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A low-profile and wideband unidirectional antenna with ferrite loading is presented for ultrahigh-frequency (UHF) applications. This design comprises a slotted bowtie antenna with parasitic elements placed 50 mm over a ground plane. A small amount of ferrite loaded on the center of the ground plane plays a crucial role in improving the performance of the low-profile antenna. The ferrite used here is a new type of magnetodielectric material with relatively high permeability and permittivity, as well as low magnetic and dielectric loss. The loaded ferrite introduces an additional phase change of the electromagnetic field reflected by the ground to improve the impedance matching, bandwidth, efficiency, and gain of the low-profile antenna. The evolution process and mechanism of the proposed antenna are elaborated. For validation, an optimized antenna prototype was fabricated and measured. The measured results are consistent well with their simulations, which shows the realized gain of 7.2–9 dBi over $\vert \text{S}_{11}\vert \le -10$ dB impedance bandwidth of 38% (480–705 MHz). The overall profile of this antenna is only $0.08\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the lowest frequency of operation. [ABSTRACT FROM AUTHOR]

A novel scheme is presented to control the frequency response on an open-ended waveguide antenna. A groove is loaded in the waveguide that is used to independently control the frequency response of the antenna without affecting the radiation pattern, and a transition is used to provide additional control. A dual-wideband antenna is taken as an example to verify the effectiveness of the scheme. To demonstrate the idea, an antenna element and its $2\times2$ array were designed, fabricated, and measured. Reasonable agreement between the measured and simulated results has been observed. The measured 10 dB impedance bandwidths of the lower and upper bands of the proposed element are achieved to be more than 22.2% and 14.2%, respectively, fully covering the 26/28 GHz band (24.25–29.5 GHz) and 39 GHz (37–40 GHz) band. [ABSTRACT FROM AUTHOR]

This article presents 3-D printed metal-only dual-band millimeter-wave circularly polarized (CP) reflectarrays (RAs). The RAs’ unit cell (UC) is made of an anisotropic metal brick mounted on a full metal ground. In-plane rotating the metal brick introduces geometric Pancharatnam–Berry (PB) phase shifting, and vertically adjusting the position of the UC provides propagation phase shifting. The geometric PB and propagation phase shifting offer two different degrees of freedom, enabling independent wavefront shaping of CP wave over dual-band. Specifically, the low-band CP beam shaping solely depends on the propagation phase. In contrast, the high-band CP beam shaping depends on the geometric PB and the propagation phases. The coupling issue between dual-band is minimal because of the unique dual-band phase-shifting methods. In addition, 3-D printed dual-band left-hand CP (LHCP) horn antennas are designed, printed, and used as the feed. To demonstrate, two RA antennas with different dual-band CP beam directions are fabricated and measured. [ABSTRACT FROM AUTHOR]

For the first time, liquid metal is incorporated with an elastomer platform for designing an electromagnetic bandgap (EBG)-backed wearable antenna that can be placed on human body. Here, the liquid metal (EGaIn) is injected into a soft and stretchable Ecoflex 0030 substrate for making a fluidic slot antenna and a liquid EBG (LEBG) structure. The LEBG is then placed at the back of the slot antenna for mitigating the effects of human body and improving the antenna performance. It has an antenna gain of 5.80 dBi in the boresight and a low specific absorption rate (SAR for 1 g U.S. standard) of 1.25 W/kg. Since liquid metal is highly dense, the ground plane of the LEBG is separated into six segments, which are connected through narrow bridges. Due to the use of such design, the wobbly effect of the dense liquid metal can be reduced significantly. The measured impedance bandwidth (3.23–3.59 GHz) of the proposed antenna is very stable and not affected much by its own structural deformation on human body. Since the elastomer platform is waterproof, it makes the antenna characteristics very stable in humid environment, which is a very desirable feature for wearable antennas. [ABSTRACT FROM AUTHOR]

The analysis, modeling, design, simulation, and experimental evaluation of a 400 GHz on-chip antenna is presented, with a novel combination of metastructures, a microstrip patch, a quartz-based dielectric resonator, and a diamond-based antireflex layer—all integrated on a 35 nm InGaAs metamorphic high-electron-mobility transistor (mHEMT) technology. The said combination represents a first-time implementation for all submillimeter-wave-capable semiconductor technologies. Circumventing a substrate-thickness limitation of $4.98 \mu \text{m}$ , a state-of-the-art broadband, efficient, and to-the-broadside radiating on-chip antenna solution is realized. It achieves a measured impedance bandwidth of 100 GHz, 25.6%, spanning from 340 to 440 GHz. A consistent pattern bandwidth of 75 GHz is recorded, with an efficiency of 50%–66% and a directivity of up to 10.4 dBi—or 27 dBi, with the utilization of a polypropylene-based dielectric lens. The theoretical analysis of the proposed on-chip antenna is presented, and two modeling approaches are shown and compared. Between the analytical and the 3-D electromagnetic (EM) model, the latter is chosen as it offers greater precision in defining the metastructure unit cell and enables the inclusion of the remaining components of the proposed antenna setup. The measured reflection coefficient and far-field patterns are compared to simulations via the utilized model, and a strong agreement is observed. These far-field patterns are acquired with the on-chip antenna inserted within a broadband 400 GHz transmitter submillimeter-wave monolithic integrated circuit, processed on the 35 nm mHEMT technology. [ABSTRACT FROM AUTHOR]

