Cross Dipole Research Articles

Design aspects of Bi2Sr2CaCu2O8+δ THz sources: optimization of thermal and radiative properties.

Impedance matching and heat management are important factors influencing the performance of terahertz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered containing either a conventional large single crystal or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes play important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts terahertz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based, devices. These results are in good agreement with presented experimental data.

Monostatic microwave ellipsometry for material characterization

We propose Microwave ellipsometry based on monostatic measurements in which the transmitter and receiver are located in the same location. The traditional ellipsometry technique is based on bi-static measurements in which the polarization state of the reflected wave from a sample is analyzed to estimate its electromagnetic properties. Initially, the ellipsometric methods had been applied in the optical spectrum since the wavelengths and the constituent atomic structure are comparable leading to the strong matter-wave interaction and polarization changes. Thanks to the recent advancements in metasurfaces, chiral sensing can now be potentially applied to characterize materials at the microwave frequencies in a compact laboratory environment. In this paper, we lay down the fundamentals of microwave monostatic elliposmetry method. We demonstrate the permittivity detection by a numerically simulated monostatic sensing set-up composed of L-shaped unit chiral unit cells etched on the dielectric sample and illuminated by a monochromatic linearly polarized electromagnetic source. We construct the Jones matrix to extract the polarization states from the reflection coefficients. The determination of the reflection coefficients is greatly simplified by using a cross-dipole antenna receiver which provides the ratio of the two corresponding orthogonal complex currents.

Development of Reconfigurable Frequency Selective Surface Associating Cross Dipoles and Matryoshka Geometries

A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geometries is described in this paper. The proposed reconfigurable FSS uses as active element PIN diodes. With the associated geometries, three resonant frequencies are achieved, two fixed, related to the matryoshka geometry, and one that can be activated or not, related to the cross dipoles geometry. Differently from previous works, an inductor was inserted into the cross dipoles’ horizontal arms, maintaining its resonance for x polarization. The PIN diode inserted into cross dipoles’ vertical arms controls the respective resonance. The design procedures for each geometry, in addition to PIN diode and RF inductor basics are outlined. The expected results are discussed based on the analysis of the resonances of each geometry and the associated geometries, as well as the different PIN diode bias states (OFF and ON). A prototype was fabricated and characterized, obtaining a good agreement between the numerical and experimental results, with a reconfiguration bandwidth of 0.24 GHz, from 2.12 GHz to 2.36 GHz, for a variation of at least 10 dB between the OFF and ON states.

Design of miniaturized dual-polarized dipole antenna for 4G & sub-6 GHz 5G applications

Abstract Dual-polarization, enhanced gain and compact size is the basic need of the base station antennas whereas a modern communication system needs a wideband antenna which can cover both the LTE & 5G applications. In the present work, a cross dipole antenna is proposed for LTE & sub 6 GHz 5G frequency band for Base Station Antenna Applications. By introducing asymmetrically shaped pentagon slots in the dipole and open-loop dipole patches, wide impedance bandwidth of 1.65–4.05 GHz at a return loss of −14 dB are achieved for 4G & 5G applications. Two symmetric feeding lines orthogonal to each other have been used to obtain the dual-polarization. Also, a high stable gain of 7 ± 1 dBi & HPBW of 80 ± 5° was achieved over the entire operating band at both the ports due to the symmetric structure. The proposed antenna is compared for size and bandwidth with the structures already proposed in the literature and significant enhancement is observed to be used for Base station antennas.

A Band-Notched Antenna With Two Radiation Zeros Using Grounded Coplanar Waveguide Filter for 2.4/5 GHz WLAN Applications

In this article, a band-notched dual-polarized crossed dipole antenna is proposed for 2.4/5 GHz WLAN applications. The proposed antenna works on the WLAN 2.4-GHz (2.4–2.48 GHz) and 5-GHz (5.15–5.85 GHz) bands for a VSWR <2 with two radiation zeros within 3.4–3.6 GHz. First, an ultra-wideband crossed dipole antenna with an operating frequency of 2.4–5.8 GHz is designed using the grounded coplanar waveguide (GCPW) feeding structure. Second, a miniaturized defected microstrip structure (DMS) is embedded in the GCPW feeding strip to form a stopband behavior with a radiation zero. Finally, combining with the design of a C-shaped split ring resonator (SRR) on the arms of the dipole antenna, a band notch (3.4–3.6 GHz) with two radiation zeros can be realized. These two radiation zeros can be adjusted independently to achieve a wide stopband performance. As a result, compared with the original ultra-wideband dipole antenna, the realized gains of the proposed antenna in the 3.4–3.6 GHz range are all suppressed from 8 dBi to less than −8 dBi. The proposed antenna can realize the stable unidirectional radiation pattern and a high gain of around 7 dBi in the lower band and 8.5 dBi in the higher band of WLAN. As a demonstration, the proposed antenna is fabricated and measured, and the measurement results are in good agreement with the simulation results.

