Design of a compact protrudent‐shaped ultra‐wideband multiple‐input‐multiple‐output/diversity antenna with band‐rejection capability

In this endeavor, a new multiple‐input‐multiple‐output antenna with a sharp rejection at wireless local area network (WLAN) band is designed and practically examined for portable wireless ultra‐wideband applications. The intended diversity antenna possess a small size of 15 mm × 26 mm and two inverted L‐strip are loaded over the conventional rectangular patch antenna to form protrudent‐shaped radiator that acts as a radiating element. The sharp band‐rejection capability at WLAN is established by incising the L‐shaped slits at the decoupling structure. More than ?21 dB isolation is accomplished for the complete working band (ie, 2.87 ‐17 GHz). Degradation in the antenna efficiency at the center frequency of band rejection corroborates the good interference rejection capability. The working capabilities of the intended antenna are tested by using the isolation between the ports, total efficiency, gain, envelope correlation coefficient, radiation pattern, mean effective gain, and total active reflection coefficient.     

Design of high gain/directional ultra‐wideband antenna for radar imaging systems

A compact size of 40 × 40 mm² ( λ₀ × λ₀ ) semi‐elliptical slotted ground structure (SESGS) directional ultra‐wideband (UWB) antenna is proposed for radar imaging applications. A vertical semi‐elliptical slot is inserted into ground and subsequently, an axis of semi‐ellipse is rotated diagonally (with 45°) in direction of the substrate. Axes of semi‐ellipse are optimized symmetrically around the circular patch to work antenna as a reflector. Furthermore, semi‐elliptical slot is rotated horizontally (with 90°) again to improve the impedance bandwidth. Proposed antenna achieves fractional bandwidth around 83% covering the UWB frequency range from 4.40 to 10.60 GHz (S₁₁ < ?10 dB) having 4.5/6/7/8/9.3/10.2 GHz resonant frequencies. Also, antenna is capable to send low‐distortion Gaussian pulses with fidelity factor more than 95% in time‐domain. Measured gain and half power beam width (HPBW) are 6.1‐9.1 dBi and 44°‐29° in 4.40‐10.60 GHz band, respectively, which show an improvement of 1‐3 dBi in gain and half power beam‐width is reduced by 5°‐10° when compared with previously designed antennas. Experimental results show good agreement with CST simulation.     

Compact ultra‐wideband slot antenna with three notched‐band characteristics

A very compact ultra‐wideband (UWB) slot antenna with three L‐shaped slots for notched‐band characteristics is presented in this article. The antenna is designed and fabricated using a new stepped slot with different size, integrated in the ground plane, and excited by a 50 Ω microstrip transmission line. The stepped slot is used to minimize the dimensions of the antenna and to achieve an impedance bandwidth between 2.65 and 11.05 GHz with voltage standing wave ratio (VSWR) less than 2. The length of the stepped slot is equal to a quarter wavelength to create a resonance in the desired frequency. Three L‐shaped slots with various sizes are etched in the ground plane to reject three frequency bands in C‐band (3.7‐4.2 GHz), WLAN (5.15‐5.825 GHz), and X‐band (7.25‐7.75 GHz), respectively. The notched‐band frequency can be controlled by changing the length of the L‐shaped slot. The proposed antenna has a very small size (20.25 × 8 × 1.27 mm³) compared with previous works. The measured and simulated results show a good agreement in terms of radiation pattern and impedance matching.     

A coplanar waveguide‐fed flexible antenna for ultra‐wideband applications

This paper presents a novel ultra‐wideband (UWB) antenna printed on a 70 μm thick flexible substrate. The proposed antenna consists of a hybrid‐shaped patch fed by coplanar waveguide (CPW). The ground planes on opposite sides of the feeding line have different height to improve antenna bandwidth. Simulation shows that the proposed antenna maintain wide bandwidth when changing its substrate's thickness and dielectric constant, as well as bending the antenna on a cylindrical foam. The proposed antenna is fabricated in laboratory with a simple and low‐cost wet printed circuit board (PCB) etching technique. Measured bandwidths cover 3.06 to 13.58, 2.8 to 13.55, and 3.1 to 12.8 GHz in cases of flat state and bent with radii of 20 and 10 mm, respectively. Measured radiation patterns show the antenna is omnidirectional in flat and bent cases.     