Based on the newly suggested wideband circularly polarized (CP) aperture-coupled magneto-electric dipole (MED), a millimeter-wave (mm-wave) frequency-scanned array (FSA) is proposed in this article. The MED is printed on two substrate layers. The electric dipole is two metal patches with perturbation structure, while the magnetic dipole is two rows of metal vias passing through the top substrate layer. The electric and magnetic dipoles, fed by a coupling slot, excite CP wave. By loading an arc-shaped vias row (AVR) at both ends of the magnetic dipole, the CP bandwidth with axial ratio (AR) less than 3 dB is extended to 40.9%. A new compact wideband transition from the rectangular waveguide (RWG) to the substrate integrated waveguide (SIW) is suggested as the feed structure for the CP FSA. A slow wave structure is etched on the ground of SIW to widen the beam scanning range. A 16-element array is designed and measured. The measured results show that the beam scanning range is 56° over 23–33 GHz band with a peak gain of 19.5 dBi. The CP mm-wave FSA has the advantages of wide scanning angle, low profile, and easy fabrication. [ABSTRACT FROM AUTHOR]

This article proposes an original structure of evanescent quadridge antenna (EQA) to conceive dual-polarized full-metal front-ends that can be used in active antennas (AAs) with wide field-of-view (FoV). An original design methodology is here proposed that allows to induce radiation from subwavelength squared apertures based on the use of evanescent and quadridge waveguides. The proposal is illustrated by means of a design with 4.5% bandwidth providing dual-circular polarization (CP) with good performance up to 50°-scanning even in the diagonal plane. For comparison purposes, a metallic benchmark is also proposed, which is based on the use of classical quadridge horns. Such comparative analysis allows to understand the superior performance of the proposed concept and its main advantage: it allows to avoid the excitation of the first high order mode in the squared quadridge aperture. The excitation of such spurious mode in the antenna is explained in terms of simple equivalent circuit models characterizing the aperture periodic discontinuity. [ABSTRACT FROM AUTHOR]

Surface impedance represents a crucial parameter for the characterization of thin films. Indeed, materials with a sheet impedance varying as a function of their elongation could be used in radio frequency piezoresistive sensors. To estimate this quantity while having the possibility of stretching the sample under test, a waveguide-based non-contact approach is proposed. The absence of contact between the sample under test and the waveguides determines an electromagnetic field leakage, which is prevented by adopting an electromagnetic band gap (EBG) structure. The surface impedance of the sample is retrieved through an inversion procedure exploiting the scattering parameters measured using the proposed setup. The inversion procedure is based on a circuit representation of the waveguide-air-waveguide Section as a $\pi $ -junction. The reliability of the proposed measurement method has been experimentally assessed using a WR137 waveguide. The proposed method allows to accurately determine the real part of surface impedance (the sheet resistance), while higher uncertainty is achieved in the estimation of the imaginary part. [ABSTRACT FROM AUTHOR]

A novel dual-beam fixed-beam leaky-wave antenna (LWA) is proposed in this article. This antenna has a very simple structure, which is basically a grounded coplanar waveguide (GCPW) printed on a specially shaped printed circuit board (PCB). Its working principle is that, for a GCPW with no ground vias (leaky GCPW), there will be a parallel plate waveguide (PPW) mode between its two ground layers, which couples with its GCPW mode. Because the GCPW mode has a phase velocity higher than that of the PPW mode, leaky-wave radiation will be generated from the GCPW to the PPW. This radiation is then radiated into the free space through a metal flare. Since the GCPW is nearly non-dispersive, the beam direction of this radiation is inherently not frequency scanning. Besides its simplicity, the proposed antenna has a pretty good performance. Measured results show a 3 dB realized gain bandwidth and −10 dB impedance bandwidth of larger than 26–40 GHz, a peak gain of 17.5 dBi, and a negligible beam scanning range of only 2.5° (±1.25°) across 26–40 GHz. [ABSTRACT FROM AUTHOR]

A novel high-efficiency polarization-selective bifunctional metasurface (MS) is proposed, which can realize cross-polarized focusing transmission for left-handed circular polarization (LHCP) incidence and co-polarized specular reflection for right-handed circular polarization (RHCP) incidence. As an example of its practical application, the designed MS is applied to form an RHCP folded transmitarray antenna (FTA) whose feed source (FS) is integrated with the bottom metallic surface. To prove the concept, a prototype of millimeter-wave (MMW) FTA based on the proposed MS is numerically simulated, physically implemented, and experimentally measured. The measured results coincide well with the simulated ones, showing a peak gain of 23.6 dBi at 27.7 GHz with the peak aperture efficiency of 43.1%, a 3 dB gain bandwidth of 15.8% (25–29.3 GHz), and a 3 dB axial-ratio (AR) bandwidth over 29.6%. The proposed high-performance antenna has the advantages of low profile, high efficiency, integration design, and broad bandwidth, which may have promising applications in the fifth-generation MMW communication system. The proposed MS and its application to high-gain antenna may promote the uses of MS to real-world applications in satellite communication, radar detection, and wireless communication. [ABSTRACT FROM AUTHOR]

In this communication, a high-order-mode (HOM)-fed open-ended rectangular waveguide antenna with high gain and broadband is proposed for fifth-generation (5G) applications. A miniaturized HOM cavity with four slots introduces hybrid modes of $TE_{340}$ and $TE_{140}$ , which act as a low loss feeding network. Furthermore, an open-ended waveguide is loaded above the HOM cavity to widen the impedance bandwidth. Compared with $TE_{340}$ HOM, hybrid modes of $TE_{340}$ and $TE_{140}$ HOM provide more compact size and higher gain. For the proof of concept, a $4\times $ 4 antenna array is designed and fabricated. The measured impedance bandwidth is 28.1% from 32.85 to 43.6 GHz. The measured peak gain is 21.7 dBi. Great compatibility between simulated and measured results is achieved. [ABSTRACT FROM AUTHOR]

