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This paper presents an innovative and condensed blueprint for an ultra‐wideband (UWB) printed monopole antenna, aiming to augment bandwidth and achieve dual band‐stop capabilities, all while accounting for the impact of the human body model on stop bands. The proposed design showcases a square radiating patch situated on the top layer of the substrate, complemented by a ground plane etched on the underside, integrating two sets of adapted U‐shaped slots. Such a configuration delivers a broad operational fractional bandwidth that surpasses 132%. Within our design, a modified C‐shaped slot in the radiation patch creates the first band‐stop property, while a pair of modified F‐shaped slots etched in the radiation patch generates the second stop‐band property. Measuring 12 mm × 18 mm × 0.8 mm, the antenna offers a compact form factor, broad bandwidth, cost‐effectiveness, omnidirectional radiation patterns within the H‐plane and acceptable behavior for using in In‐body microwave applications. [ABSTRACT FROM AUTHOR]

This article presents two monopole antennas with an endfire radiation pattern in the UHF band that can be installed on dry walls or metallic cabinets as a part of wireless sensor nodes, making them a suitable choice for smart home applications, such as the wireless remote control of house appliances. Two different antennas are proposed to cover the RFID bands of North America (902–928 MHz) and worldwide (860–960 MHz). The antennas have wide horizontal radiation patterns that provide great reading coverage in their communication with a base station placed at a certain distance from the antennas. The structures have two ground planes, one in-plane and the other vertical. The vertical ground helps the antenna to have a directive radiation and also makes it easily installed on walls. The antenna feeding line lies over the vertical ground substrate. The maximum dimensions of the narrow-band antenna are L × W = 0.3 λ   × 0.14 λ , and those for the wide-band antenna are L × W = 0.39 λ   × 0.14 λ. The measured results show that the bandwidth of the proposed antennas for the North America and worldwide RFID bands are from 902 MHz to 939 MHz and 822 MHz to 961 MHz, with maximum gains of 4.2 dBi and 4.9 dBi, respectively. [ABSTRACT FROM AUTHOR]

This letter proposes a millimeter‐wave dual‐polarized (DP) end‐fire frequency scanning antenna utilizing low temperature co‐fired ceramic (LTCC) technology. The antenna features DP radiating elements, each comprising a quasi‐Yagi antenna for horizontal polarization (H‐pol) and a pyramidal horn antenna for vertical polarization (V‐pol). These elements are excited via a mode‐composited transmission line (MCTL), integrating substrate integrated coaxial line (TEM mode) with substrate integrated waveguide (TE10 mode). To mitigate phase imbalances between polarizations during beam scanning, a delay line is embedded in each quasi‐Yagi element, ensuring consistent scanning ranges for the two polarizations. Furthermore, the implementation of amplitude weighting in the feeding networks contributes to the enhancement of antenna efficiency. A 1 × 8‐element prototype was fabricated and its performance is assessed. The results show closely matched beam scanning ranges for the two polarizations (±28° for H‐pol and −30° to +34° for V‐pol) across the 26–29 GHz frequency band, with a measured maximum peak gain exceeding 9.2 dBi for both polarizations. The proposed design emerges as a promising candidate for compact mmW frequency scanning front‐end antenna systems. [ABSTRACT FROM AUTHOR]

Abstract A novel design of a high‐frequency multiband with a circular polarisation antenna based on a four‐patch antenna system consolidated with an Archimedean spiral antenna for CubeSat applications. The geometry and size are compatible with the CubeSat standard structure dimensions of 10 × 10 cm2. The antenna consists of a spiral antenna in the middle of four patch antennas surrounding it; the first antenna structure consists of two sets of two orthogonal identical patch antennas with a 90° phase shift to cover the band from 1.55 to 1.94 GHz at L‐band, 2, 2.1, and 2.3 GHz at S‐band, the second antenna is an Archimedean spiral antenna to cover all C‐bands, all X‐bands, all Ku‐bands, all K‐bands, and from 26 to 29 GHz at Ka‐band. The measured results show that the reflection coefficients (S11) and (S22) achieve

A novel design of a high-frequency multiband with a circular polarisation antenna based on a four-patch antenna system consolidated with an Archimedean spiral antenna for CubeSat applications. The geometry and size are compatible with the CubeSat standard structure dimensions of 10 x 10 cm². The antenna consists of a spiral antenna in the middle of four patch antennas surrounding it; the first antenna structure consists of two sets of two orthogonal identical patch antennas with a 90° phase shift to cover the band from 1.55 to 1.94 GHz at L-band, 2, 2.1, and 2.3 GHz at S-band, the second antenna is an Archimedean spiral antenna to cover all C-bands, all X-bands, all Ku-bands, all K-bands, and from 26 to 29 GHz at Ka-band. The measured results show that the reflection coefficients (S11) and (S22) achieve < -10 dB and the axial ratio achieves <3 dB, with a reference impedance of 50 Ω. The simulated and the measured results give a better agreement. [ABSTRACT FROM AUTHOR]

Abstract This letter proposes a millimeter‐wave dual‐polarized (DP) end‐fire frequency scanning antenna utilizing low temperature co‐fired ceramic (LTCC) technology. The antenna features DP radiating elements, each comprising a quasi‐Yagi antenna for horizontal polarization (H‐pol) and a pyramidal horn antenna for vertical polarization (V‐pol). These elements are excited via a mode‐composited transmission line (MCTL), integrating substrate integrated coaxial line (TEM mode) with substrate integrated waveguide (TE10 mode). To mitigate phase imbalances between polarizations during beam scanning, a delay line is embedded in each quasi‐Yagi element, ensuring consistent scanning ranges for the two polarizations. Furthermore, the implementation of amplitude weighting in the feeding networks contributes to the enhancement of antenna efficiency. A 1 × 8‐element prototype was fabricated and its performance is assessed. The results show closely matched beam scanning ranges for the two polarizations (±28° for H‐pol and −30° to +34° for V‐pol) across the 26–29 GHz frequency band, with a measured maximum peak gain exceeding 9.2 dBi for both polarizations. The proposed design emerges as a promising candidate for compact mmW frequency scanning front‐end antenna systems.

