and 23) are connected to a central base station (100) by optical fibers. The central base station is connected to a mobile switching center (50). Each of the base radio stations is provided with an O/E converter (201) and E/O converter (207). The O/E converter converts a optical signal containing speech signals and a call connection control signal into RF signals. The E/O converter (207) converts RF signals, received from a mobile terminal (11) via an antenna (204), into optical signals and transmits the optical signals to the central base station. The central base station comprises O/E converters (301-303) for converting optical signals from each base radio station into RF signals; receivers (401-403) for demodulating these RF signals; transmitters (406-408) for converting speech signals and a call connection control signal from the mobile switching center into RF signals; and E/O converters (304-306) for converting these RF signals into optical signals and transmitting the optical signals to a base radio station.

A GaAs high-power RF single-pole double-throw switch IC for digital mobile communication system

Abstract: Much effort has been devoted to integrate the receiving/transmitting switch since time divided multiple access (TDMA) became widely used for digital mobile communication systems. Conventional Si pin-diode switches require increased current bias as the transmit power is increased to maintain the ON state. A recently-developed GaAs monolithic switch IC can be operated with nearly zero power dissipation. However, there is distortion of the waveform as the transmit power is increased. This limits the power handling capability. Another disadvantage of the GaAs switch IC is that negative voltages are needed to control the ON and OFF states. The high-power GaAs monolithic RF switch IC reported here handles over 5W (PldB: 37dBm) with insertion loss less than 1.0 dB using a circuit to feed forward the signal to the control gate. Positive voltage switching is achieved by integrating large coupling capacitors using high dielectric material, barium strontium titanate (BST), at inputs and outputs. The RF single-pole double-throw (SPDT) switch IC is mounted in an SSO10 package, where better than 25 dB isolation is achieved at a frequency of 1 GHz. >

Authors' reply [to comments on "Theoretical model for an MRI radio frequency resonator"]

Abstract: A theoretical model of magneto-acoustic current imaging is derived, based on fundamental equations of continuum mechanics and electromagnetism. In electrically active tissue, the interaction between an applied magnetic field, B, and action currents, J, creates a pressure distribution. In the near field limit, this pressure obeys Poisson's equation, with a source term (∇ x J ) · B. The displacement and pressure fields are calculated for a dipole (q), oriented either parallel or perpendicular to the applied magnetic field (B), at the center of an elastic, conducting sphere (radius a, shear modulus G). Surface displacements are on the order of qB/(4πGa), which is about 1 nm for typical biological parameters. If the applied magnetic field is changing with time, eddy currents induced in the tissue may be larger than the action currents themselves. The frequency of the pressure and displacement arising from these eddy currents, however, is twice the frequency of the applied magnetic field, so it may be possible to eliminate this artifact by filtering or lock-in techniques. Magneto-acoustic and biomagnetic measurements both image ∇ x J in a similar way, although magneto-acoustic current imaging has the disadvantage that acoustic properties vary among tissues to a greater degree than do magnetic properties.

Wide band stepped frequency ground penetrating radar

Abstract: A wide band ground penetrating radar system (10) embodying a method wherein a series of radio frequency signals (60) is produced by a single radio frequency source (16) and provided to a transmit antenna (26) for transmission to a target (54) and reflection therefrom to a receive antenna (28). A phase modulator (18) modulates those portion of the radio frequency signals (62) to be transmitted and the reflected modulated signal (62) is combined in a mixer (34) with the original radio frequency signal (60) to produce a resultant signal (53) which is demodulated to produce a series of direct current voltage signals (66) the envelope of which forms a cosine wave shaped plot (68) which is processed by a Fast Fourier Transform unit 44 into frequency domain data (70) wherein the position of a preponderant frequency is indicative of distance to the target (54) and magnitude is indicative of the signature of the target (54).

Near homodyne radio frequency receiver

Abstract: A radio frequency receiver and method for operating one is disclosed. The receiver includes a tuning unit, an inphase-quadrature (I/Q) mixer, and a calibrated image rejection processor. The tuning unit selectably tunes to a tuning frequency close but not equal to an input modulated radio frequency and creates thereby a periodic signal having the tuning frequency. The I/Q mixer convolves the modulated radio frequency signal with inphase and quadrature versions of the periodic signal and low pass filters the resultant signals. The calibrated image rejection processor corrects at least one of the filtered resultant signals and performs image rejection on the corrected signals.

