Improved Radiation Pattern Research Articles

Wide Bandwidth Ratio of 10-to-1 CPW-Fed Whip Antenna With Improved Radiation Patterns

In this communication, a novel compact single whip wideband antenna with an improved omnidirectional wideband antenna is proposed. First, a single whip antenna is designed on a thin flexible printed circuit (FPC) with a tapered coplanar waveguide feed line. This proposed antenna shows a wide impedance matching performance in a frequency range from 194 to 2124 MHz with a bandwidth ratio of 10:1, while a measured return loss is better than 10 dB within the desired passband. The single whip antenna has demonstrated an ultrawide bandwidth with satisfactory radiation properties in the lower frequency band. However, the omnidirectional radiation pattern deteriorated in the higher frequency band. Three whipped antennas are codesigned to form an improved omnidirectional radiation pattern. Finally, the measured performance of the fabricated antenna shows a good agreement with that obtained through simulation results.

Aperture Reduction Using Downward and Upward Bending Arms for Dual-Polarized Quadruple-Folded-Dipole Antennas

A method to miniaturize the aperture of a dual-polarized quadruple-folded-dipole (QFD) antenna by bending its arms downward or upward is proposed in this letter. Two practical prototypes called downward-bending-arm (DBA) antenna and upward-bending-arm (UBA) antenna are presented and elaborated. Both the DBA and UBA antennas have four pairs of arms bent downward or upward along the four edges of the planar QFDs, respectively, which enable the aperture of the DBA and UBA antennas to shrink to around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.24{\lambda }_0 \times 0.24{\lambda }_0$</tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\rm{\lambda }}}_{0}$</tex-math></inline-formula> is the free-space wavelength at 2 GHz). Both antennas can achieve relatively small apertures while ensuring good matching, isolation, and radiation performances within the band of interest. Especially, the DBA antenna has a lower profile than the UBA antenna while the UBA antenna outperforms the DBA antenna in realized gain by approximately 1 dB. Meanwhile, the UBA antenna has narrower half-power beam width, which will be beneficial in compact massive multiple-input–multiple-output antenna arrays for improved radiation patterns.

Leaky-wave radiating surface on heterogeneous high-κ material for monolithic antenna-frontend integration

In a highly integrated analog radio-over-fiber transceiver, seamless integration of the antenna-frontend is crucial as an antenna is generally implemented on a high-κ material, which is set to highly degrade the antenna's performance. This work is concerned with the radiation behavior improvement of a planar leaky-wave antenna with an inductive partially reflecting surface (PRS) on a high-κ substrate for the development of a highly directive antenna. To begin with, we show how a thin and single-mode resonance (SMR) inductive PRS on high-κ materials in a planar leaky-wave antenna is set to provoke two resonance frequencies (i.e., PRS and cavity resonances) to converge, thereby diminishing the antenna's broadside directivity. By applying an equivalent circuit model, we explain how a multi-mode resonance (MMR) PRS can adequately be applied to address the underlying challenges. Subsequently, the leaky-wave radiation behavior of an antenna with a heterogeneous substrate is investigated and analytical equations are derived and verified with a full-wave simulation. The effects of material permittivity and thickness in a heterogeneous-cavity antenna on leaky-wave performance are investigated using these approximate yet accurate-enough equations. To justify the findings, two 9 × 9 planar leaky-wave antennas are prototyped on heterogeneous substrates based on SMR and MMR PRS and the radiation performances are compared. Our investigations reveal that in the proposed scenario, an MMR PRS can significantly enhance the antenna's broadside directivity by over 4 dBi at the resonance frequency (27.5 GHz), which is also set to improve radiation pattern compared to a SMR-based antenna. Finally, a single-fed dual-band aperture-shared antenna with a large frequency ratio (S-band and Ka-band) is developed and fabricated on a high-κ substrate based on the proposed MMR PRS.