Dual‐band dual‐polarized transmitarray with independent control of polarization at each band

This article presents a dual-band dual-polarized transmitarray (TA) with independent control of polarization at each band. Five-layer cross dipoles and rectangular patches are utilized to control the transmission characteristics at Ku (13.5 GHz) and K (22 GHz) bands, respectively. Cross loops are used to improve the independence between two bands and transmission response. The phases can be controlled independently at both bands because of the band independence of the element. The vertical polarization and horizontal polarization phases at each band can also be controlled independently because of the polarization independence of the element. A TA with the specific beam direction for each polarization at each band is designed to verify the characteristics of the element. The TA antenna is fabricated and measured. The simulated results are consistent with the experimental results.

A small footprint printed cross-dipole antenna with wide impedance bandwidth and circular polarization

Wideband circularly polarized (CP) cross-dipole antennas with flat, cavity and artificial magnetic conductor (AMC) reflectors are proposed. Each proposed antenna consists of a pair of driven dipoles, a pair of vacant-quarter printed rings, and a 50Ω coaxial probe. The boomerang shape has been adopted in the crossed-dipole. This shape makes the design more compact, so it can be a good candidate in the antenna array because of reducing the mutual coupling. All numerical simulation works have been done using the ANSYS electromagnetic (EM) software based on the finite element method (FEM) algorithm. The presented crossed-dipole with a cavity has the best performance compared to ones with conventional flat and AMC grounds. However, the crossed-dipole with the AMC ground is a low-profile structure. Thus, the paper investigates and discusses the results of the proposed strctures thoroughly. The obtained impedance bandwidth (IBW) is 42% (5.1-7.85 GHz) and the axial-ratio bandwidth (ARBW) is 7.72% (5.86-6.32 GHz) for the crossed-dipole with the conventional flat ground (i.e., reflector). Furthermore, the IBW and ARBW for the antenna with the cavity reflector are 50.37% (5.08-8.5 GHz) and 26.4% (5.72-7.46 GHz), respectively. The antenna with the AMC ground has the characterstics of the IBW and ARBW as 38.16% (5.36-7.89 GHz) and 15.16% (5.79-6.74 GHz), respectively. All structures are designed to operate for the C-band and wireless local area networks (WLAN) applications.

Design of an Ultrawideband Circularly Polarized Printed Crossed-Dipole Antenna Based on Genetic Algorithms for S-Band CubeSat Applications

As in any satellite, onboard antennas for CubeSats are crucial to establish communication with ground stations or other satellites. According to its application, antennas must comply with standardized requirements related to size, bandwidth, operating frequency, polarization, and gain. This paper presents an ultrawideband circularly polarized two-layer crossed-dipole microstrip antenna for S-band CubeSat applications using genetic algorithms optimization tools included in the 3D electromagnetic simulation software Ansys HFSS. The antenna is constructed on a 10 × 10 cm Cuclad-250 substrate with a back copper flat plane, located at λ/4 at 2.25 GHz operating frequency. The backplane with the exact substrate dimensions improves gain and reduces inside satellite radiation. Measured bandwidth defined by S11 at a −10 dB was higher than 1835 MHz with S11 = −24.68 dB at the central frequency of 2.25 GHz, while measured VSWR at the same frequency was 1.124. At 2.25 GHz, the maximum measured gain and the minimum measured axial ratio in the broadside direction were found to be 6 dBi and 0.22 dB, respectively. There are antenna simulations and measurements, as long as its fabrication guarantees application requirements that make it ready for prespace testing.

