GHz Domain Research Articles

Circularly Polarized Parasitic Strips Loaded Broadband Printed Antenna for Sub-6 GHz (n77/n78/n79) Domain

A novel broadband circularly polarized compact antenna is designed with broad axial ratio bandwidth (ARBW) for Sub-6 GHz fifth-generation applications. The antenna is printed on a Duroid substrate (ϵr = 2.2, thickness of 0.8 mm). The proposed configuration consists of two diagonally opposite symmetric parasitic strips energized by the matched transmission line and supported by a defected ground plane on the other side. By utilizing two parasitic strips and DGS concepts, wideband bandwidth of 3.4 GHz (2–5.4 GHz) Simulated and 3-dB ARBW of 2.5 GHz (2.9–5.4 GHz) is achieved. The CP behavior of the proposed antenna is investigated and discussed in detail with the help of the surface current distribution plot and magnitude/phase vs frequency plot. Simulated findings are justified by the measured results. The suggested antenna's simple design and high AR bandwidth make it a promising option for a wide range of wireless networks.

Hard-X-ray-selected active galactic nuclei – II. Spectral energy distributions in the 5–45 GHz domain

ABSTRACT A wide-frequency radio study of active galactic nuclei (AGN) is crucial to evaluate the intervening radiative mechanisms responsible for the observed emission and relate them with the underlying accretion physics. We present wide-frequency (5–45 GHz), high-sensitivity (few $\mathrm{{\mu }Jy\, beam^{-1}}$), (sub)-kpc Jansky Very Large Array (JVLA) observations of a sample of 30 nearby ($0.003\, \le \, z\, \le \, 0.3$) AGN detected by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL)/Imager on Board the INTEGRAL Satellite (IBIS) at hard X-ray. We find a high detection fraction of radio emission at all frequencies, i.e. ≥95 per cent at 5, 10, and 15 GHz and ≥80 per cent at 22 and 45 GHz. Two sources out of 30 remain undetected at our high sensitivities. The nuclear radio morphology is predominantly compact, sometimes accompanied by extended jet-like structures, or more complex features. The radio spectral energy distributions (SEDs) of the radio cores appear either as single or as a broken power law, a minority of them exhibit a peaked component. The spectral slopes are either flat/inverted or steep, up to a break/peak or over the whole range. The sample mean SED shows a flat slope up to 15 GHz that steepens between 15 and 22 GHz and becomes again flat above 22 GHz. Significant radio–X-ray correlations are observed at all frequencies. About half of the sample features extended emission, clearly resolved by the JVLA, indicating low-power jets or large-scale outflows. The unresolved cores, which often dominate the radio power, may be of jet, outflow, and/or coronal origin, depending on the observed frequency.

An Overview of Current and Future Vehicular Communication Technologies

The present paper provides a technical overview about the most relevant vehicular communication technologies including IEEE 802.11p, IEEE 802.11bd, LTEV2X and NRV2X. IEEE 802.11p is the most matured one Wi-Fi based technology, and its successor, the IEEE 802.11bd is expected to be released in 2021. As CV2X (Cellular Vehicle to Everything) technologies, LTEV2X (Long Term Evolution V2X) and NRV2X (New Radio V2X) are discussed in this paper. The former one is already available, while the latter one’s final specification will be finalized in 2020 by the 3GPP (Third Generation Partnership Project). These four technologies also motivate the already started transformation of vehicle industry by enabling basic safety features and more efficient traffic management, as well as cooperative maneuver execution towards high-level automated driving. The comparison of these technologies is essential to clarify their benefits completely. These technologies are considered as competitors, however, it is expected that they will coexist in the same geographical region. Thus, they will share on the same unlicensed frequency bands in 5.9 GHz domain. Therefore, different coexistence scenarios are also discussed in the paper to see how their advantages could be utilized.

Electromagnetic pulse (EMP) radiation by laser interaction with a solid H2 ribbon

The electromagnetic pulses (EMPs) generated during the interaction of a focused 1.315-μm sub-nanosecond laser pulse with a solid hydrogen ribbon were measured. The strength and temporal characteristics of EMPs were found to be dependent on the target density. If a low density target is ionized during the interaction with the laser, and the plasma does not physically touch the target holder, the EMP is weaker in strength and shorter in time duration. It is shown that during the H2 target experiment, the EMP does not strongly affect the response of fast electronic devices. The measurements of the EMP were carried out by Rohde&Schwarz B-Probes, particularly sensitive in the frequency range from 30 MHz and 1 GHz. Numerical simulations of resonant frequencies of the target chamber used in the experiment at the Prague Asterix Laser System kJ-class laser facility elucidate the peaked structure of EMP frequency spectra in the GHz domain.