Broadband operation of a Ka-band tapered gyro-traveling wave amplifier

Abstract: A wideband low-voltage millimeter-wave gyro-traveling wave tube (gyro-TWT) amplifier operating in the TE/sub 10/ rectangular waveguide mode at the fundamental cyclotron frequency is under investigation, The device incorporates precise axial tapering of both the magnetic field and the interaction circuit for broadband operation. Experimental results of a wide (33%) instantaneous bandwidth with a small signal gain in excess of 20 dB and saturated efficiency of /spl sim/10% were achieved and shown to be in good agreement with the theory. Reflective instability due to multi-pass effects by mismatches was observed and characterized. Gain and efficiency have been limited by this reflective instability rather than by absolute instabilities which limit the performance of gyro-TWT's with uniform cross-section. The start-oscillation current in terms of the relevant experimental parameters such as the beam velocity ratio (/spl alpha/), magnetic field detuning and reflection coefficient has been measured and compared with theory. Measurements of the phase variation in terms of the RF frequency have shown that the phase varies /spl plusmn/30/spl deg/ from fitted linear phase line. >

Apparatus and method for varying the coupling of a radio frequency signal

Abstract: An apparatus and method for varying coupling of a radio frequency (RF) signal (408). This is advantageously used for increasing the dynamic range of a power detector (406) in an automatic power level control loop (403) of a transmission unit (404), while maintaining transmission unit efficiency at higher power levels. This is accomplished by selecting between a first operating mode of the RF coupler (405) having strong coupling, responsive to a first predetermined power level, such that the RF coupler (405) produces a first coupled RF signal (509) responsive to the RF signal (408) and a second operating mode of the RF coupler (405) having weak coupling, responsive to a second predetermined power level, such that the RF coupler (405) produces a second coupled RF signal (510) responsive to the RF signal (408).

Radio frequency broadcasting systems and methods using two low-cost geosynchronous satellites and hemispherical coverage antennas

Abstract: The methods and systems for reducing multipath fading and outage from blockage in a radio broadcasting system that is adapted to simultaneously broadcast signals having frequencies in the range of about 300 MHz to about 3,000 MHz from two or more satellite sources traveling on a substantially geosynchronous orbit with the satellite sources separated from one another by a sufficient distance to minimize outage from physical blockages and multipath fading of signals from these satellites and received by a plurality of fixed and mobile platforms using substantially flat, hemispherical coverage antennas, each antenna having an outer diameter no greater than about 10 inches and each adapted to receive frequencies in the range of about 300 MHz to about 3,000 MHz.

MMIC FET mixer and method

Abstract: A MMIC FET mixer and method includes a RF input port for receiving a RF signal, a feedback control input for receiving a feedback signal, and a LO input port for receiving a LO signal. A feedback controller is coupled to the RF amplifier, the feedback controller for producing a controlled RF signal in response to the feedback signal. A constant current source is coupled to the feedback controller, to the RF amplifier and to the LO input port. The constant current source receives a DC offset voltage, the controlled RF signal, and the LO signal and produces an IF output signal at an IF output port. The IF output signal is proportional to the DC offset voltage, to the RF signal, and to the LO signal.

Investigation of Telstar 4 spacecraft Ku-band and C-band antenna components for multipactor breakdown

Abstract: Multipactor is an electron resonance phenomenon which occurs at radio frequencies in components and transmission lines operating in vacuum. Multipactor represents a possible payload failure mechanism for communications satellites since it can destroy RF components or transmission lines, or it can significantly raise noise levels. The Telstar 4 series of spacecraft presently being built for AT&T by Martin Marietta will carry 24 high-power transponders for Ku-band (/spl sim/60 W/transponder) and 24 medium-power transponders for C-band (/spl sim/25 W/transponder). The outputs of a number of transponders are frequency multiplexed prior to being input to the Ku-band or C-band antenna feed networks (AFN). Computation shows that instantaneous peak powers due to the combined signals can reach 4500 W at Ku-band and 3900 W at C-band. For the purpose of ensuring that the AFN would not suffer multipactor breakdown in orbit, each of the individual components in the C-band and Ku-band AFN were subjected to instantaneous peak powers well in excess of that which will be experienced in space. The high instantaneous peak powers required for this pre-flight testing were realized by phasor addition of the high-VSWR standing waves of two diplexed carriers of slightly different frequencies. This technique effectively provided an instantaneous peak power 32 times the average power output of each of the two input carriers. Test sets to accomplish this were constructed at both C-band and Ku-band. The ability to detect multipactor (by two independent means) was assured by measuring test cells which were specifically designed to break down for the test levels previously mentioned. Investigations of the separate AFN components for the Telstar 4 spacecraft showed that all components passed with substantial margin. >

Direct conversion FSK receiver using frequency tracking filters

Abstract: In a direct conversion receiver in which received radio frequency signals are mixed with quadrature local oscillator signals in I and Q channels, the output signals from the mixers are applied to a phase detector by way of respective frequency tracking filters to reduce the noise bandwidth and improve the sensitivity.

