Cross-dipole Elements Research Articles

A compact polarization independent stop band frequency‐selective surface for WLAN shielding

AbstractThis paper presents the design and prototype development of a compact frequency‐selective surface (FSS) for shielding WLAN signals. The FSS unit‐cell geometry is evolved by modifying the arms of the conventional crossed dipole element. The footprint of the unit cell is only 6 mm × 6 mm × 1.6 mm. The proposed FSS offers stop band characteristics at 5 GHz for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the FSS offers angular stability up to 60°. A prototype of the proposed FSS is fabricated and measured to validate its simulations. Measured bandwidth of the stop band is 410 MHz, referenced at −20 dB for both TE and TM modes. Equivalent circuit model of the FSS is derived and the results are compared with the simulations.

Investigation of mutual coupling coefficients in dual-polarized antenna arrays

Background. Antenna arrays are widely used in various fields of radio engineering, such as radio and telecommunications, satellite communication systems, etc. One of the important characteristics of an antenna array is its radiation pattern. The estimation of impedance matrices, scattering matrices, and partial radiation patterns is usually performed based on the results of numerical electrodynamic modelling. In the case of a large number of antenna elements, such modelling and optimization of the array requires significant time.
 Aim. To investigate the mutual coupling between dual- polarised antenna elements included in a linear antenna array.
 Methods. Modelling of antenna arrays based on cross-dipole elements was performed using methods of electrodynamic modelling software. The study of the mutual coupling of antenna elements in the antenna array and verification of the developed mathematical model were carried out by numerical methods.
 Results. A physical interpretation of that there is no almost interaction between the elements operating in orthogonal polarizations, and the coefficients of mutual coupling decrease with increasing distance between antenna elements is given. Proposed a simplified model of mutual coupling, which reduces the computational complexity of the problem of determining the mutual coupling matrices.
 Conclusion. It is developed a mathematical technique that allows to calculate the characteristics of antenna arrays with a large number of antenna elements, meanwhile electrodynamic modelling is carried out only for an isolated antenna element and a two-element array.

A Transmissive Metasurface Generating Wideband OAM Vortex Beam in the Ka-Band

In this paper a wideband transmitting metasurface is proposed to generate the orbital angular momentum (OAM) vortex beam in the Ka-band. The proposed unit cell is a novel combination of dual-square loops and a cross dipole element printed on four dielectric layers separated by an airgap. This combination of two types of elements helps to attain a linear transmission phase response with more than a 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> phase compensation range with a transmission magnitude equal to or better than 1.1 dB. The proposed structure of the unit cell is also suitable for dual polarized applications due to its symmetrical configuration. The proposed metasurface is also fabricated and measured to verify its simulated performance. The overall measured outcome shows that the proposed structure has successfully achieved wideband performance for the OAM vortex beam with +1 mode. The overall mode purity is greater than 72% from 28.0 to 38.0 GHz, which is about 33.3% OAM bandwidth. Moreover, the peak gain of 23.8 dBi is achieved with 22.1% aperture efficiency.

A Ku Wideband Circularly Polarized Microstrip Antenna Array with Low Profile Crossed-Dipole Element

This paper presents a novel Ku wideband circularly polarized (CP) antenna array composed of crossed-dipole element (CDE) and fed through sequential rotation (SR) feeding technique. Unlike the traditional CP-CDE fed by coaxial cable that usually works at low frequencies, the proposed CDE consists of two orthogonal heart-shaped patch dipoles that can work at frequencies as high as Ku-band, at the same time achieving a larger bandwidth. A feeding structure is proposed without welding, so potential errors in the antenna assembly process can be mitigated. A 2 × 2 CP antenna array with wideband SR feeding network is designed based on the CDE to further expand the axial ratio (AR) bandwidth. The designed antenna array is fabricated using the multilayer printed circuit board (PCB) technology and measured in anechoic chamber using the planar near-field measurement facility. The measured results show that −10 dB impedance bandwidth of 44% (11.6–18.15 GHz) along with 3 dB AR bandwidth of 38.7% (12–17.65 GHz) and 3 dB gain bandwidth of 34.6% (12.2–17.3 GHz) as well as 11.02 dBic peak gain have been achieved while maintaining a lower profile.

