Search

The exponential growth of mobile data traffic in the last decades is expected to continue in the forthcoming years, and multi-gigabit-per-second connections will soon be experienced by the users at any place and time. Next-generation communication systems will have to sustain a highly immersive and interconnected world (e.g., the metaverse) in which both physical items/persons and their digital twins will have to continuously exchange massive amounts of high-resolution data. Therefore, the wireless infrastructures will have to guarantee unprecedented link performance levels, while minimizing the complexity, the power consumption, and the costs. Towards this end, alternative solutions to the traditional approach “more information and data through more power and more emissions of electromagnetic (EM) waves” will be mandatory because of the current EM congestion. [ABSTRACT FROM AUTHOR]

The article proposes methodology to use circularly polarized (CP) ultra-wideband (UWB) signals for simultaneous measurement of orientation and distance changes between transmitter and receiver. The proposed technique uses the rotational Doppler effect on CP pulsed communication. The amplitude of a CP signal is immune to polarization misalignment in the presence of rotation; however, the phase is subjected to a frequency-invariant shift proportional to the rotation angle. This significantly distorts the pulse shape in the time domain and can be used for the measurement of the rotated angle. By combining the technique with the well-known localization capability of UWB systems, one can precisely measure not only the distance but also the orientation. This is demonstrated by both numerical and experimental studies presented in this article. [ABSTRACT FROM AUTHOR]

This article presents a signal generator and a digital beamforming receiver (DBR) with high phase control resolution and high beam control resolution, respectively. The signal generator is designed based on a direct digital synthesizer (DDS) and a phase lock loop (PLL). In the DDS–PLL signal generator, the conventional divider in PLL is replaced with a mixer, comb generator, and a doubler to utilize high phase control resolution of DDS (14 bit, 0.022°) as it is to synchronize the DDS–PLL signal generator with the entire system. In the DBR, the output signals of the DDS–PLL signal generators are used as the second local oscillator (LO) signal, and the beamforming technique is implemented through the change of the phase of the second LO signals. Also, for sophisticated beamforming, all signal generator components in the DBR are synchronized for generating same and fixed frequency and phase. Finally, the DBR has the same phase control resolution as the DDS, and the phase of each chain of the DBR can be adjusted up to 0.022° (14 bit). The DBR using the DDS–PLL signal generator is designed and fabricated. The DBR consists of a $1 \times 8$ array tapered slot antenna (TSA) part, a first and second frequency conversion part, a $1 \times 8$ data acquisition and combiner part, DDS–PLL signal generator part, and a reference signal generator part. The phase control performance of the DBR was verified by measuring the phase change of the chain in the DBR according to the DDS phase change. Also, to verify the beamforming performance of the DBR with high beam control resolution, the radiation pattern of the DBR when the angle of the main lobe was 0°, 0.2°, 0.4°, 15°, and 30° was measured in the 28 GHz band. At the main lobe, the gain error is within 1 dB and the beam angle error is within 0.2°. The simulation results are in good agreement with the measured results. A high-resolution beamforming performance is achieved in the DBR using the DDS–PLL signal generator. [ABSTRACT FROM AUTHOR]

In this communication, a low radar cross section (RCS) antenna array with reconfigurable scattering patterns based on digital antenna units is proposed. The digital antenna unit has two scattering states that are controlled by p-i-n diodes. For $y$ -polarized normally incident waves, the phases of the two reflected states exhibit a 180° phase difference at approximately 5 GHz. For $x$ -polarized incident waves, the antenna units act as meta-absorbers, and the incident power is absorbed by the antenna units. Moreover, the radiation properties of these two states are approximately the same at 5 GHz. Thus, the scattering patterns of the antenna array can be tuned by controlling the scattering states of the digital antenna units without affecting the radiation performance. By tuning the directions of the scattering pattern nulls to dynamically align to the direction of the incident wave, both the monostatic and bistatic RCS can be significantly reduced. An $8\,\, {\times }\,\,8$ antenna array was fabricated and measured to validate the proposed concept. The measured results are in good agreement with the simulated ones. This indicates that the proposed antenna array is a promising solution to address the challenges of bistatic radar systems. [ABSTRACT FROM AUTHOR]

The spoof surface plasmon polariton (SPP) waveguide, which could support well-confined surface waves along an ultrathin corrugated metallic strip, is one of the most advantageous candidates in integrated circuits due to the remarkable properties of low crosstalk, low loss, and packaging minimization. Many devices based on the spoof SPP waveguide have emerged, but it is still a challenge to manipulate the SPP waves freely in real-time. Here, we propose a programmable multifunctional spoof SPP device by loading varactor diodes between adjacent metallic teeth of SPP waveguides. By programming the bias voltages of the varactor diodes dynamically, the coupling waves propagating on two SPP waveguides can be freely controlled. Simulations and experiments demonstrate that the programmable SPP device can realize high-efficiency SPP through transmission, unequal coupling, 3 dB direction coupling, and crossover transmission with better isolation effect. Different functions and operational frequency ranges can be reconfigured in real-time. The proposed method lays the groundwork for applications in large-scale microwave integrated circuits and digital communication systems. [ABSTRACT FROM AUTHOR]