An ultrawideband (UWB) full-metal planar array antenna based on a combination of ridge gap waveguide (RGW) and E-plane groove gap waveguide (E-GGW) is presented for millimeter-wave (mmWave) applications. First, the radiation element of a double-step double-ridged slot structure is proposed and designed. By removing the vertical walls of the cavity in the H-plane, the impedance matching characteristics presents a UWB bandwidth of 53%. Second, a UWB double-layer feeding network is achieved by combining RGWs and double-side-pin E-GGWs for the radiation elements. Finally, an 8 $\times $ 8 full-metal planar array antenna with the presented elements and network is designed, prototyped, and measured. The measured results agree well with the simulated results. The proposed antenna provides an impedance matching bandwidth ($\vert \text{S}_{11}\vert < -10$ dB) of 46.8% from 18.8 to 30.3 GHz. The maximum gain is 27.7 dBi at 27 GHz and a stable gain of 26 $\pm ~1.7$ dBi is obtained over the operation band. [ABSTRACT FROM AUTHOR]

A wideband dual-polarized metal lens is proposed in this article for millimeter-wave (mm-wave) applications. Compared with the traditional lens, the focal length of the proposed novel metal lens can be of any value in theory; in other words, the focal diameter ratio ($f/D$) can be arbitrarily adjusted. The metal 3-D printed technology is used to reduce the fabrication cost. The unit cell of the lens is a square open-ended waveguide. Since the phase velocity of the electromagnetic wave in the metal waveguide is faster than that in the air, the phase compensation can be controlled by adjusting the height of each unit of the lens. It helps to realize the conversion from the quasi-spherical wave of the feed source to the plane wave radiation of the lens. Due to the use of symmetrical elements, the lens can support different dual-polarized radiation (dual-linear polarization and dual-circular polarization). Considering the processing cost and design difficulty, a metal lens with $9\times $ 9 unit cells was processed to verify our design. The $f/D$ is selected as 1. Simulated results for the lens antenna show a peak aperture efficiency (AE) of 43.8% and 38% for linearly polarized (LP) and circularly polarized (CP) radiation, respectively. The antenna shows a stable pattern and wide 3 dB gain bandwidth (26–40 GHz), which covers the entire Ka-band. The measured results of the lens demonstrate a peak gain of 24 dBi and 23 dBic for LP and CP radiation with an aperture of about $7.5\,\,\lambda \times 7.5\,\,\lambda $ ($\lambda $ is the free space wavelength at 30 GHz). The proposed lens features a wide gain bandwidth with dual polarization, low cost, and good radiation performance, which is well suited for mm-wave wireless applications. [ABSTRACT FROM AUTHOR]

This communication presents a novel bifunctional metasurface (MS) combining the reflectarray (RA) and transmitarray (TA) with dual-band orthogonally polarized dual-beam characteristics. The proposed reflect-transmit-array (RTA) is capable of reflecting the $x$ -polarized incidence without changing its polarization state around 10 GHz while transmitting the $y$ -polarized incidence and converting it into the circularly polarized (CP) waves around 14 GHz. To completely cover the working frequency bands of both modes, an antipodal Vivaldi antenna (AVA) is introduced as the source feed due to its intrinsic ultrawideband characteristics. As a proof of concept demonstration, a prototype consisting of 20 $\times20$ elements is also designed, fabricated, and measured. We observe a good agreement between the measurement and simulation results that shows a peak gain of 26.2 dBi and 27.3 dBic, 1 dB gain bandwidth (BW) of 9.8–11.3 GHz (14.2%) and 12.8–14.2 GHz (10.4%), and peak aperture efficiency (AE) of 48.7% and 35.1% for the reflection and transmission modes, respectively. [ABSTRACT FROM AUTHOR]

This article presents a tri-band shared-aperture full-corporate-feed continuous transverse stub (CTS) antenna based on hollow-waveguide. The multiband operation is enabled by a broadband CTS radiator and a novel six-port parallel-plate waveguide (PPW) multiplexer. The CTS radiation slot is fed by a broadband vertical PPW power divider. The six-port multiplexer is composed of three diplexers, which defines the three frequency bands—Ku, K, and Ka. The quasi-TEM mode in the PPW structure is generated by single-layer linear source generators (LSGs). Four such LSGs operating at three different bands are used to feed into the multiplexer. The amplitude and phase precompensation method is applied in the LSG to overcome the imbalance and spurious reflection caused by the metal walls at the terminal ends of the PPW. This has resulted in improved radiation performance in all three bands. A prototype antenna is designed, fabricated, and measured. Good agreement between simulation and measurement has been shown. The peak gains of the antenna over the frequency range of 11.25–15 GHz, 17.7–22 GHz, and 27.5–32 GHz are better than 24.7, 28.2, and 32.1 dBi, respectively. Over 80% antenna efficiency has been achieved in all three frequency bands. [ABSTRACT FROM AUTHOR]