Single-layer frequency selective dual-band reflectarray operating at 28 GHz and 39 GHz

We report a single-layer frequency selective dual band reflectarray operated at 28 and 39GHz simultaneously. The reflectarray consists of cross dipole and spiral elements aligned on the surface of a substrate and dual band frequency selective surfaces aligned on the rear side. We aligned the cross dipole and spiral elements that can control the reflection direction at 28 and 39GHz aligned on the same plane of the substrate, resulting in a simultaneous dual-band control of the reflection direction up to ±30° independently. Furthermore, the dual band reflectarray showed higher transmittance at frequencies except for the target frequencies, indicating the reflectarray function only at 28 and 39GHz and does not interfere with the other communication bands.

A Size-Reduced, Circularly Polarized, Log-Periodic Dipole Array

A single-feed, circularly polarized, log periodic dipole array (CPLPDA) with size-reduced, cross-dipole elements is proposed. Size reduction in elements is achieved with curved T-shaped, top loading. Compared to the full-sized CPLPDA elements, the achieved element-length reduction is 50%. With six elements, the antenna shows a -10-dB impedance bandwidth (IBW) of 87.0%, and a 3-dB axial ratio bandwidth (ARBW) of 50.0% in measurement. The common bandwidth (CBW) between the -10-dB IBW and 3-dB ARBW of the CPLPDA is 50.0%. The peak realized gain in the direction of the shortest element is 6.60 dBi over the CBW.

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.

The effects of mutual coupling and polarization on the performance of steered-beam adaptive arrays

The polarization of the electromagnetic waves impinging on adaptive antenna arrays has a significant impact on their performance. The effects of desired and undesired polarized signals and mutual coupling on the performance of adaptive antenna arrays with an electronically steerable beam are studied based on the ratio of the output signal to the interference plus noise. The performance of adaptive antenna arrays composed of single- versus cross-dipole antenna elements is studied to illustrate the effect of signal polarization. The experimental and simulation results show that, for randomly polarized signals, adaptive antenna arrays using cross-dipole elements provide better performance compared with those using single dipoles. However, if the desired signal polarization is well known, single-dipole antenna arrays offer better performance.

Design of a Cylindrical Crossed Dipole Phased Array Antenna for Weather Surveillance Radars

We present a cylindrical dual-polarization phased array antenna for weather surveillance radars that features high isolation, matched copolar beams, low sidelobe levels, and adaptive null steering. We present a crossed dipole antenna element to replace the patch antenna on the currently deployed cylindrical polarimetric phased array radar (CPPAR). The crossed dipole element offers suppressed surface wave and lower coupling between adjacent elements of an array. As a result, we achieved lower backlobe and sidelobe levels, and a higher match between copolar beams of CPPAR compared to the currently deployed multi-layer patch antenna. Further reduction of the sidelobe level and adaptive null steering are obtained using a modified particle swarm optimization. The proposed null steering mitigates the interference among the four concurrent beams of a cylindrical phased array radar. The improvement in CPPAR radiation characteristics has been verified by comparing the presented crossed dipole antenna’s radiation patterns and the existing aperture coupled patch antenna. The proposed crossed dipole phased array can benefit national weather radar networks to provide accurate multiparameter measurements enabling reliable observation of severe weather phenomena.

Development of Method of Moment Based Programme to Analyze Cross Dipole Frequency Selective Surface and its Verification with Measured Results

Theoretical analysis of frequency selective surface comprising of cross dipole elements has been presented in this paper. Algorithm for theoretical analysis based on method of moment has been implemented by MATLAB programming. Theoretical, simulated and experimental results are compared. Simulated result is obtained by ANSOFT designer version 2.2 software. Experimental result is obtained by standard microwave test bench. Good parity in the results is observed. The presented FSS Structure has relevance in the field of mobile and satellite communication.

A low‐profile circularly polarized transmitarray antenna using rotated cross dipole elements

A low profile circularly polarized (CP) transmitrarray using double-layer cross dipole elements is presented in this letter. The proposed element exhibits an overall thickness of only 0.22λ0, which offers the advantages of light weight, easy fabrication, and low cost compared to conventional transmitarray elements. The transmission coefficient of the element is analyzed by Ansys HFSS, and the results show that the element manifests a high transmission rate and good CP performance. Then, by using angular rotation technique, transmitarray with this type of element is designed, fabricated, and tested. The size of the transmitarray is 6.6 × 6.6λ0 at the center frequency of 10 GHz. The measured peak gain is 22.5 dB at 9.5 GHz, resulting in an aperture efficiency of 36%. The measured 1-dB gain and 3-dB axial ratio bandwidths are 10.2% and 12%, respectively.