Metasurfaces are well-designed artificial periodic or quasiperiodic structures to achieve customized electromagnetic responses. Based on the time-domain digital coding metasurface (TDCM) with dynamic reflection or transmission characteristics, one can realize direct information modulation on the metasurface, which has been used in wireless communications. In comparison with the classical architectures of wireless communication systems, the TDCM has advantages for simple architecture, easy manufacture, and low cost. However, the wireless communication systems based on the TDCM are still limited by low conversion efficiency, spectrum pollution, and hard to implement high-order modulation schemes. To solve these limitations, we propose a new route to achieve multi-modulation schemes in wireless communications by regulating the reflection phases of the TDCM in a nonlinear way. By carefully designing the regulation voltages applied to the diodes on TDCM, arbitrary constellation diagrams are successfully synthesized. The novel systems can implement various modulation schemes such as quadrature phase shift keying (QPSK), 8PSK, and 16QAM with good communication quality, high stability, and free scheme switching. The presented method may find important applications in modern wireless communication technologies. [ABSTRACT FROM AUTHOR]

This communication proposes an analog orbital angular momentum (OAM) transmission method based on dual-circular polarization (CP), where the low-gain modes are excluded to enhance the achievable data rate. The transmitter and receiver antennas, which face each other directly, are identical circular arrays, each of which has four circular microstrip antennas with dual CP. A discrete Fourier transform (DFT) feed network is used at both sides to realize quasi-eigenmode transmission, where mode orthogonalization is achieved by using just analog circuits; digital interference cancellation is not used. The key idea of the proposed method is its mode selection technique, which simply chooses some of the highest modes and distributes all available power to the chosen modes equally. An analysis shows that this method increases the achievable rate by 2 bits/s/Hz compared to short-range multiple input and multiple output (SR-MIMO) when the number of the ports at each side is 8 and the distance between transmitter and receiver antennas is $10 \lambda _{0}$ ($\lambda _{0}$ is the wavelength in vacuum) or more. Also, it is found that the achievable rate of the proposed scheme is asymptotic to that of SR-MIMO with water-filling. [ABSTRACT FROM AUTHOR]

This paper presents the results of the first propagation measurement campaign conducted in the 2.4 GHz industrial, scientific and medical (ISM) band for low antenna heights in a North American boreal forest. The $2 \times 1$ multiple-input, single output measurements capture propagation conditions for wireless peer-to-peer or sensor networks in the boreal environment. Unlike many other forests, it is shown that ground reflections strongly influence large scale propagation for the low antenna boreal case. Results also indicate that scattering is severe but that both frequency diversity and multiple antenna techniques will be effective for mitigating and/or exploiting the fading caused by this scattering. [ABSTRACT FROM AUTHOR]

A semi-analytical solution for the input reflections, inner field distribution and radiated fields for a wideband traveling-wave antenna based on a tapered half-mode substrate-integrated waveguide (HMSIW) is proposed in this paper. The analysis validates the operation mechanism for this type of traveling-wave antenna which exhibits omni-directional radiation properties with horizontal polarization (“magnetic dipole”). The derived expressions allows the design and efficient optimization of different antennas towards fulfilling various predefined specifications of reflection coefficient and operating bandwidth. The antenna utilizes a wideband transition from coaxial cable to a HMSIW, which is also considered in the model to provide highly accurate semi-analytical results. Utilizing the proposed method, three antennas of different specifications have been optimized, manufactured and tested. The analysis, simulation and measurement results show good correspondences, which verifies the design process and demonstrates the versatility of the concept. [ABSTRACT FROM PUBLISHER]

A new single-layer microstrip dual-resonance conformal loop (DRCL) element is proposed to design a printed beam deflector array for broadband application. By utilizing variable parameters of the DRCL element, a nearly progressive phase-shift ranging more than 550^\circ is achieved for deflecting wave within a wide band. It is important that a small DRCL element can be flexibly used to generate a 360^\circ phase shift, which decreases the cell period between the neighboring elements. The DRCL is less sensitive to the variation of incidence angles for both TE and TM polarizations. An X-band plane wave beam deflector array is designed, fabricated and measured. The results show a significant improvement in gain-bandwidth performance of the deflector array using the new structure element. The 1 dB gain-bandwidth of 20% can be achieved. The measured results agree well with the simulation results. [ABSTRACT FROM PUBLISHER]