A miniaturized ultra‐wideband planar monopole antenna with L‐shaped ground plane stubs

This article presents a miniaturized ultra‐wideband planar monopole antenna with an oval radiator. The proposed antenna is fed by a coplanar waveguide (CPW), and two L‐shaped stubs are extended from the ground plane of the CPW. This presented antenna is able to produce resonances in the lower frequency band and realize better impedance matching performance in the middle and higher frequency bands with the aid of the L‐shaped stubs. The antenna was built and tested. The total size of the proposed antenna is only 26 × 20 × 1.6 mm³. Its measured –10 dB impedance bandwidth is 10.1 GHz (3.1‐13.2 GHz). The measured far‐field radiation patterns are stable in the whole operating frequency band.     

Design of ultra‐wideband antenna using tapered slot for low‐end frequency extension

In order to extend the lower frequency down, resonant cavities are added to a tapered slot Vivaldi antenna. Using a full‐wave time‐domain method, the effect of the dielectric substrate on the performance of the antenna has been investigated. Permittivity was shown to play an important role in comparisons of wideband frequency range antennas with dielectric constant cases in similar geometries. When dielectric permittivity is increased, the bandwidth is improved, and when the resonant cavity is added, the low‐end frequency response is extended even lower than 500 MHz. Results from a conventional tapered slot edge compared to a tapered slot edge with resonant cavity Vivaldi antennas with different dielectric permittivity qualitatively supports the effect of the different substrate. Verification has been implemented by using the numerical method of pseudospectral time‐domain with alternating‐direction‐implicit method, and by the experiment. The simulation results show very good agreement with the experiment. Both results proved that our design is available.     

Novel compact planar electromagnetic band‐gap structure using for ultra‐wideband simultaneous switching noise suppression

In this article, by analyzing the equivalent circuit mode for electromagnetic bandgap (EBG), a novel compact planar EBG structure is proposed for overcoming the drawback of narrow bandwidth of conventional EBG structures. The novel design is based on using meander lines to increase the effective inductance of EBG patches. The simulated and measured results demonstrate the simultaneous switching noise (SSN) can be mitigated with an ultra‐wideband from 280 MHz to 20 GHz at the restraining depth of ?40 dB. Compared with the traditional L‐bridge and meander lines EBG structures, this novel structure has the advantages of suppression bandwidth and fabrication cost. Moreover, signal integrity is achieved by the time‐domain simulation. The proposed structure provides a new kind of theoretical designing reference for EBG structure to improve the bandwidth of restraining SSN. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:429–436, 2014.     

Flower‐shaped ultra‐wideband fractal antenna

A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S ₁₁ ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm². In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures.     

Reconfigurable ultra‐wideband monopole antenna with single‐, dual‐, and triple‐band notched functions

A miniaturized ultra‐wideband (UWB) monopole antenna with reconfigurable multiple‐band notched performance is demonstrated. By modifying the shape of the patch and the ground plane, the UWB operation is achieved. The first and second band‐notches are respectively generated by etching a rectangular slot with open ends and a U‐shaped slot in the patch, and the third band‐notch is produced by loading a C‐shaped parasitic element beneath the patch. To realize the reconfigurable band‐notched functions, four PIN diodes are inserted in three band‐rejected structures. The antenna has a compact dimension of 30 mm × 26 mm. It can switch between a UWB state and several band‐notch states by alternating the states of the diodes. Also, good radiation patterns are obtained.     

Band‐notched ultra‐wideband antennas using nonperiodic composite right/left‐handed resonators

This article investigates the characteristics of a single/double‐cell composite right/left‐handed (CRLH) resonator and its application on multiple band‐notched ultra‐wideband (UWB) antennas while suggesting an accurate design procedure. Periodicity assumption and calculating a dispersion diagram allow band‐notched frequencies to adequately predict prior to antenna design. Zeroth‐order resonance (ZOR) frequency due to the CRLH characteristics of a mushroom resonator and higher‐order resonance frequencies are predictable through the hypothetical dispersion diagram. To demonstrate this method, compact, printed, ultra‐wideband circular monopole antennas with four/five‐band notched characteristics using a single/double mushroom resonator are presented. The effects of mushroom cell size on ZOR and the other band notched resonant frequencies are also investigated. The numerical simulations show that the asymmetrical unit cell provides the capability to tune both ZOR and band notched frequencies. Comparison between the simulation and measurement results shows reasonable agreement.     

