Showing papers on "Frequency band published in 2004"

Effective negative-/spl epsiv/ stopband microstrip lines based on complementary split ring resonators

Abstract: In this letter a super-compact stopband microstrip structure is proposed. The frequency gap is produced by an array of complementary split ring resonators (CSRRs)-a concept proposed here for the first time-etched on the ground plane. This behavior is interpreted as due to the presence of a negative effective dielectric permittivity in the vicinity of resonance. The resulting device produces a deep rejection frequency band with sharp cutoff, and a pass band that exhibits very low losses and good matching. Due to the sub-lambda operation of CSRRs, the electrical size of the device is very small.

Left-handed materials composed of only S -shaped resonators

Abstract: We analyze an $\mathsf{S}$-shaped inclusion for the realization of metamaterials exhibiting left-handed properties. Unlike most of the conventional inclusions used so far that are composed of two separate geometries---typically a split ring and a rod---the inclusion proposed in this paper is made of only one $\mathsf{S}$-shaped element which yields an overlapping negative permittivity and negative permeability response over a frequency band of about $2.6\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. By adopting this geometry, we manage to lower the negative permittivity frequency band down to the level of the negative permeability frequency band, thus allowing the overlapping to occur. Therefore, the structure works as a stand alone and does not require the use of an additional rod. A theoretical analysis is carried out to study this inclusion and numerical simulations, as well as a Snell refraction experiment, clearly show that the material indeed exhibits a negative index of refraction at some frequencies. The simple pattern of the inclusion, the wide left-handed frequency band exhibited, and the low losses measured indicate the superiority of this inclusion in the realization of left-handed metamaterials.

CPW-fed planar ultra wideband antenna having a frequency band notch function

Abstract: A CPW-fed planar ultra-wideband antenna with hexagonal radiating elements is presented. The antenna also has a frequency band notch characteristic. By inserting a V-shaped thin slot on the hexagonal radiating element, the narrow frequency band notch has been created very close to the desired frequency.

Experimental confirmation of negative refractive index of a metamaterial composed of Ω-like metallic patterns

Abstract: A one-dimensional metamaterial is realized using three connected Ω rings printed back-to-back and reversed on two sides of a dielectric substrate. Both transmission and prism experiments are reported, yielding concordant results of the presence of a left-handed frequency band. Experiments show reduced losses and an enlarged left-handed frequency band.

User interface and time-shifted presentation of data in a system that monitors activity in a shared radio frequency band

Abstract: An intelligent spectrum management (ISM) system and method that includes sophisticated features to detect, classify, and locate sources of RF activity. The system comprises one or more radio sensor devices positioned at various locations in a region where activity in a shared radio frequency band is occurring. A server is coupled to the radio sensor devices and aggregates the data generated by the sensor devices. Data collected and processed by the server from the sensors may be coupled to a console application that displays the data in desirable user interface format. According to one aspect, the server continuously stores spectrum analysis data pertaining to activity in a frequency band over time and/or protocol analysis data pertaining to analysis of packets transmitted in the frequency band according to a communication protocol. A console application includes a time-shift display mode that permits a user to specify an instant of time prior to the current time from which to playback spectrum analysis data and/or protocol analysis data generated by one or more radio sensor devices.

Double-sided printed bow-tie antenna for UWB communications

Abstract: This letter proposes a double-sided printed bow-tie antenna for ultra wide band (UWB) applications. The frequency band considered is 3.1-10.6 GHz, which has been approved by the Federal Communications Commission as a commercial UWB band. The proposed antenna has a return loss less than 10 dB, phase linearity, and gain flatness over the above frequency band.

Three-layer printed reflectarrays for contoured beam space applications

Abstract: A procedure for designing contoured beam reflectarrays in a defined frequency band is proposed. The reflectarray consists of three layers of rectangular patch arrays backed by a ground plane. The phase of the reflection coefficient for both linear polarizations is controlled at each reflective element by adjusting the patch dimensions. To overcome the frequency band limitation of reflectarrays, the patch dimensions are adjusted to match the required phase distribution and its variation with frequency. A phase-only synthesis technique based on the intersection approach has been applied to obtain the phase distribution on the reflectarray surface. An experimental demonstration is presented by means of a medium-size two-layer reflectarray that radiates two pencil beams separated by 55/spl deg/. An 80-cm three-layer reflectarray has been designed for typical South America DBS coverage at Ku-band for dual polarization. After the optimization of the patch dimensions to match the phase distribution in the 12.8-14.2 GHz band significant improvements have been achieved in the contoured patterns. As a result, the theoretical radiation patterns practically fulfill the requirements in the coverage region within a 10% bandwidth.