A novel method is presented to design single-feed high-gain EBG resonator antennas (ERAs) with significantly wider bandwidths. Dielectric contrast is introduced to 1-D EBG superstructures composed of unprinted dielectric slabs, and the thicknesses of each of these slabs is optimized to achieve a wideband defect mode in a unit-cell model. Next, antennas are designed and their superstructure areas are truncated to increase the antenna bandwidth and aperture efficiency while decreasing antenna footprint. We demonstrate that a small superstructure area increases the 3-dB bandwidth of ERAs significantly. A prototype ERA designed with a single feed and superstructure area as small as \ 1.5 \lambda_0 \times \ 1.5 \lambda_0 has a measured 3-dB directivity bandwidth of 22% at a peak gain of 18.2 dBi. This prototype antenna was made out of three slabs of different dielectric constants, two of them touching each other. This prototype demonstrates more than 85% reduction in the ERA footprint alongside a drastic improvement in bandwidth over the 3%–4% measured bandwidth of the classical single-feed ERAs with unprinted slabs. [ABSTRACT FROM PUBLISHER]

Although conventional Yagi antenna has the advantage of unidirectional radiation patterns, it is not suitable for wideband applications due to its drawback of narrow bandwidth. In this communication, a compact wideband planar printed quasi-Yagi antenna is presented. The proposed quasi-Yagi antenna consists of a microstrip line to slotline transition structure, a driver dipole, and a parasitic strip element. The driver dipole is connected to the slotline through a coplanar stripline (CPS). The proposed antenna uses a stepped connection structure between the CPS and the slotline to improve the impedance matching. Two apertures are symmetrically etched in the ground plane to improve the unidirectional radiation characteristics. Simulation and experimental results show that the unidirectional radiation patterns of the proposed antenna are good. A 92.2% measured bandwidth with S 11 < -10~dB from 3.8 to 10.3 GHz is achieved. A moderate gain, which is better than 4 dBi, is also obtained. [ABSTRACT FROM PUBLISHER]

A compact hyper-band (>10:1 impedance bandwidth) printed antenna design is investigated numerically and experimentally. It is based on an elliptical-slot antenna augmented with a parasitic oval patch and driven with a specially engineered microstrip-line-fed elliptical tuning fork element. The parasitic and driven elements are adjusted along with the elliptical slot to create additional resonance modes; adjust the coupling strengths among all of the design components; facilitate the overlap of adjacent resonance modes; and fine tune the input impedance. The total size of the final optimized antenna is only 30\times40 mm^2. It exhibits a -10-dB impedance bandwidth from 2.26 to 22.18 GHz. Desirable radiation performance characteristics, including relatively stable and omni-directional radiation patterns, are obtained over this range. A prototype was fabricated and tested. The experimental results confirm the predicted input impedance bandwidth and radiation characteristics. While the hyper-band performance could be used for high fidelity short pulse applications, the antenna could also be used for multi-band operations from 3.1–10.6 GHz since it covers that entire ultra-wideband (UWB) spectral range. [ABSTRACT FROM PUBLISHER]

A novel planar octagonal-shaped antenna with reduced radar cross section (RCS) for ultra-wideband (UWB) applications is designed and demonstrated experimentally. The proposed antenna is modified using the geometrical shaping method in order to get the RCS reduction. This method is based on the subtraction of metal areas which have the minimum current distributions on the surface of printed antenna. Both of the reference and modified octagonal-shaped antennas are operating at 2.5–18 GHz frequency range with %151 fractional bandwidths. The full-wave electromagnetic simulations and laboratory measurements are performed to characterize their RCSs as a function of frequency, radiation patterns and scattering characteristics. The radiation performance of modified antenna is stable and consistent with the reference antenna. Also the results show that the designed UWB antenna has lower RCS compared to the reference antenna. About 10 dBsm RCS reduction is obtained in the whole operation bandwidth. The designed antenna has very large RCS reduction up to 25 dBsm, especially in the low frequency range. [ABSTRACT FROM PUBLISHER]

We propose a slot array antenna for dual-polarization operation in the 60 GHz band. To realize the dual-polarization, cross-shaped radiating slots and a multilayer feeding structure are employed. A 16\,\times\,16-element array is fabricated by diffusion bonding of laminated thin copper plates, which has the advantages of high precision and low loss characteristics. To suppress the grating lobes, we employ several design techniques, such as a thick cavity structure and dense element spacing. The high antenna gain higher than 32.0 dBi and the antenna efficiency near 80.0% are obtained over 60.0–64.0 GHz for two different polarizations. The 1-dB-down gain bandwidths reach 10.4% and 10.9%. High isolation above 50 dB is achieved between the two input ports. [ABSTRACT FROM PUBLISHER]

Random arrays bound by a spherical volume are rigorously analyzed through a stochastic approach for uniform and Gaussian element distributions. The full mathematical derivation and process to determine the array characteristics are discussed and a key result is the form solution which describes both the sidelobe behavior and main beam characteristics. It is also shown that the proposed approach shares many conceptual similarities to the probabilistic approach applied to circular random arrays and comparisons are made. The 3-dB beamwidth, directivity, grating lobes, and sidelobe level are examined analytically and in numerical simulation for a conceptual system of isotropic wide-band radiators with a 100:1 bandwidth. [ABSTRACT FROM PUBLISHER]