Note: A four-pass acousto-optic modulator system for laser cooling of sodium atoms.

We present a four-pass acousto-optic modulator (AOM) system for providing the repumping light for laser cooling of sodium atoms. With only one 400 MHz AOM, we achieve a tunable laser frequency shift around 1.6 GHz with total efficiency up to 30%. This setup provides an alternative over conventional methods to generate a sodium repumping light using more expensive high frequency AOMs or electro-optical modulators (EOMs) in the GHz domain. This compact and reliable setup can be easily adapted to other frequencies and may find applications in laser spectroscopy, laser cooling and trapping, and coherent manipulation of atomic quantum states.

Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba2/3Sr1/3TiO3 thin films

We present the conduction mechanisms of Ba2/3Sr1/3TiO3 thin films integrated in metal-insulator-metal (MIM) capacitors and the modelling of the frequency-dependent electrostrictive resonances (in the 100 MHz–10 GHz domain) induced in the devices upon applying different voltage biases. Au/BST/Ir MIM structures on MgO substrates have been fabricated and, depending on their specific polarization, we highlighted different conduction mechanisms in the devices. Depending on the dc bias polarity, the conduction current across the material shows a space-charge-limited-current behavior under negative polarization, whereas under positive bias, the conduction obeys an electrode-limited Schottky-type law at the Au/BST interface. The application of an electric field on the device induces the onset of acoustic resonances related to electrostrictive phenomena in the ferroelectric material. We modeled these acoustic resonances over a wide frequency range, by using a modified Lakin model, which takes into account the dispersions of acoustic properties near the lower electrode/thin film interface.

Ultra-High Tunability of <inline-formula> <tex-math notation="LaTeX">$\text{Ba}_{(2/3)}\text{Sr}_{(1/3)}\text{TiO}_{3}$</tex-math> </inline-formula>-Based Capacitors Under Low Electric Fields

We report the high-frequency electrical characterization of $\text{Ba}_{2/3}\text{Sr}_{1/3}\text{TiO}_{3}$ (BST) thin films exhibiting a very high dielectric tunability with low losses at 2.45 GHz under very low applied electrical fields. BST layers were integrated in out-of-plane Metal-Insulator-Metal (MIM) devices with optimized Ir/MgO(100) bottom electrodes. The high frequency properties of BST films with thicknesses of 200 nm, 450 nm and 1450 nm were thoroughly investigated in the 100 MHz–10 GHz domain and exhibit extremely high capacitance tuning abilities of 82%, 81% and 70% respectively, under applied voltages as low as 10 V. MIM devices responses show the onset of acoustic resonances associated with the BST electrostrictive behavior under an electric field. By combining high tunability with low resistive losses under low applied voltages, these devices are opening promising avenues for their integration in high-performance tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used ISM (industrial, scientific and medical) frequency band.

An evolutionary design methodology of printed circuit boards for high-speed VLSIs

As operation frequencies of the printed circuit boards (PCBs) increase in keeping with VLSI frequencies in the GHz domain, two independent serious problems occur in the PCB design. One is waveform distortion problem, or signal integrity (SI) degradation problem, in PCB traces. And the other is power-supply drop problem, or power integrity (PI) degradation problem, in PCB power planes. Those problems are barely able to be overcome on case-by-case empirical designs conventionally. In this paper we newly propose a design approach for each problem, both of which are based on the genetic algorithm. And we obtained improvement ratios of more than double compared with the both conventional designs for SI and PI degradations, respectively.

Restarting radio activity and dust emission in radio-loud broad absorption line quasars