A novel 2‐D beam steering technology using a Fabry–Pérot antenna with a liquid‐based reconfigurable metasurface is presented. The antenna employs a reconfigurable partially reflecting surface to regulate phase distribution and adopts a microstrip antenna as feed to realise 2‐D beam steering. The antenna beam can be tilted in four different directions by injecting liquid metal into the specific area of the microfluidic channels embedded in the metasurface. Moreover, the antenna has a simple and compact structure with a low profile. A prototype is manufactured, and good agreement between simulated and experimental results verifies the correctness of the design. The measured results of the manufactured antenna prototype demonstrate that the main beam tilts to maximum values of ±15° and ±28° in the yoz and xoz planes, respectively, between 9.5 and 9.7 GHz. [ABSTRACT FROM AUTHOR]

The aspects of monitoring the energy characteristics of radio navigation signals of the global navigation satellite system (GLONASS) have been considered. It has been noted that the power of the incoming radio navigation signal in the lower atmosphere depends on the parameters of the onboard antenna system of the navigation spacecraft, primarily, on the shape of the antenna amplitude pattern. The amplitude pattern of the onboard antenna of the spacecraft has a complex shape, and in order to compensate for changes in the power of the radio navigation signal due to the navigation spacecraft moving away from (or approaching) the signal user, the shape of the amplitude pattern should be axisymmetric, i.e., resembling a figure of revolution. Based on regular monitoring of the energy characteristics of the GLONASS radio navigation signals, the shapes of the amplitude patterns of the onboard antenna feed systems of the spacecraft from the orbital group have been evaluated. As a result, asymmetry in the amplitude patterns of some spacecraft has been detected. It has been shown that the asymmetry of the amplitude pattern leads to a dependence of the power of the incoming radio navigation signal on the spacecraft aspect angle, i.e., the position of the spacecraft emitting antenna system relative to the signal user. The probable cause of such asymmetry has been identified as the gradual aging of the active devices in the antenna feed path. The obtained results indicate the need for regular and prompt monitoring of the energy characteristics of radio navigation signals in the lower atmosphere. The observed effect of asymmetry in the amplitude patterns should be taken into account when developing spacecraft antenna feed systems. [ABSTRACT FROM AUTHOR]

In this study, an inset fed rectangular patch antenna is designed for 5G application. The proposed antenna has been designed by utilizing a U-shaped lot loading technique introduced on ground plane for bandwidth improvement. The designed antenna is integrated with parasitic patch as FSS unit cell in order to obtain gain improvement. FR-4 substrate with (εr = 4.4 and tanδ = 0.02) is used to design the antenna. The bandwidth and gain parameters are improved by altering the length of the ground plane initially and frequency selective surface (FSS) placed at the back of the substrate to enhance the radiation property of the antenna. Bandwidth improvement of 30 % is obtained for proposed wideband high gain antenna compare to conventional inset feed patch antenna. Maximum gain obtained for proposed wideband high gain antenna is 6 dB at 25 GHz. The obtained return loss is also well below 10 dB range from 24.57 GHz to 27.57 GHz. Bandwidth obtained for the proposed antenna is 3.0 GHz. Slot loading technique with ground optimization is useful for bandwidth improvement without affecting radiation pattern of the antenna. Further FSS integration is an efficient approach to improve the gain of convention antennas. The proposed antenna features good characteristics in terms of return loss, gain and bandwidth which makes it highly suitable for 5G applications in mm-wave band. [ABSTRACT FROM AUTHOR]

Slotted waveguide antennas have received much attention due to features such as low loss, high efficiency, and high power capacity. In this article, a 2-D slot array antenna based on a ridged waveguide with a low level of side lobe is synthesized. The antenna consists of four slotted ridged waveguides, each of which consists of eight slots as the radiating elements. A fast and easy way is proposed to synthesize the aperture distribution in the H-plane. Further, a corporate feed network based on ridged waveguide is designed to feed the antenna. The feed network is designed such that the desired aperture distribution in the E-plane is achieved. A prototype of the antenna is fabricated and measured. The measured sidelobe levels in the H- and E-planes are, respectively, -24.5 dB and -23.9 dB, and the reflection coefficient of the antenna is -19 dB at the design frequency, indicating the accuracy of the design procedure. The measured antenna gain is approximately 20.4 dBi at the entire frequency band. The stable radiation pattern of the antenna makes the antenna suitable for radar applications. [ABSTRACT FROM AUTHOR]

In practice, the broadband feeding network on the back side of an antenna can have a nonnegligible effect on the antenna's back radiation due to the feeding network's radiation contribution. Thus, a back-radiation cancellation scheme is proposed by co-designing the antenna and its feeding network to solve this problem. The antenna and its feeding network can be viewed as a two-element array. Their radiation toward the antenna's backward direction can cancel each other when both have equal amplitude and opposite phases along the back direction. A differential fed dielectric resonator antenna (DRA) through a rat-race coupler (${180}^\circ $ hybrid coupler) and a T-shaped broadband differential feeding network are compared and analyzed to verify the proposed scheme. In addition, a $1\!\times\!4$ DRA array with a T-shaped broadband differential feeding network in a previous work (where the feeding network's radiation effect on the back side was overlooked) is used for experimental validation of the proposed scheme. Simulations and measurements demonstrate significant back-radiation suppression than the ideal differential feeding network. [ABSTRACT FROM AUTHOR]

In this letter, a differential antenna with high common-mode (CM) rejection is proposed, which consists of dual improved half-mode substrate-integrated waveguide (HMSIW) cavities and a square substrate-integrated waveguide (SIW) coupling-feeding cavity (CFC). First, a novel approach to enhance the differential-mode (DM) radiation performance by flipping the symmetrical TE201 cavity is presented. The two E-field components excited from reversed magnetic walls are superposed in phase. Then, a pair of improved HMSIW cavities with oppositely magnetic walls is adopted to suppress the CM and enhance the uniformity of the radiation pattern on E- and H-planes. The square TE202 CFC with four coupling holes is discussed for the DM excitation. Meanwhile, it is equivalent to a band-stop filter further to improve CM rejection under CM excitation. The four perturbation holes in the CFC for the adjacent E-field isolation are analyzed. Finally, the proposed antenna is fabricated. The measured and simulated results show good agreement. The high CM rejection (27.3 dB) is achieved through the two-step rejection of the radiator and CFC. [ABSTRACT FROM AUTHOR]