The design of a new miniature broadband implantable antenna and a dual-band on-body antenna are presented along with the transmission performance between the two. The former and latter antennas are intended for integration into implantable medical devices (IMDs) and on-body repeaters, respectively. The on-body repeater antenna favors the use of very low power IMDs. The on-body repeater receives low power data from an IMD (MedRadio band, 401–406 MHz) and retransmits it to remote devices placed further apart (ISM band, 2400–2480 MHz ). The MedRadio implantable antenna maintains miniature size (399 mm^3), and exhibits two close resonances which increase the -10 dB bandwidth inside muscle tissue (87 MHz). The on-body antenna is relatively small (6720 mm^3), and exhibits dual resonances in the MedRadio and ISM bands. Assuming a typical arm implantation scenario and an on-body receiver sensitivity of -75 dBm, the proposed configuration is found to enable reduction of the IMD power by a factor of 100. Patient safety and tolerance to electromagnetic interference are, thus, preserved, and lifetime of the IMD is increased. The setup is, finally, shown to be robust to antenna misalignment and polarization rotation. [ABSTRACT FROM PUBLISHER]

This paper presents compact and low profile two-port antennas that can provide polarization or pattern diversity schemes from a common aperture. The proposed antennas make use of a novel small microstrip antenna topology with an open area at its waist. The two sections of the small-size microstrip antenna are connected through a magnetic coupling mechanism facilitated by two vertical metallic strips connecting the top plates to the ground plane. This allows for placement of another small antenna element within the same aperture having either polarization or pattern that is orthogonal to the microstrip antenna with low envelope correlation. Topologies of polarization and pattern-diversity antennas are optimized for size reduction and minimum envelope correlation. Although the proposed diversity antenna consists of two antenna elements with different polarizations or radiation patterns, they just occupy about 30% of the area of a conventional microstrip antenna over the same substrate. It is shown that the envelope correlation between radiation patterns of the two antenna elements is lower than -30 dB over the 10-dB return loss bandwidth of the proposed antenna. [ABSTRACT FROM PUBLISHER]

A novel design of a two-port printed microstrip rectenna with compact structure for communication systems is presented. An aperture-coupled dual polarization patch antenna is utilized as the receiving antenna. The vertical feed port receives the microwave energy and transfers it to the rectifying circuit for dc power generation, while the horizontal feed port is used for data communication, with high isolation between the two ports. This patch antenna includes harmonic suppression functionality, which is essential for high microwave—direct current (mw-dc) conversion efficiency. A co-simulation procedure using HFSS and ADS for the analysis of the rectenna and the rectifying circuit design is used. This design assumes low input power for the rectifying circuit to comply with safety standards. A mw-dc conversion efficient of 63% is measured with a 900 \Omega load, 5.78 GHz operation frequency, and 25 mW receiving power. For the communication port, the measured reflection coefficient is -18 dB at 6.1 GHz center frequency, the gain is 7.0 dBi, and the cross polarization in the broadside direction is -15 dB. [ABSTRACT FROM PUBLISHER]

A CPSS-based unit-cell is proposed as a building block of future reconfigurable dual-CP reflectarrays illuminated by a dual CP primary feed. It is based on an enhanced version of the original Pierrot's cell with multiple wires bent in a crank-like shape. It provides a 2-bit phase resolution in reflection for the left hand circular polarization (LHCP) and is nearly transparent in right hand circular polarization (RHCP). The main design steps and measurement procedure of the optimized cell are described in detail. The simulated and measured characteristics are in good agreement. The experimental results demonstrate a 6.4% bandwidth for a phase resolution better than 1.9 bits and an insertion loss of 0.5 dB at resonance. [ABSTRACT FROM AUTHOR]

This paper studies the optimum design of antennas. The objective function to be maximized is the ratio of gain to quality factor (Q) (i.e., the product of gain and bandwidth) in a specified direction. The theoretical upper bounds for the ratio of gain to Q are first rederived by using the IEEE standard definition of antenna Q. The ratio of gain to Q in a specified direction may be considered as a linear functional of the current distribution, and once it is maximized, an eigenvalue equation can be obtained from the variational principle. This eigenvalue equation can then be solved, yielding an optimum current distribution that maximizes the ratio of gain to Q in the specified direction. A number of numerical examples for small antennas have been presented to demonstrate how the theoretical upper bounds for the ratio of gain to Q can be approached by optimizing the current distributions as well as antenna geometries. [ABSTRACT FROM AUTHOR]

A broadband vertically/horizontally dual-polarized omnidirectional antenna is proposed for mobile communications. The dual-polarized antenna is a combination of a modified low-profile monopole for vertical polarization (VP) and a circular planar loop for horizontal polarization (HP). The modified low-profile monopole is a circular folded patch shorted by four tubes while the circular loop consists of four half-wavelength arc dipoles. The dual-polarized omnidirectional antenna achieves a bandwidth of \sim 25\% (1.7–2.2 GHz) with an isolation of around 40 dB. The gain variations in the horizontal plane are less than 2.5 dB for VP and 1.5 dB for HP. An eight-element dual-polarized antenna array is developed for base station applications. The antenna gains of the array for both VP and HP are \sim 8~dBi with a difference of less than 1 dB. The beamwidths in the vertical plane are 9\pm 1^\circ for VP and 9\pm 1.5^\circ for HP. The cross-polarization levels in the horizontal plane for both VP and HP are lower than -20~dB. [ABSTRACT FROM PUBLISHER]