A single-layer tuneable microwave absorber using an active FSS

Abstract: An experimental single-layer active microwave absorber in described. The absorber is a planar structure based upon the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by an active frequency selective surface (FSS) controlled by pin diodes. The resulting structure has superior reflectivity-bandwidth characteristics compared to conventional passive absorbers of corresponding thickness. Measured data are presented and show that the reflectivity response of the absorber can be controlled over the frequency band from 9 to 13 GHz.

Transmission cable structure for GHz frequency band signals and connector used for transmission of GHz frequency band signals

Abstract: A differential signal transmission cable structure for transmitting differential signals having GHz frequency band in the present invention is provided with a differential signal transmission pair cable 30 connecting a driver circuit 23 a and a receiver circuit 23 b, for transmitting differential signals having GHz frequency band, and a power supply ground transmission pair cable 31 connecting ground and a first power supply 26 a connected to the driver circuit and ground and a second power supply 26 b connected to the receiver circuit Further characteristic impedance of the differential signal transmission pair cable is matched to that of the driver circuit and the receiver circuit, thereby enabling TEM waves of differential signals having GHz frequency band transmission mode to be maintained when the differential signals are transmitted

Apparatus and method for communicating voice and data between a customer premises and a central office

Abstract: Systems and methods are provided for communicating data over a subscriber loop using a modem. One such method includes: transmitting data on the loop in a first frequency band; sensing an indication that simultaneous transmission on the loop in a POTS frequency band is imminent; and adjusting transmit power in the first band, in response to the sensing step. One such system includes an input/output connection in communication with the loop, a processor operable in at least two states, a means for sensing demand for simultaneous usage of the loop, and a means for controlling the state. The first state is characterized by a first transmit power spectrum in the first band. The second state is characterized by a second transmit power spectrum in the first band, reduced relative to the first spectrum. Upon sensing demand, the control means causes the processor to operate in the second state.

The Late-Time Radio Emission from SN 1993J at Meter Wavelengths

Abstract: This paper presents the investigations of SN 1993J using low-frequency observations with the Giant Metrewave Radio Telescope (GMRT). We analyze the light curves of SN 1993J at 1420, 610, 325, and 243 MHz during 7.5 10 yr after the explosion. The supernova has become optically thin early on in the 1420 and 610 MHz bands, while it has only recently entered the optically thin phase in the 325 MHz band. The radio light curve in the 235 MHz band is more or less flat. This indicates that the supernova is undergoing a transition from an optically thick to optically thin limit in this frequency band. In addition, we analyze the supernova radio spectra at five epochs on days 3000, 3200, 3266, 3460, and 3730 after the explosion. The spectral break in the day 3200 composite spectrum from the GMRT and Very Large Array implies that the plasma is dominated by a magnetic field, and the latter is far from being in equipartition with relativistic particles. SN 1993J is the only young supernova for which the magnetic field and the size of the radio-emitting region are determined through unrelated methods. Thus, the mechanism that controls the evolution of the radio spectra can be identified. We suggest that at all epochs, the synchrotron self-absorption mechanism is primarily responsible for the turnover in the spectra. Light-curve models based on free-free absorption in homogeneous or inhomogeneous media at high frequencies overpredict the flux densities at low frequencies. The discrepancy is increasingly larger at lower and lower frequencies. We suggest that an extra opacity, sensitively dependent on frequency, is likely to account for the difference at lower frequencies. The evolution of the magnetic field (determined from synchrotron self-absorption turnover) is roughly consistent with $B \propto t^{-1}$. The radio spectral index in the optically thin part evolves from \alpha \sim 0.8 1.0 at a few tens of days to 0.6 in about 10 yr.

Sparse frequency transmit-and-receive waveform design

Abstract: A computationally efficient algorithm derives complex digital transmit and receive ultra-wideband radar and communication waveforms with excellent arbitrary frequency band suppression and range sidelobe minimization. The transmit waveform minimizes a scalar function penalizing weighted spectral energy in arbitrary frequency bands. Near constant power results from another penalty function for deviations from constant power, or constant power is enforced by a phase-only formulation. Next, a least squares solution for the receive waveform minimizes a weighted sum of suppressed band spectral energy and range sidelobes (for pulse and continuous wave operation), with a mainlobe response constraint. Both waveforms are calculated by iterative algorithms whose updates require only linear order in memory and computation, permitting quick calculation of long pulses with thousands of samples.