Abstract Circularly polarised multiple‐input‐output antennas embedded in wearable wireless devices attract importance in the individual security and beauty fabric modelling industry involving technology embedded on‐clothes wearables. A circularly polarised wideband is designed and analysed in the present design‐study where a wearable application uses a multiple‐input‐output. It adds 2 symmetric ‘Multi‐Input‐Multi‐Output’ antennas that are good looking design like a swan‐shaped, and the ground plane is similar to the shape of a swan. The designed novel antenna comprises a ground plane having a line feed and a rectangular inverted L‐type micro‐strip which is supporting circular polarisation. The antenna element is spanning at 3‐DeciBell (dB) Axial Ratio Band‐Width of 5.2–7.1 GHz and an impedance bandwidth (S11 less than or equal to −10 dB) of 3.6–13 GHz. The proposed antenna manifesting a channel capacity loss less than 0.2 b/s/Hz, and envelope correlation coefficient less than the value 0.02, total active reflective coefficient less than −10 dB, and diversity gain greater than the value of 9.96, Mean Effective Gain (also represented as MEG) ratio is within ±0.5 dB. There is a twin‐sense circular polarisation in this antenna and superior isolation between resonating elements (greater than 18). The proposed antenna for human tissues specimens is also discussed with its specific absorption rate (also pronounced as SAR) in different situations that pertain to the living body. The overall size of the proposed ‘Circularly Polarised’ textile ‘Multi‐Input‐Multi‐Output’ antenna is 34:5 × 42 × 1 mm3. Because of its textile layers, reasonable performance, and compact size, the designed ‘Multi‐Input‐Multi‐Output’ antenna may be useful for wearable applications. The presented novel antenna can be made unrecognisable with a beautiful swan‐shaped design that can simply comingle with the other designs of fabric (in the fashion dress). The simulated antenna was made‐up following regular and general manual techniques and verified in the proposed conditions. The corner‐to‐corner distance between the ‘Multi‐Input‐Multi‐Output’ antennas is 14.2 mm, and the achieved isolation is beyond 18 dB after suitable adjustments of the designed final antenna.

In this letter, a low-profile metasurface (MS) antenna with multi-polarization and pattern reconfigurability is presented. The antenna mainly consists of two parts, including a loop antenna fed by balun, and a MS antenna excited by the coupled aperture.When switching the PIN diode and rotating the MS, the multi-polarization and pattern reconfigurable ability of the antenna is obtained. While the loop antenna is excited, a horizontally linear polarized (HLP) wave and omnidirectional pattern are obtained. Besides, when the MS is operated, due to the differential phase between the orthogonal surface impedance components, the antenna can be switched between vertical linear polarization (VLP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Furthermore, the antenna could achieve a directional pattern. As the simulated and measured results shown, the proposed antenna has an overlapped impedance bandwidth (IMBW) of 24.7% for all polarization modes and a 3-dB axial ratio (AR) bandwidth of 11.8% for L/RHCP modes. Moreover, the antenna owns a low profile of 0.06 λ (under the operating centre frequency). [ABSTRACT FROM AUTHOR]

Conventional transmitarray antennas are designed to produce a directional pattern with the beam peak in a single direction when the feed is placed at a distinct location. A real-life application requiring conical beam scanning necessitates the development of antennas with patterns that sweep out a cone in space through successive excitation of feeds placed at multiple locations along the body of the revolution ring focus. In this communication, we propose transmitarrays as an antenna solution that can achieve the conical beam sweep. Compared to the previously reported transmitarrays, the development of an off-axis-fed transmitarray for conical beam scanning requires significant advancements regarding the synthesis and optimization of the off-axis-fed transmitarray. A novel synthesis algorithm is presented based on the optimization of the feed location and a modified transmitarray phase compensation. To validate the approach, an 18 cm transmitarray with a thickness of 0.8 cm operating at 13.4 GHz is designed, simulated, prototyped, and measured. Predictions obtained by full-wave simulations agree well with the measured results. The conical beam scanning capability of the transmitarray is demonstrated through measurements taken with the feed placed at five locations within the ring focus. [ABSTRACT FROM AUTHOR]

An on-body matched differentially fed magnetoelectric (ME) dipole antenna is proposed for the head imaging system to detect intracranial hemorrhage (ICH). The ME dipole with its differential feed achieves a wide impedance bandwidth of 137% from 0.45 to 2.4 GHz. The antenna exhibits unidirectional and symmetrical radiation patterns in the near-field region, leading to a stable main beam toward the 2-D imaging domain inside the human head. The high front-to-back ratio (FBR) above 18 dB is realized in the whole frequency band by this antenna. The values of specific absorption rate (SAR) always remain safe level under 0.82 W/kg in the entire band with an input power of 10 dBm. To validate the detection capability of the proposed antenna, a head imaging system composed of eight antenna elements in a co-polarization state is designed and fabricated. The reconstructed 2-D images of the head interior using a confocal imaging algorithm demonstrate the successful detection and localization of the circular bleeding area as small as 3 mm in radius numerically and 5 mm in radius experimentally, and it has the capability to detect multiple bleeding areas of the human brain, which indicates the head imaging system has the potential to be used in clinical trials. [ABSTRACT FROM AUTHOR]

A two‐port planar ultra‐wideband (UWB) pattern diversity antenna is proposed in this letter. The design consists of an array of two rotated identical monopole antennas and two feeding ports with 0° in‐phase and 180° out‐of‐phase excitations. The single monopole antenna includes a circular patch, a rectangular truncated ground plane and a fork‐shaped feeding structure. In this antenna, a modified partial common ground plane is used to enhance the input matching, increase the isolation between antenna elements and improve the desired radiations. The measured results show an |S11| < −10 dB bandwidth ranging from 2 to over 20GHz, with conical and broadside beams, high efficiency, and good isolation across the entire UWB band. Also, the proposed antenna exhibits a smaller footprint, larger bandwidth, and more straightforward design compared with the existing designs. To the best of authors' knowledge, all these characteristics have never been presented in previously reported UWB pattern diversity antennas. [ABSTRACT FROM AUTHOR]