Broadband circularly polarized crossed‐dipole antenna and its array for long‐term evolution communication systems

The performance of a broadband circularly polarized crossed-dipole antenna for long-term evolution services is presented in this study. The antenna consists of a pair of trapezoidal-shape dipoles, four trapezoidal parasitic elements, and a pair of three-quarter printed rings that generate a 90° phase difference between the dipoles. The axial ratio (AR) bandwidth is extended using two principal factors in this article. The first one is using trapezoidal parasitic elements, and the second one is employing the feed network in the sequentially rotated technique. Its 2 × 2 array with a sequential-phase feeding network is introduced to achieve a noticeable improvement on the proposed dipole antenna performance. The measured results approve that the impedance and AR bandwidths of the proposed crossed-dipole antenna are 44% (1.95–3.05 GHz) for S11 < −10 dB and 31% (2.2–3 GHz) for AR ≤ 3 dB, respectively. Furthermore, by applying a 2 × 2 array structure for the proposed antenna, the impedance, and AR bandwidths increased by 63% and 31%, respectively. Indeed, using trapezoidal parasitic elements adjacent to the dipole arms leads to generating further surface currents and causes to extend the impedance. A sequential-phase feeding network is in charge of extending the AR bandwidth of the antenna simultaneously.

A Simple Printed Cross-Dipole Antenna with Modified Feeding Structure and Dual-Layer Printed Reflector for Direction Finding Systems.

In this paper, a simple printed cross-dipole (PCD) antenna to achieve a right-hand circular polarization (RHCP) at the L/S-band for direction finding (DF) systems is presented. The radiating part of the antenna consists of two printed dipoles that interlock with each other and are mounted orthogonally on a dual-layer printed reflector. To connect the feedlines of the dipole elements to the antenna’s feed network, which is located on the backside of the reflector, a through-hole signal via (THSV) is employed as the signal interconnection instead of the mainstream approach of using coaxial bead conductor. This feeding technique provides a degree of freedom to control the impedance of the signal path between the feedlines and the feed network in the numerical simulation for improved matching conditions. The proposed THSV extending through the dual-layer printed reflector is more reliable, durable, and mechanically robust to stabilize the matching conditions of the fabricated antenna in contrast to the coaxial-based approach that is more susceptible to impedance mismatch due to solder fatigue. Thus, the proposed PCD antenna offers advantages of broadband, flexible impedance matching, and fabrication ease. The antenna exhibits an impedance bandwidth (IBW) of 59% (1.59–2.93 GHz), a 3-dB axial ratio bandwidth (ARBW) of 57% (1.5–2.7 GHz), and a peak of 7.5 dB within the operating frequency band.

Cavity-Backed Circularly Polarized Cross-Dipole Phased Arrays

In this letter, a 16 × 16 Ku-band circularly polarized phased array is proposed. The antenna element comprises a cross dipole, a metal cavity, and a threaded SMP connector. The metal cavity makes the gain of the antenna increased and the mutual coupling between the array elements is reduced, thus ensuring good impedance matching and axis ratio (AR) during the two-dimensional beam scanning. The mutual coupling of the center element at center frequency is -26.6 dB when the cavity is added. The proposed phased array achieves the impedance bandwidth (| <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ - 10 dB) of 10.1% (13.1-14.5 GHz) when scanning ±40° in the xz plane and yz plane. AR of the main lobe is less than 2 dB in the total scanning range. The gain fluctuation is less than 3 dB during scanning. This letter presents the measurement and simulation results, verifying that the phased array has good performance.

Performance enhancement of cross dipole circularly polarized antenna using parasitic elements

AbstractThis study designs a wideband circularly polarized (CP) cross dipole antenna (CDA) with modified characteristics. The CP CDA consists of four quarter disks, four sector rings, four rotated grounded metal sheets and a pair of vacant quarter rings as a continuous‐phase feeding geometry. In contrast to the conventional vacant quarter rings, the modified vacant quarter rings increase the impedance bandwidth (IBW) and provide a 90° phase difference to obtain CP radiation. In addition to exploiting the quarter disks and sector rings to broaden the CP bandwidth, grounded metal sheets are utilized to widen the CP bandwidth of the proposed antenna. By utilizing the multiple CP resonant modes excited by these elements, the CP bandwidth of the antenna can be improved. As a result, the proposed antenna exhibits broad –10‐dB IBW of 109% (2.13, 0.97–3.29 GHz) and a wide 3‐dB axial ratio bandwidth of 88.9% (2.34, 1.30–3.38 GHz).

A compact ultra-wideband crossed-dipole antenna for 2G/3G/4G/IMT/5G customer premise equipment applications

A compact ultra-wideband crossed-dipole antenna for 2G/3G/4G/IMT/5G customer premise equipment applications

Metamaterial-inspired optically transparent active dual-band frequency selective surface with independent wideband tunability.