The technique of using a parallel-resonant (PR) strip for bandwidth enhancement of a small-size uniplanar tablet computer antenna for the WWAN operation (824–960/1710–2170 MHz) is presented. The antenna is printed on a thin FR4 substrate of small size 12\, \times \,40 mm^2, and has a simple uniplanar structure of comprising a feeding strip, a shorted strip, and a PR strip. The antenna's wide lower band is formed by the quarter-wavelength resonant mode of the shorted strip and an additional resonant mode generated owing to the presence of the PR strip, which occupies a very small area of about 7\,\times \,7 mm ^2 only. The PR strip contributes a parallel resonance at about 1100 MHz which in turn generates an additional resonance near the quarter-wavelength mode of the shorted strip, thereby resulting in a new resonant mode to greatly enhance or double the bandwidth of the antenna's lower band for the GSM850/900 operation. For the antenna's upper band, it is formed by a higher-order mode of the shorted strip and a quarter-wavelength mode of the feeding strip, and covers the GSM1800/1900/UMTS operation. Details of the proposed antenna are presented. [ABSTRACT FROM PUBLISHER]

Novel circular polarization (CP) design of planar broadband antenna with square slot for UHF RFID system is proposed and experimentally studied. By insetting the arc-shaped strip into the square slot, the proposed CP design can easily be achieved with the impedance bandwidth (RL \geqq 10 dB) of about 142 MHz (15.3% @ 931 MHz) and the 3 dB axial-ratio (AR) bandwidth of about 166 MHz (17.7 % @ 940 MHz) for UHF RFID applications. The measured peak gain and radiation efficiency are about 6.8 dBic and 98% across the operating band, respectively, with nearly bidirectional pattern in the XZ- and YZ-plane. [ABSTRACT FROM PUBLISHER]

Two new phased array design techniques are introduced that utilize rotational symmetry to avoid grating lobes during scanning and over ultra-wide bandwidths. The first is an optimization method, which employs the covariance matrix adaptation evolutionary strategy to determine the best locations of elements inside a sector of a circle. The second technique uses standard periodic lattices inside the same circular sector. Although the segments themselves are internally periodic, the rotational symmetry of the full array eliminates the occurrence of grating lobes and is capable of generating antenna element layouts with useful ultra-wideband properties. These design techniques yield arrays with not only ultra-wideband characteristics, but properties that lend themselves to relatively straightforward modular construction, especially the semi-periodic variety. [ABSTRACT FROM PUBLISHER]

In this paper, a hybrid zeroth-order resonance (ZOR) patch antenna with a broad E-plane beamwidth is presented. In order to obtain the broad beamwidth of an antenna, a TM010(\lambda0/2) mode and a ZOR mode are combined. By dividing the incident power to two modes, the E-plane beamwidth of a TM010 mode can simply be controlled. To generate the TM010 mode and the ZOR mode, simultaneously, the mushroom antenna is inserted in a rectangular patch antenna with an etched rectangular hole and a single feed is employed between two radiators. The incident power to each antenna can be controlled by using the gap of a feed. Thus, the optimum incident power ratio having the broadest E-plane half power beamwidth (HPBW) is obtained. As a result, the E-plane HPBW of the proposed antenna is measured as 115^\circ and broadened by 53%, compared with that of the conventional rectangular patch antenna. Moreover, the bandwidth and the efficiency of the antenna are measured to be 3.3% and 92%, respectively. Finally, the measured results show good agreements with the simulated ones. [ABSTRACT FROM PUBLISHER]

A design methodology is presented which applies band-pass filter principles to form wideband small-aperture evanescent-mode waveguide antenna designs. This approach permits matching of the complex antenna aperture admittance of an evanescent-mode open-ended waveguide to a real impedance generator, and thereby to an SMA coaxial feeding probe. A reflection coefficient of less than -10 dB was obtained over a measured bandwidth of 15%, from 2.30–2.68 GHz, in 2.72 GHz cutoff waveguide. Capacitive posts and evanescent-mode waveguide sections are used to form the resonators/coupling elements of the antenna's filtering sections. Measured realised gain variation from 3.5–4.7 dBi is observed across the bandwidth. The antenna's maximum aperture dimension is <0.5\lambda0 at the upper frequency in the bandwidth and so it is suitable for use in a wide angle scanning phased array. [ABSTRACT FROM PUBLISHER]

In this paper, we present a novel 2–18 GHz modified Archimedean polygonal spiral antenna that approximates a circular spiral in its highest frequencies and gradually transforms itself into a square spiral antenna at its lowest frequencies of operation. The design has successfully addressed the problem of high axial ratios associated with ultra-wideband (UWB) rectangular spiral antenna systems. A low-profile, cavity backed polygonal model and two variations of the original design are presented in this study. Our results demonstrate that the polygonal spiral antenna demonstrates excellent axial ratio and gain-bandwidth performance with \leq 3~dB axial ratio over 97.5% of its operational bandwidth. [ABSTRACT FROM PUBLISHER]