Broad absorption line quasars (BAL QSOs) are objects showing absorption from relativistic outflows, with velocities up to 0.2c. These manifest, in about 15% of quasars, as absorption troughs on the blue side of UV emission lines, such as C iv and Mg ii. In this work, we complement the information collected in the cm band for our previously presented sample of radio loud BAL QSOs with new observations at m and mm bands. Our aim is to verify the presence of old, extended radio components in the MHz range, and probe the emission of dust (linked to star formation) in the mm domain. We observed 5 sources from our sample, already presenting hints of low-frequency emission, with the GMRT at 235 and 610 MHz. Other 17 sources (more than half the sample) were observed with bolometer cameras at IRAM-30m and APEX. All sources observed with the GMRT present extended emission at a scale of tens of kpc. In some cases these measurements allow us to identify a second component in the SED, at frequencies below 1.4 GHz, beyond the one already studied in the GHz domain. In the mm-band, only one source shows emission clearly ascribable to dust. Upper limits were obtained for the remaining targets. These findings confirm that BAL QSOs can also be present in old radio sources, or even in restarting ones, where favourable conditions for the outflow launching/acceleration are present. A suggestion that these outflows could be precursors of the jet comes from the fact that ~70% of our sample can be considered in a GigaHertz Peaked Spectrum (GPS) or Compact Steep Spectrum (CSS)+GPS phase. This would confirm the idea proposed by other authors that these outflows could be recollimated to form the jet. Comparing with previous works in the literature, dust emission seems to be weaker than the what expected in 'normal' QSOs, suggesting that a feedback mechanism could inhibit star formation in radio-loud BAL QSOs.

CogCell: cognitive interplay between 60 GHz picocells and 2.4/5 GHz hotspots in the 5G era

The rapid proliferation of wireless communication devices and the emergence of a variety of new applications have triggered investigations into next-generation mobile broadband systems, i.e. 5G. Legacy 2G-4G systems covering large areas were envisioned to serve both indoor and outdoor environments. However, in the 5G era, 80 percent of all traffic is expected to be generated indoors. Hence, the current approach of macrocell mobile networks, where there is no differentiation between indoors and outdoors, needs to be reconsidered. We envision 60 GHz mmWave picocell architecture to support highspeed indoor and hotspot communications. We envisage the 5G indoor network as a combination of, and interplay between, 2.4/5 GHz having robust coverage and 60 GHz links offering a high data rate. This requires intelligent coordination and cooperation. We propose a 60 GHz picocellular network architecture, called CogCell, leveraging ubiquitous WiFi. We propose to use 60 GHz for the data plane and 2.4/5GHz for the control plane. The hybrid network architecture considers an opportunistic fall-back to 2.4/5 GHz in case of poor connectivity in the 60 GHz domain. Further, to avoid the frequent re-beamforming in 60 GHz directional links due to mobility, we propose a cognitive module, a sensor- assisted intelligent beam switching procedure, that reduces communication overhead. We believe that the CogCell concept will help future indoor communications and possibly outdoor hotspots, where mobile stations and access points collaborate with each other to improve the user experience.

Physics of giant electromagnetic pulse generation in short-pulse laser experiments.

In this paper we describe the physical processes that lead to the generation of giant electromagnetic pulses (GEMPs) at powerful laser facilities. Our study is based on experimental measurements of both the charging of a solid target irradiated by an ultra-short, ultra-intense laser and the detection of the electromagnetic emission in the GHz domain. An unambiguous correlation between the neutralization current in the target holder and the electromagnetic emission shows that the source of the GEMP is the remaining positive charge inside the target after the escape of fast electrons accelerated by the ultra-intense laser. A simple model for calculating this charge in the thick target case is presented. From this model and knowing the geometry of the target holder, it becomes possible to estimate the intensity and the dominant frequencies of the GEMP at any facility.

Flexible transparent graphene/polymer multilayers for efficient electromagnetic field absorption.

Thanks to its high electrical conductivity, a graphene plane presents a good shielding efficiency against GHz electromagnetic radiations. Several graphene planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties of isolated graphene. Maximum absorption of radiations for frequency around 30 GHz is achieved with six separated graphene planes, which is the optimum number. This remarkable result is demonstrated experimentally from electromagnetic measurements performed in the Ka band on a series of multilayers obtained by piling 1, 2, 3 … graphene/PMMA units on a silica substrate. Theoretical calculations convincingly explain the observed absorption and transmission data in the GHz domain. It is concluded that graphene/PMMA multilayers can be used as an efficient optically transparent and flexible shielding media.

Enhancing the magnetic field intensity with a dielectric gap antenna

We measure strong magnetic field intensities in a subwavelength gap separating two dielectric resonators. This dimer magnetic antenna is characterized in the GHz spectral regime when considering three conditions of illumination. We detail the different magneto-electric couplings involved in the enhancement of the near magnetic field and derive the analytical expressions of the magnetic field intensities. The results reported here in the GHz domain can be extended to other spectral domains, since they are obtained with a dielectric permittivity of 16 that can be observed in a very broad spectrum ranging from optics to radio-frequencies.