Numerical Simulations of Fractional Systems: An Overview of Existing Methods and Improvements

Abstract: An overview of the main simulation methods of fractional systems is presented. Based on Oustaloup’s recursive poles and zeros approximation of a fractional integrator in a frequency band, some improvements are proposed. They take into account boundary effects around outer frequency limits and simplify the synthesis of a rational approximation by eliminating arbitrarily chosen parameters.

Automated real-time site survey in a shared frequency band environment

Abstract: An intelligent spectrum management (ISM) system and method that includes sophisticated features to detect, classify, and locate sources of RF activity The system comprises one or more radio sensor devices positioned at various locations in a region where activity in a shared radio frequency band is occurring A server is coupled to the radio sensor devices and aggregates the data generated by the sensor devices The server receives data from each of the plurality of sensor devices and executes functions to process the data One feature of the system is to correlate data collected from the sensor or from suitably equipped devices that operate (and may move about) in a space with locations where provocation of that data occurs To this end, radio frequency energy is received at each of a plurality of known positions (eg, the sensors) in a space The positions in the space of one or more devices emitting radio frequency energy in the space is determined from the received radio frequency energy at the plurality of known positions (eg, the sensors) A variety of positioning techniques may be employed, such as received signal strength, time-difference-of arrival, time-of-arrival, etc Activity data representing characteristics of received radio frequency energy in the space is generated at the sensors or at suitable equipped devices that may move about the space The server correlates the activity data with the positions in the space that are associated with the provocation of the activity data

Monitoring and representing complex signals

Abstract: A method of displaying signals containing a spatial and a temporal aspect, where multiple signals are received by multiple sensors. The received signals are decomposed into separate signal components within one or more distinct frequency bands. Signal components are isolated within each frequency band based on differences between the signal components within the same frequency band, and the signal components are displayed. The signal components may be analyzed to determine a time course of activity and a location of the associated source. Representations of the source may also be generated and displayed to aid in monitoring the signals.

Energy-aware communications for a multi-radio system

Abstract: Described herein is an implementation that reduces the battery consumption of an energy-constrained computing device that is capable of communicating over a wireless network. As conditions and circumstances warrant, the implementation selects one of multiple radios (e.g., two)—with each having a unique combination of characteristics (in terms of power-consumption, data-rate, range and/or frequency band of operation) for wireless communications to and from a wireless device. The implementation selects one radio to minimize power-consumption while maintaining effective wireless data communication. This abstract itself is not intended to limit the scope of this patent. The scope of the present invention is pointed out in the appending claims.

A new 94-GHz six-port collision-avoidance radar sensor

Abstract: A new 94-GHz collision avoidance radar sensor is proposed The receiver front-end module is based on a six-port phase/frequency discriminator (SPD) The SPD, composed of four 90/spl deg/ hybrid couplers, is manufactured in a metal block of brass using a computer numerically controlled milling machine Simulation and measurement S-parameters of the SPD are presented in the frequency band New SPD computer models are generated and used in the system simulations Preliminary measurements and system simulations performed to obtain the relative velocity of the target and its distance are presented Statistical evaluations show an acceptable measurement error of this radar sensor

Signal classification methods for scanning receiver and other applications

Abstract: Signal classification techniques for classifying signals occurring in a frequency band using a plurality of classifier procedures each dedicated to identify a particular signal or signal type. The classification procedures operate on spectrum activity data that may include pulse event data describing particular types of signal pulses occurring in the frequency band, power versus frequency data for sampling intervals of activity in a frequency band and/or raw analog-to-digital converter samples take of a received signal. The signal classification techniques are useful to identify wireless radio signals or other radio emissions occurring in an unlicensed radio frequency band. One type of classification procedure is a pulse timing template that is compared against accumulated signal pulse data to determine occurrence of a particular signal type. To enhance the pulse timing template signal classifier, techniques are provided to examine the center frequency distribution of signal pulses that match the timing template in order to confirm that certain signal pulses are associated with a particular frequency hopping signal type. This is particularly useful when the accumulated signal pulse data is obtained from a scanning radio receiver that is tuned to different portions/channels of the frequency band in which the frequency hopping signal is expected to hop.

Method for automatic control of rf level of a repeater

Abstract: A method and apparatus for controlling an output power level of a radio frequency (RF) repeater (100 or 200). A system includes a receiver to receive a signal, a filtering unit configured to pass frequency components at or around a frequency band of a predetermined communication channel, an attenuator (124 or 142) to produce an attenuated signal by attenuating a parameter of the signal, a power amplifier (150) to adjust the output power level of repeater to a desired level by adjusting the gain of one or more components of the system, and a microprocessor (170) to receive an input responsive to the output power level of the repeater and, in response to the input, to transfer control signals to the receiver and the attenuator. The method includes sampling traffic load characteristics during operation of a network and adjusting a gain of one or more components of the repeater based on the traffic load characteristics.