In this article, a fast and efficient hybrid method that combines the volume-surface integral equation (VSIE) and the modified surface integration (MSI) method is proposed to evaluate the electromagnetic (EM) performance of the large-/medium-sized radome-enclosed antennas (REAs). An approximate equivalence principle is presented to formulate the physical model for the EM radiation of the REA, and then, the full-wave VSIE for the antennas and the high-frequency MSI method for the dielectric radome are coupled with each other in an iterative manner. Since mutual interactions up to the second order among the antennas and the radome are considered, the method shows good accuracy in both the near- and far-field regions of the REA system. In addition, all the computation processes involved in the method, including the method of moments (MoM) solution of the VSIE, surface integrations (SIs) in the MSI, and ray tracing for determining the local transmission matrix for the dielectric radome, are accelerated by the multilevel fast multipole algorithm (MLFMA), which makes the method highly efficient in terms of both computational time and memory requirement. Numerical results show that the proposed hybrid method can predict the EM performance, e.g., the input impedance and radiation pattern, of the REA system with good accuracy compared with the full-wave simulations. [ABSTRACT FROM AUTHOR]

A novel planar pattern reconfigurable antenna is presented. The proposed antenna consists of four identical antenna elements distributed at different positions on a F4B255 substrate forming a cross shape. Each antenna element is composed of a direct fed magnetic dipole with bow tie shape and four coupling fed magnetic dipoles with rectangular shape which achieves wide bandwidth and titled radiation pattern. The ground plane under each antenna element is etched with taper shape to reduce the coupling among antenna elements. The four antenna elements are linked to and fed by one port via a step shaped metal strip on the ground plane and radiation layer, respectively. A PIN diode is mounted in each strip to switch the connection/disconnection of each antenna element with the feeding port. Pattern reconfiguration is obtained by electrically choosing the excitation of each antenna element. The proposed antenna operates in four states with four steerable beam directions of θ = ±45° in both xoz and yoz planes. The measured common bandwidth for the four states is 5.15–5.93 GHz and the measured gain ranges from 6.14 to 8.45 dBi for four states within the bandwidth. The proposed antenna has a low profile and wide bandwidth which makes it a good candidate of micro base station for IEEE 802.11ac Wireless Local Area Network (WLAN) (5.15–5.85 GHz) applications. [ABSTRACT FROM AUTHOR]

In this article, a dual circular polarized antenna fed by double quadrature couplers is presented. The proposed structure consists of three parts: dual‐polarization antenna, quadrature couplers, and connection structure. This structure is not sensitive to orientation due to its circular polarization. The antenna gain can be easily increased by cascading orthogonal dipoles. Therefore, this array structure has a fan beam circular polarized radiation pattern. This structure is fabricated on the Rogers 4003C substrate. The simulation and measurement results show that this proposed antenna achieves return loss above 10 dB in the frequency range of 9.8–10.2 GHz. [ABSTRACT FROM AUTHOR]

The irregularly located element array within the antenna aperture can be applied to obtain narrow main lobe width and low sidelobe levels with fewer elements as compared with the traditional (periodic) array configurations. In this article, a reconfigurable reflectarray antenna (RRA) combined with hyperuniform disordered distribution is presented. Based on the theoretical radiation pattern of reflectarray, it has been found that the proposed array with reduced elements holds a similar radiation pattern as that of a corresponding periodic array. Meanwhile, the reflectarray avoids the design of complicated feeding network for the disordered phased array antenna. In addition, for a reconfigurable reflectarray to achieve beam scanning, active devices are necessary. In such case, the design of RRA with fewer elements is of particular importance. A 1 bit RRA of 64 elements prototype has been designed, fabricated, and measured. The side length of each element is $0.625\lambda $. Experimental results agree well with the full-wave simulations, and scan beams within ± 50° range have been obtained with a peak gain of 17.4 dBi at 12.5 GHz. [ABSTRACT FROM AUTHOR]

This article presents a state-of-the-art 3-D-printed dielectric reflectarray antenna featuring one-shot deployability and wide-angle beam-scanning ability. The design is enabled by a series of a “kirigami”-inspired two-stage snapping-like element structure that can be retracted by 66% to save space. The prototype is fabricated with a stereolithography (SLA) 3-D printing method with the Formlabs Flexible 80A photopolymer. A bifocal phase distribution method is utilized to optimize the RF performance of the array, realized −30° to −10° and 10° to 30° beam-scanning ability. The outcome of this work demonstrated a high-performance dielectric reflectarray design with ease of fabrication for 5G and satellite communication applications. [ABSTRACT FROM AUTHOR]

Compact and lightweight antennas are required for future ground communication systems to provide wide-angle $4\pi $ steradians coverage for man-pack radio communication units carried by soldiers on the ground. Two innovative “Bunker” antennas at K-band are described in this article. The novelty includes antenna deployment from folded to unfolded configurations, compact size, low mass, $4\pi $ steradians coverage, low cost, wide bandwidth performance, and built-in radome for protection from severe environmental conditions. Design of these antennas, trades, RF simulations, mechanical design, antenna deployment, and material selection leading to product development are described for the first time in this article. A prototype antenna has been fabricated and measured results are presented. An excellent correlation between measured and simulated patterns has been achieved. The Bunker antenna has very wide frequency bandwidth of 86% covering Ku and Ka secondary frequency bands in addition to its primary K-band and thus could in the future replace three antennas on a dedicated man-pack with a single tri-band antenna solution. [ABSTRACT FROM AUTHOR]

This work presents a novel on- body wideband dual-polarized antenna to stabilize and enhance the link performance of wireless capsule endoscopy systems. By introducing a cross-bowtie structure with a planar compact feed method, the antenna achieves a dual-polarized performance with high port-to-port isolation. A loaded ring with additional stubs is also implemented to further enhance the bandwidth and provide a flat in-band performance from 381 to 990 MHz. The proposed antenna is measured with both homogeneous phantom and ex vivo test to validate the impedance matching performance. To validate the effectiveness of the proposed on- body antenna on the communication link, a capsule helical antenna with omnidirectional radiation pattern is designed and measured. Finally, comprehensive link studies are conducted considering the varied capsule orientations and locations, with a peak $\vert S_{21}\vert $ value of–25.5 dB at the 60 mm implant depth and an acceptable link loss due to the capsule position error. The proposed on- body antenna can be regarded as a good candidate for a practical capsule endoscopy system due to its stable and enhanced transmission performance when compared with its counterparts. [ABSTRACT FROM AUTHOR]

