Showing papers in "IEEE Transactions on Antennas and Propagation in 2013"
TL;DR: Measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks are provided and insight into antenna beam steering algorithms for these systems are given.
Abstract: The spectrum crunch currently experienced by mobile cellular carriers makes the underutilized millimeter-wave frequency spectrum a sensible choice for next-generation cellular communications, particularly when considering the recent advances in low cost sub-terahertz/millimeter-wave complementary metal–oxide semiconductor circuitry. To date, however, little is known on how to design or deploy practical millimeter-wave cellular systems. In this paper, measurements for outdoor cellular channels at 38 GHz were made in an urban environment with a broadband (800-MHz RF passband bandwidth) sliding correlator channel sounder. Extensive angle of arrival, path loss, and multipath time delay spread measurements were conducted for steerable beam antennas of differing gains and beamwidths for a wide variety of transmitter and receiver locations. Coverage outages and the likelihood of outage with steerable antennas were also measured to determine how random receiver locations with differing antenna gains and link budgets could perform in future cellular systems. This paper provides measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks and gives insight into antenna beam steering algorithms for these systems.
812 citations
TL;DR: A framework for physically-accurate computational modeling and analysis of CAP-MIMO is presented, and measurement results on a DLA-based prototype for multimode line-of-sight communication are reported.
Abstract: Millimeter-wave wireless systems are emerging as a promising technology for meeting the exploding capacity requirements of wireless communication networks. Besides large bandwidths, small wavelengths at mm-wave lead to a high-dimensional spatial signal space, that can be exploited for significant capacity gains through high-dimensional multiple-input multiple-output (MIMO) techniques. In conventional MIMO approaches, optimal performance requires prohibitively high transceiver complexity. By combining the concept of beamspace MIMO communication with a hybrid analog-digital transceiver, continuous aperture phased (CAP) MIMO achieves near-optimal performance with dramatically lower complexity. This paper presents a framework for physically-accurate computational modeling and analysis of CAP-MIMO, and reports measurement results on a DLA-based prototype for multimode line-of-sight communication. The model, based on a critically sampled system representation, is used to demonstrate the performance gains of CAP-MIMO over state-of-the-art designs at mm-wave. For example, a CAP-MIMO system can achieve a spectral efficiency of 10-20 bits/s/Hz with a 17-31 dB power advantage over state-of-the-art, corresponding to a data rate of 10-200 Gbps with 1-10 GHz system bandwidth. The model is refined to analyze critical sources of power loss in an actual multimode system. The prototype-based measurement results closely follow the theoretical predictions, validating CAP-MIMO theory, and illustrating the utility of the model.
748 citations
TL;DR: In this article, a metasurface (MS) is used to convert the linearly polarized (LP) signal from a source antenna into a circularly polarized (CP) signal.
Abstract: A metasurface (MS) used to convert the linearly polarized (LP) signal from a source antenna into a circularly polarized (CP) signal is proposed and studied. The MS consists of 16 unit cells arranged in a 4 × 4 layout. Each unit cell is a rectangular loop with a diagonal microstrip. By placing close to a source antenna, the MS converts the LP signal generated from the source antenna into a CP signal. Two source antennas (patch and slot antennas) are used for studies. The source antenna together with the MS is here called a MS antenna. A total of four low-profile MS antennas operating at the frequency of about 2.45 GHz are designed using computer simulation. For verification of simulation results, the MS antennas are fabricated and measured. Simulated and measured results show good agreements. Results show that the MS antennas have substantially better performances, in terms of gain, return-loss bandwidth (RLBW), axial-ratio bandwidth (ARBW) and radiation pattern, than the source antennas. Moreover, the ARBW of the MS antennas is mainly determined by the MS.
518 citations
TL;DR: In this paper, a planar-monopole (PM) antenna with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation is proposed.
Abstract: A compact multiple-input-multiple-output (MIMO) antenna with a small size of 26×40 mm2 is proposed for portable ultrawideband (UWB) applications. The antenna consists of two planar-monopole (PM) antenna elements with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation. To enhance isolation and increase impedance bandwidth, two long protruding ground stubs are added to the ground plane on the other side and a short ground strip is used to connect the ground planes of the two PMs together to form a common ground. Simulation and measurement are used to study the antenna performance in terms of reflection coefficients at the two input ports, coupling between the two input ports, radiation pattern, realized peak gain, efficiency and envelope correlation coefficient for pattern diversity. Results show that the MIMO antenna has an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than -15 dB, and a low envelope correlation coefficient of less than 0.2 across the frequency band, making it a good candidate for portable UWB applications.