Through-wall radar images taken from man-portable systems have limited resolution due to the finite bandwidth and aperture size. However, these images can be enhanced by exploiting scene sparseness (leading to sharper images) or homogeneity (leading to more natural, i.e., visually intuitive, images). To realize these enhancements, we employ a constrained non-linear optimization algorithm based on the Lagrange multiplier method. This approach has an advantage over related image optimization algorithms in that the Lagrange multipliers are solved within the algorithm rather than being selected a priori. This yields a system of equations that is solved iteratively rather than by gradient search. Data from a portable wideband UHF radar is used to test algorithm performance for several through-wall (cinder block) and free-space scenarios. [ABSTRACT FROM PUBLISHER]

A miniaturized modified planar inverted-F antenna (PIFA) is presented and experimentally studied. This antenna consists of a planar rectangular monopole top-loaded with a rectangular patch attached to two rectangular plates, one shorted to the ground and the other suspended, both placed at the optimum distance on each side of the planar monopole. The fabricated antenna prototype had a measured impedance bandwidth of 125%, covering 3 to 13 GHz for reflection coefficient better than -10 dB. The radiator size was 20\times 10\times 7.5\ mm^3, making it electrically small over most of the band and suitable for incorporation in mobile devices. The radiation patterns and gains of this antenna have been cross-validated numerically and experimentally and confirm that this antenna has adequate characteristics for short range ultra-wideband wireless applications. [ABSTRACT FROM PUBLISHER]

In order to achieve broadband and unidirectional radiation, a planar printed antenna based on closely spaced loading method is proposed and fabricated. This antenna consists of a printed rectangular loop with two gaps and a metallic strip. The rectangular loop has a good direction but has a drawback of narrow band. According to the closely spaced loading theory, the impedance at the upper frequency will decrease when a metallic strip is placed at the maximum radiation direction of the rectangular loop. This improves the impedance matching. A new resonant frequency point is induced. Meanwhile, the resonant frequency point can be changed by modifying the length of the metallic strip. The impedance matching between the two resonant peaks (One peak is determined by the rectangular loop, the other is determined by the metallic strip) is improved by changing the length and the position of the metallic strip. Thus the impedance bandwidth is greatly expanded. Experimental results show good performance of the proposed antenna. It has a 40.7% measured bandwidth, ranging from 2.29 to 3.46 GHz. The measured front-to-back (F/B) ratio of the proposed antenna is larger than 10 dB in the whole frequency band. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We describe an approach to construct a pulsed signal which, when propagating in an obscuring, discrete-scatterer medium (such as clouds, fog, dust or other aerosols) experiences reduced attenuation. The approach can thus find possible applications in communication or high resolution target detection. In the proposed scheme, the transmitted signal consists of a coherent train of short wide-band pulses emitted at chirped (linearly varying) time intervals. As the energy of a single pulse which has traveled a large distance in the medium is almost entirely concentrated in the precursor-type structures associated with its leading and trailing edges, the increase of the signal total energy is achieved by using trains with a large number of pulses. The (down-)range resolution is controlled by the chirp bandwidth characterizing the distribution of individual pulses in the train (that bandwidth may be sufficiently large to achieve a resolution typical of millimeter-wave radar), while the high cross-range resolution can be attained in analogy to the usual synthetic-aperture imaging. Processing of the received signal involves filtering associated with the chirp characteristics, analogous to that in the conventional matched-filter techniques. It is also shown that the proposed approach provides flexibility in choosing the chirped-train center frequency, e.g., to maximize the amount of energy passing through a selected atmospheric absorption window or to maximize the signal energy carried to a desired penetration depth. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We present an analytical model and practical design tools to realize cylindrically-symmetric compact antennas based on the anomalous transmission properties of \varepsilon-near-zero (ENZ) ultranarrow radial channels. The flexibility and exotic propagation properties in ENZ metamaterial channels are exploited here to tune and match cylindrically-symmetric antennas, without the need of complex external matching networks, in order to realize exciting antenna designs in terms of size, complexity and efficiency. We first model a homogenized Drude dispersive ENZ metamaterial channel to feed a radial parallel-plate waveguide; next we suggest a practical realization of this channel by using radial fins; eventually, we apply the obtained design formulas to realize single- and multi-band cylindrical antennas with a wide tunability range. The designed antennas may operate in the ultra-high frequency (UHF) band and may be realistically tuned over a large bandwidth. We envision applications in frequency-hopping, multi-band, compact, omnidirectional antennas. [ABSTRACT FROM PUBLISHER]