This article presents a full metal wideband high-performance cosecant squared (CSC2) pattern antenna. A highly compact structure is achieved by a convoluted feeding network routed in multiple layers. Double metal ridges are added to the flared radiation slot to reduce the aperture size of the antenna element. A line of 40 such elements are excited by a full-corporate feed network arranged longitudinally, so as to form a phased array in the future. A hybrid of single-ridge waveguide and coaxial line in a sandwich structure is used to construct the feed network. The absorbing wedge loaded coupler and magic-T are incorporated into the feed network to achieve high isolation and large power-division ratio, thereby improving the stability of the amplitude and phase distribution. This ensures the desired CSC2 patterns over a wide frequency band. A prototype operating at C-band is designed, fabricated, and measured. Experimental results show that the antenna has an impedance bandwidth ($\vert \text{S}_{11}\vert < -13.1$ dB) from 6 to 7.4 GHz. Stable CSC2 patterns in the E-plane with the peak gain of over 16.5 dB and sidelobe level (SLL) of less than −17.5 dB are observed across the same frequency band. [ABSTRACT FROM AUTHOR]

A wideband low radar cross-section (RCS) circularly polarized (CP) reconfigurable patch antenna array based on liquid metal (LM) has been proposed in this article. The array was formed by $4\,{\times }\,4$ CP C-shaped antenna elements fed with a sequential feeding network. The antenna element was designed with a pair of narrow slots, and a microchannel adhered to the top metal layer. The CP reconfiguration depends on the tuning of the slots by moving the LM in the channel. The patch antenna array can obtain good CP radiation and low RCS features without any extra RCS reduction structures other than the array elements. RCS reduction (RCSR) can be realized by $180^{\circ }\,{\pm }\,37^{\circ }$ reflection phase variations between two different antenna elements under normal incidence for both $x$ - and $y$ -polarizations. The antenna prototype has been fabricated and measured. The measured results show good agreement with simulated results. [ABSTRACT FROM AUTHOR]

This paper presents the design of a flat-panel metasurface reflectarray antenna fed by a circular horn antenna for satellite applications. A metasurface-based reflectarray antenna is similar to a flat-panel reflector and is characterized by a reflection angle adjustment that is free from the well-known Snell's law. This was done by compensating the angle of the incident wave using the structure of each unit cell. A unit cell of the designed metasurface is composed of a dual-ring resonator. Many satellites use a reflectarray antenna due to its flat-panel structure and the capability of steering the reflection angle of the incident wave. This paper presents the detailed design procedure using a commercial 3D EM simulator and the operation principle of the flat-panel metasurface reflectarray antenna, including the simulation setup, design environment and automation. The proposed design method is scalable to any EM solvers for numerical analysis. A reflectarray composed of a 16 × 16-unit cell array at 5.8 GHz (C-band) was designed and validated by measurement as a proof of concept. It is excited by a low-cost linearly polarized circular horn cantenna. The measured antenna gain and radiation patterns show good agreement with the simulation. The measured antenna gain of the reflectarray was 22.4 dBi (cross-pol suppression level: 36 dB), and the reflection angle was 15° at normal incidence. [ABSTRACT FROM AUTHOR]

Abstract In the study, a miniaturised printed quadrifilar helix antenna (PQHA) with isoflux coverage and wide‐angle circular polarisation is presented. It is composed of a three‐stage stepped impedance spiral arm and open stubs. Each of the three‐stage spiral arms has different pitches and number of turns. For the last‐stage spiral arm, meander lines are used. The proposed PQHA features the characteristics of wide bandwidth, isoflux radiation, small size, and wide‐angle circular polarisation. Moreover, in order to feed the proposed PQHA, a miniaturised quad‐feed network is designed to provide equal amplitude signals with sequential orthogonal phases. For demonstration, a prototype is designed, fabricated, and measured. The overall size of the proposed antenna is 88 × 88 × 132 mm (0.44 λ0 × 0.44 λ0 × 0.66 λ0). The results show that isoflux radiation with a coverage of about ±60° is realised from 1.40 to 1.62 GHz (14.6%) while maintaining more than 10 dB return loss and larger than 200° 3‐dB axial ratio beamwidth.

Abstract Two metamaterial‐based linear phased array antennas with improved wide‐angle scanning bandwidth are designed in this study. Metamaterial antenna element consists of a metamaterial patch, periodic metal strips, distributed metal strips and slot coupling feeding structure. The bandwidth of the metamaterial antenna is improved by loading the periodic metal strips. Wide‐angle scanning bandwidth of arrays is attributed to the distributed metal strips. For an E‐plane array, the central element has a relative bandwidth of 30.0% (4.33‐5.86 GHz) for Voltage standing wave ratio (VSWR)

A new broadside and conical beam reconfigurable dielectric resonator antenna (DRA) with three orthogonal linear polarizations (LPs) and two orthogonal circular polarizations (CPs) agility is presented. It consists of a quad-strip-fed DRA element and a reconfigurable feeding network. First, the DRA element is designed to make unidirectional ${\mathrm{HEM}}_{11 \delta }$ mode and omnidirectional ${\mathrm{TM}}_{01 \delta }$ mode operate in the same wide band by tactfully removing a concentric annular column from its interior. Furthermore, a center-loaded metal post helps to improve the impedance matching of the ${\mathrm{TM}}_{01 \delta }$ resonance significantly. Afterward, the switchable feed network is designed to implement diverse phase distributions of four output ports, i.e., providing the quad-port in-phase excitation, dual-port differential excitations, and quad-port sequentially rotated phase excitation strategies for a vertical LP, ±45° slant horizontal LPs, and two CPs, respectively. Finally, a fully functional prototype is designed, fabricated, and measured to validate the design. The measured results show that the overlapping impedance bandwidth of 36.8% for all the states and the axial-ratio bandwidth of 33.8% for the CPs are obtained. [ABSTRACT FROM AUTHOR]