Antipodal Vivaldi Antenna with enhanced gain and improved radiation patterns for 5G-IoT applications using metamaterial and Substrate Integrated Waveguide

An analysis of a novel antipodal Vivaldi antenna (AVA) with constant high gain and enhanced radiation patterns is presented in this paper. The antenna consists of a 1 × 4 AVA array, fed by substrate integrated waveguide (SIW). Next, the corrugations are added to the AVA array with SIW (AVAS) to increase the gain up to 1.5 dBi. Further gain enhancement and radiation pattern improvement are achieved by incorporating square-shaped split-ring resonator (SRR) metamaterial at the aperture of the AVAS array with corrugations (AVAS-C). The designed AVAS-C array with metamaterial (AVAS-CM) provides an enhanced gain of 16.2 ± 0.8 dBi over the 37.9 GHz to 45 GHz frequency range. Also, the proposed AVAS-CM array gives stable radiation patterns. Its front-to-back ratio (FBR) is above 21.3 dB, the sidelobe level (SLL) is below −13.6 dB, and E-plane beam titling is ±1∘. In compact devices, an antenna with low FBR and SLLs is essential to avoid radiations in the wanted directions to alleviate the degradation of electronic components. This paper presents the first time use of the SIW technique for improving the radiation pattern characteristics of the AVA array. Experimental and simulated results show that it is suitable for compact 5G-IoT devices.

220 GHz High-Gain Substrate Integrated Antennas With Low Fabrication Cost Based on Higher Order Mode and PCB Technology

In millimeter-wave (MMW) and terahertz (THz) bands, the operation frequency is high and there are challenges in fabrication and microassembly processes, bringing high-accuracy requirements and high manufacturing cost. In this article, high-gain substrate integrated antennas with low fabrication cost are presented for MMW/THz applications. The basic antenna consists of two parallel TE201 resonant cavities and is directly fed by a grounded coplanar waveguide (GCPW). Radiation slot apertures are modified to increase aperture radiation efficiency and improve radiation patterns and gain. The antenna scheme is analyzed and a 220 GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times2$ </tex-math></inline-formula> slot array antenna is developed as an example. To further improve the antenna gain with low fabrication cost and low feeding network loss, the basic antenna is explored to feed a modified dielectric plate lens. The high-gain scheme and design flowchart are provided. Both basic and improved structures are fabricated by normal single-layer printed circuit board (PCB) technology and high antenna gains are achieved. The measured peak gain of the basic antenna and the antenna with dielectric plate lens are 13.5 and 20.2 dBi, respectively. The measured return losses are better than 10 dB from 192 to 247 GHz. The antennas have advantages of simple antenna feeding structure, low fabrication cost, wide bandwidth, and high gain.

A Multiband Tree-shaped Microstrip Antenna for Wireless Communication

In the modern world, wireless communications are growing very fast and changing the world of antennas. Conventional antennas are insufficient to meet the requirements in the field of wireless communications. The continuous evolution of wireless communication systems has added cost, size, bandwidth, gain, and polarization constraints to the antennas used. In this paper, the performance of the microstrip antenna is enhanced by overlapping the patch elements. A tree-shaped micro-strip antenna is presented here, in which the tree-shaped geometry emerged from five overlapping circles on the substrate. The proposed antenna could operate in the X and Ku bands. The antenna is resonant at 9.3 GHz, 10.07 GHz, 11.76 GHz, and 13.16 GHz frequencies and has various applications such as satellite communications, radar, terrestrial broadband, space communications, and amateur radio. The built antenna has an improved radiation pattern as compared to conventional antennas.

A wearable low profile asymmetrical slotted ultra-wide band antenna for WBAN applications

In this article a low profile asymmetrical slotted Ultra-Wide Band (UWB) antenna is proposed for Wireless Body Area Networks (WBANs) applications. The antenna was fabricated using Printed Circuit Boards (PCBs). An improved radiation pattern was obtained with an optimized patch shape of the antenna that broadens the bandwidth and lowers the antenna’s profile. The proposed antenna is simulated in HFSS and CST Simulator, and the proposed antenna is fabricated on FR4 substrate with the reduced ground plane. In frequency ranges from 2.50 to 10.97 GHz simulation as well as measured results show that the reflection coefficient (S11) of the antenna is below − 10 dB and increased impedance bandwidth of 126%. The proposed antenna has desired radiation pattern and gain for wearable application. The wearable performance of proposed antenna on chest, leg, and the arms of the human body is analyzed with Specific Absorption Rate (SAR). The maximum value of the SAR is 0.785 W/Kg which is less than threshold value of 1.6 W/kg. The time-domain behavior of proposed antenna is investigated with the time domain parameters such as Group delay, Fidelity factor and Mean realized gain. The time domain results are evident for the proposed antenna is capable of pulse signal transmission and reception.