427 citations
TL;DR: Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas, which makes it a good candidate for the wearable telemedicine application.
Abstract: We present a flexible, compact antenna system intended for telemedicine applications. The design is based on an M-shaped printed monopole antenna operating in the Industrial, Scientific, and Medical (ISM) 2.45 GHz band integrated with a miniaturized slotted Jerusalem Cross (JC) Artificial Magnetic Conductor (AMC) ground plane. The AMC ground plane is utilized to isolate the user's body from undesired electromagnetic radiation in addition to minimizing the antenna's impedance mismatch caused by the proximity to human tissues. Specific Absorption Rate (SAR) is analyzed using a numerical human body model (HUGO) to assess the feasibility of the proposed design. The antenna expresses 18% impedance bandwidth; moreover, the inclusion of the AMC ground plane increases the front to back ratio by 8 dB, provides 3.7 dB increase in gain, in addition to 64% reduction in SAR. Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas. Furthermore, it offers a compact and flexible solution which makes it a good candidate for the wearable telemedicine application.
349 citations
TL;DR: In this article, a single-layer circuit analog absorber using double-square-loop array reveals that three resonances can be obtained within its operating frequency band, and an equivalent circuit model is proposed to explain how these three resonance can be produced and its absorption bandwidth can be widened.
Abstract: A detailed study of a single-layer circuit analog absorber using double-square-loop array reveals that three resonances can be obtained within its operating frequency band. An equivalent circuit model is proposed to explain how these three resonances can be produced and its absorption bandwidth can be widened. Simple guidelines for the design of this double-square-loop absorber are then formulated. It is shown through measurements that the fractional bandwidth of 126.8% is realized for at least 10 dB reflectivity reduction under the normal incidence. Furthermore, the total thickness of the proposed design is only 0.088λL at the lowest operating frequency. A good agreement between simulated and measured results demonstrates the validity of our design.
347 citations
TL;DR: In this paper, a planar broadband chessboard structure is proposed to reduce the radar cross-section (RCS) of an object by combining two artificial magnetic conductor (AMC) cells.
Abstract: This paper presents the design, fabrication, and characterization of a planar broadband chessboard structure to reduce the radar cross-section (RCS) of an object. The chessboard -like configuration is formed by combining two artificial magnetic conductor (AMC) cells. The bandwidth limitations intrinsic to AMC structures are overcome in this work by properly selecting the phase slope versus frequency of both AMC structures. A 180 ° phase difference has been obtained over more than 40% frequency bandwidth with a RCS reduction larger than 10 dB. The influence of the incidence angle in the working bandwidth has been performed. A good agreement between simulations and measurements is achieved.
319 citations
TL;DR: In this article, a tightly coupled dipole array with an integrated balun (TCDA-IB) is developed which achieves 7.35:1 bandwidth (0.68 - 5.0 GHz) while scanning to ±45° in all directions, subject to.
Abstract: A key challenge in the design of wideband dipole phased arrays is the design of equally wideband baluns which are sufficiently compact to fit within the unit cell (typically in the linear dimension at low frequencies). In this paper, we exploit the reactance of a compact Marchand balun as an impedance matching network for each array element. The elimination of bulky external baluns results in a significant reduction of size, weight and cost, while the bandwidth is simultaneously improved by over 30%, compared to standard feeding techniques. In this manner, a tightly coupled dipole array with an integrated balun (TCDA-IB) is developed which achieves 7.35:1 bandwidth (0.68 - 5.0 GHz) while scanning to ±45° in all directions, subject to . In a dual-polarization configuration, the TCDA-IB has low cross polarization of over the majority of the band. Measured results are presented for a prototype 8 × 8 element TCDA-IB, showing good agreement with simulation.
304 citations
TL;DR: In this paper, a new microstrip monopolar patch antenna is proposed and analyzed using a cavity model, which is constructed on a circular patch antenna that is shorted concentrically with a set of conductive vias.
