Radio Frequency Band Research Articles

QPSK Vector Signal Generation Based on Photonic Heterodyne Beating and Optical Carrier Suppression

We propose a novel scheme for quadrature phase-shift keying (QPSK) modulated vector signal generation based on photonic heterodyne beating, phase precoding, and optical carrier suppression (OCS). Different from our previous OCS-based vector signal generation schemes, in our proposed scheme, the precoded vector signal at the radio-frequency (RF) band, which is used for the drive of the intensity modulator operating at its OCS point, is generated by photonic heterodyning beating rather than a single digital-to-analog converter (DAC). Photonic heterodyne beating accomplishes the upconversion of the precoded vector signal from the baseband to the RF band, and thus, the DAC in our proposed scheme is used to generate the precoded vector signal at the baseband rather than that at the RF band, which significantly reduces the DAC bandwidth requirement. We experimentally demonstrate 17.6-GHz QPSK modulated vector signal generation based on our proposed scheme. The generated 17.6-GHz vector signal can carry up to 3-GBd QPSK data with a bit error ratio (BER) less than the hard-decision forward-error-correction (HD-FEC) threshold of $3.8\times 10^{-3}$ .

Multivariable algorithm for dynamic channel selection in cognitive radio networks

The spectral handoff is important in cognitive wireless networks to ensure an adequate quality of service and performance for secondary user communications. This work presents a multivariable algorithm for dynamic channel selection used in cognitive wireless networks. The channel selection is based on the fuzzy analytical hierarchical process (FAHP) method. The selected criteria for choosing the best backup channel are probability of channel availability, estimated channel time availability, signal to noise plus interference ratio, and bandwidth. These criteria are determined by means of a customized Delphi Method and using the FAHP technique; the corresponding weight and significance is calculated for two applications classified as best effort (BE) and real time (RT). The insertion of the fuzzy logic in the AHP algorithm allows better handling of inaccurate information because, as shown the results, consider more options to evaluate in contrast to a conventional AHP. As a difference with related work, the performance of our proposed FAHP method was validated with captured data in experiments realized at the GSM frequency band (824–849 MHz). This is due to the challenge of finding white spaces to communicate in this frequency band. This band represents more disputes in accessing spectral opportunities than other radio frequency (RF) bands because of the high demand for mobile phone communications. The proposed FAHP algorithm has a practical computational complexity and provides an effective frequency-channel selection. This proposed FAHP algorithm presents a new methodology to select and classify the variables based on a modified version of the Delphi method. The results of the proposed method were contrasted numerically with other three methods.

QAM Vector Signal Generation by Optical Carrier Suppression and Precoding Techniques

We numerically and experimentally investigate and compare photonic constant- and multi-amplitude quadrature-amplitude-modulation (QAM) vector signal generation at radio frequency (RF) bands enabled by a Mach-Zehnder modulator (MZM)-based optical carrier suppression (OCS) modulation. In order to attain an electrical vector RF signal displaying multi-amplitude QAM modulation, such as 8 QAM and 16 QAM, after square-law photodiode detection, the driving RF signal carrying multiamplitude QAM transmitter data, should be both amplitude- and phase-precoded before used to drive the MZM. However, for constant-amplitude QAM modulation, such as quadrature-phase-shift-keying (QPSK), only phase precoding is needed. We experimentally demonstrate 1-GBd vector signal generation at 12 GHz enabled by an MZM-based OSC modulation, adopting QPSK, 8 QAM, and 16 QAM modulation, respectively. We also experimentally compare the bit error rate performance of the three different vector signals, and the QPSK case is the best, while the 16 QAM case is the worst.

Performance of the MAC protocol in wireless recharging under E-limited scheduling

Recharging through radio frequency (RF) pulses is a promising approach to enhance the lifetime of wireless sensor networks (WSNs). In this paper, we propose a polling-based MAC protocol with round robin scheduling under E-limited service policy. In this model, the WSN coordinator sends a recharging pulse upon reception of a recharging request from one of the nodes. As both recharging and data communication use the same RF band, the latter process is interrupted by the former. A probabilistic model for energy depletion within the proposed MAC along with queueing delay model is evaluated as well. Later, we assess the behavior of time interval between two consecutive recharging events and packet waiting time under varying network size and traffic load.

