Добірка наукової літератури з теми "Wideband beam tilt"

In this paper, 3D printed surfaces are presented to study this technology’s application in generating beam tilt for the electromagnetic waves in the Ku-band. Additionally, the input source is maintained by a feed horn that is additively manufactured and is coated with copper spray paint to add conductivity, which is fed by a WR-75 waveguide. The proposed beam tilt generating surface is also referred to as a Beam Deviating Surface (BDS). There is no relative gap between the BDS and the aperture of the horn, which eventually decreased the overall antenna height. The BDS layer is able to deviate the beam for a fixed elevation angle of 22.5∘ and could be consequently rotated along with the rotation of the BDS prototype. The voltage standing wave ratio value is less than two over the operating frequency range, which depicts the wideband behavior. The measured and simulated radiation patterns show that we can tilt the electromagnetic waves in ranges of up to +/−22.5∘ with a minimum side lobe level of −5 dB at frequencies from 10 to 15 GHz. This signifies the wideband characteristic of the proposed prototype, which is achieved by Vero material from Multijet Printing that is a low-cost and rapid manufacturing 3D printing technology.

Antenna beam deflection, along with miniaturization and wideband of the antenna is in demand for practical applications. In this paper, a cylindrical conformal array antenna with a small-tilt forward beam was designed. The microstrip antenna unit was loaded with the artificial electromagnetic structure, which reduced the size of the antenna unit. As a result, the center spacing of the array elements can be shortened with the same array element spacing. The beam deflection angle can be increased in this way without increasing the coupling effect between the parts. Changing the number of line array elements and the number of line arrays can regulate the beam width of E-field and H-field, respectively. The bandwidth of the antenna can be significantly extended by slotting the ground plane. This work implemented a cylindrical conformal array of the antenna’s forward beam with a small dip angle using a cylindrical carrier as an example. The measurement results showed that the angle between the main beam and the carrier axis of the conformal antenna was less than 30°, the bandwidth was more than 30%, and the antenna volume decreased by 40.4%.

Communication with low radar signature platforms requires antennas with low backscatter, to uphold the low observability attribute of the platforms. In this work, we present the design for a Fabry–Perot (F-P) cavity antenna with low monostatic radar cross section (RCS) and enhanced gain. In addition, peak radiation is tilted inthe elevation plane. This is achieved by incorporating phase gradient metasurface (PGM) with absorptive frequency selective surface (FSS). The periodic surface of metallic square loops with lumped resistors forms the absorptive surface, placed on top of a partially reflecting surface (PRS) with an intervening air gap. The double-sided PRS consists of uniform metallic patches etched in a periodic fashion on its upper side. The bottom surface consists of variable-sized metallic patches, to realize phase gradient. The superstrate assembly is placed at about half free space wavelength above the patch antenna resonating at 6.6 GHz. The antenna’s ground plane and PRS together construct the F-P cavity. A peak gain of 11.5 dBi is achieved at 13° tilt of the elevation plane. Wideband RCS reduction is achieved, spanning 5.6–16 GHz, for x- and y-polarizations of normally incident plane wave. The average RCS reduction is 13 dB. Simulation results with experimental verifications are presented.

