Boresight Direction Research Articles

Interferometric Phase Transmitarray for Spatial Power Combining to Enhance EIRP of Millimeter-Wave Transmitters

An interferometric phase transmitarray is proposed for spatial power combining to enhance the equivalent isotropically radiated power (EIRP) of the millimeter-wave (mmW) transmitters. The study shows that the multiple beams emitting from the ideal point sources located at different positions are combined into one beam to radiate in the boresight direction of the transmitarray, namely, achieving spatial power combining. As an example, the prototyped transmitarray fed by two patch antennas operating over the bandwidth of 23–27 GHz shows that with the spatial power combining, the proposed antenna achieves the combined gain realized by two feeds of 19.6 dBi at boresight 2.5 dB higher than the realized gain of the single feed, so that the EIRP of the two-feed transmitarray is enhanced by 5.5 dB because of 2.5 dB from the gain enhancement of two-feed transmitarray and 3 dB by the two-way power combining.

Automotive communication applications based circular ring antenna with reconfigurability and conformal nature

SummaryThis work presents a compact and conformal frequency reconfigurable antenna for automotive applications. The antenna is designed on a liquid crystal polymer substrate of footprint 40 × 30 × 0.1 mm3. The proposed antenna is having coplanar waveguide feeding with a circular ring radiating element and a pair of parasitic circular elements to obtain the multiband operation. The proposed antenna is studied for frequency reconfigurable characteristics by placing the PIN diodes as switching elements in the desired locations and obtained the reconfigurability in the 4.5–6.5 GHz region. Further, the bending effects of the antenna with respect to its operating bands and the conformal effects with PIN diodes for the reconfigurable performance make this study a trailblazing work. The simulated and measured results describe that the on‐glass conformal antenna is covering 1.58–2.33 (GPS, PCS, GSM1800/1900), 3.22–3.7 (WiMAX), and 4.25–6.8 GHz (WLAN, DSRC, WAVE, V2X) bands for vehicular communications with various switching cases. The obtained gain varies from 3.2 to 4.1 dB in the boresight direction and 6.9 to 9.8 dB in the lateral directions of the vehicle with placement on the vehicle body. As per the obtained results, the antenna is suitable to use for conformal usage on the windshield glass of the vehicle for connected driving scenarios.

Norman window slot antenna with sectoral feed backed by linear phase reflector for ultra wideband applications

An ultra wideband (UWB) slot antenna is proposed, developed, and experimentally validated in this article. The Norman window-shaped UWB slot antenna demonstrates stable radiation characteristics in both directions—zenith (θ = 0°) and nadir (θ = 180°) over the entire UWB frequency range (3.1–10.6 GHz) as observed in both simulations and experiments. A linear phase reflecting UWB frequency selective surface (FSS) is proposed by printing two orthogonal layers of pair of double rectangular loops on the same side of dielectric substrate as a merged frequency selective surface (MFSS). The UWB MFSS is then loaded with the slot antenna and the impact of MFSS on the impedance and radiation characteristics in different configurations of antenna and MFSS together is studied. One configuration with optimum solution is developed for experimental validations followed by the analysis of its radiation characteristics. The proposed antenna demonstrates a directional radiation pattern due to suppression of back lobe radiation when integrated with the UWB MFSS. The proposed antenna demonstrates maximum gain of 7.86 dB with a gain enhancement of 3.6 dB in boresight (θ = 0°) direction when MFSS is applied as a reflector to opposite side of the antenna slot.

Design of a Compact Indirect Slot-Fed Wideband Patch Array with an Air SIW Cavity for a High Directivity in Missile Seeker Applications

This research proposes a compact indirect slot-fed wideband patch array antenna for a missile seeker application. The proposed single antenna consists of three dielectric layers for a radiator, an air substrate-integrated waveguide (SIW) cavity, and an indirect feeding network. The rectangular patch is used as a radiator on the first substrate layer, and the air SIW cavity (ASIWC) is employed to obtain high directivity and low mutual coupling characteristics in the second substrate layer. In the third layer, an indirect feeding structure is used to achieve the wideband characteristics in the Ka-band. The single element is extended to a 4 × 1 linear array with fabrication, and the fabricated array characteristics are measured in a full anechoic chamber. The measured operating fractional frequency bandwidth is 9.2%, and the measured array gain is 11.7 dBi at the bore-sight direction (θ0 = 0∘).