A 1.3 mW low-IF, current-reuse, and current-bleeding RF front-end for the MICS band with sensitivity of -97 dbm

A low-power, low-intermediate frequency (IF) radio frequency (RF) front-end, including low-noise amplifier (LNA) and mixer for the medical implant communications service (MICS) RF band, is presented. The frequencies of LNA and mixer range from 402 MHz to 405 MHz, while the IF of the mixer is 450 KHz. Current-reuse, back-gate coupling, current-bleeding, and feedback circuit design techniques are utilized in the LNA design to achieve 10 dB of gain and the required noise figure (NF) under the low power consumption of 0.94 mW. By contrast, the Gilbert-type mixer generates 20 dB of conversion gain by using current-reuse, back-gate coupling, and current-bleeding techniques. The front-end is operated using a 1.8 V power supply and is capable of achieving a -97 dBm sensitivity using quadrature phase shift keying modulation while consuming 1.3 mW. The proposed front-end is implemented in TSMC 0.18 μm CMOS process with a total area of 1.4 mm × 1.2 mm. The gain enhancement technique has been substantially optimized compared with previous works and measurement results indicate that the front-end obtains the highest figure of merit compared with previous works.

The application of the fractional calculus model for dispersion and absorption in dielectrics I. Terahertz waves

An empirical model has been recently derived and used to modify Maxwell’s equations for dielectric materials based on viscoelastic analysis techniques that employs concepts from the fractional calculus. The empirical model was originally used to curve fit complex permittivity data of dielectrics exposed to electromagnetic fields oscillating in the radiofrequency band. The model was then incorporated into Maxwell’s equations giving rise to a fractional order Ampere’s law that subsequently produced a fractional order wave equation. This wave equation was shown to accurately describe the behavior of an electromagnetic wave propagating through a dielectric material. This work demonstrates that the application of these techniques can seamlessly be extended into the terahertz frequency band (ranging approximately from 1011Hz to 1013Hz) producing results of comparable accuracy to that which was shown in the radiofrequency band (ranging approximately from 102Hz to 1010Hz) while still remaining consistent with thermodynamic principles. The procedure is briefly reviewed and compared to the historical dielectric models of Debye and Cole–Cole and then applied to model the dielectric behavior of select materials in the terahertz frequency band. The work concludes with an analysis on the dispersion and absorption of terahertz waves using the aforementioned fractional order wave equation.

The observed radio/gamma-ray emission correlation for blazars with the Fermi-LAT and the RATAN-600 data

We study the correlation between gamma-ray and radio band radiation for 123 blazars, using the Fermi-LAT first source catalogue (1FGL) and the RATAN-600 data obtained at the same period of time (within a few months). We found an apparent positive correlation for BL Lac and flat-spectrum radio quasar (FSRQ) sources from our sample through testing the value of the Pearson product-moment correlation coefficient. The BL Lac objects show higher values of the correlation coefficient than FSRQs at all frequencies, except 21.7 GHz, and at all bands, except 10–100 GeV, typically at high confidence level (>99 per cent). At higher gamma-ray energies the correlation weakens and even becomes negative for BL Lacs and FSRQs. For BL Lac blazars, the correlation of the fluxes appeared to be more sensitive to the considered gamma-ray energy band, than to the frequency, while for FSRQ sources the correlation changed notably both with the considered radio frequency and gamma-ray energy band. We used a data randomization method to quantify the significance of the computed correlation coefficients. We find that the statistical significance of the correlations we obtained between the flux densities at all frequencies and the photon flux in all gamma-ray bands below 3 GeV is high for BL Lacs (chance probability ∼10−3–10−7). The correlation coefficient is high and significant for the 0.1–0.3 GeV band and low and insignificant for the 10–100 GeV band for both types of blazars for all considered frequencies.