Quarter-wave gap-coupled tunable strip antenna

Abstract: An antenna has a quarter wave resonant strip (10) and first and second parasitically excited strips (12 and 14) resonant at a lower and upper frequency, respectively, of the antenna bandwidth. The strips (10, 12 and 14) have trim tabs (20, 22 and 24) for adjusting the resonant frequency of each strip. The location of a feed (30) is set to provide a desired impedance match for use by a radio (60) such as a pager. A ground plane (40) provides a grounding for the strips (10, 12 and 14) and inhibits undesirable radio frequency interaction between the radio (60) and the strips (10, 12 and 14).

Magnetic resonance guided hyperthermia

Abstract: A hyperthermia treatment apparatus includes an annular radio frequency (RF) antenna array with bolus that is compatible with a magnetic resonance imaging (MRI) machine. Antenna elements polarized parallel to the axis of the cylinder are used for forming a Specific Absorption Ratio (SAR) map as well as for directing the energy to accomplish hyperthermia. The array may be dynamically controlled to focus energy at any specified region within the cylinder. The array is positioned inside an MRI machine and is tuned to the machine's hydrogen resonant frequency. For treatment planning, the array is employed to form an SAR map via RF current density imaging. Using this map, array phase, amplitude, and temporal weighting are optimized until the SAR maxima is congruent with the treatment volume. For treatment, RF radiation is applied to the subject to induce heating of the treatment volume using these optimal array parameters. Temperature is periodically determined via noninvasive MRI methods (i.e., diffusion imaging, T 1 map, etc.) in order to obtain an image that includes isotherms from which the pattern of heating can be observed. Feedback is provided such that adjustment may be made to compensate for bioheat transfer.

Radio frequency sharing personal communications system

Abstract: A radio communications system which is channelized and constituted in cellular array shares the spectrum with other fixed radio communications systems but complies with FCC rules as to interference to these fixed systems. It still maintains however good quality in its signals. Interference is determined by real-time field measurements of interference received from fixed stations on both forward and reverse offset channels by base stations and a mobile terminals. Such real-time measurements besides sensing the quality of a signal can be used to determine interference to the nearby microwave fixed users. In addition compensation is made for multiple users and thus no worst case compromises need be adopted as in prior systems.

Direct conversion tuner

Abstract: A direct conversion tuner for tuning either analog or digital television signals includes a first and second channels, each having first and second mixers and an intervening filter stage, coupled between an RF input and an output combining unit. The first mixers receive respective first local oscillator signals which have the same frequency but a quadrature phase relationship. The frequency of the first local oscillator signals is controlled according to the selected channel so that it is located within the spectrum of the respective RF signal. The second mixers receive respective second local oscillator signals which have the same frequency but a quadrature phase relationship. The frequency of the second local oscillator signal is located above the passband of the filter stages. A digital gain and phase equalization network is included in one of the channels for adjusting the relative gain and phase shift of the two channels and is automatically controlled by a microcomputer in response to signals sampled at respective points within the first and second channels to reduce the relative gain and phase shift. As a result, near perfect cancellation of unwanted components occurs in the output combining unit.

Architecture for RF signal automatic test equipment

Abstract: An RF module useful for configuring RF sources and receivers to make a wide range of measurements on a device under test. The module includes a directional element which allows one receiver to measure both the input and the output signals from one test point. In addition, the module allows multiple input signals to be combined for intermodulation testing. Multiple copies of the module are used to construct multiple channels in an RF tester. At least one RF source and one RF receiver can be connected to each channel. Each lead of a device under test is assigned to a channel, but one channel may be multiplexed to more than one lead. Switching circuitry included in each module allows the source from one channel to be used as an intermodulation signal for another channel. The module includes calibration standards for source and receiver level accuracy. With this arrangement, numerous RF measurements, including measurement of s-parameters, can be made on a device under test without dedicated instruments.

Multibit magnetic radio frequency tag using micromechanics

Abstract: A radio frequency (RF) multibit tag structure useful for identifying objects of interest is described. An array of thin cantilevers of slightly different lengths produced by differential etching are coated with a soft magnetic material which upon interrogation with an RF magnetic field vibrate at their resonant frequencies in the presence of an appropriate bias or direct current (DC) field. The oscillating magnetic fields generated by the vibrating bars and the stationary DC field can be readily detected by a receiver and processed to determine the code of the tag and thus provide information related to the object.

RF shielded I/O connector.