We present two designs that improve the gain and cross-polarization performance of the waveguide-fed short backfire (SBF) antenna by introducing a choke (SBF-2) and by loading the cavity with a metallic ring feature (SBF-2-Ring). A series of parametric simulation studies on antenna dimensions provides information on how to improve the antenna gain and cross-polarization performance while simultaneously extending the impedance bandwidth. For SBF-2, the peak gain was 16.6 dBi, the minimum cross-polarization ratio was −23.8 dB, and the maximum impedance bandwidth was 27.3%, with a gain bandwidth of 19.2%. For SBF-2-Ring, the peak gain was 15.8 dBi, the minimum cross-polarization ratio was −29.1 dB, and the maximum impedance bandwidth was 43.5%, with a gain bandwidth of 31.8%. The concepts were verified by designing, fabricating, and testing two prototypes in the microwave C-band. Excellent agreement between simulation and measurement was achieved. The measured gain for SBF-2-Ring was >14 dBi for 4.7–6.2 GHz and the worst case cross polarization in the diagonal plane was $< -22$ dB for 5.3–5.8 GHz. Cross-polarization in the principal planes has significantly greater bandwidth and the worst case analysis is presented to give limitations on the performance. [ABSTRACT FROM AUTHOR]

A wideband metasurface antenna operating at millimeter-wave spectrum in substrate-integrated waveguide (SIW) technology is proposed. Coupled by a slot etched on an SIW section, the proposed metasurface antenna achieves a wide 10 dB impedance bandwidth in simulation from 19.2 to 42.4 GHz, indicating a fractional bandwidth of 75%. The development of the proposed metasurface antenna can be divided into four stages, i.e., a slot antenna, dielectric loading, adding covered metasurface, and connecting to a transition. The input impedance and the resonance of these stages are elaborated in detail to explain the working mechanism. Parametric study is carried out to inspect into the design process. By analyzing the $E$ -field distributions, the proposed metasurface antenna is characterized by TM10 mode, antiphase TM20 mode, and TM30 mode. Compared with other similar designs in the open literatures, the proposed metasurface antenna displays a widest impedance bandwidth. The dimension of the proposed metasurface antenna is $0.80\,\,\lambda _{0} \times 0.72\,\,\lambda _{0} \times 0.24\,\,\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at 30 GHz. The maximum gain within the interested frequency spectrum is 7.0 dBi. [ABSTRACT FROM AUTHOR]

A single layer 77 GHz dual circularly polarized (CP) antenna array is proposed based on ridge gap waveguides (RGWs) technology. The antenna consists of eight U-shaped slots, fed by two feeding networks for generation of dual CP. The proposed antenna array has been fabricated and measured. The experimental results show good agreement with the simulations. The axial ratio is below 2 dB, and the return loss and port isolation are better than 13 and 18.6 dB over 76–81 GHz, respectively. The measured gain for the integrated array is 14.8 dBi at the center frequency of 78.5 GHz. With integration of feeding networks and the radiating elements in a single layer, this antenna has potential to be used in automotive radars. [ABSTRACT FROM AUTHOR]

We report, here, the design and experiments of dual-wideband dual-circularly polarized (dual-CP) shared-aperture reflectarrays (RAs) operating at the K-/Ka-band utilizing a single functional substrate. By coupling the adjacent but separated resonances of the H-shaped aperture and circular patch, and utilizing the shorted microstrip phase delay lines, the proposed RA cells can offer wideband performance. Then, these RA cells are interleaved in a shared aperture for the dual-band operation. By combining the dynamic phase and Berry phase compensation techniques, the RA cells can independently control the reflective phase delay of orthogonal CP beams at both of the targeted bands, providing four degrees of freedom for beamforming. The diffractive property of an infinite periodic gradient array of the interleaved K- and Ka- band cells is investigated, which verifies the wideband performance of the proposed cells. Two RAs with a thin panel thickness of $0.27\lambda _{K}$ ($\lambda _{K}$ is the free-space wavelength at the K-band) are fabricated and characterized, generating symmetrically and asymmetrically distributed dual-wideband dual-CP beams at the K-/Ka-band, respectively. The measured bandwidths for the two RAs are wider than 14.1% for the K-band right-handed CP (RHCP)/left-handed CP (LHCP) beams and about 11% for the Ka- band RHCP/LHCP beams with both the gain variation and axial ratio of smaller than 2 dB. [ABSTRACT FROM AUTHOR]

A wideband differentially-fed slot antenna is presented for millimeter-wave (mmWave) applications. A novel method of using stepped corner-shaped slot is first utilized to establish the wideband circularly polarized (CP) radiation. In the configuration of corner-shaped slot, two wide open slots at the ends are utilized for effective orthogonal radiation, while the narrow slot at the center is utilized for power transmission and quadrature phase delay. An equivalent circuit is given to illustrate the inner working principle for CP radiation. In addition, square cuts are etched on the four corners of the radiating patches to further increase the axial ratio (AR) and impedance bandwidth. Based on this design concept, the antenna element was first designed and fabricated for performance verification. Then, a $1\times $ 4 linear array with beam-scanning performance and a $4\times $ 4 planar array with high gain and stable radiation were designed and fabricated. Both the simulated and measured results show that the $1\times $ 4 linear array and $4\times $ 4 planar array can have the wide overlapped impedance and AR bandwidths of 30.6% and 33.6% with a thickness of $0.16\lambda _{0}$ , respectively. The advantages of compact size and wide bandwidth make the presented antenna a good candidate for mmWave applications. [ABSTRACT FROM AUTHOR]