A beam broadening method for phased arrays in wireless communications

5G and IEEE 802.11ay introduce the use of the millimeter band as one promising solution to provide broadband wireless communication at multi-Gb/s user data rate. Due to the severe path-loss at such frequencies, it is generally assumed that large antenna arrays are used at the base station to steer narrow beams and build highly directional communication links towards the terminal points. However, broader and less directional beams are also of high interest in some of the steps involved in the establishment or the maintenance of the communication links . Indeed, search of a large area by narrow beams becomes too time consuming and link outage becomes more critical, thus affecting the latency and the robustness of the communications. A method enabling an adaptation of the beam widths is then worthwhile to consider. In this article, we investigate how narrow beams naturally produced by large antenna arrays can be broadened to adapt the beam width to a desired angular sector. We consider that the multi-antenna processing is performed by phase shifters on the radio-frequency stage since fully digital beamforming is hardly feasible in practice at such high frequencies. The main idea of our systematic phase-only beam broadening technique relies on the determination of a quadratic phase excitation law from a desired beam width and steering angle. We first lead a thorough analysis of the radiation behavior regarding the coefficients of such quadratic excitation. We then propose a calculation method for determining the polynomial coefficients as a function of the desired beam width and steering angle. This non-iterative beam broadening method is described for boresight and non-boresight directions and is intended for discrete antenna arrays.

A compact triple band circular polarized slotted microstrip patch antenna with low frequency ratio

A pentagon shaped triple band circular polarized (CP) slotted microstrip patch antenna with asymmetric single microstrip feed line is designed. The proposed patch antenna is loaded with a pair of asymmetric slits, a pair of symmetric slots and a triangle shape truncation at the right side of the antenna. The antenna is drafted within the size of 0.43λ × 0.43λ and resonates at 2.17, 3.08, and 3.48 GHz with impedance bandwidth (IBW; IS11I < −10 dB) 2.14–2.20, 3.06–3.10, and 3.45–3.51 GHz, respectively. The Axial Ratio Bandwidth (ARBW; AR < 3 dB) is obtained as 2.17–2.40, 3.07–3.10, and 3.48–3.54 GHz at the three resonances which almost cover the IBW. An additional feature of the design is that the CP bands are very closely spaced with frequency ratio of 1.36 between first and second CP resonances and 1.13 between second and third CP resonances. The obtained gain at three resonances is 3.9, 3.79, and 4.81, respectively. The CP radiation patterns are found to be stable with good right hand CP (RHCP) to left hand CP (LHCP) isolation at the boresight direction. This antenna is suitable for S-band applications. The advantage of the proposed design has been highlighted with respect to multiband CP, CP frequency ratio, compactness and RHCP to LHCP isolation. A prototype of the proposed design is fabricated and the measured results are in accord with the simulated results.

Effects of petal misalignment errors on radiation pattern of deployable reflectors

ABSTRACT As one source type of random surface errors, misalignment errors usually lead to petal rigid body rotation or translation for petal-type deployable reflectors, which deteriorate petal-type surface from its ideal parabolic shape. To evaluate the effects of misalignment errors on antenna performance, a novel method is proposed to reveal the degradation of petal misalignment errors on average radiation pattern for petal-type deployable reflectors. Based on coordinate transformations, the surface deviation from ideal parabolic shape caused by petal misalignment errors is introduced into an explicit far-field formula, which promotes the far-field formula as explicit functions of petal misalignment displacements in this novel method. By assuming Gaussian distribution of misalignment errors, the average radiation patterns with varying standard deviations of petal misalignment errors are obtained. Compared with the existing methods of random error characterisation, the effectiveness of the proposed method is verified. Simulations show that among the petal misalignment errors, both the petal rigid body rotation around hinge link axis and translation along boresight direction provide deterioration effects on antenna radiation pattern, and the proposed method can provide design guidelines for hinge structural design.