This paper presents an optically transparent active bandstop frequency selective surface (FSS) with wideband tunability of two resonance frequencies using the concept of miniaturized element FSS (MEFSS). The proposed design consists of metallic square loop arrays on a new optically transparent substrate as the top layer, a glass interlayer, and periodic patterns of cross dipoles on the substrate as the bottom layer. Two kinds of resonant elements loaded with varactors and the designed bias networks achieve two independent tunable stopbands. The proposed FSS has two large tuning ranges, one is from 1.20 GHz to 2.63 GHz and another is from 2.0 GHz to 5.9 GHz (75% and 99% with respect to the center frequency, respectively). The wideband dual-tuning mechanism is theoretically analyzed and demonstrated by deriving its equivalent circuit (EC) model. The experiment results exhibit reasonable agreement with the numerical simulation responses. This proposed design, with low profile, angular stability, polarization insensitivity, optical transparency, and wideband dual-tunability can play an important role in manipulating electromagnetic wave propagation for manifold applications.

NOAA Image Data Acquisition to Determine Soil Moisture in Arequipa, Perú

In recent years, irrigations have been built on dry areas in Majes-Arequipa. Over time, the irrigations water forms moist areas in lower areas, which can have positive or negative consequences. Therefore, it is important to know in advance where the water from the new irrigation will appear. The limited availability of real-time satellite image data is still a hindrance to some applications. Data from environmental satellites National Oceanic and Atmospheric Administration (NOAA) are available fee and license free. In order to receive data, users must obtain necessary equipment. In this work, we present a satellite data acquisition system with an RealTek (RTL) software-defined radio (SDR) receiver, two 137-138-MHz designed antennas, and Orbitron, SDRSharp, WXtolMG, and MATLAB softwares. We have designed two antennas: a turnstile crossed dipole antenna with Balun and a quadrifilar helicoidal antenna. The antennas' parameter measurements show very good correspondence with those obtained by simulation. The RTL SDR RTL2832U receiver, combined with our antennas and software, forms the system for recording, decoding, editing, and displaying automatic picture transmission (APT) signals. The results show that the satellite image receptions are sufficiently clear and descriptive for further analysis.

Wideband circularly polarized antenna with metallic walls for L-band applications

PurposeTo achieve right-hand circular polarization (RHCP), a 3-dB Wilkinson power divider with a λ/4 phase shifter is used. The crossed-dipoles are placed at almost λ/4 elevation on the ground plane and connected to two coaxial cables. Experiments show that the impedance bandwidth of 49.40% (913.7–1,513.1 MHz) and axial ratio bandwidth (ARBW) of 22.88% (1,145.8–1,441.8 MHz) are achieved.Design/methodology/approachIn this study, a wideband crossed-dipole antenna with circularly polarized (CP) radiation for L-band satellite and radar applications is presented. The proposed CP antenna comprises two orthogonally placed printed dipoles, a quadrature coupler and a box-shaped ground plane.FindingsFurthermore, by fixing the box-shaped ground plane under the radiators, 5.13 dBic RHCP peak gain at 1,300 MHz and maximum half-power beamwidth (HPBW) of 84.5° at 1,170 MHz are realized for the antenna.Originality/valueEight metallic walls are connected to four corners of the substrate to stabilize the radiation properties in this study. Results show that the ARBW and front-to-back ratio are improved and the maximum HPBW around 127° across the operating frequency band is achieved. The proposed CP antenna is a good candidate for Global Positioning System (GPS) L2 (1.227 GHz), GPS L5 (1.176 GHz) and air route surveillance radar system at 1,215–1,390 MHz frequency band.