Defect Detection for Bearings Using Envelope Spectra of Wavelet Transform

Abstract: In order to overcome the shortcomings in the traditional envelope analysis in which manually specifying a resonant frequency band is required, a new approach based on the fusion of the wavelet transform and envelope spectrum is proposed for detecting and localizing defects in rolling element bearings. This approach is capable of completely extracting the characteristic frequencies related to the defect from the resonant frequency band. Based on the Shannon entropy of wavelet-based envelope spectra, a criterion to select optimal scale to monitor the condition of bearings is also presented. Experiment results show that the proposed approach is sensitive and reliable in detecting defects on the outer race, inner race, and rollers of bearings.

Adaptive radar absorbing structure with PIN diode controlled active frequency selective surface

Abstract: A brief description of the theory of passive and active absorbers is presented followed by details of an experimental study of a new design of adaptive absorber. The absorber is a single-layer planar structure based upon the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by an active frequency selective surface (FSS) controlled by PIN diodes. The resulting structure has superior reflectivity–bandwidth characteristics compared to conventional passive absorbers of corresponding thickness. Experimental results are presented and compared to those obtained from a transmission line model, and show that the reflectivity response of the absorber can be dynamically controlled over the frequency band from 9 to 13 GHz.

Carrier search methods and apparatus

Abstract: Transmitting signals, e.g., high power narrow band signals on a periodic basis to facilitate detection of a frequency band and/or carrier signal to be used for communication with a basestation are described. The detected frequency band may be a downlink frequency band. The uplink frequency band to be used can be determined from a know frequency relationship between the detected downlink carrier and a corresponding uplink carrier or by monitoring the detected downlink frequency band for information indicating the uplink frequency band/carrier to be used. Carrier search methods involving searching for the narrowband high power signals used to provide carrier information and/or to indicate the frequency band to be monitored are described. Power detection methods can be used to detect the high power signals avoiding the need for symbol timing synchronization and/or channel estimation with regard to detection of the signals used to locate the frequency band to be used.

Hearing aid and processes for adaptively processing signals therein

Abstract: An improved hearing aid, and processes for adaptively processing signals therein to improve the perception of desired sounds by a user thereof. In one broad aspect, the present invention relates to a process in which one or more signal processing methods are applied to frequency band signals derived from an input digital signal. The level of each frequency band signal is computed and compared to at least one plurality of threshold values to determine which signal processing schemes are to be applied. In one embodiment of the invention, each plurality of threshold values to which levels of the frequency band signals are compared, is derived from a speech-shaped spectrum. Additional measures such as amplitude modulation or a signal index may also be employed and compared to corresponding threshold values in the determination.

Sampling frequency of the RR interval time series for spectral analysis of heart rate variability.

Abstract: Spectral analysis of heart rate variability (HRV) is an accepted method for assessment of cardiac autonomic function and its relationship to numerous disorders and diseases. Various non-parametric methods for HRV estimation have been developed and extensive literature on their respective properties is available. The RR interval time series can be seen as a series of non-uniformly spaced samples. To analyse the power spectra of this series using the discrete Fourier transform (DFT), we need to interpolate the series for obtaining uniformly spaced intervals. The selection of sampling period plays a critical role in obtaining the power spectra in terms of computational efficiency and accuracy. In this paper, we shall analyse the RR interval time series from selected subjects for different sampling frequencies to compare the error introduced in selected frequency-domain measures of HRV at a constant frequency resolution for a specific duration of electrocardiogram (ECG) data. It should be pointed out that, although many other error causes are possible in the frequency-domain measures, our attention will be confined only to the performance comparison due to the different sampling frequencies. While the choice of RR interval sampling frequency (f(s)) is arbitrary, the sampling rate of RR interval series must be selected with due consideration to mean and minimum RR interval; f(s = )4 Hz was proposed for a majority of cases. This is an appropriate sampling rate for the study of autonomic regulation, since it enables us to compute reliable spectral estimates between dc and 1 Hz, which represents the frequency band within which the autonomic nervous system has significant response. Furthermore, resampled RR intervals are evenly spaced in time and are synchronized with the samples of the other physiologic signals, enabling cross-spectral estimates with these signals.

