Closed-form expressions for computer-aided design of microstrip ring antennas

This article presents closed-form expressions for the resonant frequency and radiation characteristics of microstrip ring antennas to assist in the computer-aided design of such antennas. Radiation fields are obtained using the vector electric potential calculated from the magnetic currents flowing along the inner and outer edges of the planar waveguide model for the microstrip ring structure. Expressions for radiated power, conductor and dielectric loss factors, resonant resistance, efficiency, and directivity are derived. The smaller the radius of curvature of the ring, the larger is the spacing between the magnetic currents flowing along the inner and outer edges and thus the radiation efficiency is higher. The effect of a dielectric layer covering the ring antenna is also included. Experimental results for the resonant frequency and the radiation patterns agree well with the theoretical predictions. © 1992 John Wiley & Sons, Inc.     

Effect of heterogeneity in additively manufactured dielectric structures on RF response of microstrip patch antennas

Microstrip patch antennas with a tunable radiofrequency (RF) response are a great candidate for additive manufacturing (AM) process. First, three separate sets of ABS samples were created at three different machine preset fill densities using an extrusion based 3D printer. Once fabricated, actual solid volume fraction of each set of samples was measured using a 3D X‐ray computed tomography microscope. It is observed that the factory preset fill‐density values are only applied to the core region and actual solid volume fractions for each sample set are different from printer‐preset values. Also, the printed materials appeared to exhibit anisotropy such that the thickness direction dielectric properties are different from the in‐plane properties (planar isotropy). Microstrip patch antennas created on the AM fabricated ABS were tested for resonant frequencies using a vector network analyzer (VNA). The measured resonant frequencies combined with ANSYS‐HFSS simulation were used to estimate bulk dielectric constant of ABS and equivalent dielectric properties in planar and thickness directions. It is observed that the antenna resonant frequency decreases with an increase in core solid volume fraction. Also, in‐plane permittivity appeared to have minimal effect on antenna resonant frequency, while the thickness direction properties have substantial effects.     

Investigations on modified rectangular fractal curve shaped dielectric resonator antenna

In this article, a modified fractal rectangular curve (FRC)‐shaped dielectric resonator antennas (DRA) with two different functionalities is reported. These antennas are split in the middle into two halves and are excited by a coaxial probe. In first configuration, the fractal geometry is used to achieve wide bandwidth from 3.5 to 5.0 GHz covering the body area network frequencies as well as the IEEE 802.11a WLAN frequencies. The average peak gain within the band is about 7 dBi. The second investigation involves miniaturization of rectangular DRA by using FRC along the cross‐sectional boundary. By this, a DRA at 3.2 GHz could be realized using second iteration of modified rectangular curve fractal geometry resulting in a 50% size reduction by maintaining same radiation characteristics. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

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.     

Recent developments in bandwidth improvement of dielectric resonator antennas

This article shows a compressed chronological overview of dielectric resonator antennas (DRAs) emphasizing the developments targeting to bandwidth performance characteristics in last three and half decades. The research articles available in open literature give strong information about the innovation and rapid developments of DRAs since 1980s. The sole intention of this review article is to, (a) highlight the novel researchers and to analyze their effective and innovative research carried out on DRA for the furtherance of its performance in terms of only bandwidth and bandwidth with other characteristics, (b) give a practical prediction of future of DRA as per the past and current state‐of‐art condition, and (c) provide a conceptual support to the antenna modelers for further innovations as well as miniaturization of the existing ones. In addition some of the significant observations made during the review can be noted as follows; (a) hybrid shape DRAs with Sierpinski and Minkowski fractal DRAs seems comfortable in obtaining wideband as well as multiband, (b) combination of multiple resonant modes (preferably lower modes) can lead to wider impedance bandwidth, (c) at proper matching wider patch with slotted dielectric resonator can exhibit better bandwidth.     