In this communication, we present a new circularly-polarized array antenna using 2\,\times\,2 linearly-polarized sub grid arrays in a low temperature co-fired ceramic technology for highly-integrated 60-GHz radio. The sub grid arrays are sequentially rotated and excited with a 90^\circ-phase increment to radiate circularly-polarized waves. The feeding network of the array antenna is based on stripline quarter-wave matched T-junctions. The array antenna has a size of 15\,\times\,15\,\times\,0.9 mm^3. Simulated and measured results confirm wide impedance, axial ratio, pattern, and gain bandwidths. [ABSTRACT FROM PUBLISHER]

This communication presents a 60-GHz wideband circularly polarized (CP) U-slot patch antenna array of 4\,\times\,4 elements on low temperature cofired ceramic (LTCC). A CP U-slot patch antenna is used as the array element to enhance the impedance bandwidth and a stripline sequential rotation feeding scheme is applied to achieve wide axial ratio (AR) bandwidth. Meanwhile, a grounded coplanar waveguide (GCPW) to stripline transition is designed for probe station measurement. The fabricated antenna array has a dimension of 14\,\times\,16\,\times\,1.1 mm^3. The simulated and measured impedance bandwidths, AR bandwidths, and radiation patterns are investigated and compared. Measured results show that the proposed antenna array has a wide impedance bandwidth from 50.5 GHz to 67 GHz for \vert S 11 \vert < -10~dB, and a wide AR bandwidth from 54 GHz to 65.5 GHz for AR< 3~dB. In addition, it exhibits a peak gain of 16 dBi and a beam-shaped pattern with 3-dB beam width of 20 ^\circ. Moreover, its AR keeps below 3 dB within the 3-dB beam width. [ABSTRACT FROM PUBLISHER]

A circularly polarized printed antenna, capable of operating over an octave bandwidth is designed and fabricated. The design is evolved from classical printed monopole/dipole geometry. It employs a microstrip-line fed rectangular radiator, printed on the top of a substrate. The ground, extended as another rectangular radiator is printed on the bottom of the substrate. Both the top and bottom radiators are asymmetrically configured in such a way that the surface currents on them are orthogonal so as to produce left-hand circular polarization (LHCP). The antenna configuration is simulated using a commercially available EM solver. The simulated and measured results closely match within the operating bandwidth. The measured results show a -10-dB return loss bandwidth of 800 MHz to 4.15 GHz and a 3-dB axial ratio bandwidth of 1.5 GHz to 3.4 GHz. For the designed center frequency of 2.45 GHz, these correspond to 136% and 77% respectively. A parametric study of the design is carried out and the mechanism of circular polarization is described. [ABSTRACT FROM PUBLISHER]

The design of a tri-band dual-polarization (TBDP) shared-aperture microstrip array antenna for synthetic aperture radar (SAR) applications is presented. It operates at L-, S- and X-bands with a frequency ratio of 1:2.8:8. This TBDP shared-aperture array is assembled by two L/S and L/X DBDP shared-aperture sub-arrays with one L-band dual-polarized sub-array. A prototype array has been fabricated and measured, which exhibits wide impedance bandwidth (VSWR \leq 2) of 13.4%, 14.8%, and 16.8% in L-, S-, and X-bands, respectively. The measured array isolation is better than 37 dB in all three bands. The measured radiation patterns agree well with the simulation, confirming the cross-polarization level of below -27 dB within the main lobe region, and the array scanning capability of \pm27^\circ in S- and X-bands. This array design approach can be further extended to shared-aperture arrays with more than three bands. [ABSTRACT FROM PUBLISHER]

Body-centric wireless communications (BCWCs) have received a great deal of attention recently. This communication proposes a compact planar inverted-F antenna (PIFA) operating at 2.45 GHz for on-body communications. Two shorting structures and a folded ground plane are used to improve the impedance matching and decrease the size of the proposed antenna. As a result, the proposed antenna is low-profile and compact in size, and it does not change significantly when in close proximity to the human body. This communication studies the characteristics of the proposed antenna close to the arm phantom by simulation and experiments. Both simulated and measured results are in good agreement. [ABSTRACT FROM PUBLISHER]

We present a novel technique to improve the input bandwidth of a conventional printed dipole antenna without actually increasing its size. We show that the proposed modification results in a considerable improvement in the input bandwidth. We also propose an equivalent circuit model for this antenna and describe a procedure to determine the values of the circuit elements. Finally, the performance of the antenna is demonstrated by a fabricated model and a comparison of experimental results with simulation. [ABSTRACT FROM PUBLISHER]

A novel hexa-band antenna for mobile handsets application is proposed and analyzed in this communication. An asymmetric T-type monopole antenna with a shorted-line is designed to be operated in code-division multiple access (CDMA, 824–894 MHz), global system for mobile communications (GSM, 880–960 MHz), digital communication system (DCS, 1710–1880 MHz), personal communication system (PCS, 1850–1990 MHz), wideband code division multiple access (WCDMA, 1920–2170 MHz) and Bluetooth (2400–2484 MHz) bands. A prototype of the proposed antenna with 50 mm in length, 3 mm in height and 15 mm in width is fabricated and experimentally investigated. The experimental results indicate that the VSWR 2.5:1 bandwidths achieved were 17.8% and 37.1% at 900 MHz and 2100 MHz, respectively. The specific absorption rate (SAR) for an input power of 24 dBm in CDMA, GSM and WCDMA bands, and an input power of 21 dBm in DCS and PCS bands all meet the SAR limit of 1.6 mW/g. Experimental results are shown to verify the validity of theoretical work. [ABSTRACT FROM PUBLISHER]