Miniaturized dual stop band frequency selective surface with broadband linear co to cross polarization conversion ability

This work presents a miniaturized angularly stable frequency selective surface (FSS) on a single layer substrate. Unit cell comprises of convoluted circular rings connected cross dipole and linear arrow headed dipole printed on both sides of the substrate. A closely spaced dual stop band resonances are obtained at 10 and 14.3 GHz with frequency ratio of 1.43. FSS shows a − 10 dB stopband bandwidth (BW) from 7.32 to 11.05 GHz (40.61%) and 12.68 to 15.97 GHz (22.97%) with >30 dB stop band rejection at center frequencies. FSS poses the features of stable performance under change in polarization and angularly stable response up to 60° incident angle. Later the proposed FSS is printed on grounded thick dielectric substrate and it shows broadband reflection type co to cross polarization conversion from 7.2 to 17.32 GHz (82.54%) with polarization conversion ratio >80% and oblique angle stability up to 35°. To the best of authors' knowledge, this is the first time in literature a single unit cell geometry with two different properties, spatial filtering on transmission and polarization conversion on reflection have been designed and analyzed in details. A finite array with size 25 × 25 of the proposed FSS is fabricated and the measured filter response shows a good agreement with simulated performance at normal and oblique incidences. The proposed FSS is used as a reflector of a dual band monopole antenna and the simulation results shows gain improvement of 5.51 and 3.8 dB at the two stopband frequencies.

A band-notched base station antenna using the grounded coplanar waveguide filter

A band-notched dual-polarized crossed dipole antenna for the 2G/3G/4G base station applications using the grounded coplanar waveguide (GCPW) filter is proposed in this paper. Firstly, the crossed dipole antenna using GCPW feeding structure is designed to cover the frequency of 1.7–2.7 GHz. Then, a compact GCPW filter is proposed inside the dipole antenna to realize a notched band of 2.2–2.5 GHz with sharp skirt selectivity. As a result, the proposed antenna has two operating bands of 1.67–2.23 GHz and 2.45–2.75 GHz for VSWR < 1.5 and a sharp notch band of 2.23–2.45 GHz. The proposed antenna is analyzed, fabricated and measured. Measured isolation of higher than 26 dB, half-power beamwidth of about 68° and average gain of around 8.3 dBi across the working band are achieved. The minimum gain in the notched band is −9 dBi, which is 17 dB less than the gain in the working frequency.

Structural Heterogeneity of Human Histone H2A.1.

Histones are highly basic chromatin proteins that tightly package and order eukaryotic DNA into nucleosomes. While the atomic structure of the nucleosomes has been determined, the three-dimensional structure of DNA-free histones remains unresolved. Here, we combine tandem nonlinear and linear ion mobility spectrometry (FAIMS-TIMS) coupled to mass spectrometry in parallel with molecular modeling to study the conformational space of a DNA-free histone H2A type 1 (H2A.1). Experimental results showed the dependence of the gas-phase structures on the starting solution conditions, characterized by charge state distributions, mobility distributions, and collision-induced-unfolding pathways. The measured H2A.1 gas-phase structures showed a high diversity of structural features ranging from compact (C) to partially folded (P) and then highly elongated (E) conformations. Molecular dynamics simulations provided candidate structures for the solution H2A.1 native conformation with folded N- and C-terminal tails, as well as gas-phase candidate structures associated with the mobility trends. Complementary collision cross section and dipole calculations showed that the charge distribution in the case of elongated gas-phase structures, where basic and acidic residues are mostly exposed (e.g., z > 15+), is sufficient to induce differences in the dipole alignment at high electric fields, in good agreement with the trends observed during the FAIMS-TIMS experiments.

FSS Design for Improving Transmission of Microwave Signals and Wireless Security in Modern Buildings

A fractal frequency selective surface (FSS) has been presented for hard coated energy saving glass (ESG) used in modern building architecture. Without FSS, the presence of coating on ESG surface blocks the transmission of useful radio frequency (RF)/microwave signals. The FSS consists of two self-similar cross dipole elements designed in the coating to provide a low-pass response from 0 GHz to 2.1 GHz with two additional band-stop responses at 2.45 GHz and 5.25 GHz. An average transmission loss of less than 2 dB has been achieved in the low-pass band while attenuations of 36 dB and 30 dB have been achieved for 2.45 GHz and 5.25 GHz wireless local area network (WLAN) bands, respectively, providing required security. The low-pass response improves the transmission of useful RF/microwave signals. However, the amount of removed coating due to FSS design is relatively higher, but heat loss has been minimized by pasting an inexpensive thin solar film on the back side of glass. This thin film has provided additional thermal insulation with almost no blockage to transmission of useful RF/microwave signals. A detailed parametric analysis has been done and their effect on FSS structure has been described. An equivalent circuit model has also been presented for the proposed FSS structure. A finite prototype containing 7 × 7 elements have been constructed and evaluated. The measured results have been found to be in good agreement with the simulated results. The proposed FSS design is an excellent candidate for WLAN security.