An I/Q mixer with an integrated differential quadrature all-pass filter for on-chip quadrature LO signal generation**Project supported by the National High Technology Research and Development Program of China (No. 2011AA010200).

A down-conversion in-phase/quadrature (I/Q) mixer employing a folded-type topology, integrated with a passive differential quadrature all-pass filter (D-QAF), in order to realize the final down-conversion stage of a 60 GHz receiver architecture is presented in this work. Instead of employing conventional quadrature generation techniques such as a polyphase filter or a frequency divider for the local oscillator (LO) of the mixer, a passive D-QAF structure is employed. Fabricated in a 65 nm CMOS process, the mixer exhibits a voltage gain of 7–8 dB in an intermediate frequency (IF) band ranging from 10 MHz–1.75 GHz. A fixed LO frequency of 12 GHz is used to down-convert a radio frequency (RF) band of 10.25–13.75 GHz. The mixer displays a third order input referred intercept point (IIP3) ranging from −8.75 to −7.37 dBm for a fixed IF frequency of 10 MHz and a minimum single-sideband noise figure (SSB-NF) of 11.3 dB. The mixer draws a current of 6 mA from a 1.2 V supply voltage dissipating a power of 7.2 mW.

Dynamic range improvement in analog photonic link by intermodulation-compensation receiver.

In this paper, a novel intermodulation-compensation optical receiver based on the bias-modulated photo detector (PD) is proposed and demonstrated to eliminate the third-order intermodulation (IMD3) for the intensity-modulation direct-detection (IMDD) analog photonic link. We directly extract the key nonlinear distortion from the distorted optical intensity by a low-pass optical receiver, which is used to modulate the home-made, high-speed PD with bias modulation. Inside the high speed PD, the distorted radio frequency (RF) band is mixed with the above extracted baseband signal, and the IMD3 elimination can be achieved. Our proposal is theoretically analyzed, and the performance of the bias-modulated PD is experimentally demonstrated. Spurious-free dynamic range (SFDR) of 123.4 dB within 1-Hz bandwidth is obtained with 18.1 dB improvement. A low-biased Mach-Zehnder modulator (MZM) is used, keeping a simple transmitter with an improved link gain. The proposed post linearization requires no digital processing, avoiding the high quantization noise.

A low power, low noise figure quadrature demodulator for a 60 GHz receiver in 65-nm CMOS technology**Project supported by the National High Technology Research and Development Program of China (No. 2011AA010200).

This paper presents the design of a low power (LP) and a low noise figure (NF) quadrature demodulator with an on-chip frequency divider for quadrature local oscillator (LO) signal generation. The transconductance stage of the mixer is implemented by an AC-coupled self-bias current reuse topology. On-chip series inductors are employed at the gate terminals of the differential input transconductance stage to improve the voltage gain by enhancing the effective transconductance. The chip is implemented in 65-nm LP CMOS technology. The demodulator is designed for an input radio frequency (RF) band ranging from 10.25 to 13.75 GHz. A fixed LO frequency of 12 GHz down-converts the RF band to an intermediate frequency (IF) band ranging from DC to 1.75 GHz. From 10 MHz to 1.75 GHz the demodulator achieves a voltage conversion gain (VCG) ranging from 14.2 to 13.2 dB, and a minimum single-sideband NF (SSB-NF) of 9 dB. The measured third-order input intercept point (IIP3) is −3.3 dBm for a two-tone test frequency spacing of 1 MHz. The mixer alone draws a current of only 2.5 mA, whereas the complete demodulator draws a current of 7.18 mA from a 1.2 V supply. The measurement results for a frequency divider, which was fabricated individually, prior to being integrated with the quadrature demodulator, in 65-nm LP CMOS technology, are also presented in this paper.

Optimization of EVM Through Diode Bias Control Using a Blind Algorithm Applied to Multiport Receivers

In this brief, we developed a detailed Simulink model that emulates the radio frequency and digital base band of a six-port receiver. In contrast to other results published in the literature, we not only provide a controlled continuous bias to the diodes. We propose a novel algorithm that reduces the error vector magnitude (EVM) by adaptively controlling the diode bias point. We will also show that when the algorithm is turned on in the model, the EVM becomes less sensitive to variations in the diode bias conditions. Another key feature of optimum diode bias control is that the local oscillator (LO) power requirements decrease and that the EVM is not sensitive to LO power variation. Results presented here show that for an LO power variation of more than 10 dB, we notice no EVM variation.

