Boresight Direction Research Articles

Metasurface-Enabled Antiparallel Dual-Beam Rectangular-Waveguide Antenna

We propose a metasurface (MTS) structure integrated at the aperture of a flanged rectangular waveguide to produce dual-beam radiation. The dual beams are antiparallel in an orientation and perpendicular to the boresight direction. The MTS is backed by a dielectric slab to produce a substrate integrated waveguide-like response above the flange. The MTS is engineered to limit the boresight emission from the waveguide aperture, as well as to allow symmetric wave splitting between the MTS and waveguide flange. A lens-like end texturing involving surface tapering and electromagnetic bandgap cells is utilized to enhance the beam directivity at endfire from the flange. The dual-beam radiation exists for all frequencies between 10.5 and 12.4 GHz. The proposed design is modeled via full-wave simulation in commercial software, then validated through the measurement of a fabricated prototype.

Elliptical Ring Antenna Excited by Circular Disc Monopole for UWB Communications

This research proposes a compact elliptical ring antenna excited by a circular disc monopole (CDM) for ultra-wideband (UWB) communications. In the study, time- and frequency-domain pulse distortions of the antenna in the transmission mode were characterized by magnitude and phase of the antenna transfer function (Hrad). The results showed that the gain and magnitude of Hrad in the boresight direction are sufficiently flat with linear phase response. The average antenna gain is 3.9 dBi over the UWB spectrum. The antenna also exhibits low pulse distortion with the correlation factors (ρ) of 0.98 and 0.93 for the fifth-order derivative Gaussian pulse and modulated Gaussian pulse with 6 GHz band rejection. The CDM-excited elliptical ring antenna possesses several attractive features, including wide bandwidth, flat gain, compactness, low cost, and low distortion.

Quarter cylindrical dielectric resonator antenna with circular polarisation for wideband MIMO systems

In this Letter, a quarter cylindrical dielectric resonator antenna (Q-CDRA) with a low profile and circular polarisation (CP) is presented for wideband and multiple-input-multiple-output (MIMO) systems. The approach used to obtain a reduced wideband CP antenna is realised by deforming the geometry of the CDR to a quarter cylinder and using a quasi-spiral feedline to excite two resonant modes in phase quadrature (HEM 11 and HEM 12 ). The proposed design exhibits a wide-impedance bandwidth (BW) of 34% (4.4-6.2 GHz) with a low measured coupling level<;-15 dB, and an axial ratio BW of 24.4% (4.5-5.75 GHz). The antenna gain is stable through the operating BW with a gain peak of 6.4 dBi. In addition, the antenna has a low cross-polarisation in the boresight direction with low envelope correlation coefficient<;0.03. The presented design is suitable for RHCP WLAN applications.

Integrated structural-electromagnetic optimization of cable mesh reflectors considering pattern degradation for random structural errors

To alleviate the effects of random structural errors on the radiation performance and directly guide the structural design of cable mesh reflectors, an integrated structural-electromagnetic optimization procedure is proposed considering the radiation pattern degradation for random structural errors. Based on analytical expressions and the structural sensitivity concept, the radiation pattern is directly expressed as two matrix-form functions with respect to the random structural errors. By applying the pattern calculation into the multidisciplinary design and selecting the average boresight directivity as the objective function, an optimum result with better radiation performance compared with the traditional structural design is obtained. To reveal the fundamentals of the optimum result, the concept of sensitivity analysis of the average boresight directivity with respect to the random structural errors is introduced. The effectiveness and benefits of this study are demonstrated via an offset cable mesh reflector.

Dual‐band dual‐polarized compact planar monopole antenna for wide axial ratio bandwidth application

In this article, a geometrically simple, microstrip line-fed planar monopole structure with slanting edge ground plane is designed to realize the dual-band dual-polarized operation. The proposed antenna consists of a rotated U-shaped patch and an electromagnetically coupled L-shaped parasitic radiating element. Owing to the combination of microstrip line-fed radiating patch and a slanting-edge rectangular ground plane on the opposite side of the substrate, the proposed dual-band antenna can generate broad axial ratio bandwidth (ARBW) in the upper frequency band. The overall dimension of the prototype is only 32 × 32 × 1.6 mm3. The measured results validate that the proposed antenna has two operational frequency bands, 29.84% (1.54-2.08 GHz) for linearly polarized radiation and 71.85% (3.96-8.4 GHz) for circularly polarized radiation. Measured result shows that 3-dB ARBW of the proposed antenna is 73.54% (3.80-8.22 GHz) in the higher frequency band. It shows that the higher frequency band exhibits a left-hand circularly polarized radiation in the boresight direction.