Coplanar waveguide wideband bandpass filter and its application to ultra‐wideband pulse generation

A technique to design wideband coplanar waveguide bandpass filters is reported. The filter is realized by etching a slot on the ground plane around a gap on its central conductor and modifying the gap in the form of parallel lines. It is shown that the 3‐dB fractional bandwidth of the filter can be varied from 60 to 110% by tuning the size of the slot aperture and the length of the parallel lines. Equivalent circuit and design steps are presented. Implementation area of the filter having passband 3.2–10.5 GHz is 0.90 λ_g × 0.26 λ_g, λ_g being the guided wavelength at 6.85 GHz while 20‐dB stopband is at least up to 18 GHz. Insertion loss is less than 2 dB up to 9 GHz. Area of the filter having fractional bandwidth 60% at 3.85 GHz is 0.67 λ_g × 0.11 λ_g. Passband loss is within 1.5 and 20 dB stopband is at least up to 12 GHz. The proposed filter structure is very simple to integrate, and the ultra‐wideband filter is used to generate an ultra‐wideband pulse as defined by the US Federal Communication Commission. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

Advanced system‐level simulation paradigm for ultra‐wideband systems using SCERNE platform

In this article, a progressive system‐level simulation framework is developed based on Simulation de Chaînes d'Emission/Réception Nouvelle gEnération (SCERNE) platform to simulate an ultra‐wideband (UWB) impulse radar transmitter and accurately predict its performance. With the purpose of demonstrating the usefulness of the SCERNE ability in system‐level modeling, we present and simulate a simplified structure of UWB impulse radar transmitter. First, after simulation each component in different circuit‐level tools such as ADS, CST, and HFSS, each part has been modeled by using different modeling methods to transfer their data into MATLAB environment. Then, we duplicate the transmitter structure in SCERNE toolbox to validate the results. The advantage conferred by the proposed SCERNE toolbox is that fast and accurate bilateral modeling method is available at multi‐medium structures in contrast with conventional unilateral modeling, and so a lower memory and higher accuracy of the behavioral model is achieved. It can also be beneficial when the user is looking for system‐level, as the increased components amounts can help as a surrogate model. The system model can be easily extended to other UWB radar systems by simply changing the input pulse shape, UWB channel environment, transceiver topology, etc. Various effects such as signal quality, and pulse shape that can easily investigate and re‐optimize for high performance are using the developed model. To validate the practicality of the proposed paradigm, the simulations and predictions through model results are being outlined.     

Circular ring structured ultra‐wideband antenna for wearable applications

This article explores the design and analysis of a novel ultra‐wideband (UWB) antenna for body‐centric applications. The designed antenna consists of circular ring structured radiating element with 24 spokes, which resembles the shape of Ashoka chakra (Indian National flag emblem). The antenna placed on the semi flexible RT/Duroid 5880 with dielectric constant of 2.2 and occupying the dimension of 30 × 25 × 0.8 mm³. The present design aims at optimizing the antenna structure to cater UWB operating spectrum (3.1‐10.6 GHz) with a novel patch shape, which looks like the Ashoka chakra. The proposed antenna is analyzed by placing on three‐layered human phantom model and examined on head, arm at three of its operating frequencies. The maximum specific absorption rate (SAR) is found to be 1.23 W/kg and 1.29 W/kg when computed at arm and head of the human body respectively. The SAR values are observed under those conditions are satisfying the international safety standards such as FCC & IEEE C95.1:2005 & ICNIPR. Analysis of system savant (ANSYS Savant) radiation performance characteristics are also studied by placing the proposed antenna on virtual human body environment.     

Reconfigurable active frequency selective surface for ultra‐wideband applications

A reconfigurable active frequency selective surface (AFSS) with ultra‐wideband (UWB) characteristics is presented in this article. The proposed AFSS consists of a periodic array of three metal layers and two dielectric layers. PIN diodes are arranged on the top and bottom metal layers which can rebuild the function of AFSS. The transmission bandwidth of the AFSS with OFF‐state diodes is 8 to 12.5 GHz with a fractional bandwidth of 44%, and the transmission coefficient of the FSS with ON‐state diodes is lower than ?10 dB from 2 to 18 GHz. Additionally, the AFSS is angular stable and polarization‐insensitive for both transverse electric and transverse magnetic polarizations. The simulation results show that the proposed AFSS is an effective candidate for radome applications.     