A Study on Gain Enhanced Leaf-Shaped Bow-Tie Slot Array Antenna within Quasi-Millimeter Wave Band

In this paper, a linear array of 4 leaf-shaped bowtie slot antennas is proposed for use in quasi-millimeter wave band. The slot antennas array is designed to operate at 28 GHz frequency band. The leaf-shaped bowtie slot antenna is a type of self-complementary antenna with low profile and low cost of fabrication. The proposed antenna structure offers improvement in radiation pattern, gain, and -10 dB impedance bandwidth. Through out of this paper radiation pattern, actual gain, and -10 dB impedance bandwidth are evaluated by Finite Different Time Domain (FDTD) simulation. Antenna characteristics are analyzed in the frequency range of 27 GHz to 29 GHz. To improve antenna characteristics such as actual gain and -10 dB impedance bandwidth, a dielectric superstrate layer with relative permittivity of 10.2 is placed on top of ground plane of the slot antennas array. Three antenna structures are introduced and compared. With two layers of dielectric superstrate on top of the antennas ground plane, analysis results show that -10 dB impedance bandwidth occupies the frequency range of 27.17 GHz to 28.39 GHz. Therefore, the operational impedance bandwidth is 1.22 GHz. Maximum actual gain of the slot antennas array with two dielectric superstrate layers is 20.49dBi and —3 dB gain bandwidth occupies the frequency range of 27.02 GHz to 28.57 GHz. To validate the analysis results, prototype of the designed slot antennas array is fabricated. Characteristics of the slot antennas array are measured and compared with the analysis results.

All 3-D Printed Antennas Based on Phase Velocity Control for Beam Steering and Size Reduction With Low Cost

A concept based on engineering a dielectric filling material to adjust the phase velocity of the propagating electromagnetic wave in a horn antenna is proposed. The resulting transformation from the spherical to plane wave at the aperture is used to prove that the size reduction of the horn is achievable. The designed antenna demonstrates more than 50% size reduction with improved radiation pattern, including the sidelobe level (SLL) and satisfactory gain when compared to the commercial horn antenna. It also offers a wide bandwidth from 22 to 26.5 GHz. This design is further elaborated for a continuous, from −21° to +21°, beam steering along the electric polarization implementation by asymmetrical dielectric insertions, with a measured relative bandwidth around 27.1%. The two simple designs are liquid crystal display (LCD) 3-D printed using a commercial UV resin, with the relative permittivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r} =2.75$ </tex-math></inline-formula> and loss tangent around 0.025. The fabrication method allows easy control of the effective permittivity of dielectric–air combined units at low cost.

Through Wall Imaging Radar Antenna with a Focus on Opening New Research Avenues

This review paper is an effort to develop insight into the development in antennas for through wall imaging radar application. Review on literature on antennas for use in through wall imaging radar, fulfilling one or more requirements/specifications such as ultrawide bandwidth, stable and high gain, stable unidirectional radiation pattern, wide scanning angle, compactness ensuring portability and facilitating real-time efficient and simple imaging is presented. The review covers variants of Vivaldi, Bow tie, Horn, Spiral, Patch and Magneto-electric dipole antennas demonstrated as suitable antennas for the through wall imaging radar application. With an aim to open new research avenues for making better through wall imaging radar antenna, review on relevant compressive reflector antennas, surface integrated waveguide antennas, plasma antennas, metamaterial antennas and single frequency dynamically configurable meta-surface antennas are incorporated. The review paper brings out possibilities of designing an optimum through wall imaging radar antenna and prospects of future research on the antenna to improve radiation pattern and facilitate overall simple and efficient imaging by the through wall imaging radar.