Compact Folded Crossed-Dipole for On-Metal Polarization Diversity UHF Tag

For the first time, the folded crossed-dipole structure is explored for designing a compact metal tag (40 mm $\times $ 40 mm $\times $ 1.6 mm) that can be read in all boresight directions. The tag structure consists of a pair of folded crossed-dipoles which are orthogonally displaced for achieving polarization diversity, where the angular reading range has been extended by removing the null points. In the design, a parasitic metal ring is loaded beneath the radiator for tuning down the tag resonant frequency effectively. Good impedance matching with high power transmission is achievable by employing additional tuning mechanisms such as slotting the radiating dipole arms and adding rectangular patches beneath the slots. Design schemes for optimizing the impedance matching between the antenna and the chip have also been thoroughly discussed. Conjugate impedance match is found to be easily achievable by tuning the design parameters. To understand the impedance characteristics, an equivalent circuit has been derived for the proposed tag antenna. When tested using a linearly polarized reader antenna with a transmitting power of 4 W EIRP, the tag antenna is detectable from 5.6 m to 7.7 m in the boresight and it can be read in all directions.

Integrated 60-GHz miniaturized wideband metasurface antenna in a GIPD process

We propose a miniaturized wideband metasurface antenna for 60-GHz antenna-in-package applications. With the glass integrated passive device manufacturing technology, we introduce a coplanar-waveguide-fed (CPW-fed) ring resonator to characterize the material properties of the glass substrate. The proposed antenna is designed on a high dielectric constant glass substrate to achieve antenna miniaturization. Because of the existence of gaps between patch units compared with the conventional rectangular patch in the TM10 mode, the radiation aperture of this proposed antenna is reduced. Located right above the center feeding CPW-fed bow-tie slot, the metasurface patch is realized, supporting the TM10 mode and antiphase TM20 mode simultaneously to improve the bandwidth performance. Using a probe-based antenna measurement setup, the antenna prototype is measured, demonstrating a 10-dB impedance bandwidth from 53.3 to 67 GHz. At 60 GHz, the antenna gain measured is about 5 dBi in the boresight direction with a compact radiation aperture of 0.31λ×0.31λ0 and a thickness of 0.06λ0.

Design of a cavity-backed spiral antenna using frequency-dependent impedance of a stepped-width arm for low frequency gain enhancement

ABSTRACTThis paper proposes a stepped-width spiral antenna for gain enhancement at a low operating frequency. The frequency-dependent characteristic of the stepped-width transmission line is applied to the spiral arm to enhance the gain at the low end of the operating frequency, and a cavity-backed ground is added to the bottom side of the antenna to further improve the gain at the bore-sight direction. To verify the gain enhancement at the low operating frequency and impedance matching characteristic, we observe the antenna performances such as bore-sight gains and reflection coefficients according to the shape of the spiral arm. The results confirm that the proposed stepped-width structure can enhance the gain at the low operating frequency by improving the impedance matching characteristic.

A Compact Hemispherical Beam-Coverage Phased Array Antenna Unit for 5G mm-Wave Applications

A compact low-profile phased array antenna unit with unidirectional hemispherical beam-coverage for 5G mm-wave applications is proposed in this paper. A four-subarray configuration is used for the proposed structure to achieve unidirectional hemispherical coverage in the boresight direction normal to the substrate. An artificial magnetic conductor (AMC)-backed slot antenna array with an optimal separation distance of 1.9 mm (= 0.31 λ at 28 GHz) is proposed as a subarray. The proposed antenna has increased H -plane beamwidth with the measured peak gain of 11.62 dBi and provides the desired wide inclined beam pattern in the elevation plane. The proposed antenna also offers steered beams over the range within ±45° in the azimuth plane. The hemispherical-coverage, phased array antenna unit composed of the four designed subarrays has overall dimensions of 80.8 mm × 80.8 mm × 2.4 mm. The coverage efficiencies of the proposed phased array antenna unit are 0.82, 0.71, and 0.61 for threshold gains of 5 dBi, 8 dBi, and 10 dBi, respectively, where the maximum solid angle is 2π steradians.