Wideband Dual-Polarized Omnidirectional Antenna Array for Base-Station Applications

A compact wideband dual-polarized omnidirectional antenna array for base-station applications is proposed. It consists of ten antenna units. To generate ±45° dual-polarized ominidirectional radiation with low gain variation for each unit, three close-in crossed-dipole elements are uniformly arranged in a regular triangle shape and excited by two 1-to-3 power dividers with equal magnitude and phase, acting as a dual-polarized loop antenna. To obtain wide impedance bandwidth for each unit, the dipole element and power divider are designed to operate in a wide and well-matched band. Moreover, the unit features steady structure, easy fabrication, and high scalability, which makes it convenient to form an antenna array. To achieve a high gain for base-station applications, a ten-unit antenna array is designed, fabricated, and measured. A wide impedance bandwidth of 52.3% (1.62–2.77 GHz) for standing-wave ratio (SWR) < 1.5 and a high port-to-port isolation of 26 dB are realized. It also features a high gain of 10.3 ± 0.9 dBi and a small gain variation of less than 2.5 dB in the horizontal plane. Additionally, the sidelobe suppression of 18 dB and null filling below the main vertical beam are obtained by the designed feeding networks. These results make the proposed design attractive in base-station applications.

Development of polarisation reconfigurable omnidirectional antennas using crossed dipoles

A new method for the development of polarisation reconfigurable omnidirectional antennas is presented. Four crossed-dipole elements around a cylinder are used to construct an omnidirectional antenna. By switching on/off four PIN diodes for each crossed-dipole element, three types of polarisation reconfigurable omnidirectional antennas are realised, including vertical or horizontal polarisation (VP/HP), ±45° slant polarisation (SP), and left-handed circular polarisation or right-handed circular polarisation (LHCP/RHCP). The VP/HP, ±45° SP, and LHCP/RHCP reconfigurable omnidirectional antennas are simulated, fabricated, and measured, respectively. Simulated and measured results show that all the three reconfigurable omnidirectional antennas feature good omnidirectional patterns with gain variations of <;2 dB in the horizontal plane.

FSS Based Circular Polarizer for High-Speed Wireless Communication at 75 GHz

An FSS based circular polarizer for high-speed wireless communication at 75 GHz is presented. It has been designed on a low loss substrate with cross-dipole elements. Both simulation and measured results showed more than 98% circular polarization at 75 GHz. Moreover, 3 dB axial-ratio bandwidth of 6.8 GHz (Simulation) and 7.8 GHz (Measured) has been achieved. The proposed design has many advantages over the recently published research such as simplicity, low-profile, percentage bandwidth, frequency of operation and relative insertion loss.

Controlled high‐gain of an UWB antenna using cross dipole RFSS based on PIN diode

AbstractThis work presents an ultra‐wideband antenna with controlled gain. The gain control of antenna is achieved by employing a Reconfigurable Frequency Selective Surface (RFSS) as superstrate which is formed by 4 × 4 array of cross dipole. The filtering characteristics of the FSS are variable and depend on the PIN diodes state. The RFSS behaves as an array of cross dipole elements with stop‐band response when all diodes are in the OFF‐state and as an array of square slots with pass‐band response when the diodes are in the ON‐state. The gain improvement depends on the PIN diodes biasing. Simulation and measurements of return loss and antenna gain are presented, demonstrating changes and improvement in the antenna gain.

Reconfigurable cross dipole: hash frequency selective surface

The authors present a reconfigurable frequency selective surfaces (RFSS) structure with two states based on the cross-dipole element. The structure is designed to behave as an array of cross-dipole elements in one state, and as an array of hash elements in the other state. The cross-dipole patch array has a stop-band filter response, and the hash array behaves as a pass band filter at the design frequency of 12.5 GHz. The frequency response of these filters is analysed using the equivalent circuit method. Computer simulation technology (CST) software simulations and experimental results are used to validate the RFSS design.