Near-zero-refractive-index metasurface antenna with bandwidth, directivity and front-to-back radiation ratio enhancement

In this paper, a novel metasurface-based Fabry–Perot Cavity antenna is presented. The antenna is wideband, directive and has a high front-to-back ratio. The idea of the antenna is based on loading a microstrip narrow band patch antenna resonating at 4.6 GHz by a metasurface superstrate. The metasurface superstrate consists of an aperiodic array of holes in contrast to the periodic nature of unit cell previously explored in the literature. The metasurface is designed as a near-zero-refractive-index material (NZRIM). By controlling the phase reflection properties of the structure, improved radiation pattern, improved front-to-back lobe ratio (7–25 dB), improved directivity (by 3 dB) and antenna bandwidth (five times) are obtained compared to a conventional microstrip antenna. The enhancement in bandwidth and directivity simultaneously using just a single layer of metasurface superstrate demonstrated for the first time, to best to authors’ knowledge, are obtained.

A monolithic missile radome with improved radiation patterns for application in frequency modulated continuous wave radar

In this letter, a monolithic missile radome for application in frequency modulated continuous wave radar (FMCWR) at missile warhead is proposed with improved radiation performance. The radome is cone-shaped and two patch antenna subarrays for transmission and reception are placed off the central line of radome. To address the issues of radiation distortion caused by radome, an improved radome with variable thickness is proposed. Theoretical analysis is conducted to reveal the working principle, which demonstrates that proper condition of radome thickness can minimize the adverse effects of field reflection and phase delay on radiation patterns. By further optimizing the radome thickness through simulation, the ripple variation of main beam is mitigated and radiation patterns become more symmetric. Simulated and measured results show that the radiation performance of the antenna with proposed radome has been significantly improved as compared with that of the antenna with uniform thickness radome (UTR).

A Wideband Pattern Diversity Antenna With a Low Profile Based on Metasurface

In this letter, a low-profile wideband pattern diversity antenna based on metasurface (MTS) is proposed. Initially, based on the theory of characteristic mode (TCM), the two adjacent intrinsic modes, which correspond to the broadside and conical radiation pattern, respectively, are exploited to realize a wideband pattern diversity characteristic under a low profile. Then, by analyzing the modal current distribution on the MTS, the optimal locations, orientations and relative phases of the four L-shaped feeding probes are determined to excite the above two modes. However, the in-band high-order modes (HOMs) introduced by the feeding structure will deteriorate the radiation pattern. Therefore, chamfering corners on the MTS is used to suppress the HOMs for radiation pattern improvement. Finally, by combining TCM and MTS, the modes are manipulated to achieve a pattern diversity antenna with an extremely low profile of 0.06 λ0 (the free-space wavelength at the center frequency) and an isolation of better than 38 dB, which also maintains an operating bandwidth of 20.24%. Based on these excellent performances, the proposed antenna is an attractive solution for pattern diversity applications requiring low profile, especially in unmanned aerial vehicle communications.

An optimal compact time-modulated circular antenna array synthesis using krill herd optimization

In this paper, an optimal far-field radiation pattern synthesis by using time modulation technique is carried out for a compact circular antenna array (CAA) design using a stochastic optimization method called krill herd (KH) optimization. A compact antenna array is achieved by reducing the inter-element spacing between the array elements, which leads to the miniaturization of the size of the array. On the other hand, an improved far-field radiation characteristic is achieved with a low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is an essential requirement to reduce the interference with the other systems operating in the same frequency band. A narrow FNBW is necessary to obtain a high directivity. In time modulation technique, ‘time’ has the most significant role. It is considered the fourth-dimensional parameter, which plays the role of an additional degree of freedom to achieve an improved radiation pattern. The time-modulated antenna array (TMAA) radiates at various harmonic frequencies for the periodic switching time sequence. In this paper, the generation of the radiation pattern at the fundamental/central frequency only is considered. The KH algorithm is a flexible and robust search algorithm. It is applied here to find out the optimum sets of switching on-time duration for each array element and to determine the optimum inter-element separation between two array elements of the 20- and 36-element time-modulated circular antenna array (TMCAA). Particle swarm optimization (PSO) and differential evolution (DE) optimization techniques are also individually applied for the same design purpose to prove the superiority of the KH algorithm–based design. Finally, statistical analysis is performed to ensure the significance of the numerical results.