Introducing SOST: An Ultra-Low-Cost Star Tracker Concept Based on a Raspberry Pi and Open-Source Astronomy Software

Absolute attitude estimation sensors provide high accuracy pointing capabilities to spacecraft, but as developed thus far, they constitute a large fraction of CubeSat mission's budget. We introduce SPE Lab Open Star Tracker (SOST), an ultra-low-cost solution that currently provides sub-arcminute precision at a frequency of 1 to 3 estimations per minute in the Lost-In-Space scenario. Our Star Tracker development rests on open source astronomy software, the Raspberry Pi 3 B+, and its camera. We developed a new algorithm to solve the Lost-In-Space problem that works by acquiring an image and comparing it with different stellar catalog segments. We tested our algorithm using images from working satellites. The functioning of our platform was evaluated by using night-sky pictures taken from ground. We also conducted environmental tests of our platform by using a thermal-vacuum chamber. We optimized the catalog segment separation by analyzing the execution time, success rate, precision, and power consumption of the full platform. SOST delivers a mean precision below 1-arcminute for the boresight direction. With a segment separation of 10°, the attitude estimation is found in the 97.3% of the cases with processing time under 20s. The success rate improves to 99.8% by using 5° as segments separation but processing time doubles. This platform is open and freely available to CubeSat researchers interested in further development or deployment.

Science Opportunities from Observations of the Interstellar Neutral Gas with Adjustable Boresight Direction

The interstellar neutral (ISN) gas enters the heliosphere and is detected at a few au from the Sun, as demonstrated by Ulysses and the nterstellar Boundary Explorer (IBEX) missions. Ulysses observed ISN gas from different vantage points in a polar orbit from 1994 to 2007, while IBEX has been observing in an Earth orbit in a fixed direction relative to the Sun from 2009. McComas et al. 2018 reported about an IMAP-Lo detector on board the Interstellar Mapping and Acceleration Probe (IMAP), with an ability to track the ISN flux in the sky. We present observation geometries for ISN gas for a detector with the capability to adjust the boresight direction along the Earth orbit over a year within a multichoice ISN observation scheme. We study science opportunities from the observations as a function of time during a year and the phase of solar activity. We identify observation geometries and determine the observation seasons separately for various ISN species and populations. We find that using an adjustable viewing direction allows for ISN gas observations in the upwind hemisphere, where the signal is not distorted by gravitational focusing, in addition to the viewing of ISN species throughout the entire year. Moreover, we demonstrate that with appropriately adjusted observation geometries, primary and secondary populations can be fully separated. Additionally, we show that atoms of ISN gas on indirect trajectories are accessible for detection, and we present their impact on the study of the ionization rates for ISN species.

Suppression of Antenna Backscatter on a Nanosat Using a Resistively Loaded FSS Absorber

A very thin microwave absorber that can be integrated into the outermost layer of thermal blankets is proposed as a means to electromagnetically decouple payload antennas from spacecraft platforms. The effectiveness of this concept is evaluated for a critical test case where a linearly polarized dipole antenna working at 10 GHz is placed at three different distances above the surface of a $\text{10 cm}$ Nanosat mock-up. This scenario is chosen as the dipole will radiate into both half spaces and any reflections from the vehicle onto which it is mounted will significantly affect its behavior. A resistively loaded frequency selective surface (FSS) absorber is employed to supress the energy contained in the antenna backlobes, and it is shown that the installed performance for all three geometries closely resembles the beam shape of the antenna in isolation. Experimental results have been obtained for one arrangement to confirm that the directive gain is increased by 18 dB in the boresight direction. The FSS absorber is composed of an array of resistively loaded hexagonal patches that are patterned on a 1.12 mm ( $\lambda /25$ ) thick foil-backed polyethylene terephthalate sheet to replicate the physical construction of commercially available space blankets.