In this communication, two composite right-/left-handed transmission line (CRLH-TL)-based reconfigurable antennas with multiple-parameter reconfiguration capability have been presented. In antenna I, the polarization is switched between circular polarization and linear polarization. In antenna II, a split-ring resonator (SRR) is introduced that is connected with the ground through another p-i-n diode D2. In the D2 OFF-state, the metamaterial behavior of the SRR establishes. Due to negative permeability at the frequency of operation, it produces magnetic coupling with the antenna and the antenna starts radiating at a new band (5.2 GHz), forming dual-band characteristics with circular polarization. Antenna II is capable of providing band/frequency and polarization/band, frequency, and polarization reconfiguration using different ON/OFF combination states of diodes D1 and D2. The antennas are suitable for 2.4/5.2 GHz WLAN and 3.5/3.6 GHz WiMAX applications. [ABSTRACT FROM AUTHOR]

A standardized design method of planar periodic structure (PPS)-based 90° linear polarization (LP) converters is presented. This procedure enables standardized designs centered at an arbitrary frequency in either reflection or transmission at normal incidence, which may be achieved with no computational cost and can be used to obtain suitable designs at oblique incidence. It uses both Foster’s equivalent circuits and the classic coupler synthesis, which allow the number of layers, the values of the lumped elements, and the lengths and impedances of the spacers needed to fulfill any prescribed requirements in terms of XP, insertion losses, and bandwidth to be known. The selection of the PPS scatterer that provides the appropriate values of the circuit elements is also studied. Several designs are presented to validate the proposed method, one of which converts a vertical polarization into the horizontal in transmission, exhibiting simulated results of XP < −30 dB, insertion losses better than 0.1 dB, and bandwidth that improves other rotators in the state of the art for the same number of layers. The designed device has been manufactured and experimentally tested, and the results validate the methodology. [ABSTRACT FROM AUTHOR]

In this communication, a broadband substrate integrated waveguide (SIW)-fed circularly polarized (CP) cross-dipole antenna is proposed for millimeter-wave (MMW) applications. Its radiation parts consist of a cross dipole and reflecting ground, which are etched on two substrates. The antenna is fed by an SIW through a double-sided parallel-strip line (DSPSL). In addition, zigzag edges and L-shaped etches are utilized to expand the impedance bandwidth (IBW) and axial-ratio bandwidth (ARBW), respectively. By these methodologies, the antenna prototype possesses a measured IBW of 34.6% from 22.5 to 31.9 GHz, an ARBW of 23.1% from 24 to 30.25 GHz, and a peak gain of 8.8 dBic at 29.5 GHz. In comparison to general coaxial-line-fed cross-dipole antennas with a nonplanar topology and high profile of $0.25\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at the center frequency), the proposed antenna with PCB process maintains broadband and owns a low profile of $0.16\lambda _{0}$ , which makes it more desirable for MMW integrated circuits. [ABSTRACT FROM AUTHOR]

In this communication, a high-efficiency rectangular waveguide-to-spoof surface plasmon polaritons transmission line (SSPPs TL) transition operating within terahertz frequencies is demonstrated. Terahertz signal fed by the rectangular waveguide is first coupled to the planar circuit through the dipole antenna. And then a taper and double-sided SSPPs TL are used to transform the resonant mode in the dipole antenna to the SSPPs mode and achieve impedance and momentum matching. The high transmission performance of the SSPPs TL is obtained by etching a series of periodically corrugated grooves on the metal strip in the top layer and a ground pad connected to the convexity of the rectangular waveguide is employed in the bottom layer. A back-to-back transition prototype was fabricated on a $50~\mu \text{m}$ -thickness quartz substrate and designed for a terahertz device with WR-4.3 standard rectangular waveguide. The measured results show that the insertion loss is lower than 2 dB from 195 to 250 GHz, and the in-band return loss is better than 10 dB. To the best of our knowledge, this work presents the rectangular waveguide-to-SSPPs TL transition using a dipole antenna for the first time, which has potential applications for plasmonic-integrated circuits and systems in the terahertz range. [ABSTRACT FROM AUTHOR]

Radial-line slot-array antennas (RLSAs) provide an extremely simple solution to achieve high-gain circularly polarized radiation patterns without the need for complicated feeding networks or polarizers. The dielectric-filled radial waveguide, however, drastically reduces the efficiency that is potentially achievable by RLSA antennas at millimeter waveband. In this article, a novel architecture for an all-metal RLSA is proposed by replacing the dielectric material with a regular bed of metallic nails, thus maintaining the required slow wave characteristic within the radial waveguide. The slot array is efficiently optimized by using an ad hoc method-of-moments solver, based on the definition of an equivalent problem in the waveguide region. This accurate optimization process, along with the all-metal nature of the antenna, allows to reach a measured peak total efficiency above 80% at 30 GHz. The fabricated prototype consists of two pieces: the bottom waveguide with the bed of nails and the top slotted plate, which are easily assembled by means of a few screws. Experimental results report a peak gain of 35.0 dBi for a radiation efficiency of 94%, and a wideband matching performance with a very pure axial ratio, below 0.6 dB. [ABSTRACT FROM AUTHOR]