Modelling of probe‐fed cylindrical dielectric resonator antennas

Probe‐fed cylindrical dielectric resonator antennas (CDRAs), with dielectric constant ϵ_r=37 and supported by an infinite ground plane, are simulated using the finite element method. From this, closed form expressions are obtained for the resonant frequency, directivity, and unloaded Q‐factor, applicable to a wide range of antenna dimensions. The effects of (a) the finite circular ground plane, (b) the air gap between the CDRA and the ground plane, (c) the air gap between the CDRA and the feed probe, and (d) the length of the probe on these parameters are studied for a particular CDRA and appropriate correction factors are derived. The simulated results are compared with those obtained experimentally for various ground planes, probe lengths, and probe spacings. The closed form expressions provide good agreement with the experiments in resonant frequency, unloaded Q‐factor, and impedance bandwidth, but less accurate prediction in antenna directivity for the specified range of parameters. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 2–13, 1999     

Rigorous analysis of uniaxial bi‐anisotropic dielectric resonators by the mode matching method

Rigorous analysis of uniaxial bi‐anisotropic dielectric resonators is carried out by the mode matching method. To validate our numerical model, results are satisfactorily compared with the literature for a uniaxial electric anisotropic dielectric resonator (DR). Then bi‐anisotropy effects of DRs dielectric materials on their resonant frequencies are studied in detail. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 385–393, 1999.     

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.     

A wideband stacked dielectric resonator antenna for 5G applications

A wideband stacked dielectric resonator antenna with stable patterns is proposed for fifth‐generation of mobile technology in this paper. With the help of inserted air gaps to reduce the radiation Q factor, the stacked structure with two thin high permittivity sheets and two hollow low permittivity slabs can provide four adjacent resonant modes to form a wide bandwidth. Measured results demonstrate that the antenna obtains an impedance bandwidth of 54% for |S₁₁| < ?10 dB and a peak gain of 9.2 dBi. The radiation patterns remain stable and symmetrical over the entire operating band.     

一种超磁致伸缩材料和声表面波谐振器构成的复合磁传感器

设计了一种新的超磁致伸缩材料和声表面波谐振器构成的复合磁传感器.该传感器将超磁致伸缩材料在磁场中产生的应力应变传递到声表面波谐振器上,改变其谐振频率,通过对谐振频率的检测进行磁场测量.该传感器可以用于静态和动态磁场测量,并且可用作无源、无线磁传感器.主要分析了该结构用于静态磁场测量的原理,给出了实验结果.传感器谐振频率的变化对于静态磁场变化的灵敏度可达132 Hz/Oe,谐振频率测量分辨率在1 Hz时,磁场测量分辨率可达10-7T数量级.     

—种超磁致伸缩材料和声表面波谐振器构成的复合磁传感器

设计了一种新的超磁致伸缩材料和声表面波谐振器构成的复合磁传感器．该传感器将超磁致伸缩材料在磁场中产生的应力应变传递到声表面波谐振器上，改变其谐振频率，通过对谐振频率的检测进行磁场测量．该传感器可以用于静态和动态磁场测量，并且可用作无源、无线磁传感器．主要分析了该结构用于静态磁场测量的原理，给出了实验结果．传感器谐振频率的变化对于静态磁场变化的灵敏度可达132Hz／Oe，谐振频率测量分辨率在1Hz时，磁场测量分辨率可达10^-7T数量级．     

Dielectric resonator antennas—a review and general design relations for resonant frequency and bandwidth

Open dielectric resonators (DRs) offer attractive features as antenna elements. These include their small size, mechanical simplicity, high radiation efficiency due to no inherent conductor loss, relatively large bandwidth, simple coupling schemes to nearly all commonly used transmission lines, and the advantage of obtaining different radiation characteristics using different modes of the resonator. In this article, we give a comprehensive review of the modes and the radiation characteristics of DRs of different shapes, such as cylindrical, cylindrical ring, spherical, and rectangular. Further, accurate closed form expressions are derived for the resonant frequencies, radiation Q-factors, and the inside fields of a cylindrical DR. These design expressions are valid over a wide range of DR parameters. Finally, the techniques used to feed DR antennas are discussed. © 1994 John Wiley & Sons, Inc.     