Abstract: A new microstrip monopolar patch antenna is proposed and analyzed. The antenna has a wide bandwidth and a monopole like radiation pattern. Such antenna is constructed on a circular patch antenna that is shorted concentrically with a set of conductive vias. The antenna is analyzed using a cavity model. The cavity model analysis not only distinguishes each resonating mode and gives a physical insight into each mode of the antenna, but also provides a guideline to design a broadband monopolar patch antenna that utilizes two modes (TM01 and TM02 modes). Both modes provide a monopole like radiation pattern. The proposed antenna has a simple structure with a low profile of 0.024 wavelengths, and yields a wide impedance bandwidth of 18% and a maximum gain of 6 dBi.
282 citations
TL;DR: In this article, a polarization reconfigurable E-shaped patch antenna with wideband performance is proposed for IEEE 802.11b/g frequency band (2.4-2.5 GHz).
Abstract: A polarization reconfigurable E-shaped patch antenna with wideband performance is proposed in this communication. The antenna is capable of switching its polarization from right hand circular polarization (RHCP) to left hand circular polarization (LHCP) and vice versa. Its structure is simple and consists of a single-layer single-feed E-shaped patch and two RF switches placed at appropriate locations in the slots. The design targets the WLAN IEEE 802.11 b/g frequency band (2.4-2.5 GHz) being used in various wireless communication systems. Full wave simulation is used for the antenna analysis, and a prototype of the antenna with an integrated DC biasing circuit has been fabricated and tested. Good agreement is obtained between simulated and measured results. The antenna exhibits a 7% effective bandwidth from 2.4 GHz to 2.57 GHz with a 8.7 dBic maximum gain. The antenna radiation symmetry is maintained upon switching between the two circular polarization modes.
259 citations
TL;DR: Wind Driven Optimization can, in some cases, out-perform other well-known techniques such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA) or Differential Evolution (DE) and that WDO is well-suited for problems with both discrete and continuous-valued parameters.
Abstract: A new type of nature-inspired global optimization methodology based on atmospheric motion is introduced. The proposed Wind Driven Optimization (WDO) technique is a population based iterative heuristic global optimization algorithm for multi-dimensional and multi-modal problems with the potential to implement constraints on the search domain. At its core, a population of infinitesimally small air parcels navigates over an $N$ -dimensional search space following Newton's second law of motion, which is also used to describe the motion of air parcels within the earth's atmosphere. Compared to similar particle based algorithms, WDO employs additional terms in the velocity update equation (e.g., gravitation and Coriolis forces), providing robustness and extra degrees of freedom to fine tune. Along with the theory and terminology of WDO, a numerical study for tuning the WDO parameters is presented. WDO is further applied to three electromagnetics optimization problems, including the synthesis of a linear antenna array, a double-sided artificial magnetic conductor for WiFi applications, and an E-shaped microstrip patch antenna. These examples suggest that WDO can, in some cases, out-perform other well-known techniques such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA) or Differential Evolution (DE) and that WDO is well-suited for problems with both discrete and continuous-valued parameters.
TL;DR: The estimation of the directions of arrival (DoAs) of narrow-band signals impinging on a linear antenna array is addressed within the Bayesian compressive sensing (BCS) framework and customized implementations exploiting the measurements collected at a unique time instant and multiple time instants are presented and discussed.
Abstract: The estimation of the directions of arrival (DoAs) of narrow-band signals impinging on a linear antenna array is addressed within the Bayesian compressive sensing (BCS) framework. Unlike several state-of-the-art approaches, the voltages at the output of the receiving sensors are directly used to determine the DoAs of the signals thus avoiding the computation of the correlation matrix. Towards this end, the estimation problem is properly formulated to enforce the sparsity of the solution in the linear relationships between output voltages (i.e., the problem data) and the unknown DoAs. Customized implementations exploiting the measurements collected at a unique time instant (single-snapshot) and multiple time instants (multiple-snapshots) are presented and discussed. The effectiveness of the proposed approaches is assessed through an extensive numerical analysis addressing different scenarios, signal configurations, and noise conditions. Comparisons with state-of-the-art methods are reported, as well.
TL;DR: In this article, a fully electronically reconfigurable 400-element transmitarray is studied numerically and experimentally in the X-band, where two p-i-n diodes are integrated on the active side of each cell to control its transmission phase.