A multiconductor transmission-line (MTL) model is proposed with which to model the uniplanar compact electromagnetic bandgap structure (UC-EBG). The model is based on a 2-D arrangement of metamaterial-based electromagnetic bandgap structures (MTM-EBGs), with a central node region. The branches of this structure are modeled as conductor-backed coplanar waveguide segments with integrated series capacitors, while the node region is modeled as a grid of microstrip (MS) lines with suitably augmented propagation velocities. The dispersion properties of the canonical UC-EBG unit cell are simulated in Ansys HFSS and compared with those of an equivalent simulation model based on a 2-D arrangement of weakly loaded MTM-EBGs, as well as similar data produced by the MTL equivalent-circuit model, which are all found to be in agreement. It is then shown that additional capacitive loading allows for substantial miniaturization, a regime in which even better agreement is produced between the equivalent circuit model’s dispersion data and the data produced by an equivalent HFSS model. Using these data, the Bloch modes of this structure are analyzed in detail. Thus, the MTL perspective offers a recipe for producing highly miniaturized UC-EBG unit cells that may be successfully integrated into printed circuit board (PCB) systems for applications in parallel-plate noise and surface-wave (SW) mode suppression, among others. [ABSTRACT FROM AUTHOR]

In this article, we present the investigation and design of high-performance transitions from coplanar waveguide (CPW) to single-conductor, corrugated waveguides (WGs), namely, terahertz spoof surface plasmon polariton (SSPP) WGs. In contrast to the previous studies in the literature on CPW-to-SSPP WG transitions, we propose a novel methodology to examine the relationship between the guided wavenumber and momentum matching, which is based on analytical calculations, together with the effects of flaring grounds on transition performance. This novel methodology allows us to design a low-loss transition circuit (TC) for any given CPW and SSPP dimensions, which is demonstrated for the first time in the literature. We verify the proposed methodology by the design, fabrication, and measurement of several TCs. The measurement results show that the insertion losses of the proposed TCs can be as low as −1.2, −1, and −2.4 dB at 0.25, 0.275, and 0.3 THz, respectively, which brings a significant improvement of 0.6–2.3 dB in the 0.25–0.3 THz band, compared with the previously reported studies in the literature for the terahertz band. [ABSTRACT FROM AUTHOR]

This article presents a high-gain slotted ridge waveguide antenna array (SRWAA) with inductive diaphragms, which can realize a wide-sector beam with a low sidelobe simultaneously. The proposed antenna can cover a wide detection range and avoid interference from other directions. The expected excitation distribution for the antenna array is extracted through a beamforming method. To reduce the influence of the dispersion phenomenon on signal quality, inductive diaphragms are inserted into the sidewall of the ridge waveguide, which is fully analyzed from the point of the equivalent circuit. A cut-off-mode power divider is utilized, which can control the power ratio flexibly. An SRWAA working at 24.125 GHz, including a six-way feeding network, and a $6\times24$ slot array with the size of 330 mm $\times66.8$ mm is designed and fabricated. The measured sidelobe level (SLL) and half-power beamwidth (HPBW) in the elevation plane are −19.6 dB and 54.41°, with the counterparts in the azimuth plane −29.8 dB and 3.15°, respectively. The measured peak gain is 22.3 dBi at 24.125 GHz. The measured results are in good agreement with the simulated ones. This work has the potential to be applied in air detection, anti-unmanned aerial vehicles (UAVs), meteorological radar, and imaging radar. [ABSTRACT FROM AUTHOR]

A compact tag antenna, which has a geometrical dimension of 31.5 mm $\times31.5$ mm $\times3.2$ mm, is constructed using a stacked planar inverted-L antenna (PILA) for metal-mountable applications in the UHF radio frequency identification (RFID) passband. The new antenna is formed by inserting a shorted patch into a PILA structure to create a double-layered inverted antenna, which can be viewed as a cascade of two parallel resonant tanks. An increase in electric field intensity in the antenna structure has brought in sufficient capacitance for reducing the tag resonant frequency effectively to the useful UHF RFID passband. Due to the increase in the antenna reactance, conjugate impedance matching can be easily achieved between the antenna and the microchip. Fine-tuning schemes such as stubs and slits are also incorporated with the proposed tag antenna for adjusting the operating frequency to an exact precision. Measurements show that the proposed tag antenna can achieve a read distance of 7.25 m at an EIRP power of 4 W. The resonance of the proposed tag antenna is found to be very stable and it is insensitive to changes in the backing metal platform. [ABSTRACT FROM AUTHOR]

A novel methodology to create metallic waveguides with multilayer integrated vertical-electromagnetic bandgap (EBG) structure is proposed in this article, and the structure realizes low-cost millimeter-wave (mmWave) slot array antennas. A multilayer stack of easy-to-process thin metallic etching plates is introduced to design mmWave waveguide using compression fit instead of diffusion bonding and welding assembly process. The electromagnetic (EM) wave leakage from the gaps between the metallic plates is suppressed using the vertical-EBG structure and antiphasing feeding. The dispersion diagrams of the vertical-EBG unit cell are investigated to illustrate the suppression of leakage. Another leakage wave intercepting methodology is adopted by antiphase feeding to prevent leakage wave from the adjacent slot subarrays. Finally, two examples of 2 $\times $ 8 and 8 $\times $ 8 slot array antennas are presented to verify our design concept. The measured impedance bandwidths of the two antennas are 77.1–84.6 GHz (9.3%) and 78.6–84.9 GHz (7.7%). In addition, the 3 dB broadside gain bandwidths are 73.1–85.3 GHz (15.1%) and 76.8–84.4 GHz (9.4%). The results show the aperture efficiencies up to 56.4%. [ABSTRACT FROM AUTHOR]