Enhancement of boresight radiation for leaky wave antenna array

An array of half-width microstrip leaky-wave antennas (HW-MLWAs) of two uniform elements was designed to obtain maximum boresight radiation. Achieve this, two uniform of HW-MLWAs are placed at 180◦ and fed by a probe located at the center between the elements, two uniforms of HW-MLWAs, loaded terminated by 50Ω lumped element. Two beams from two branches individual merge to form the resultant directive beam. The simulation represents the susceptibility of the proposed array of uniform HW-MLWAs to the radiation broadside direction effectively. The predict bandwidth matched of the array is 582 MHz (4.18–4.76 GHz). The direction of its main beam in boresight happens over a wide 13%, relatively (4.18-4.76 GHz) band. The proposed peak gain at the boresight direction of the array is 9.91 dBi.

Controlling systematics in ground-based CMB surveys with partial boresight rotation

ABSTRACT Future CMB experiments will require exquisite control of systematics in order to constrain the B-mode polarization power spectrum. One class of systematics that requires careful study is instrumental systematics. The potential impact of such systematics is most readily understood by considering analysis pipelines based on pair differencing. In this case, any differential gain, pointing or beam ellipticity between the two detectors in a pair can result in intensity leakage into the B-mode spectrum, which needs to be controlled to a high precision due to the much greater magnitude of the total intensity signal as compared to the B-mode signal. One well-known way to suppress such systematics is through careful design of the scan-strategy, in particular making use of any capability to rotate the instrument about its pointing (boresight) direction. Here, we show that the combination of specific choices of such partial boresight rotation angles with redundancies present in the scan strategy is a powerful approach for suppressing systematic effects. This mitigation can be performed in analysis in advance of map-making and, in contrast to other approaches (e.g. deprojection or filtering), results in no signal loss. We demonstrate our approach explicitly with time ordered data simulations relevant to next-generation ground-based CMB experiments, using deep and wide scan strategies appropriate for experiments based in Chile. These simulations show a reduction of multiple orders of magnitude in the spurious B-mode signal arising from differential gain and differential pointing systematics.

One-dimensional beam-steering Fabry–Perot cavity (FPC) antenna with a reconfigurable superstrate

AbstractIn this work, a new reconfigurable discrete 1D beam-steering Fabry–Perot cavity antenna with enhanced radiation performance is presented. It consists of a probe-fed patch antenna printed on the ground plane and a reconfigurable metasurface acting as the upper partially reflective surface to realize beam steering. By utilizing 6 × 6 proposed reconfigurable unit cells on the superstrate, the beam-steering angle can be effectively enhanced from ±7° to ±17° with fewer active elements and a much simpler biasing network. The proposed antenna was fabricated to validate the feasibility. Good agreement between the simulated and measured results is achieved. Moreover, the measured realized gains are over 11 dBi with a gain variation from the boresight direction to the tilted direction &lt;0.2 dBi.

An Integrated Circularly Polarized Transmitter Active Phased-Array Antenna for Emerging Ka-Band Satellite Mobile Terminals

This paper presents the design, development, and measurement results of a low-cost integrated circularly polarized (CP) active phased-array antenna (CP-APAA) technology with sidelobe level (SLL) control, operating at $Ka$ -band, for high throughput land-mobile satellite communication. The proposed CP-APAA is comprised of ( $4\times 16$ ) 64 elements in a rectangular grid array configuration. Eight commercial monolithic monolithic microwave/millimeter-wave integrated circuit. (MMICs) with eight-RF output channels have been used to control the phase and amplitude over the antenna aperture. For simplicity, the array antenna was designed in three metal layers and fabricated by a low-cost printed circuit board (PCB) technology as a proof-of-concept for a modular and scalable $Ka$ -band PAA with a wide steering angle. Measured radiation pattern shows a right-hand CP (RHCP) pattern with an axial-ratio (AR) level < 3 dB and low pointing error ≤1.5° over a scanning angular range of 0° to ±40°. Moreover, the amplitude excitation of the CP-APAA was tapered exponentially to control and reduce the SLL from 11 to 25 dB in boresight direction. Finally, toward a multibeam array implementation, two RHCP beams have been simultaneously generated at −30° and +20° scan angles.