Coverage and Meta Distribution Analysis in Ultra-Dense Cellular Networks With Directional Antennas

This article proposes a one-tier ultra-dense cellular network framework based on the characteristics of directional beamforming to explore the downlink signal-to-interference ratio (SIR) performance. The features of the proposed cellular network include: small base stations (SBSs) are equipped with directional antennas; the beam boresight directions of antennas are adaptively adjusted with the locations of users on the two-dimensional horizontal plane while the boresight directions are perfectly aligned with their associated users. In addition, an angle fading model, which follows from the exponential distribution, is developed to simulate the signals attenuation of interference links. The angle fading of the interference signals depends on the angle offset between the locations of users and the beam boresight directions of their interfering SBSs. With the assistance of stochastic geometry, the analytical expressions of coverage probability and average ergodic rate are derived by combining with the probability density function of angle offset variable. Then, the meta distribution of SIR is obtained to capture the performance changes of individual links for users. The numerical results indicate that the performance advantages of the proposed directional network obviously exceed that of the conventional isotropic antennas case. Monte-Carlo simulations validate the correctness of numerical results.

Performance Analysis of WDM in LoS Communications With Arbitrary Orientation and Position

This letter considers the wavenumber-division-multiplexing (WDM) scheme that was recently presented by Sanguinetti <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2022) line-of-sight communications between parallel (i.e., side-by-side) spatially-continuous electromagnetic segments. Our aim is to analyze the performance of WDM, combined with different digital processing architectures, when the electromagnetic segments have an arbitrary orientation and position. To this end, we first show how the general electromagnetic MIMO (multiple-input multiple-output) model from Sanguinetti <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2022) can be particularized to the case of interest and then use numerical results to evaluate the impact of geometric parameters (e.g., horizontal and vertical distances, azimuth and elevation orientations). It turns out that WDM performs satisfactorily also when the transmit and receive segments are not in boresight direction to each other.

79-GHz SIW slot-coupled patch antenna array with low cross polarization and wide beamwidth

ABSTRACT A 79-GHz wide-beam patch antenna and 1×8 antenna array with low cross-polarization levels are presented for automotive radar applications. A substrate-integrated-waveguide slot-coupled scheme was employed to reduce the cross-polarization level of the patch antenna. Two parasitic elements were added to the main patch to form a three-element subarray for beamwidth enhancement. The simulated E-plane half-power beamwidth (HPBW) of the patch antenna is 148°, and the cross-polarization level is 32.5 dB less than the co-polarization level at the boresight direction. For further gain enhancement, a 1×8 patch array was designed and fabricated. The measured results show that the proposed design can offer a wide HPBW of 144° and a low cross-polarization level of 28.3 dB less than the co-polarization level at 79 GHz.

A Portable 5.8 GHz Dual Circularly Polarized Interferometric Radar Sensor for Short-Range Motion Sensing

The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX–RX isolation. However, they are subject to increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX–RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX–RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX–RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment.

Bandstop filtering for integrated substrate gap waveguide high‐gain and wideband slot antenna for 5G

Slot antenna based on microstrip line and waveguide is a popular design for future 5G antennas. To improve performance of slot antenna, a high-gain wideband slot antenna based on integrated substrate gap waveguide (ISGW) is presented, in which a stepped impedance feeding line is adopted to broaden bandwidth, and ISGW is used to increase gain. First, the transmission characteristics and the effective relative permittivity of ISGW is discussed and calculated, with operation band from 25 to 45 GHz. The antenna has a passband of 24.9–38.1 GHz, that is, almost Ka band, and an average gain of ~9 dB. Further, bandstop filtering (BSF) characteristic is introduced in the above wideband antenna to achieve filtering antennas for 5G millimeter-wave (mm-wave) bands of 24.75–27.5 GHz for China, and 26.5–29.5, 27.5–28.5, and 37–40 GHz for n257, n258, and n260 of 5G new-radio (NR). The BSF is obtained by etching U-shaped CSRR on feeding patch of the antenna. First- and second-order BSF are achieved by etching first and second U-shaped CSRR on the antenna feeding patch, respectively, thus correspondingly one bandstop resonance at 34.6 GHz, and two bandstop resonances at both 32.5 and 34 GHz are obtained. It is found that the passband performance is unchanged, but the stopband radiation drops sharply at the boresight direction. The three antennas (wideband, and first- and second-order BSF antennas) proposed are all fabricated and verified.

Research on Space-Based Visible Detection for Conical Space Targets

We conducted research into the visible light detection of conical space targets and proposed a method to determine the caliber of a space-based detection system. We constructed a three-dimensional conical space target radiation transfer model and analyzed the effect of the phase angle between the solar incident direction, the detector’s bore sight direction, and the conical target inclination on the radiation intensity of the space target received by the detector. Finally, we obtained the threshold caliber which can meet the detection requirements of the system with the system signal-to-noise ratio as the evaluation standard, and we took the SBV sensor as an example to verify that the caliber determination method in this paper is effective.