1.4 GHz femtosecond comb generation by Fabry‐Pérot filtering of optical parametric oscillator frequency comb

Laser frequency combs based on optical parametric oscillators provide widely tunable sources of regularly spaced frequencies from the visible to the mid-infrared, with potential applications in precision metrology, spectroscopy and astronomy. Reported is the extension of the comb mode spacing into the GHz domain by using a Fabry-Perot cavity, the length of which was electronically stabilised to a harmonic of the original pulse repetition frequency via a dither-locking technique. A 1500 nm femtosecond optical parametric oscillator frequency comb, the repetition frequency and carrier-envelope offset frequency of which were locked to 280 MHz and 10 MHz, respectively, was filtered by a high-finesse cavity to generate a pulse sequence at 1.4 GHz, corresponding to a factor of five increase in the mode spacing of the comb.

Temperature-dependent bulk viscosity of nitrogen gas determined from spontaneous Rayleigh–Brillouin scattering

Values for the bulk viscosity η(b) of molecular nitrogen gas (N2) were derived from spontaneous Rayleigh-Brillouin scattering at ultraviolet wavelengths (λ=366.8 nm) and at a 90° scattering angle. Analysis of the scattering profiles yields values showing a linear increasing trend, ranging from η(b)=0.7×10(-5) to 2.0×10(-5) kg·m(-1)·s(-1) in the temperature interval from 255 to 340 K. The present values, pertaining to hypersound acoustics at frequencies in the gigahertz domain, are found to be in agreement with results from acoustic attenuation experiments in N2 performed at megahertz frequencies.

Acoustical Spectroscopy of Carbohydrate Aqueous Solutions: Saccharides; Alkyl Glycosides; Cyclodextrins. Part I. Conformer Variations

Acoustical attenuation spectra in the frequency range 12 kHz - 2 GHz and non-equilibrium time domain measurements are briefly reviewed for aqueous solutions of various mono- and disaccharides as well as alkyl glycosides. Several relaxation regimes emerge with relaxation times between 10-11s and 103s. In this paper relaxation terms reflecting conformational changes are discussed, particularly mutarotation (103s), chair-chair ring inversion (1 μs), two modes of pseudorotation (100 ns, 10 ns), disaccharide ring isomerisation (10 ns), and exocyclic side group rotation (1 ns).

Low power compact radio galaxies at high angular resolution

We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLA images of five low power compact (LPC) radio sources, and phase referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA resolution we resolve the structure and identify component positions and flux densities. The phase referenced VLBA data at 1.6 GHz reve als flat-spectrum, compact cores (down to a few milliJansky) in f our of the five sources. The absolute astrometry provided by t he phase referencing allows us to identify the center of activi ty on the VLA images. Moreover, these data reveal rich structures, including two-sided jets and secondary components. On the basis of the arcsecond scale structures and of the nuclear properties, we rule out the presence of strong relativistic effects in our LPCs, which must be intrinsically small (deprojected linear sizes < 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range 10 5 − 10 7 yrs. In LPCs, the outermost edge may be advancing more slowly than in more powerful sources or could even be stationary; some LPCs might also have ceased their activity. In general, the properties of LPCs can be related to a number of reasons, including, but not limited to: youth, frustration, low kinematic power jets, and short-lived activity in the radio.

Low-cost setup for generation of 3 GHz frequency difference phase-locked laser light

We have devised an all-optical setup for the generation of two phase-locked laser fields with a frequency difference of 3 GHz using only standard optics and two acousto-optical frequency shifters, that are operated at 253 MHz in sixtupel pass. The spectral width of the beat frequency is measured to be 300 Hz (full width at half maximum) limited by the resolution bandwidth of the spectrum analyzer. We routinely obtain an overall efficiency of more than 15% and demonstrate that the frequency shifted light can be further amplified by injecting it into additional “slave” lasers. This setup provides a low-cost alternative over conventional methods to generate laser fields with difference frequencies in the GHz domain, as for example, used in laser spectroscopy, laser cooling and trapping, and coherent manipulation of atomic quantum states.

Estimation of Velocities and Energy Densities of GHz Domain Shear Fluxes Propagating in Sapphire by Brillouin Scattering Technique

Energy densities and velocities of GHz domain shear fluxes in sapphire were estimated using the Brillouin scattering theory. The Brillouin scattering cross section was calculated from sapphire’s material parameters. The experiment was done using CdS domain shear fluxes. Direct contact was used to mirror surfaces of the CdS and the sapphire. Injection efficiency of shear fluxes ranging from 0.2 GHz to 1.1 GHz into the sapphire from CdS was measured by this method. In addition, energy density distributions of domain fluxes in the sapphire were estimated from scattering light intensities by employing the scattering cross section of the sapphire.