MineLoc — Personnel Tracking System for Longwall Coal Mining Sites

The localization of people and objects in indoor environments is an ongoing research challenge with a diverse set of possible positioning sensors. For the harsh environment of an underground coal mine, a system relying on received signal strength (RSS) measurements of common radio modules has been proven to deliver accurate and reliable positioning results. However, in tunnel environments of a longwall mining facility, conventional indoor radio propagation models are not valid due to waveguide effects. Additional investigations regarding the RSS-based ranging and the localization algorithm will be proposed. Ray tracing is used to find an appropriate propagation model and to define suitable range sections for different radio frequency bands. Simulation and experiment ranging results are compared for 2.4 GHz and sub- GHz radios. An enhanced weighted centroid localization (WCL) approach is essential, taking into account the peculiarities of the longwall mining environment.

Enhancing RF-to-DC conversion efficiency of wideband RF energy harvesters using multi-tone optimization technique

In this paper, a 1.8–2.6 GHz wideband rectenna is designed for radio frequency (RF) energy harvesting in the context of wireless sensor nodes (WSN). To assess the feasibility of ambient RF energy harvesting, the power density from RF base stations is analyzed through statistical measurements. Power density measurements are also performed close to Wi-Fi routers. Using these results, a methodology based on impedance matching network adaptation and maximum power transfer is proposed to design the wideband RF harvester. Using this method, three RF bands,i.e.GSM1800, UMTS and WLAN, are covered. The theoretical analysis is confirmed by simulations and measurements. From measurements results, the prototype RF-to-DC conversion efficiency is 15% at −20 dBm from 1.8 to 2.6 GHz. It is shown that with three RF sources in the chosen bands, each emitting at 10 dBm, the RF-to-DC conversion efficiency is 15% better compared to that measured with a single RF source. Finally, 7 µW is harvested at 50 m from a GSM1800 and UMTS base station. This value confirms the RF harvester workability to supply small sensors.

Folded down-conversion mixer for a 60 GHz receiver architecture in 65-nm CMOS technology

We present the design of a folded down-conversion mixer which is incorporated at the final down-conversion stage of a 60 GHz receiver. The mixer employs an ac-coupled current reuse transconductance stage. It performs well under low supply voltages, and is less sensitive to temperature variations and process spread. The mixer operates at an input radio frequency (RF) band ranging from 10.25 to 13.75 GHz, with a fixed local oscillator (LO) frequency of 12 GHz, which down-converts the RF band to an intermediate frequency (IF) band ranging from dc to 1.75 GHz. The mixer is designed in a 65 nm low power (LP) CMOS process with an active chip area of only 0.0179 mm2. At a nominal supply voltage of 1.2 V and an IF of 10 MHz, a maximum voltage conversion gain (VCG) of 9.8 dB, a double sideband noise figure (DSB-NF) of 11.6 dB, and a linearity in terms of input 1 dB compression point (P in,1dB) of −13 dBm are measured. The mixer draws a current of 5 mA from a 1.2 V supply dissipating a power of only 6 mW.

Transverse Plasma Resonans Mode in an Nonmagnetized Plasma and Its Practical Applications

Is shown that in the nonmagnetized plasma, besides longitudinal Langmuir resonance can exist the transverse plasma resonance. The resonance indicated can exist in the confined plasma. It is known that with the nuclear explosions the electromagnetic radiation in the very wide frequency band is observed, up to the radio-frequency range. And if the emission in field of light range can be explained by the emission of separate atoms, then emission in the region of radio-frequency band can be caused only by collective processes, which occur in the confined plasma. The use of transverse resonance makes it possible to create resonators and band-pass filters, and also lasers on the collective plasma oscillations. Transverse plasma resonance can be used also for the warming-up of plasma and its diagnostics. Is introduced the concept of magnetoelectrokinetic waves.