Abstract: A fully electronically reconfigurable 400-element transmitarray is studied numerically and experimentally in X-band. The array operates in linear polarization and consists of 20 × 20 unit-cells. A 1-bit phase resolution has been selected for the unit-cell in order to reduce the complexity of the biasing network and steering logic, the insertion loss and the overall cost of the antenna system. The unit-cell stack-up is simple and is made of four metal layers: active side, biasing lines, ground plane and passive side. Two p-i-n diodes are integrated on the active side of each cell in order to control its transmission phase. The active array contains 800 diodes in total. It demonstrates experimentally pencil beam scanning over a 140 × 80-degree window over a 15.8% fractional bandwidth, with a maximum gain of 22.7 dBi at broadside. We also show that the same antenna array can be used for beam shaping applications (flat-top beam). The experimental results presented between 8 and 12 GHz are in good agreement with the theoretical performance calculated using full-wave electromagnetic simulations and an in-house CAD tool based on analytical modeling.
TL;DR: In this paper, a dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation was designed on a FR4 substrate.
Abstract: A compact dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation is designed on a FR4 substrate (27 × 30 × 0.8 mm3). To improve the input impedance matching and increase the isolation for the frequencies ≥ 4.0 GHz, the two antenna elements with compact size of 5.5 × 11 mm2 are connected to the two protruded ground parts, respectively. A 1/3 λ rectangular metal strip producing a 1.0 λ loop path with the corresponding antenna element is used to obtain the notched frequency from 5.15 to 5.85 GHz. For the rejected band of 3.30-3.70 GHz, a 1/4 λ open slot is etched into the radiator. Moreover, the two protruded ground parts are connected by a compact metal strip to reduce the mutual coupling for the band of 3.0-4.0 GHz. The simulated and measured results show a bandwidth with |S11| ≤ -10 dB, |S21| ≤ -20 dB and frequency ranged from 3.0 to 11.0 GHz excluding the two rejected bands, is achieved, and all the measured and calculated results show the proposed UWB MIMO antenna is a good candidate for UWB MIMO systems.
TL;DR: In this article, a perfect metamaterial absorbing structure over a thin low-loss grounded substrate is studied by resorting to an efficient transmission line model, which allows the derivation of simple and reliable closed formulas describing the absorption mechanism of the subwavelength structure.
Abstract: A popular absorbing structure, often referred to as Perfect Metamaterial Absorber, comprising metallic periodic pattern over a thin low-loss grounded substrate is studied by resorting to an efficient transmission line model. This approach allows the derivation of simple and reliable closed formulas describing the absorption mechanism of the subwavelength structure. The analytic form of the real part of the input impedance is explicitly derived in order to explain why moderate losses of the substrate is sufficient to achieve matching with free space, that is, perfect absorption. The effect of the constituent parameters for tuning the working frequency and tailoring the absorption bandwidth is addressed. It is also shown that the choice of highly capacitive coupled elements allows obtaining the largest possible bandwidth whereas a highly frequency selective design is achieved with low capacitive elements like a cross array. Finally, the angular stability of the absorbing structure is investigated.
TL;DR: In this paper, a differentially-driven dual-polarized magneto-electric dipole antenna was proposed to achieve wide impedance and gain bandwidth with high differential port-to-port isolation.
Abstract: A novel differentially-driven dual-polarized antenna is proposed in this communication. It is a magneto-electric dipole antenna whose gain and beamwidth keep constant along frequency within the operation bandwidth. If the antenna is ideally symmetrical, its differential port-to-port isolation is theoretically infinite. Due to the differentially-driven scheme, its cross-polarization level can be very low. Measurement shows that the proposed antenna achieves a wide impedance bandwidth of 68% (0.95 to 1.92 GHz) for differential reflection coefficients less than -10 dB and high differential port-to-port isolation of better than 36 dB within the bandwidth. The 3-dB-gain bandwidth of the proposed antenna is 62% (1.09 to 2.08 GHz), and the radiation pattern across it is stable and unidirectional. The broadside gain within the 3-dB-gain bandwidth ranges from 6.6 to 9.6 dBi. The cross-polarization level is lower than -23 dB across the 3-dB-gain bandwidth. The proposed antenna is the first differentially-driven dual-polarized magneto-electric dipole antenna. A feeding structure is specially designed to fit the differentially-driven scheme, and also to achieve wide impedance and gain bandwidths.
TL;DR: In this article, the authors proposed a method based on general relations between the reflection and transmission coefficients and the polarizabilities of arbitrary bi-anisotropic particles to synthesize different polarization-transforming devices realized as arrays of small particles.