A parametric study of band-notched UWB planar monopole antennas

Abstract: Due to the collocation of the UWB frequency band with frequency bands reserved for narrowband wireless technologies, there is a need in the UWB device to provide filtering in those bands to avoid interference from, or causing interference to, narrowband devices. In this paper, a parametric study of a planar monopole antenna with a simple etched band-notching feature is presented. Results obtained using numerical simulation are presented which demonstrate the degree to which notch bandwidth can be varied and good wideband performance can be maintained with this antenna.

Wireless Communication with Medical Implants: Antennas and Propagation

Abstract: With the increased sophistication of medical implants, there is a growing need for flexible high-speed communication with the implant from outside the body. Today the communication is done by an inductive link between the implant and an external coil at a low carrier frequency. Extended range and communication speed are possible to achieve by increasing the carrier frequency and the bandwidth. One frequency band that is available for this application is the newly standardized 400 MHz MICS band, which has the benefit of being reserved mainly for medical and metrological applications. In addition, the 2.45 GHz ISM band is a possibility, but has the drawback of being heavily used by other applications, such as wireless computer networks and microwave ovens. In order to assess the usability of wireless communication with medical implants, we have investigated the design of implantable antennas to be used in the body. Both theoretical limits and practical designs of the antennas are described. The SAR levels of the implanted antennas have been calculated and have been found to be at a safe level. We have investigated the wave-propagation from the implanted antenna to the outside, and its dependence on the position of the patient’s limbs and the size of the body. Full wave 3D-simulations of the wave propagation are feasible, as the radio link between the patient and a base station placed in the same room is very short in terms of wavelengths in the MICS band. We have simulated the wave propagation in a furnished room and compared the results with measurements of the same room. The results from these investigations are evaluated in terms of their impact on the link budget for a prototype MICS system. From these calculations conclusions on the necessary complexity of the transceivers are drawn, such as the need for both spatial and polarization diversity to fully exploit the potential of the communication link.

Methods and apparatus of improving inter-sector and/or inter-cell handoffs in a multi-carrier wireless communications system

Abstract: A wireless communications system, e.g., an OFDM system, uses a plurality of carrier frequencies each with an associated frequency band. A base station sector transmitter in the system transmits ordinary signaling, e.g., user data, in its own assigned band. In addition the sector base station transmitter periodically transmits beacon signals into its own frequency band and the frequency bands used by adjacent sector transmitters for their ordinary signaling. Beacon signals, being short duration high power signals with sector transmission power concentrated on one or a few tones, are easily detectable. Each beacon signal may be identified as to the source base station sector transmitter, e.g., based on tone. A mobile node, tuned to a single carrier band, receives a plurality of beacon signals, identifies the sources of the received beacons, compares the received strength of the beacons, and makes handoff decisions, without having to switch carrier band.

A Tunable Upconverter Mixer With Image Rejection

Abstract: Tunable upconversion mixers (200) that have a controllable pass-band response and provide substantial image rejection, making costly post-mixing filtering at least optional, if not unnecessary for many applications A single mixer is able to support several frequency bands (and/or be accurately tuned within one frequency band) by means of varying the capacitance in a tunable load circuit (130) for the mixer circuit The tunable mixer (200) comprises a mixer circuit (110) having inputs for receiving a signal to be up-converted and an oscillator signal to be mixed with the signal to be up-converted The mixer generates a mixer output signal at a desired sideband frequency and an image signal at an image frequency A tunable load circuit (130) is coupled to the mixer circuit (110) and responsive to a control signal (134) to resonate and pass signals in a desired pass-band corresponding to the mixer output signal at the desired sideband frequency, and which attenuates signals in an attenuation band that includes the image signal at the undesired image frequency

Mitigating interference with frequency hopping signals by deriving future hop frequencies

Abstract: Techniques to avoid interference with a frequency hopping signal that are of a periodic or quasi-periodic nature that may operate in the same frequency band and proximity with other devices. For example, the frequency hopping signals may be transmitted by Bluetooth devices operating in the same frequency band as IEEE 802.11 WLAN devices. When a frequency hopping interfering signal is detected, sufficient knowledge of the frequency hopping sequence is derived without obtaining state of a frequency hop sequence from information carried in the frequency hopping signal. This knowledge is used to predict or determine when future transmissions of the frequency hopping signal will be present in a particular frequency channel of concern. Using knowledge of future hop frequencies, operating parameters of a communication device or network can be adjusted to mitigate interference with the frequency hopping signal only at times when the frequency hopping signal will be in a particular frequency channel or channels of interest.