An ultrawide-angle frequency beam scanning leaky-wave antenna (LWA) with a high scanning rate based on spoof surface plasmon polaritons (SSPPs) waveguide is proposed in this communication. A row of elliptical patches is placed periodically near the SSPPs waveguide, which can shift the fundamental mode of SSPPs waveguide to the fast-wave region and radiate electromagnetic (EM) waves. The simulated results show that the proposed LWA achieves an ultrawide scanning angle range of 172° over a narrow operation bandwidth of 9.8–12.28 GHz, which implies a high scanning rate. The simulated average gain of the proposed LWA is 10.13 dBi and its average total efficiency is 75.35%. The proposed LWA is fabricated and measured. The measured scanning angle range is 167° in the frequency band of 9.9–12.25 GHz, and the measured average gain is 9.73 dBi. Good agreements between the simulated and measured results are obtained, validating the proposed design. [ABSTRACT FROM AUTHOR]

A dual-polarized endfire array is presented in this article for millimeter application. The substrate integrated mode-composite transmission line is introduced to exciting the dual-polarized radiation. Specially, the horizontal polarization is excited by the transverse electromagnetic (TEM) mode, whereas the vertical polarization is based on the TE10 mode. Two metal blocks sandwich the substrates to form a sandwich structure, and an open-ended slot is designed on the block edge to construed complementary sources radiation. Benefiting from the wideband feature of complementary sources, the proposed dual-polarized endfire array achieved a considerable bandwidth performance of 26.9% (24.8–32.5 GHz) based on the standard that both the voltage standing wave ratios of the two ports are less than 2. In terms of the key factor of dual-polarized antenna and isolation, measured results show a high port isolation of over 36 dB and a cross-polarization discrimination rate of over 30 dB. The excellent dual-polarized performance gives the proposed endfire array the potential of application in millimeter-wave mobile communications. [ABSTRACT FROM AUTHOR]

We present single- and dual-frequency antennas based on the shorted helical slot in hepatic microwave ablation. The single-frequency antenna is designed by lathing a helical slot on shorted traditional semirigid coaxial cable, which is expected to be operated at the frequency of 2450 MHz, and the dual-frequency antenna is designed with the combination of an annular slot and a helical slot, which can be operated at 915 and 2450 MHz. We use full-wave electromagnetic simulation and transient thermal simulation to analyze the performance of the proposed ablation antennas. Both the proposed antennas are fabricated and used in ex vivo ablation experiments at different frequencies with a power level of 23 W for 2 or 5 min. We observe that the proposed single-frequency antenna with helical slot has more concentrated specific absorption rate (SAR) pattern than those antennas with conventional slots does at 2450 MHz, and the dual-frequency one has the capability to control the roundness of ablation zone from 0.34 to 0.63 under the different combination of frequencies and operation times. The proposed microwave ablation antennas are expected to lead to a potential solution of curing the liver cancers with various characteristics. [ABSTRACT FROM AUTHOR]

In this article, a new type of Vivaldi antenna with heat dissipation enhancement is proposed and manufactured based on 3-D printing and printed circuit board (PCB) technologies. A longitudinal slot on substrate integrated waveguide (SIW) is employed to feed Vivaldi radiation structure, which replaces the balun structure of traditional Vivaldi antennas. The measured 10 dB bandwidth of antenna element reaches up to 34.48% (21.77–30.39 GHz) and the in-band realized boresight gain is 6.5–8.8 dBi. The $1\times 4$ Vivaldi antenna array with 28.72% (21.63–28.81 GHz) bandwidth and a gain range of 10.5–12.5 dBi is achieved. The fin-shaped structure of the antenna array further enhances the heat dissipation while increasing the gain up to the range of 13.4–15.5 dBi. The measured results are in good agreement with the simulated ones. The proposed antenna array has important application potential in 5G millimeter-wave systems. [ABSTRACT FROM AUTHOR]

Wideband slot-coupled microstrip antenna (SCMSA) is a distinctive electromagnetic wave radiator in recent years with wide bandwidth and low profile. In such a wide frequency range, the electrical distance, i.e., normalized to operating wavelength, between dual equivalent magnetic currents increases obviously with upward frequency. Therefore, the realized gain is usually with a large variation, which limits the wideband performance of SCMSA. In this communication, a feasible method is proposed to stabilize the realized gain of an SCMSA over its entire impedance bandwidth by utilizing a properly designed reflector-plus-sidewall structure (RPSS), which includes a reflector with an optimized height and two vertical sidewalls. Each part has its own function in realized gain compensation and enhancement, performing a flatter and higher realized gain in a wide frequency range. To validate this method, an antenna prototype is fabricated and tested. Compared with the referenced SCMSA, the measured results indicate that the proposed one adding RPSS maintains a wide impedance bandwidth of 24.8% (3.75–4.81 GHz), but reduces gain variation from 4.1 to 0.5 dB (10.5–11 dBi) with an average realized gain increment of 2.1 dB. [ABSTRACT FROM AUTHOR]

A beam-tilted circularly polarized (CP) corporate-fed waveguide slot array is accomplished in the 60 GHz band. The main beam tilting in the 45° cut-plane is achieved by introducing a corporate feeding circuit with a linearly tapered phase distribution. The T- and H-junctions with nonidentical output waveguide widths are newly proposed to realize progressive output phases. By cascading asymmetric T- and H-junctions into a $16\times16$ way power divider, we design a $32\times32$ element array consisting of $256\,\,2\times 2$ element CP subarrays. The simulated tilt angle coincides with the theoretical one over the whole frequency band. The test antenna is fabricated by the diffusion bonding of thin copper plates. Stable beam directions and wideband operations are verified by the experimental evaluations. The overall reflection is sufficiently suppressed below −14 dB over the 56–67 GHz frequency band. The realized gain higher than 37 dBic is achieved over the frequency range of 59–64 GHz, while the AR is suppressed below 3.5 dB over the frequency range of 57.25–66.75 GHz. [ABSTRACT FROM AUTHOR]