Abstract: We study the possibility of analytically synthesizing different polarization-transforming devices realized as arrays of small particles. The proposed method is based on general relations between the reflection and transmission coefficients and the polarizabilities of arbitrary bi-anisotropic particles. As an example, we reveal all possible types of inclusions which can be used to realize twist polarizers, select one of them and synthesize a novel twist polarizer. The synthesized twist polarizer is then fitted on a standard printed circuit board, optimized numerically, and finally manufactured and measured. The experimental results for the twist polarizer show good correspondence with the simulations and the new method is found to be a useful tool for developing any polarization-transforming devices. As one more example, a novel circular polarization selective surface is synthesized.
TL;DR: In this paper, the authors proposed a quarter-mode substrate integrated waveguide (QMSIW) which is the quadrant sector of a square waveguide resonator and investigated its performance with TE101 and TE202 modes.
Abstract: A quarter-mode substrate integrated waveguide (QMSIW) which is the quadrant sector of a square waveguide resonator is proposed and investigated in this paper. The QMSIW is realized by bisecting the half-mode substrate integrated waveguide (HMSIW) into two parts along the fictitious quasi-magnetic wall when it operates with TE101 and TE202 modes as the way bisecting the substrate integrated waveguide (SIW) to HMSIW. The QMSIW can almost preserve the field distribution of original SIW and leaky wave is achieved from the dielectric aperture of the QMSIW. When the feeding port is placed at one corner of the QMSIW, a linearly polarized radiation is obtained when the QMSIW resonates in TE101QM mode, and when the QMSIW resonates in TE202QM mode, a circularly polarized (CP) wave is achieved. An antenna is designed, fabricated, and measured based on the proposed QMSIW. The measurement results match with the simulation results very well.
TL;DR: In this article, a transition printed on the same SIW substrate is proposed to improve the matching performance of SIW horn antennas in the Ku-band with a substrate thinner than λ 0/10.
Abstract: The substrate integrated waveguide (SIW) technology allows to construct several types of commonly used antennas in a planar way. However, some practical constraints limit their performances when frequencies below 20 GHz are considered. In the case of SIW horn antennas, the available substrates are much thinner than the wavelength yielding to poor matching and undesired back radiation. In this paper, an innovative structure to overcome these limitations is presented. It consists of a transition printed on the same SIW substrate, which improves both the radiation and the matching performances of conventional SIW horns. The horn shape is also further optimized by reducing its dimensions required for a given directivity. This is obtained by modifying the horn profile in order to effectively combine different TE modes. Guidelines are provided to design this type of thin and compact SIW horn antenna. They were applied to manufacture a prototype in the Ku-band with a substrate thinner than λ0/10. Measurement results validate the proposed concepts showing excellent performances.
TL;DR: In this article, the authors proposed the concept and design of terahertz phase shifters for phased antenna arrays based on integrally-gated graphene parallel-plate waveguides (GPPWGs).
Abstract: We propose the concept and design of terahertz (THz) phase shifters for phased antenna arrays based on integrally-gated graphene parallel-plate waveguides (GPPWGs). We show that an active transmission-line may be realized by combining GPPWGs with double-gate electrodes, in which the applied gate voltage can control the guiding properties of the gated sections. This may enable the realization of THz electronic switches and tunable loaded-lines for sub mm-wave antenna systems. Based on these active components, we theoretically and numerically demonstrate several digital and analog phase shifter designs for THz frequencies, with a wide range of phase shifts and small return loss, insertion loss and phase error. The proposed graphene-based phase shifters show significant advantages over other available technology in this frequency range, as they combine the low-loss and compact-size features of GPPWGs with electrically-programmable phase tuning. We envision that these electronic phase shifters may pave the way to viable phased-arrays and beamforming networks for THz communications systems, as well as for high-speed, low-RC-delay, inter/intra-chip communications.
TL;DR: In this article, a new microstrip Yagi array antenna with end-fire radiation and vertical polarization is proposed, which has a low profile, a wide bandwidth and a high gain.
Abstract: A new microstrip Yagi array antenna with endfire radiation and vertical polarization is proposed. The Yagi antenna has a low profile, a wide bandwidth and a high gain. Each element of the Yagi array is based on a new microstrip antenna that has one edge opened and the other three edges shorted, working as a “magnetic dipole antenna”. As opposed to previous microstrip Yagi array antennas, the proposed Yagi antenna could produce a beam radiating at exactly endfire for infinite ground plane, with vertical polarization in the horizontal plane. A coupling microstrip line is introduced between the driven element and the first director element to strengthen the coupling between them, and therefore the front-to-back ratio and bandwidth of the array can be improved. The endfire gain can be enhanced as the number of the director elements increases, in either case where the array has an infinite or a finite ground plane.