We discuss the use of measurements of the solar granulation contrast as a measure of optical quality. We demonstrate that for data recorded with a telescope that uses adaptive optics and/or post-processing to compensate for many low- and high-order aberrations, the RMS granulation contrast is directly proportional to the Strehl ratio calculated from the residual (small-scale) wavefront error (static and/or from seeing). We demonstrate that the wings of the high-order compensated point spread function for the Swedish 1-m Solar Telescope (SST) are likely to extend to a radius of not more than about 2″, which is consistent with earlier conclusions drawn from stray-light compensation of sunspot images. We report on simultaneous measurements of seeing and solar granulation contrast averaged over 2 s time intervals at several wavelengths from 525 nm to 853.6 nm on the red-beam (CRISP beam) and wavelengths from 395 nm to 484 nm on the blue-beam (CHROMIS beam). These data were recorded with the SST, which has been revamped with an 85-electrode adaptive mirror and a new tip-tilt mirror, both of which were polished to exceptionally high optical quality. Compared to similar data obtained with the previous 37-electrode adaptive mirror in 2009 and 2011, there is a significant improvement in image contrast. The highest 2 s average image contrasts measured in April 2015 through 0.3−0.9 nm interference filters at 525 nm, 557 nm, 630 nm, and 853.5 nm with compensation only for the diffraction limited point spread function of SST are 11.8%, 11.8%, 10.2%, and 7.2%, respectively. Similarly, the highest 2 s contrasts measured at 395 nm, 400 nm, and 484 nm in May 2016 through 0.37−1.3 nm filters are 16%, 16%, and 12.5%, respectively. The granulation contrast observed with SST compares favorably to measured values with SOT on Hinode and with Sunrise as well as major ground-based solar telescopes. Simultaneously with the above wideband red-beam data, we also recorded narrowband continuum images with the CRISP imaging spectropolarimeter. We find that contrasts measured with CRISP are entirely consistent with the corresponding wideband contrasts, demonstrating that any additional image degradation by the CRISP etalons and telecentric optical system is marginal or even insignificant. Finally, we discuss the origin of the 48 nm RMS wavefront error needed to bring consistency between the measured granulation contrast and that obtained from 3D simulations of convection.

In this paper, 1 × 2 MIMO of Palm Tree Coplanar Vivaldi Antenna is presented that simulated at 0.5–4.5 GHz. Some GPR applications require wideband antennas starting from a frequency below 1 GHz to overcome high material loss and achieve deeper penetration. However, to boost the gain, antennas are set up in MIMO and this is costly due to the large size of the antenna. When configuring MIMO antenna in the E-plane, there is occasionally uncertainty over which antenna model may provide the optimum performance in terms of return loss, mutual coupling, directivity, beam squint, beam width, and surface current using a given substrate size. However, the configuration of E-plane antenna in MIMO has an issue of mutual coupling if the distance between elements is less than 0.5λ. Furthermore, it produces grating lobes at high frequencies.We implement several types of patch structures by incorporating the truncated, tilt shape, Hlbert and Koch Fractal, Exponential slot, Wave slot, the lens with elips, and metamaterial slot to the radiator by keeping the width of the substrate and the shape of the feeder. The return loss, mutual coupling, directivity, beam squint, beamwidth, and surface current of the antenna are compared for 1 × 2 MIMO CVA. A continuous patch MIMO has a spacing of 0.458λ at 0.5 GHz, which is equivalent to its element width. From the simulation, we found that Back Cut Palm Tree (BCPT) and Horizontale Wave Structure Palm Tree (HWSPT) got the best performance of return loss and mutual scattering at low-end frequency respectively. The improvement of directivity got for Metamaterial Lens Palm Tree (MLPT) of 4.453 dBi if compared with Regular Palm Tree-Coplanar Vivaldi Antena (RPT) at 4 GHz. Elips Lens Palm Tree (ELPT) has the best beam squint performance across all frequencies of 0°. It also gots the best beamwidth at 4.5 GHz of 3.320. In addition, we incorporate the MLPT into the radar application.

Abstract Fifth-generation technology is not fully deployed in the world wireless communication till date. Millimeter-wave (mm-wave) band needs to be used due to plenty of available bandwidth and for achieving the goals of 5G such as greater data rate, ultra-high-speed video broadcasting, low latency services, and many more. Wideband antenna is required for 5G applications to access the high speed, low latency Internet services, and ultra-high-definition video streaming. Various bandwidth enhancement techniques have been reported by the researchers for microstrip antennas operating at microwave bands. High link losses, small wavelength, limited coverage, and environmental losses are the major challenges of mm-wave band. To mitigate these issues and satisfy 5G standard, an antenna with wide bandwidth, high gain, narrow steerable beam, high isolation, low side lobe levels, and multiband characteristics is required. Modifications in conventional antenna design techniques are required to achieve broader bandwidth along with stable radiation characteristics, improved gain, and low side lobe levels at mm-wave frequencies. This paper presents the survey of various bandwidth enhancement techniques which has been used in the 5G antennas designed by researchers. Reviews of some wideband 5G antennas with their performance comparisons are also discussed.