A Linearly Polarized Patch Antenna With a Continuously Reconfigurable Polarization Plane

A linearly polarized (LP) wave with an arbitrary polarization plane is generated by combining left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) waves radiated from a dual-circularly polarized patch antenna. The polarization plane of the LP wave is continuously controlled by changing the phase difference between the LHCP and RHCP waves by using variable phase shifters composed of a quadrature hybrid and varactor diodes. Experimental results show that the polarization plane rotates continuously from −95° to 107° with a cross-polarization discrimination kept better than 22 dB in the boresight direction at 5.2 GHz.

Beam Steering Conformal Transmitarray Employing Ultra-Thin Triple-Layer Slot Elements

A novel conformal transmitarray with beam steering ability is presented. First, an ultra-thin transmitarray element consisting of three layers of identical square ring slots is developed. The element has a thickness of 0.508 mm (0.04 wavelength in the free space at 25 GHz), achieving a transmission phase range of 330° with a maximum 3.6 dB loss. The element is then applied to a curved transmitarray conformal to a cylindrical surface fed by a standard gain horn with about a 10-dBi gain. A prototype is fabricated radiating a boresight beam with a peak measured gain of 19.6 dBi and an aperture efficiency of 25.1%. Second, when the transmitting surface of the above array is divided into two parts from the middle with different main beam directions, the combined beam can be radiated to an oblique angle with respect to the boresight direction. Using this method, a mechanical beam scanning conformal transmitarray antenna is designed. Its size is about 2.5 times larger than the fixed-beam one and consists of six transmitting surfaces with main beams directed to different angles. By rotating the feed horn to different positions, the main beam of the array can be switched to ±15°, ±10°, ±5°, and 0°. A prototype is fabricated with a stable gain of about 18.7 dBi at all beam angles.

A low profile broadband circularly polarized planar antenna with an embedded slot realized on a reactive impedance surface

A low profile and broadband slotted microstrip patch antenna on reactive impedance surface (RIS) is proposed as a circularly polarized (CP) planar antenna. The proposed structure consists of metallic via, complementary Landolt C-shape slot loaded patch antenna and a 7 × 7 array of rectangular RIS. The inductive RIS, having magnetic energy storing ability, is utilized to achieve miniaturization and enhancement of circular polarization bandwidth (CPBW). The 3-dB CPBW is further increased by using metallic via and embedding a complementary Landolt C shape slot in the second quadrant of the patch. A fabricated prototype was developed that has an overall size of 61.5 mm × 57 mm × 4.08 mm (0.984λ0 × 0.912λ0 × 0.0652λ0 at 4.8 GHz). Measured and simulated results are in good agreement. The measured 3-dB-axial ratio (AR) bandwidth of the proposed antenna is 28.9% (4428–5815 MHz). The measured impedance bandwidth is 46.52% (3743–5976 MHz), which covers WLAN, Wi-Max and 5G communications. The antenna radiates left-handed CP wave at boresight direction with realized gain ranging from 5.3 to 6.8 dBic within the 3-dB AR bandwidth.

Compact near zero index metasurface lens with high aperture efficiency for antenna radiation characteristic enhancement

In this paper, a high gain, aperture efficient, low profile compact, near zero index (NZI) metasurface (MS) lens antenna with enhanced radiation characteristic is proposed. A high-performance transmissive MS is designed by using modified double circular ring resonator as unit cell with measured 3 dB transmission band from 8.80 to 11.90 GHz. It is observed that a triple layer stacked MS lens has the maximum ability to converge the electromagnetic radiation. The focusing mechanism of multiple stacked MS is studied by using measured E- and H-plane radiation pattern plot and H-Field distribution. A high gain low profile antenna is designed by placing the proposed small single surface NZI MS lens over a microstrip patch antenna acting as a microwave source. The proposed NZI MS lens is found to increase the measured gain of E- and H-plane by 10.70 dB in boresight direction at operating frequency 10.15 GHz. The front to back ratio is improved by 8 and 3 dB in E- and H-plane, respectively. The proposed MS lens antenna is able to achieve a broadside gain of 97.50% of the maximum gain achieved due to ideal effective radiation surface.