TL;DR: In this article, the authors investigated the application of metamaterial absorber (MA) to waveguide slot antenna to reduce its radar cross section (RCS) and demonstrated that the monostatic and bistatic RCS of the slot antenna are reduced significantly, and the performance of antenna is preserved simultaneously.
Abstract: This communication investigates the application of metamaterial absorber (MA) to waveguide slot antenna to reduce its radar cross section (RCS). A novel ultra-thin MA is presented, and its absorbing characteristics and mechanism are analyzed. The PEC ground plane of waveguide slot antenna is covered by this MA. As compared with the slot antenna with a PEC ground plane, the simulation and experiment results demonstrate that the monostatic and bistatic RCS of waveguide slot antenna are reduced significantly, and the performance of antenna is preserved simultaneously.
TL;DR: This paper proposes a range-angle dependent beampattern synthesis scheme for linear frequency diverse array (FDA) using the discrete spheroidal sequence, with an aim to focus the transmit energy in a desired two-dimensional spatial section.
Abstract: Phased-array is widely used in communication and radar systems, but the beam steering is fixed in an angle for all the ranges. In this paper, we propose a range-angle dependent beampattern synthesis scheme for linear frequency diverse array (FDA) using the discrete spheroidal sequence, with an aim to focus the transmit energy in a desired two-dimensional spatial section. Different from conventional phased-arrays, FDA employs a small frequency increment, compared to the carrier frequency across the array elements. The range-angle dependent beampattern synthesis method allows the FDA to transmit energy over a desired range or angle sector. This provides a potential to suppress range-dependent clutter and interference, which is not accessible for conventional phased-arrays. The system performance of the proposed FDA is evaluated by the output signal-to-interference-plus-noise ratio (SINR). The effectiveness is verified by comprehensive numerical simulation results.
TL;DR: In this paper, a low-profile, ultrawideband, true-time-delay (TTD) equivalent microwave lenses are designed, fabricated, and experimentally characterized at X-band.
Abstract: We present a new technique for designing low-profile, ultrawideband, true-time-delay (TTD) equivalent microwave lenses. Such a lens is composed of numerous spatial time-delay units (TDUs) distributed over a planar surface. Each spatial TDU is the unit cell of an appropriately designed miniaturized-element frequency selective surface and provides a frequency-independent time delay within the frequency band of interest. Two TTD lens prototypes with focal length to aperture dimension (f/D) ratios of 1 and 1.6 are designed, fabricated, and experimentally characterized at X-band. The 3-dB gain bandwidths of these lenses are respectively 7.5-11.6 and 7.8-11.5 GHz. Each fabricated lens has an overall thickness of 4.76 mm, which corresponds to ~ 0.150λ0, where λ0 is the free-space wavelength at the center frequency of operation. Each lens uses spatial TDUs with physical dimensions of 6 × 6 mm2, or ~ 0.19λ0 × 0.19λ0. Both lenses have a system fidelity factor close to 1, when excited with a broadband pulse. Furthermore, due to their true-time-delay equivalent behavior, the fabricated lenses do not suffer from chromatic aberration within their operational bands. When used in a beam-scanning antenna system, each lens demonstrates an excellent scanning performance in a field of view of ± 60°.
TL;DR: Convex optimization is used to determine current distributions that provide upper bounds on the antenna performance and formulations for maximal gain Q-Factor quotient, minimal Q-factor for superdirectivity, and minimum Q for given far-fields are presented.
Abstract: The high Q-factor (low bandwidth) and low efficiency make the design of small antennas challenging. Here, convex optimization is used to determine current distributions that provide upper bounds on the antenna performance. Optimization formulations for maximal gain Q-factor quotient, minimal Q-factor for superdirectivity, and minimum Q for given far-fields are presented. The effects of antennas embedded in structures are also discussed. The results are illustrated for planar geometries.
TL;DR: In this article, a printed transition is proposed to match a H-plane SIW horn antenna built in a thin substrate at different frequency bands at the Ku-band at the same time.