Rotationally symmetric FDTD for wideband performance prediction of TM01 DR filters

The generalized perfectly matched layer (GPML) coupled with rotationally symmetric (RS)‐FDTD method has been utilized to extract the S‐parameters for several probe‐coupled TM₀₁ dielectric resonator (DR) filters to directly obtain the theoretical wideband spurious performance. The computationally efficient (RS)‐FDTD method has also been used to obtain accurate filter parameters for TE₀₁ and TM₀₁ dielectric resonators loaded in cylindrical cavities. The RS‐FDTD method combined with digital filtering and the Matrix Pencil technique are used to analyze the resonant frequencies, inter‐resonator coupling, and external Q values. When perturbation theory is used with RS‐FDTD, accurate values of unloaded Q are obtained. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 259–271, 2002.     

Modeling of electromagnetic band gap structures: A review

This article represents a comprehensive review of the research carried out on analytical and numerical methods modeling of electromagnetic band‐gap (EBG) structures used in around last two decades. Because of the unique characteristics of the surface wave reduction as well as perfect magnetic conductor (PMC) like behavior, the EBG structures have created their separate existence in antenna engineering society. These structures are being widely used in designing of several microwave planar circuits including printed antennas, printed microwave filters, etc. The purpose of this article is to present an inclusive review of analytical methods as well as numerical methods in the context of modeling of EBG‐structures. Such a review process is rarely carried out in the open literature to the best of authors' knowledge. The review exercise might be helpful to the researchers working on modeling of EBG‐structures as well as of EBG‐structured printed antennas, microwave planar filters, etc.     

CPW fed grid dielectric resonator antennas with enhanced gain and bandwidth

Metal embedded grid artificial dielectric resonator antennas (GDRAs) fed by different coplanar waveguide (CPW) feeding techniques at mm‐wave frequencies are investigated in detail. GDRAs involve embedding tall nickel metal inclusions in polymethyl‐methacrylate (PMMA) using deep X‐ray lithography and electroforming, which dramatically increases the effective permittivity of the polymer up to 5‐6 times and results in miniaturized antenna structures operating at millimeter‐wave frequencies. The options for different coplanar waveguide (CPW) feeding at 22.6‐26.6 GHz and 26.6‐29.3 GHz are studied by applying a thin 300 μm PMMA layer between the feed layer and metal inclusions of the GDRA to avoid short‐circuiting the underneath feed line structures. In addition, this results in a GDRA structure that improves the impedance bandwidth up to 16.26%, while providing a maximum realized gain of 7.2 dBi across the frequency band with excellent broadband patterns and ?18 dB cross‐polarization levels.     

Pole‐zero analysis and wavelength scaling of carbon nanotube antennas

Carbon nanotube (CN) antennas have applications in the THz electromagnetic spectrum. Nanotubes have a highly dispersive and frequency dependent conductivity model. In this article, we compare the poles and zeros in the input impedance of CN antennas at different lengths. We used model‐based parameter estimation to approximate the input impedance of the antenna with a rational function in the complex frequency domain. Despite dispersive conductivity of CN, the imaginary part of the poles and zeros are respectively the integer multiples and odd multiples of the imaginary part of the first pole and zero. However, the real part of poles is almost constant, while the pattern was not observed for the real part of zeros. We also show that CN dipoles operating between 43 and 53 GHz are well matched if the source impedance is much higher than 50 ohms, and even higher than 12.9 kΩ. The fundamental resonances (f₀) of CN dipoles plotted versus their inverse‐half‐length (1/L) are linearly related, but the intercept of the fitted straight line is non‐zero unlike that for perfect electric conductor (PEC) dipoles. This leads to non‐linear variation in wavelength scaling of CN dipoles. The resonant CN antennas are relatively much shorter than PEC dipoles.     