An antenna is one of the essential elements in a wireless system, that converts the guided waves in an electronic circuit to unguided waves in the air and vice versa. They are often designed according to the specifications of the underlying system. Compact antennas are required in miniaturised systems such as those used in an aircraft. They are designed by modifying or appending the antenna with additional structures or circuit elements without degrading its responses. In this thesis, the design of compact antennas is investigated with metasurface for two unique purposes - i. wideband applications for detection/sensing application, and ii. spatial modulation to communicate a multipath environment. For wideband applications, a spiral antenna is considered a primary radiator due to its wideband impedance matching and circular polarization (CP) response with simple and planar geometry. It has a bidirectional radiation pattern on either side of the structure, along the axis of the antenna. But in many practical applications, a single-sided radiation pattern is extracted by placing it above a metallic body of a ship or aircraft, which disturbs the freestanding radiation response of the antenna. A conductor placed more than half a wavelength away from the spiral reduces the boresight gain significantly at high frequency, whereas the same placed too close to the antenna degrades the matching and polarization performance at low frequency. These issues have been addressed over years with different techniques, but the design of compact spiral still possesses significant challenges especially when a frequency band of 1-18~GHz is considered. As this research work begins, the spiral is placed at different heights above a metallic conductor and the effects are observed over the considered frequency range. It is followed by an investigation with profiled metallic geometries to combine the benefits of varying antenna heights at different frequencies. Based on these observations, a compact spiral antenna is designed by placing it above a modified conical conductive backing to radiate a CP wave over a wide frequency band. In the next part of this thesis, some of the challenges at low frequencies are addressed using different absorber techniques when the spiral is kept extremely close to a conductor. A hybrid technique consisting of absorbing material and resistors is proposed to design such a compact spiral antenna for wideband application. To improve the performance below 2~GHz, a wideband metasurface absorber is investigated with the spiral. The metasurface possesses significant electromagnetic absorption at low frequency and has been used to design a spiral antenna for 1-18~GHz with an extremely low profile. Another work with a compact spiral antenna approaches to tilt its main beam over a wide frequency range. This investigation is required to compensate for the shift in the antenna main beam due to the supporting structure or to tilt the antenna main beam in a given direction for different purposes. A semicircular lens made of lossy dielectric material is placed above a compact spiral to fulfil this requirement. Effects of different material properties and lens profiles are investigated to arrive at the final design. Since placing the lens along the spiral affects the compactness of the antenna and disturbs the planar profile required in a flush mounting configuration, a sectoral metasurface is designed and printed on the backside of the antenna substrate. The metasurface possesses effective material properties to tilt the antenna main beam at a consistent angle. For all cases, numerical investigations were carried out to optimize the antenna geometries followed by prototyping and characterization of some of these structures. The measured results are compared with the simulated outcomes and the numerical predictions have been verified. This required the design and realization of a wideband balun and appropriate fixtures to integrate various parts of this antenna in a flush-mount arrangement. For a unique wireless application with a compact antenna, a digitally reconfigurable metasurface in the vicinity of a patch antenna is proposed, to realize for the first time a modulator for a spatial modulation technique known as media-based modulation (MBM). MBM facilitates a fast, secure, and multiuser wireless link in a multipath environment (e.g., indoor or office environments) by exploiting the multipath components of the channel. The metasurface works as an electromagnetic window as the power flowing through the unit cell can be electronically controlled by switching a PIN diode embedded within. A significant difference in transmission coefficient is observed between the two switching states of the unit cell. A meander geometry is used to make it compact and the diode is placed between the meander and one of the two contiguous strips that provides the necessary biasing to the diode. Numerical investigations are carried out to characterize the unit cell, and to optimize the array dimensions and the gap between metasurface and antenna. A prototype of the array is fabricated with the necessary control circuitry and a complete wireless link is set up to communicate in a real-time environment. Experiments are carried out in different scatter free and scattering environments in line of sight and non-line of sight configurations to validate the theoretical predictions of MBM. The effects of multipath as a factor that improves communication performance are also validated. In the end, data transmission over a wireless link is also demonstrated using this scheme.
Ministry of Education, Govt. of India and Thales Defence Mission Systems