A 1 <formula formulatype="inline"><tex Notation="TeX">$\times$</tex> </formula> 2 Dual-Band Antenna Array for Radio-Frequency Identification (RFID) Handheld Reader Applications

In this paper, an aperture-coupled dual-band antenna array for ultra-high-frequency (UHF) and microwave band radio-frequency identification (RFID) handheld reader application is presented. The proposed two-element antenna array is composed of a feeding network, a ground plane with coupling apertures, patch radiators, and parasitic elements serving as directors. The spacing between the radiators is optimized to achieve the desired radiation patterns. The experimental results demonstrate that the proposed antenna features good impedance bandwidth, moderate gain, and good radiation efficiency from 840 to 960 MHz (covering a universal UHF band) and 2.38-2.48 GHz (microwave band). The antenna is well suited for applications in RFID handheld readers.

Magnetic topological transition in transmission line metamaterials

We study the magnetic topological transition of the isofrequency curves in the wave vector space from a closed ellipsoid to an open hyperboloid in a metamaterial based on artificial transmission lines. In the radio frequency band we directly measure the emission pattern of a point source placed in the center of the lattice and demonstrate the elliptical wave fronts below the topological transition frequency and hyperbolic wave fronts above the topological transition frequency.

Synthesis of high magnetic moment soft magnetic nanocomposite powders for RF filters and antennas

Fe60Co40 alloy nanoparticles with an average particle size of 30nm were successfully synthesized in gram scale batches using the modified polyol process. The X-ray diffraction and microstructure studies clearly show the formation of the alloy nanoparticles. The saturation magnetization for the gram scale synthesized Fe60Co40 alloy nanoparticles is in the range of 190-205 emu/g at room temperature. The as-synthesized nanoparticles were used to fabricate transmission lines on FR4 substrate to perform radio frequency (RF) characterization of the nanoparticles at ISM RF bands of interest (all in GHz range). The complex permeability extraction of composite Fe60Co40 nanoparticles were performed using perturbation technique applied to microstrip transmission lines by relative measurement of full two port scattering parameter with respect to a baseline FR4 substrate. The extracted results show attractive characteristics for small size antennas and filters.

Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion.

Many of today's radiofrequency-emitting devices in telecommunication, telemedicine, transportation safety, and security/military applications use the millimeter wave (MMW) band (30–300 GHz). To evaluate the biological safety and possible applications of this radiofrequency band for neuroscience and neurology, we have investigated the physiological effects of low-intensity 60-GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. We applied incident power densities of 1, 2, and 4 mW/cm2 to the whole ganglion for a period of 1 min while recording the action potential with a standard sharp electrode electrophysiology setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm2 for 6 min. During the exposure to MMWs and gradual bath heating at a rate of 0.04°C/s (2.4°C/min), the ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane and decrease in the action potential amplitude. However, narrowing of the action potential half-width during MMW irradiation at 4 mW/cm2 was 5 times more pronounced compared with that during equivalent bath heating of 0.6°C. Even more dramatic difference in the effects of MMW irradiation and bath heating was noted in the firing rate, which was suppressed at all applied MMW power densities and increased in a dose-dependent manner during gradual bath heating. The mechanism of enhanced narrowing of action potentials and suppressed firing by MMW irradiation, compared with that by gradual bath heating, is hypothesized to involve specific coupling of MMW energy with the neuronal plasma membrane.

Contactless measurement of nonlinear conductivity in the radio-frequency range.

We have developed a system for contactless measurement of nonlinear conductivity in the radio-frequency band, and over a wide temperature range. A non-resonant circuit is used to electrically excite the sample, and the induced signal is detected by a resonant circuit whose natural frequency matches higher harmonics of the excitation. A simple modification of the probe allows non-resonant detection suitable for stronger signals. Two measurement procedures are proposed that allow significant excitation power variation, up to 150 W. The apparatus has been validated through the measurement of the nonlinear response at the superconducting transition of a high-Tc superconductor, and the nematic transition of an iron pnictide.