Phased Array Calibration Based on Measured Complex Signals in a Compact Multiprobe Setup

Phased array calibration is typically carried out in plane-wave conditions, which requires expensive far-field setups. This letter presents a novel phased array calibration method based on measured complex array signal, which works in the cost-effective compact testing setup. The basic principle is to employ multiprobe antennas in a short measurement distance such that we can effectively retrieve the array element patterns in the boresight direction based on the recorded complex signals at the multiple probes using the interpolation technique. Both theoretical derivations and measurement validations are provided to demonstrate the effectiveness of the proposed method.

Design of a High-Durability X-Band Patch Antenna with a CPW Feeding Network Based on a Durability Evaluation Analysis

In this paper, we propose a high-durability X-band patch antenna with a coplanar waveguide (CPW) feeding network that can directly connect the upper antenna and the lower transmitting receiver modules without additional cabling. To improve the durability of the antenna, both the sub miniature push-on (SMP) connector and the feed-pin are separated through the CPW layer. This separated structure can minimize the deterioration of the antenna performance when the unwanted movement of the SMP connector occurs from external shocks. To verify the design feasibility, the reflection coefficient and radiation patterns of the proposed antenna are measured in a full anechoic chamber. The reflection coefficient of the proposed antenna is −27 dB at 10 GHz, and the operating frequency bandwidth (|Γ| &lt; −10 dB) is 4.7% (9.82~10.29 GHz) in X-band. The proposed antenna has a maximum gain of 5.7 dBi at the bore-sight direction. In addition, the durability evaluations of the proposed design according to unwanted SMP connector movements provoked by external shocks are investigated using Monte Carlo simulations. The results demonstrate that the proposed high-durability antenna design is suitable for military ship applications that involve exposure to various external shocks.

Wideband, High-Density Circularly Polarized Array With Reduced Mutual Coupling and Enhanced Realized Gain

A planar single-layer parasitic swastika-shaped structure, which serves as an effective isolator, is developed for mutual coupling reduction in wideband, high-density circularly polarized (CP) arrays. A closely spaced two-element CP antenna array demonstrates the efficacy of the approach. The currents induced by the CP coupling are effectively canceled out when this isolator is integrated into it. The antenna elements are co-planar. They are arranged with a center-to-center distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4\lambda _{\mathrm {L}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {L}}$ </tex-math></inline-formula> being the wavelength of the lower bound of the array’s operational bandwidth) and have an extremely small edge-to-edge distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.024\lambda _{\mathrm {L}}$ </tex-math></inline-formula> . The parasitic element yields an increase of the isolation level between the antenna elements of more than 9.4 dB over the entire operational band, with a maximum improvement of 20.4 dB. Moreover, the antenna elements realize a modest maximum gain improvement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.2$ </tex-math></inline-formula> dB in the boresight direction over the same band. The overlapped impedance matching and 3 dB axial ratio (AR) bandwidths cover the range of 1.7–2.7 GHz, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 45$ </tex-math></inline-formula> % fractional bandwidth. A prototype was fabricated and measured; the measured results are in good agreement with their simulated values.

Broadband Circularly Polarized Microstrip Patch Antenna With Diamond-Shaped Artificial Ground Structure

This paper presents a broadband circularly polarized patch antenna with an artificial ground structure (AGS), which has rotated rectangular unit cells with respect to the sides of the rectangular ground plane, as a polarizer. A two-element ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 1$ </tex-math></inline-formula> ) array configuration of the antenna is also presented. The rectangular unit cells are rotated by 45° with respect to the sides of a square dielectric substrate, named a diamond-shaped AGS (DAGS). The overall dimensions of the AGS are smaller than those of the ground plane. The rotated unit cells and the smaller AGS patch dimensions effectively suppress surface wave resonance on the AGS. The proposed antenna achieves a wide 3-dB axial ratio bandwidth in the boresight direction. The proposed design has a flatter gain curve in the operating frequency band compared to that for conventional designs. It is found that the array configuration outperforms the single-element structure.