Abstract: An electrical device for propagating an electrical signal which emits radio frequency electromagnetic energy, the electrical device having a medium for propagating the electrical signal and a radio frequency electromagnetic energy absorbing material, radially surrounding a portion of the medium, for attenuating the radio frequency electromagnetic energy emissions generated by the signal.

High-speed external integrated optical modulator

Abstract: An improved high-speed external optical modulator, modulated by RF waves, which velocity matches the RF waves with the optical waves is disclosed. The apparatus includes a lithium niobate substrate on which is formed an optical waveguide, electrically floating electrodes, a low dielectric buffer layer and electrodes carrying the modulating RF energy. At least one floating electrode may comprise a series of spaced electrode segments for enhanced performance at high frequencies.

Method of and apparatus for using the digitizer sensor loop array of a computing device as an antenna for a radio frequency link to an external data source

Abstract: A pen-enabled computer system in which the digitizer sensor loop array is employed as a radio frequency antenna for receiving signals from an external signal source such as a wireless keyboard or wireless local area network interface. This radio frequency datalink arrangement allows for greatly enhanced freedom of movement when using external system components, as well as reduced component count and weight.

Nuclear magnetic resonance (NMR) imaging

Abstract: The invention describes an improved NMR imaging technique having particular application in imaging of solid objects using gradient echo techniques. By applying a so called 90° rf pulse substantially at zero gradient crossing it is possible to obtain frequency encoded information about an object being imaged, using a so called gradient echo technique. However, profile degradation occurs as a result of the very large magnetic fields which are used which spoil the rf pulse. By shortening the length of pulses below 90° it has been possible to improve gradient echo imaging. However, this has resulted in the reduction in the signal-to-noise ratio of the echo following each pulse. The present invention overcomes this problem by providing a rapidly oscillating magnetic field gradient and applying a radio frequency pulse away from a zero gradient crossing and by substantially phase rotating the resultant profile. The result is the surprising effect that information is preserved, the pulse bandwidth remains constant and the signal-to-noise ratio is superior to that in existing systems.

Method and system for identifying process conditions

Abstract: A plasma processing system 10 for fabricating a semiconductor wafer 24 is disclosed. The system includes a plasma processing tool 12 and an RF energy source 20 coupled to the plasma processing tool 12. An optional matching network 22 may be included between the RF energy source 20 and the plasma processing tool 12. Circuitry 18 for monitoring the RF energy to obtain a measurement characteristic is also provided. At least one transducer 14 or 16 is coupled between the plasma processing tool 12 and the circuitry 18 for monitoring the RF energy. The RF energy is typically applied at a fundamental frequency and the electrical characteristic is monitored at a second frequency different than the fundamental frequency. Also included is circuitry 19, such as a computer, for interpreting the measurement to determine a condition of the processing system 10. Other systems and methods are also disclosed.

Method and apparatus for avoiding desensitization of a radio frequency receiver

Abstract: A subscriber terminal (104) operable in a wireless communications system (100) having an infrastructure (111) and arranged and constructed to provide data communications between the infrastructure and the subscriber terminal, includes a radio frequency receiver (201) arranged to receive communications from the infrastructure during an active time period (303); and a portable computing device (105) operatively coupled to the radio frequency transceiver and arranged to forego a desense generating activity during the active period. A corresponding method includes determining an active time period for the RF receiver (403); directing the computer to forego desense generating activities (405) during the active time period; and activating the RF receiver (407) during the active time period.

Animal control system

Abstract: There is described a system for controlling the movement of an animal relative to a controlled area delineated by a wire loop antenna. The controlled area may be inclusive or exclusionary. A frequency modulated signal is transmitted by the FM transmitter connected to the loop. An FM receiver attached to the animal detects the transmitted signal and provides an alarm signal to the animal. The loop antenna is untuned. Low radio frequencies are used and the carrier frequency deviation is large to reduce the systems susceptability to noise. The modulating frequency is limited, also to reduce susceptibility to noise. Integrated circuits are especially designed to permit operation with very low power.

Radio frequency electron cyclotron resonance plasma etching apparatus

Abstract: A radio frequency electron cyclotron resonance (RF·ECR) plasma etching apparatus in which electron cyclotron resonance is caused to occur by radio frequency waves of 100-500 MHz introduced in by an antenna. The antenna is disposed within a plasma-producing chamber and connected to a coaxial cable for introducing the radio frequency waves. A plurality of permanent magnets are provided for producing magnetic fields that perpendicularly intersect electric fields produced around the antenna within the plasma-producing chamber. A process gas forms plasma to the electron cyclotron resonance phenomena resulting from the electric fields generated by the radio frequency waves and the magnetic fields perpendicularly intersecting the electric fields in the plasma-producing chamber. The plasma thus produced is applied to the substrate for etching.