A novel low-profile phased antenna with dual-port and its two types of 1-D linear array to 2-D space wide-angle beam scanning are proposed. The antenna unit is composed of fishbone structure and rhombus parasitic patch, which is folded into n-shaped to low profile $0.08\lambda $. By adjusting the phase difference ($\Delta \varphi$) from 0° to 180°, the antenna working mode is changed from even mode to hybrid mode and to odd mode eventually. Therefore, the proposed antenna unit realizes wide-angle scanning characteristics and continuous switching state from broadside lobe to endfire lobe. Furthermore, the proposed phased antenna element is extended to two kinds of 1-D linear phased array (Array#1 and Array#2) based on the generalized principle of the pattern multiplication. The fabricated Array#1 can realize beam scanning range $- 116^{\circ }< \theta _{\mathrm {m}} < 0^{\circ }$ (xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 63^{\circ }$ (yo z plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 169^{\circ }$ (xoy plane) and the fabricated Array#2 can achieve $0^{\circ }< \theta _{\mathrm {m}} < 60^{\circ }$ (xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 65^{\circ }$ ($\text{y}{o}\text{z}$ plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 152^{\circ }$ (xoy plane). The proposed phased antenna unit and its 1-D array can realize 2-D space wide-angle scanning, improving scanning performance and expanding scanning dimensional space in phased array. [ABSTRACT FROM AUTHOR]

A wideband cup dielectric resonator antenna (CDRA) with a monopole-like mode is presented. A new coil feeding structure is used, creating an equivalent magnetic current loop above the ground plane, exciting the CDRA $\textrm {TM}_{01 \delta } $ mode and an equivalent electric dipole at the adjacent frequency band. Thus, a broad bandwidth is achieved from two adjacent resonances. A CDRA with $0.25\lambda _{0} $ diameter and $0.23\lambda _{0} $ height ($\lambda _{0} $ is the center frequency free-space wavelength) is fabricated and measured. About 29% of −10 dB matching bandwidth (2.98–4.00 GHz) is achieved. The structure has a low cross-polarization level and stable radiation patterns within the entire operating bandwidth. [ABSTRACT FROM AUTHOR]

A design approach to a planar dual-sense bidirectional circularly polarized (CP) antenna is advanced. The resultant antenna can exhibit orthogonal CP radiations in arbitrary directions between 90° and 180°, i.e., the flared angle formed by pure left-handed CP (LHCP) and right-handed CP (RHCP) directions could be set in a wide range from 90° to 180°. The operational principle is revealed by an equivalent source model at first. Then, prototype antennas are advanced by incorporating a high-order mode resonant, V-shape dipole to a planar magnetic dipole, and a parasitic electric dipole. As numerically simulated and experimentally validated, the flared angle formed by LHCP and RHCP directions can be adjusted as 90° and 135°. In the 90° case, the presented bidirectional CP antennas can exhibit impedance bandwidth of 6.6%, 3 dB axial ratio (AR) bandwidth of 13.0% in the $+ x$ -axis, and 8.9% in the +z-axis. The advanced low-profile (height < 0.05 wavelength) antenna can simultaneously provide spatial and polarization diversity abilities in one principal-cut elevation plane. Therefore, it would be a promising colocated, spatial/polarization diversity antenna in future wireless systems. [ABSTRACT FROM AUTHOR]

The maximum radiation efficiency can be obtained when the feed array excitation of a reflector antenna is synthesized by the conjugate field matching (CFM) method. However, the CFM method can only get the strongly tapered feeding power distribution. This will lead to most of power amplifiers (PAs) working in low efficiency states and reduce the equivalent isotropic radiated power (EIRP) with the limited power consumption. In this work, combining the radiation efficiency and the PA efficiency, the radiated power efficiency (RPE) is defined as the new design goal and is to be raised to achieve higher EIRP. For this reason, a method based on the near-field pattern synthesis is proposed. In this method, all the ON-state PAs are required to work in the highest efficiency state. Then, with well-trained support vector machine (SVM), the ON–OFF states of the PAs are adjusted so that the reflected focal field can be better synthesized by the near-field pattern of the feed array. Thus, the loss of the radiation efficiency is minimized. As a result, the RPE is about 22% higher than that of the CFM method and about 10% higher than that of the optimum CFM truncation case. [ABSTRACT FROM AUTHOR]

Antenna noise temperature calculation for a reflector antenna system can be a computationally expensive operation if the structure is electrically large. Several approximate methods have been suggested to speed up the calculation. These rely on removing one or more of the reflecting surfaces from the calculation domain and compensating for the effect through geometric optics arguments. This article presents a unified multilevel approximation formalism, which allows the user the freedom to tradeoff the simulation time, implementation complexity, and result accuracy as required for a specific application. As part of the formalism, a strategy to reliably remove both reflectors in a dual-reflector system from the calculation domain and rely on ray tracing to correct the background temperature is developed. It is shown that this new method reduces calculation time by several orders of magnitude while maintaining accuracy in the final antenna temperature result of the order of 1%. It is fast and accurate enough to be used in numerical optimization loops. The method requires the implementation of a ray tracing algorithm, and thus, may present some unnecessary complexity if only rough temperature estimates are required. To this end, a simplified method is also presented requiring no ray tracing and only simple postprocessing of readily available feed pattern data. Though not as accurate as of the ray tracing-based method, temperatures may be estimated with around 10% accuracy over bandwidths well in excess of a decade. [ABSTRACT FROM AUTHOR]

This letter proposes a 60 GHz planar waveguide array antenna with high antenna efficiency, low cost, and low processing difficulty. The array integrates the radiating elements and the hollow E-plane waveguide feed network in a single-layer structure in a simple way. To demonstrate the idea, a 16×16 prototype was designed, fabricated, and measured. The measured 10 dB impedance bandwidth (|S11| ≤ −10 dB) is 16.4% with the antenna efficiency being 89.1% at 61.5 GHz. To the best of our knowledge, it has the highest antenna efficiency and the lowest processing difficulty among similar waveguide arrays. [ABSTRACT FROM AUTHOR]