Abstract: The substrate integrated waveguide (SIW) technology allows to construct several types of commonly used antennas in a planar way. However, frequency limitations associated to commercial substrates appear in the implementation of certain types of antennas, e.g., SIW horn antennas are not well matched when the substrate thickness is much smaller than the wavelength. A printed transition is proposed to overcome this problem. Differently from current solutions, no bulky elements are required allowing to maintain the most important features of this technology namely its compactness and ease of manufacturing. In order to quickly analyze and design the transition, both a coupled resonator and a transmission line models are developed, together with design guidelines. The proposed transition is designed to match a H-plane SIW horn antenna built in a thin substrate $({\rm thickness} at different frequency bands at the Ku-band. Experimental results for 3 different transitions show that the matching characteristics are efficiently improved compared with the conventional SIW horn antenna and validates the proposed models.
TL;DR: In this article, a L-probe patch antenna array using multilayer low temperature co-fired ceramic (LTCC) technology is presented for 60 GHz band applications. The proposed antenna array is designed with a high gain in the impedance bandwidth by introducing a novel soft-surface structure.
Abstract: A 4 $\,\times\,$ 4 L-probe patch antenna array using multilayer low temperature co-fired ceramic (LTCC) technology is presented for 60-GHz band applications. The proposed antenna array is designed with a high gain in the impedance bandwidth by introducing a novel soft-surface structure. The soft-surface structure comprised of metal strips and via fences reduces the losses caused by severe surface waves and mutual coupling between adjacent elements to improve the radiation performance. The proposed antenna array is convenient for integrated applications. The fabricated antenna array excluding the measurement transition has dimension of 14.4 $\,\times\,$ 14.4 $\,\times\,$ 1 mm $^{3}$ . The simulated and measured impedance and radiation performance are studied and compared. Good agreement is achieved between simulation and measurement. The proposed antenna array shows a wide simulated impedance of 29% from 53 GHz to 71 GHz for $\vert {S}_{11}\vert dB, measured broadband 3-dB gain bandwidth of 18.3% from 54.5 GHz to 65.5 GHz and the gain up to 17.5 dBi at 60 GHz, respectively.
TL;DR: In this article, an effective approach for finite-difference time-domain modeling of graphene as a conducting sheet is proposed, where a new technique for implementing a conducting surface boundary condition in the FDTD method is presented.
Abstract: An effective approach for finite-difference time-domain modeling of graphene as a conducting sheet is proposed. First, we present a new technique for implementing a conducting surface boundary condition in the FDTD method; then, the dispersive surface conductivity of graphene is imposed. Numerical examples are presented to show the stability, accuracy, applicability, and advantages of the proposed approach. Validation is achieved by comparison with existing analytic methods.
TL;DR: A dual-polarized planar antenna consisting of two broadband antenna elements is proposed, which achieves a bandwidth of about 50% and an isolation of 30 dB, suitable for mobile communication base stations.
Abstract: A novel broadband planar antenna is developed for mobile communication base stations. The antenna is composed of a pair of folded dipoles which are coupling fed by an L-shaped microstrip line. Both the dipoles and the coupling microstrip line are etched on the same substrate. The planar antenna achieves a bandwidth of 53% for ${\rm return\ loss} > 15$ dB, covering the frequency range 1.65–2.85 GHz for 2G/3G/LTE applications. The antenna gain of the broadband antenna element is about 9 dBi. A ${\pm}45^{\circ}$ dual-polarized planar antenna consisting of two broadband antenna elements is proposed, which achieves a bandwidth of about 50% and an isolation of 30 dB. Two 8-element antenna arrays are developed respectively for the broadband antenna and for the ${\pm}45^{\circ}$ dual-polarized antenna. Both antenna arrays achieve a bandwidth of more than 58% (1.6–2.9 GHz). The antenna gains achieved for the both antenna arrays are higher than 15.5 dBi. The half-power beam widths in the horizontal plane for the antenna arrays are approximately $65\pm 10^{\circ}$ , suitable for base station applications.
TL;DR: In this paper, the design of sparse planar arrays is yielded through a set of innovative and efficient pattern matching algorithms within the Bayesian Compressive Sensing (BCS) framework and the single-task and the multi-task BCS solutions are derived.
Abstract: In this paper, the design of sparse planar arrays is yielded through a set of innovative and efficient pattern matching algorithms within the Bayesian Compressive Sensing (BCS) framework. Towards this end, the 2D sparse synthesis problem is formulated in a probabilistic fashion and the single-task (ST) and the multi-task (MT) BCS solutions are derived. The results from a numerical validation concerned with different aperture size and target patterns prove that the proposed implementations enable an element saving ranging from 25% up to 87%, while achieving a reliable beam control.