Ultralow Profile, Low Passive Intermodulation, and Super-Wideband Ceiling Mount Antennas for Cellular and Public Safety Distributed Antenna Systems.

This paper presents an ultralow profile, low passive intermodulation (PIM), and super-wideband in-building ceiling mount antenna that covers both the cellular and public safety ultra high frequency (UHF) band for distributed antenna system (DAS) applications. The proposed antenna design utilizes a modified 2-D planar discone design concept that is miniaturized to fit into a small disc-shaped radome. The 2-D planar discone has an elliptical-shaped disc monopole and a bell-shaped ground plane, a stub at the shorting path, with asymmetrical structure and an additional proximity coupling patch to maximize the available electrical path to support the 350 MHz band range. The proposed design maximizes the radome area with a reduction of about 62% compared to similar concept type antennas. Besides, the proposed design exhibits an improved radiation pattern with null reduction compared to a typical dipole/monopole when lies at the horizontal plane. A prototype was manufactured to demonstrate the antenna performance. The VSWR and radiation pattern results agreed with the simulated results. The proposed antenna achieves a band ratio of 28.57:1 while covering a frequency range of 350–10000 MHz. The measured passive intermodulation levels are better than −150 dBc (2 × 20 Watts) for 350, 700 and 1920 MHz bands.

A Miniaturized Butler Matrix Based Switched Beamforming Antenna System in a Two-Layer Hybrid Stackup Substrate for 5G Applications

This work presents a Butler matrix based four-directional switched beamforming antenna system realized in a two-layer hybrid stackup substrate for 28-GHz mm-Wave 5G wireless applications. The hybrid stackup substrate is composed of two layers with different electrical and thermal properties. It is formed by attaching two layers by using prepreg, in which the circuit components are placed in both outer planes and the ground layers are placed in the middle. The upper layer that is used as antenna substrate has εr = 2.17, tanδ = 0.0009 and h = 0.254 mm. The lower layer that is used as a Butler matrix substrate has εr = 6.15, tanδ = 0.0028 and h = 0.254 mm. By realizing the antenna array on the lower-εr layer while the Butler matrix on the higher-εr layer, the Butler matrix dimension is significantly reduced without sacrificing the array antenna performance, leading to significant overall antenna system size reduction. The two-layer substrate approach also significantly suppresses parasitic radiation leaking from the Butler matrix toward the antenna side, allowing overall radiation pattern improvement. The fabricated beamforming antenna is composed of 1 × 4 patch antenna array and a 4 × 4 Butler matrix. The measured return loss is lower than −8 dB at all ports in 28-GHz. It demonstrates the switched beam steering toward four distinct angles of—16°, +36°, −39°, and +7°, with the sidelobe levels of −12, −11.7, −6, and −13.8 dB, respectively. Antenna gain is found to be about 10 dBi. Due to the two-layer hybrid stackup substrate, the total antenna system is realized only in 1.7λ × 2.1λ, which shows the smallest form factor compared to similar other works.

A Low-Profile Printed Cavity Antenna With Simultaneous Bandwidth and Radiation Pattern Improvement

A low-profile printed cavity antenna (PCA) under triple-mode resonance is proposed towards a simultaneous impedance bandwidth and a radiation pattern improvement. Based on the cavity model, the far-zone radiated fields of the PCA are theoretically investigated. The results demonstrate that its E -plane half-power beamwidth (HPBW) could be significantly improved by using two half-mode cavities instead of a single-patch resonator. After that, the width of the radiating patch is progressively enlarged and separated in order to excite three resonant modes for bandwidth-enhancement. Moreover, two additional conductive vias are loaded below the radiating patch in order to reduce its increased E -plane cross polarization. In final, the proposed antenna is fabricated and tested. Experimental results show that its impedance bandwidth is obviously extended to about 14.3% with appearance of three in-band attenuation poles. Meanwhile, a low-profile property with the height of 0.027 free-space wavelength is achieved. In particular, the PCA has acquired a wide E -plane HPBW of around 135°, while keeping a low cross polarization of below –20 dB in both E- and H-planes.