This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain Gi and the mean effective gain Ge if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, respectively. The obtained limitations are on the maximum of Gi/Q and Ge/Q, which establish a trade-off between link gain and Q. [ABSTRACT FROM AUTHOR]

Four compact asymmetric-slit microstrip antennas are proposed and studied for circular polarization. By cutting asymmetrical slits in diagonal directions onto the square microstrip patches, the single coaxial-feed microstrip patch antennas are realized for circularly polarized radiation with compact antenna size. The performances of the proposed antennas with several asymmetric-slit shapes onto the patch radiators are compared. The measured 10-dB return loss and 3-dB axial-ratio bandwidths of the antenna prototype are around 2.5% and 0.5%, respectively. The proposed asymmetric-slit configurations are useful for compact circularly polarized microstrip patch antennas and array design. [ABSTRACT FROM AUTHOR]

A ceramic antenna which provides UWB functionality over band group 1 is proposed for integration into a mobile handset. Two separate PIFA antennas are incorporated into a single feed structure enabling separate resonances to be independently controlled and combined to achieve wide bandwidth. This surface mounted ceramic block antenna which maintains a volume of 315 mm^3 is suitable for automated production. A prototype was tested and agreement with numerical work was observed for the S11, radiation pattern and efficiency. [ABSTRACT FROM AUTHOR]

A novel ultrawideband (UWB) antenna referred to as the inverted-hat antenna (IHA) is described. Specifically, the paper provides a systematic approach to generate a frequency-scaled IHA structure subject to aperture width and height constraints. An experimental verification is also given. The proposed compact wideband antenna exhibits frequency-independent behavior by introducing a moderate number of appropriately scaled elliptical segments and by controlling the outer surface growth profile. A modified seven-ellipse IHA is demonstrated in this paper to provide a 10:1 impedance bandwidth with satisfactory radiation properties. The simulation and measurement results are in reasonably good agreement. [ABSTRACT FROM AUTHOR]

An array with pattern-reconfigurable elements is used to generate a digital modulation by switching the elements for every symbol. This technique is known as directional modulation. Because the modulation is generated at the antenna level, it gives control over the directions in which data is sent, unlike baseband modulation which transmits the same data in all directions at different power levels. A procedure for determining how to switch the elements to transmit only in a specified direction is outlined. Results indicate that compared to a traditional reconfigurable array, the directional modulation array allows information to be sent over a narrower beamwidth. Additionally, the method provides more selectivity in the possible transmit angles. Measured and calculated results from a four-element reconfigurable array are presented. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a 2 x 4 T-type folded substrate integrated waveguide (TFSIW) slot array antenna. Each linear array is fed through a microstrip line and a TFSIW Y-junction. The size of the proposed antenna is reduced by 40% and the impedance bandwidth (-- 10 dB) is 5.6%. The dimensions of the structure are presented and the proposed array antenna is fabricated in a two-layer substrate. Simulation and measurement of the proposed antenna are compared. [ABSTRACT FROM AUTHOR]

A four-layer transmitarray operating at 30 GHz is designed using a dual-resonant double square ring as the unit cell element. The two resonances of the double ring are used to increase the per-layer phase variation while maintaining a wide transmission magnitude bandwidth of the unit cell. The design procedure for both the single-layer unit cell and the cascaded connection of four layers is described and it leads to a 50% increase in the -1 dB gain bandwidth over that of previous transmitarrays. Results of a 7.5% -1 dB gain bandwidth and 47% radiation efficiency are reported. [ABSTRACT FROM AUTHOR]

In order to reduce the thickness of a steerable beam square loop antenna, the effects of combining it with various periodic high impedance surfaces (HISs) are investigated. When a via-less HIS is used, the radiation pattern has high side lobes, which are shown to be due to surface waves propagating in the HIS lattice. Using a HIS with vias between the plates and ground removes the surface waves, but the beam is distorted due to strong coupling between the HIS's vias and the antenna element. Consequently a hybrid HIS is designed. This uses a via-less lattice beneath the loop, with vias at the edge of the HIS to suppress surface wave propagation. Consequently, a square loop antenna with four feeds on a hybrid HIS substrate is proposed for beam steering applications. This antenna has a low-profile with a total thickness of 4.69 mm for a test frequency band of 4.3 GHz to 5.0 GHz. It exhibits a gain of 8.65 dB at the test frequency (4.7 GHz). Compared to the earlier reported steerable square loop antenna, the new antenna achieves a 61% reduction in substrate thickness, a bandwidth enhancement by 150 MHz and an increase in gain by 1.95 dB. [ABSTRACT FROM AUTHOR]