In this letter, a simple decoupling method is proposed to improve the isolation in a dual-polarized patch antenna array that operates in the frequency range of 3.4–3.8 GHz. The method includes the decoupling network based on the π-shaped architecture of the transmission line and matching network. The distance of the two adjacent antenna elements is 0.48 λ0. The cross-polarization isolation of the antenna element using Y-probes and differential feeding is higher than 35 dB in the operating frequency band. The proposed scheme is able to deal with the decoupling requirement and obtains 37 dB isolation at 3.6 GHz, which shows a significant improvement compared with the original antenna array. The measured results demonstrate that the proposed scheme is suitable for multiple–input–multiple-output (MIMO) systems. [ABSTRACT FROM AUTHOR]

Abstract This study presents a simple and low‐profile cylindrical dielectric resonator antenna (CDRA) for the fifth‐generation (5G) band (3.5 GHz) with switchable polarization. The antenna can operate with linear or circular polarization (right‐handed circular polarization [RHCP] or left‐handed circular polarization [LHCP]) by changing the states of the PIN diodes below the CDRA, while keeping the same operating frequencies. The antenna operates at three modes (Mode 1, Mode 2, and Mode 3). It exhibits linear polarization in Mode 1, RHCP in Mode 2, and LHCP in Mode 3. The 10‐dB bandwidths of 750 MHz (3.1–3.85 GHz), 950 MHz (3.03–3.98 GHz), and 960 MHz (3.03–3.99 GHz) are noted for Mode 1, Mode 2, and Mode 3, respectively. The 3‐dB axial ratio bandwidth of 22.2% (3.09–3.86 GHz) and 21.4% (3.08–3.82 GHz) is achieved for Mode 2 and Mode 3, respectively. The reported antenna has high gain ( >5.25 dBi for all operating modes) and high radiation efficiency ( >79.8% for all operating modes). The proposed antenna is suitable for use in polarization diversity applications.

In this communication, a pattern-reconfigurable filtering patch antenna is presented which consists of a driven patch, a stacked patch, an embedded filtering feeding line, and two vertical switchable elements with gaps from the suspended patches. Compared with the conventional stacked patch antenna, the proposed antenna does not increase the volume. A novel filtering feeding network is designed which consists of a hairpin-shaped resonator and a half-wavelength coupled microstrip line. It is used to generate the radiation nulls near the lower and higher passband edges. A U-shaped slot is etched on the driven patch to generate another radiation null. Three radiation nulls are excited to realize filtering performance. Meanwhile, the radiation beam of the proposed antenna can be reconfigured by switching the function of switchable elements between a director and a reflector using p-i-n diodes. Good radiation pattern reconfigurability, filtering, and wideband performance can be achieved simultaneously. The simulated and measured results show that the radiation beam can be switched to the directions of −33°, 33°, and 0°. The proposed antenna can maintain a wide operating bandwidth of 2.22–2.84 GHz (25%), out-of-band suppression of over 14 dB, and flat in-band gain of about 8 dBi in different states. [ABSTRACT FROM AUTHOR]

A method to realize the flat-topped radiation pattern of Fabry–Pérot cavity antenna is proposed based on the ray-tracing model. In the design, a nonuniform partially reflective surface of dielectric substrate is proposed to reduce the sidelobe level and get a fast roll-off in the operating frequency band. Besides, a dumb source array is added around the dual-polarized feed array to minimize the disparity of beamwidth between E- and H-plane. The antenna was calculated with the proposed method, simulated by the full-wave simulation, and validated by the experiment. Compared with the traditional array synthesis method, there is no need to design a complex feed network because each coaxial port is fed equally in phase and amplitude. In addition, based on the proposed method, the aperture size is small and the flat-topped beamwidth is flexible. [ABSTRACT FROM AUTHOR]

This letter proposes a novel wideband wing conformal vertical polarized omnidirectional antenna for the very high frequency/ultrahigh frequency band. The antenna adopts symmetrical radiation and feed structures to obtain quasi-omnidirectional radiation. To be conformal with the ultrathin body of the wing, this construction is realized using double-layer flexible metal films that cover the surface of the wing. Moreover, there are several symmetric grooves on the upper metal film that are beneficial to improve the efficiency of radiation. The upper and lower metal films are connected by two shorting plates with same exponential gradual outline for vertical polarization and wideband potential. The ultrawide operating band can be realized by loading resistors and inductors. A conformal prototype of the antenna was fabricated and validated. The wing thickness determines the profile, which is only 0.013 λL, where λL is the wavelength at the lowest operating frequency. Its acquired bandwidth ranges from 100 to 600 MHz; high radiation efficiency and vertically polarized quasi-omnidirectional characters are also obtained in this band. [ABSTRACT FROM AUTHOR]

In this letter, a compact high-isolated multiple-input–multiple-output (MIMO) antenna module based on a chip capacitive decoupler is proposed for the fifth-generation (5G) smartphones. The antenna module consists of two feeding ports, radiating metal strips, and a chip capacitive decoupler within a compact size of 16 × 6 mm2. In this design, two L-shaped metal strips are used as distributed capacitors to compress the size of the module. Meanwhile, a chip capacitive decoupler is added to improve isolation between the two feeding ports, which is realized with an analysis of common and differential modes. In addition, spiral slots are used to adjust the isolation between the modules. A prototype MIMO antenna with four such dual-port antenna modules was tested in the 3.5 GHz band. The measured –6 dB bandwidths of the two ports are 310 MHz (3.42–3.73 GHz) and 360 MHz (3.33–3.69 GHz), respectively, and the isolation is 24 dB at 3.5 GHz. The measured efficiencies are 60.5% and 52.7% at 3.5 GHz. The compact MIMO antenna module with high-isolation property provides a hopeful solution for the 5G mobile terminals. [ABSTRACT FROM AUTHOR]

A differentially driven transmission-line-excited magnetoelectric dipole (ME-dipole) array antenna is designed for fifth-generation (5G) applications. It is derived from our previous work using a single-layered printed circuit board (PCB) with plated-through-hole technology. The proposed antenna is composed of a 2 × 4 ME-dipole array surrounded by a rectangular cavity. A pair of differential ports feed the antenna. Experiments show that the proposed antenna presents an impedance bandwidth of 26.8% from 55.3 to 72.4 GHz, a 3 dB gain bandwidth of 25% from 55.4 to 71.2 GHz, and a peak gain of 15.3 dBi at 62 GHz. Moreover, the proposed antenna retains all the salient features of the ME-dipole in symmetric radiation patterns and low cross-polarization and back radiation levels. [ABSTRACT FROM AUTHOR]