An optimal far‐field radiation pattern synthesis of time‐modulated linear and concentric circular antenna array

AbstractIn this paper, an optimal far‐field radiation pattern synthesis by using time modulation technique is carried out for linear antenna array (LAA), and concentric circular antenna array (CCAA) designs using a stochastic optimization method called grey wolf optimization (GWO). An improved far‐field radiation characteristic mainly depends on the synthesis of low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is a requirement to reduce the interference by the other systems operating in the same frequency band. A narrow FNBW is necessary to obtain a high directivity. In time modulation technique, “time” has a most significant role. It is considered as the fourth‐dimensional parameter as it plays the role of an additional degree of freedom to achieve an improved radiation pattern. The time‐modulated antenna array (TMAA) radiates at various harmonic frequencies for the periodic switching time sequence. In this paper, the generation of radiation pattern only at the fundamental/central frequency and at its first two harmonic frequencies are considered. The GWO algorithm is a flexible and robust search algorithm and is applied here to find out the optimum sets of switching on‐time duration for each array element and to determine the optimum inter‐element separation between two array elements of the 16‐element time‐modulated linear antenna array (TMLAA) and the nine‐ring time‐modulated concentric circular antenna array (TMCCAA). The GWO algorithm‐based results show a substantial improvement in far‐field radiation pattern synthesis compared with the uniform radiation pattern and those of the methods reported in state‐of‐the‐art literature.

A Low-Profile Wideband Aperture-Fed Microstrip Antenna With Improved Radiation Patterns

A low-profile wideband aperture-fed microstrip patch antenna (MPA) under radiation of TM12 and TM30 modes is proposed with improved radiation patterns. Initially, the radiation characteristic of a rectangular MPA operating in TM30 mode is theoretically investigated. The results demonstrate that its E-plane sidelobe could be gradually reduced by decreasing the resonant frequency of TM30 mode ( ${f} _{30}$ ). As such, a pair of parallel slots is etched out on the radiating patch so as to significantly decrease the ${f} _{30}$ . After that, the MPA under an operation of TM12 mode is further studied. It illustrates that its radiation pattern has the maximum off broadside direction and can be transformed into the broadside radiation by enlarging the length of the parallel slots. In addition, the width of the radiating patch is progressively enlarged in order to reallocate the dual modes in proximity to each other. With these arrangements, a wide bandwidth with improved radiation characteristics is obtained for the antenna under dual resonance. Finally, a prototype aperture-coupled MPA is fabricated and measured. The simulated and measured results agree well with each other, thus demonstrating that its impedance bandwidth is dramatically extended to about 14.8% with a low-profile property of about 0.048 free-space wavelength in thickness. Besides, the antenna has achieved a stable gain varied from 7.0 to 9.9 dBi over the operating band. In particular, the E-plane sidelobe level of the proposed antenna has been successfully suppressed.

Wideband High Gain Printed Quasi-Yagi Diffraction Gratings-Based Antenna for 5G Applications

A broadband high-gain printed Quasi-Yagi antenna with a perturbation-based planar dielectric lens is presented. The perturbation design parameters are based on the diffraction gratings theory for gain enhancement, radiation pattern improvement, and higher order modes suppression. The proposed antenna provides 94.5% aperture efficiency with a high gain of 15 dBi at 30 GHz, high radiation efficiency of ~90%, and (24-40) GHz ultra-wide matching (S11 <; -10 dB) bandwidth. The measured cross-polarization is lower than -20 dB in both E - and H- planes. With these features in addition to being low-profile and lightweight, this antenna is suitable for various millimeter-wave applications.