Generation, reception and separation of mixed-state orbital angular momentum vortex beams using metasurfaces

In this paper, metasurfaces are designed, fabricated and experimentally demonstrated to transmit and receive a mixed-mode orbital angular momentum (OAM) vortex wave. Firstly, the theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce the mixed-state vortex wave. Then, simulations and near-field scanning experiments are performed to verify that mixed-state vortex waves can be generated and received by using metasurfaces. The receiving experiments for mixed-mode OAM beam are conducted in the near-field zone, covered frequency band from 4.5 GHz to 7.0 GHz. In transceiving experiments, the TX is the proposed reflective metasurface generating the mixed-state OAM wave (P = 2, l1 = 1, l2 = 2), which is composed of square loop elements. The RX is an OAM receiving metasurface composed by crossed dipole elements, which can receive OAM mode l = 1 in vertical polarization but OAM mode l = 2 in horizontal polarization. Experimental results show that mixed-state vortex waves can be detected, received and separated by pure OAM-mode transmitting and receiving reciprocal metasurfaces. The proposed method paves an effective way to generate and detect the OAM vortex wave of mixed modes for microwave wireless communication and detection applications.

The Path to a Transportable Ionospheric Heater—Tuning Methods

A tunable electrically small antenna (ESA) designed to be naturally resonant at 100 MHz is evaluated for its range of tuning and feasibility for use in a mobile ionospheric heating (MIH) setup. The overarching goal is to match the ionospheric heating performance of the 180 element array at the high frequency active auroral research program (HAARP), which occupies approximately $1.2 \times 10^{5}~\text{m}^{2}$ of land in Gakona, Alaska. While each HAARP crossed dipole element occupies 440 $\text{m}^{2}$ of land and is tunable in the range of 2.7–10 MHz using automatic matching networks, the presented ESA approach is aimed toward enabling the fabrication of a transportable MIH array platform capable of high continuous wave (cw) power, albeit with a linear dimension five to ten times smaller than that of an equivalent dipole antenna. It is elucidated that the capacitively tuned ESA is continuously tunable to a frequency about 50% lower than that of the ESA’s base frequency, albeit the resonant antenna structure carries a fractional bandwidth of merely 1%–2%.

Ka/W Dual-Band Reflectarray Antenna for Dual Linear Polarization

In this letter, a dual-layer dual-band dual linear polarization reflectarray is proposed, which consists of three different types of dual-layer elements: cross-dipole element for the Ka-band, modified phoenix square loop, and square patch for the W-band operation. A new unit choice strategy based on the characteristic of the proposed unit is presented to eliminate the coupling effect and improve the local periodic condition. The proposed reflectarray is fabricated on a dual-layer Taconic substrate, which covers an area of 600 × 600 mm2. Its measured peak gain is 44.1 and 49.6 dB at 35.5 and 94.05 GHz, respectively, and maximum sidelobe level is –22 dB. The proposed reflectarray architecture may find applications in missions requiring dual-frequency operations with these types of separations.

A novel wideband and circularly polarized cross-dipole antenna

In this paper, we present a novel wideband circularly polarized (CP) composite, called cavity-backed crossed dipole antenna for 2.45 GHz industrial, scientific, and medical (ISM) band wireless communication. To excite the CP radiation effectively, a curved-delay line providing an orthogonal phase difference among the cross-dipole elements is attached at corners of the sequentially rotated elements. By choosing a proper radius of the curved-delay line, a wide input impedance of the antenna can be realized. Unlike conventional cross-dipole antennas, the proposed cross-dipole antenna is designed with an open stub added to the radiating arms of the dipole so that both impedance and axial ratio bandwidths are enhanced. The antenna is center-fed by a 50-Ω coaxial cable and is placed above a cavity-backed reflector to obtain a directional CP radiation pattern. With the advantage of being center-fed, a symmetric CP radiation pattern can be achieved across the entire operating bandwidth. To further improve the directivity and the radiation pattern, a rectangular cavity-backed reflector is used. Simulated and measured results confirm that the proposed antenna has good CP characteristics. The proposed antenna obtains a broad 3-dB axial ratio bandwidth of 49% (1.20 GHz, 1.96–3.16 GHz) and an impedance bandwidth of 67.7% (1.66 GHz, 1.69–3.35 GHz) for reflection coefficient (S11) ≦ −10 dB. It also yields an average CP gain of 9.2 dBic across the operating bandwidth and a peak CP gain of 10 dBic. Copyright © 2016 John Wiley & Sons, Ltd.