In multi-band shared-aperture base station antennas, cross-band mutual couplings always lead to unwanted radiation characteristics. In this article, the influence of the cross-band mutual coupling is investigated from the point of view of induced currents and their secondary radiation fields. A low-band (L-band, 0.76–0.88 GHz) cascade comb dipole antenna is proposed to passively cancel the induced current and therefore suppress the secondary radiation field. Owing to the passive current cancellation capability, the proposed L-band cascade comb antenna does not affect the radiation performance of the middle-band (M-band, 1.9–2.7 GHz) and high-band (H-band, 3.3–3.9 GHz) antennas in stacked multi-band shared-aperture antenna arrays. The proposed L-band antennas are thus electromagnetic-transparent to the M- and H-band antennas. Based on the novel electromagnetic-transparent cascade comb dipole antenna, a triple-band shared-aperture antenna array that consists of the L-, M-, and H-band antennas are developed, manufactured, and measured. Both simulated and measured results validate the attractive features of the cascade comb dipole antenna in multi-band shared-aperture massive MIMO base station antenna array developments. [ABSTRACT FROM AUTHOR]

We describe a new type of ultrawideband feed antenna based on nested coaxial waveguides. The feed is for radio astronomy applications and covers two closely spaced bands: 400–800 and 900–1800 MHz. New design techniques are described for a three-cavity choke, a wideband iris matching network, and printed circuit board (PCB) excitation structures. The design methods were developed to improve broadband impedance matching, to control radiation patterns, to separate bands, and to suppress unwanted waveguide modes. The feed has nearly constant beamwidth over the entire 4.5:1 frequency range and a stable phase center. On an $f/D=0.43$ reflector antenna, the aperture efficiency exceeds 70% and the phase efficiency exceeds 95%. Other features include low ohmic loss and a compact, lightweight, and low-cost structure. Experimental results are shown for a scaled prototype to verify the design methodology. The methods described are general and can be applied to continuous frequency coverage on reflectors of different geometries. [ABSTRACT FROM AUTHOR]

In this article, a self-decoupling method is proposed for antenna arrays by exploring the coupling path through high-order characteristic modes (CMs) of the antenna elements. Mathematical formulas for coupling energy calculation are developed by combining the equivalent circuit of a receive mode antenna with the CM theory. With the CM analysis, radiating mode (RM) and decoupling mode (DM) of the antenna element are identified. An effective loading technique is proposed to enhance the modal significances of the DMs. The coupling between the DMs and the adjacent antenna element is enhanced, while the coupling with the dominant rms of the antennas is suppressed. Because of the coupling energy dispersion in the DMs, the corresponding unwanted induced currents flowing into the feed ports of the antenna element are suppressed, and the port isolations are efficiently improved. The decoupling structure composed of a simple metal ring and an impedance matching layer could be directly introduced into an antenna element, and the radiation performance of the previously optimized antenna element is preserved. Both simulated and measured results demonstrate that the port isolations are improved from 15 to 20 dB, and the radiation pattern distortion due to the mutual couplings is eliminated. [ABSTRACT FROM AUTHOR]

A miniaturized electrical beam-scanning reflectarray antenna providing a directional beam and wide steering ranges with fixed $\theta $ -polarization is proposed. To accomplish these properties, we devise a new active reflectarray cell that can control both the phase and polarization of incident waves. Accordingly, we can enforce all reflected waves to constructively interfere with each other in all target directions. To feed the proposed reflectarray cells, an omnidirectional monopole antenna is installed at the center of the reflectarray, which illuminates the reflectarray evenly. In addition, because the monopole feeder is directly connected to the reflectarray, we can significantly reduce the overall volume of the antenna down to about $0.5~\lambda ^{3}$ with a small F/D ratio of 0.147. Consequently, the proposed antenna attains a wide scan coverage and directional beam patterns. Moreover, the antenna can also maintain polarization direction stably, which is strongly required for dynamically moving platforms such as drones and unmanned aerial vehicles (UAVs). The experimental results agree well with the predictions, proving the validity of our approach. [ABSTRACT FROM AUTHOR]

A low-profile single-layer endfire circularly-polarized (CP) antipodal linearly tapered slot antenna (ALTSA) is proposed and investigated through simulations and experiments. This antenna is a composite structure consisting of a novel width-tapered slotted substrate-integrated waveguide (SIW) and an ALTSA fed by the SIW. The former also serves as a radiator to produce vertically polarized radiation, which is crucial to achieve a fully planar endfire CP antenna when a thin substrate is deployed. Compared to the previous ALTSA fed by the SIW, this proposed antenna utilizes slots on the spare broad walls of the SIW to form an extra slotted width-tapered SIW radiator, which presents an extension of the conventional width-uniform slotted SIW. Moreover, there are no space harmonics in the slotted width-tapered SIW; it is a slow wave that produces the vertically polarized radiation. The proposed antenna is demonstrated at 28 GHz, which is one of the millimeter-wave bands specified for 5G. An experimental prototype of the antenna has an impedance bandwidth of about 9 GHz from 23.8 to 32.8 GHz and an axial ratio bandwidth of about 1.4 GHz from 27.35 to 28.75 GHz, which coincide well with simulated results. [ABSTRACT FROM AUTHOR]

In this letter, a dual-feed circularly polarized slot antenna with polarization diversity is proposed. The proposed antenna consists of a circular slot that acts as a radiator, a dual-microstrip line as a feeding structure, a slit applied to a ground plane (GND), and a protruded stub. The circular polarization (CP) is easily obtained by protruding stub because it acts as perturbation in circular slots. The good isolation between two ports is achieved by the protruding stub and the slit applied to ground plane. From the measured results, the CP operating bandwidth is 22.4%. The isolation is less than −15 dB within the operating bandwidth. [ABSTRACT FROM AUTHOR]