Microwave antennas—An intrinsic part of RF energy harvesting systems: A contingent study about its design methodologies and state‐of‐art technologies in current scenario

With the significant rise of low power embedded devices in various applications of both consumer and commercial usage, the surge for continuous power requirements has initiated promising research toward alternative sources of energy. It includes the domain of wireless power transmission, internet‐of‐things, wireless sensor nodes, machine‐to‐machine, and radio frequency identification. Thus, the overall scope of this review article is to witness microwave antennas and its implementation in RF energy harvesting system through ambient RF signals. For this reason, unified understanding of classical electromagnetism is needed; beginning with the fundamentals of RF transmission and the exploration of concepts such as Fraunhofer's Distance and Friis Transmission Equation. It is followed up by the analogy of dependency of parameters like circuit build‐up, conversion efficiencies and amount of power harvested, which is quite crucial from the rectifier point‐of‐view. For better improvisement in RF energy harvesting systems, five different cases of monopole antennas are explored with reflector surfaces such as PEC (perfect electrical conductor) and AMC (artificial magnetic conductor) integrated with the rectifier circuit. Implementation with wide diversity has proposed a generalized solution for achieving tradeoffs: polarization and pattern diversity with consistent system efficiency; leads to clean and sustainable energy for low power‐embedded devices.     

Parametric study of novel types of dielectric resonator antennas based on fractal geometry

Dielectric resonator antennas with fractal cross sectional areas have been investigated. Two main configurations of these novel types of dielectric resonator antennas have been examined. Analyses of these proposed dielectric resonator antennas are performed numerically using the finite element method and verified by the finite integration technique. Agreement between the methods is excellent. The effects of antenna parameters, such as fractal iteration level and tapering rate of dielectric resonator, are investigated. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Design guidelines for single and dual wide band leaky periodic microstrip line antennas

Leaky wave antennas using periodic microstrip lines are natural choices for versatile beam scanning applications. In this work, a shorted stub and an open stub are simultaneously used in the same unit cell to generate resonant frequencies dependent on the stub dimensions. Placing one such resonant frequency at the second Bragg stop band, a single wideband response is obtained. Next, the stub lengths are tuned to obtain two resonant frequencies which are placed at the second and fourth Bragg stop bands, respectively to obtain a dual wideband response. Design guidelines are outlined for obtaining these wide bands and corresponding radiation regions. Two such geometries with single and dual‐band nature are fabricated. The single wide‐band antenna has a pass‐band from 5.89 to 11.57 GHz with a beam scanning range of ?56° to 33°. The dual‐band antenna has two pass‐bands radiating in the frequency range 5‐6.5 GHz and 10.7‐14.7 GHz. Beam scanning range in the first pass‐band is ?72° to ?5°. The second pass‐band, in part, demonstrates a dual‐beam nature with the forward beam scanning from 28.9° to 54.5° and backward beam scanning from ?54.5° to 14.76° as the frequency varies from 12 to 14.5 GHz.     

Stacked rectangular dielectric resonator antenna with different volumes for wideband circular polarization coupled with step‐shaped conformal strip

This paper presents a wideband circularly polarized broadside radiation characteristics by using stacked rectangular dielectric resonator antenna (DRA) with different volumes. In this designed antenna, the wide input impedance‐ and axial ratio (AR)‐bandwidths come from three factors: stacked rectangular DR with different volumes, stepped‐shaped conformal strip associated with microstrip line as a feed and different type of partial ground plane. Here, the orthogonal TE^x_δ11 and TE^y_1δ1 modes have been responsible for the generation of CP radiation in stacked rectangular DRA. Measured results show that the proposed stacked rectangular DRA with different volumes achieves input impedance bandwidth of 54.84% while AR bandwidth has been found to be 11.53%. The proposed antenna provides broadside right‐handed CP radiation pattern with gain ranges from 2.27–5.80 dBic and offers an average radiation efficiency of 89.48%, across the entire working bandwidth, respectively. Therefore, this antenna is very much useful for the ISM 2400 band applications.