An ultra‐wideband rectenna using optically transparent Vivaldi antenna for radio frequency energy harvesting

This paper presents a novel ultra‐wideband rectenna which consists of a transparent Vivaldi antenna and a wideband rectifying circuit for radio frequency energy harvesting. The antenna is realized on a 2.2‐mm‐thick soda‐lime glass substrate coated with fluorine‐doped tin oxide of thickness 650 nm. It provides an optical transmittance greater than 80% in the visible region. The rectifying circuit with a cascaded matching network and the Greinacher doubler circuit are fabricated on an FR4 substrate with a thickness of 0.8 mm. The antenna provides the best matching characteristics and the realized peak gain is 3.2 dBi. The designed matching network enables maximum power transfer from the antenna to the rectifier. The rectenna provides a peak power conversion efficiency of 69% for ?10 dBm input power. The proposed antenna can be realized on the windscreen of automobiles and glass windows without causing any obstruction to normal view.     

Double‐layer microstrip ultra‐wideband filtering power divider with high selectivity and large isolation

In this article, a compact double‐layer microstrip ultra‐wideband (UWB) filtering power divider with high selectivity and isolation is proposed. The filtering power divider consists of a multimode resonator at the top layer coupled with a pair of branch lines at the bottom through a slotline in the middle ground. The slotline provides strong coupling between the two layers and equally distributes the power to two branch lines. The resistor loaded about a quarter‐wavelength away from the slotline achieves high isolation within UWB range. The UWB filtering properties with controllable transmission poles and zeros as well as power splitting with enhanced isolation have been analyzed. The adjustable transmission zeros of the filter unit enables the bandwidth control of the filtering power divider. Finally, a UWB filtering power divider operating at 3.1 to 10.6 GHz has been designed, fabricated, and measured. It achieves a compact size of only 26 × 28 mm², high isolation about 20 dB, and good out‐of‐band suppression of 40 dB.     

A modified design approach for compact ultra‐wideband microstrip filters

A modified design approach for compact ultra‐wideband microstrip filters with cascaded/folded stepped‐impedance resonators is described. The key feature of the proposed method is to facilitate stronger coupling between stepped‐impedance resonators and, at the same time, eliminate the requirement of extremely small gaps in coupled‐line sections, as found in traditional designs. Simulations and measurements demonstrate that the filters designed with this technique exhibit good reflection, insertion‐loss, and group‐delay performance within the 3.1–10.6 GHz band. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

A wideband reflectarray antenna using single‐layer dipole element attached with T‐shaped stubs

A wideband reflectarray antenna consisting of single‐layer dipole element attached with T‐shaped stubs is proposed. By varying the lengths of the T‐shaped stubs, the unit cell can provide a linear phase curve covering about 420°. Critical design parameters are analyzed to understand its wideband operating mechanism. Using this novel type of unit cells, a 441 element 25° offset‐fed reflectarray with grid spacing of λ/3 at 10 GHz is designed, fabricated, and measured. The experimental results show that the proposed reflectarray can achieve 1‐dB gain bandwidth of 24% and 1.5‐dB gain bandwidth of 37%. In addition, aperture efficiency of 66.6% and cross polarization level of 29 dB are obtained at 10 GHz, respectively.     

Bandwidth and gain‐enhanced composite right/left‐handed antenna for ultra‐wideband applications

A coplanar waveguide‐fed metamaterial antenna is presented for ultra‐wideband (UWB) applications. The proposed antenna is designed with single unit‐cell composite right/left‐handed transmission line (CRLH‐TL) loaded with a split‐ring resonator (SRR). The UWB characteristic is obtained by merging the zeroth‐order resonance of CRLH‐TL with two additional resonances due to the ground plane and SRR respectively. Subsequently, a partial reactive impedance surface is embedded on the rear side of the proposed antenna to enhance the realized gain without affecting the UWB response. The overall size of the antenna is 0.241λ_o x 0.267λ_o x 0.013λ_o (28.8 x 32 x 1.6 mm³), where λ_o is the free space wavelength at 2.51 GHz. The measured results indicate –10 dB fractional bandwidth of 139.19% (2.51‐14 GHz) with realized gains of 2.3, 4.6, and 6 dBi at the resonant frequencies 4, 7.84, and 10.29 GHz respectively. The measured peak realized gain is 6.6 dBi at 10.6 GHz. The radiation efficiency is above 63.85% for the entire UWB range with a peak value of 86.84%. A fairly stable group delay with variation within 1 ns is obtained throughout the operating frequency band. A good agreement has been observed between the measured and simulated results.