Design and Characterization of 10-Elements MIMO Antenna With Improved Isolation and Radiation Characteristics for mm-Wave 5G Applications

A ten-elements MIMO antenna with improved isolation and reduction of X-polar radiation (XPR) in millimeter (mm) wave region is presented. The individual antenna element consists of stub loaded coplanar waveguide (CPW) structure with elliptical shaped radiator. Defected ground structure (DGS) has been incorporated by engraving partial elliptical shaped slots at the coplanar ground to reduce the mutual coupling effect between the adjacent antenna pairs of the MIMO. The backside of the substrate has a metallic plane with defects which is not connected to the coplanar ground of the antenna. This defected metal structure (DMS) acts as a reflector to improve the radiation characteristics by lowering of XPR as well as improving the co-pol to X-pol isolation. The proposed MIMO structure has a fractional bandwidth of 23.52% (22.5GHz-28.5 GHz) which entails the mm-wave 5G frequency spectrum n258 (24.25-27.5 GHz). The isolation| characteristics of the proposed MIMO antenna are below -35 dB over the operating bandwidth for any pair of adjacent antenna elements which imply significantly improved isolation between the adjacent antenna elements with highly compact layout area of 3.4λ × 8.5λ, where λ is wavelength corresponding to the mid-point of the bandwidth. The inter-element spacing of the MIMO structure is 0.44 λ. The main attractive feature offered by this structure is reduction of XPR in the operating frequency range thus improving the co-pol to X-pol isolation up to 20 dB and 28 dB in the boresight direction in both the XZ and YZ planes respectively. Furthermore, the co-pol to X-pol isolation is maintained above 15 dB almost throughout the elevation angular region -180° to 180° thereby negating the hindrance imposed by surface waves in mm-wave region. The diversity performances in terms of Envelope Correlation Coefficient (ECC), Diversity Gain (DG) and Channel Capacity Loss (CCL) are obtained as 0.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , 10 dB and 0.005 bps/Hz respectively which are within the acceptable limits. Mean effective gain (MEG) values with respect to the excited port 2 and port 3 is identical and approximately -3dB thus indicating the mean value of these two ports to be almost 1 dB. The multiplexing efficiency of the proposed MIMO antenna is satisfactory over the bandwidth. The group delay is investigated and found to be almost constant with a variation of 1.2 ns thus indicating linear phase characteristic of the antenna. The proposed structure is compared with other mm-wave MIMO antennas and found to be advantageous with respect to the number of antenna elements, compactness, low mutual coupling, co-pol to X-pol isolation, and ECC. A prototype of the proposed 10-elements MIMO is fabricated, and the measured results resemble with the simulated results.

A simple configuration of beam steering substrate integrated waveguide aperture antenna loaded with metamaterials

AbstractThis letter presents a novel broadband substrate integrated waveguide aperture antenna with simple structure and beam steering performance. By using the left‐hand and band gap characteristics of the mushroom‐shaped metamaterials, the main beam of the substrate‐integrated waveguide aperture antenna can be easily switched between the back‐fire and boresight directions. Above all, the beam scanning characteristic does not depend on three‐dimensional structures or complex loaded structures, therefore it is a promising technology for designing planar two dimensional beam steering array. Experimental results indicate that the impedance bandwidth of the antenna covers the frequency range from 13.3 to 16.7 GHz and the relative bandwidth is 22.7%. The accordance between the simulated and measured E‐plane radiation pattern of the antenna at three representative frequencies verifies the beam steering capability of the proposed antenna.

Tapered post‐wall slotline antenna loaded with dielectric lens for short‐pulse applications

AbstractAn exponential tapered post‐wall slotline antenna loaded with dielectric lens is proposed and demonstrated. The theoretical profile of the loaded dielectric lens is derived, and its physical explanation is presented. Besides, the proposed post‐wall structure in the antenna ensures low available characteristic impedance as well as low cross‐polarization levels of the antenna. The proposed antenna exhibits an 18.12 GHz impedance bandwidth between 1.88 and 20 GHz and a peak gain of 10.9 dBi. The measured E‐plane and H‐plane cross‐polarization level is −37.0 and − 26.0 dB in boresight direction, respectively. Compared to the antenna without dielectric lens, the average gain of the proposed antenna increases by 3 dB from 14 to 20 GHz, and the pulse peak‐peak gain increases by 1.59 dB, and the tailing signal levels is about 0.35 dB lower.