A high-gain low-profile leaky-wave antenna (LWA) for vertically-polarized (VP) fixed-beam endfire radiation is proposed in this article. The LWA is composed of two back-to-back half-mode waveguides with grooves etched at the margins of both radiation edges. By etching grooves, the phase velocity of the traveling wave can be tailored to slower than the wave velocity in free space for fitting the Hansen–Woodyard condition. Compared with periodic LWAs, the proposed antenna continuously radiates at two symmetric apertures, contributing to a high endfire gain. A prototype is fabricated and tested to validate the concept. The measured and simulated results are in good agreement. A simulated gain of 14.29 dBi and a measured gain of 13.37 dBi are achieved within an antenna length of $3.05\lambda _{0}$. Moreover, a measured overlapping bandwidth of 2.74–3.17 GHz (14.3%) is realized with $S_{11} < - 10$ dB and gain variation less than 3 dB. To the best of the authors’ knowledge, the proposed VP endfire LWA realizes the highest aperture efficiency and shows great advantages in high gain, low profile, and wide bandwidth. [ABSTRACT FROM AUTHOR]

This communication presents a Fabry–Pérot cavity antenna with a thin polarizer loaded inside the cavity. The antenna is excited by a linearly polarized magneto-electric dipole. To realize self-circular-polarizing characteristics, a polarizer with the meander line is placed between the partially reflective surface and the reflective ground plane. Sharing the same radiating aperture, left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) waves can be generated by separate input ports. After analyzing the mechanism of the circular polarization, simulation and measurement are carried out to verify the proposed design. The operating bandwidth is 4%, from 27.4 to 28.5 GHz, covering fifth-generation (5G) 28 GHz band. The peak gain is 16.85 and 17.20 dBi for LHCP and RHCP, respectively. [ABSTRACT FROM AUTHOR]

This article presents a dual-wideband dual-polarized aperture-shared antenna array with low blockage effect between cross-band elements, including a low-band (LB) element with a $4 \times 4$ high-band (HB) antenna array underneath. The radiator of the proposed LB element consists of four slim loops with loaded periodic split-ring resonators (SRRs) for achieving low scattering property in the high band. As a result, the blockage effect of the LB element on the HB antenna array is nearly indistinct. The radiation performance, as well as the S-parameters of the HB elements in the dual-band array, is almost the same as the isolated case. For demonstration, the dual-band aperture-shared antenna array, operating in the LB of 0.69–0.96 GHz (32.7%) and the HB of 3.3–4.2 GHz (24%), is fabricated and measured. Besides, the isolated LB antenna and HB array are designed for comparison. Compared with the isolated case, the measured peak gain variation of a $1 \times 4$ HB array in one column is lower than 0.7 dB after adding the proposed LB element. In addition, the radiation pattern variation within 3 dB beam coverage is less than 1.5 dB. Therefore, the proposed dual-band aperture-shared array is very suitable for tackling the integration of 5G and 4G/3G/2G base station antennas. [ABSTRACT FROM AUTHOR]

In this article, a high-isolation dual-polarized leaky-wave antenna (LWA) with a fixed beam is proposed for full-duplex millimeter-wave (mm-wave) applications. The proposed antenna consists of a dual-polarized LWA array and an orthogonally differential feeding network. The proposed dual-polarized LWA array is developed based on the proposed LWA unit cell, which is suitable for differential feed, and the open stopband is eliminated. The proposed feeding network provides two pairs of orthogonally differential excitation for the LWA array to realize the fixed beam with orthogonal polarization in boresight direction; the high interport isolation is implemented as well. The prototype for demonstration purposes is fabricated and measured. The measured results show that the proposed antenna exhibits an operating band from 27.6 to 29.5 GHz with a maximum gain of up to 24 dBi. Furthermore, the measured interport isolation is higher than 51 dB within the operating band, where the maximum isolation is up to 60 dB. The measured cross-polarization levels are also very low, less than −27 dB. The proposed antenna features high gain, high interport isolation, and good co-/cross-polarization isolation, achieving a good Tx/Rx separation for the in-band full-duplex applications at mm-wave frequencies. [ABSTRACT FROM AUTHOR]

A 2.4 GHz industrial, scientific, and medical band on-chip antenna (OCA) is integrated into an on-chip broadband balun in $0.18~\mu \text{m}$ CMOS technology on a die of size 4 mm2. Antenna miniaturization is achieved from the capacitive loading of meandered dipole arms. A back-to-back configuration of the balun on a separate die is characterized with in-band insertion and return loss of better than 0.9 dB and 20 dB, respectively. A commercial low-cost package is used to provide a decoupling effect to the OCA when immersed in tissue, enabling it to maintain stable impedance matching as in the air. A detailed explanation of the decoupling mechanism is provided using field plots and equivalent circuit analysis. The OCA is characterized in air and different tissue phantoms with a gain of −23.8 dBi in air and −25.9 dBi inside skin mimicking gel. The maximum simulated uplink specific absorption rate is obtained as 160 $\mu \text{W}$ /kg for an input power of $25~\mu \text{W}$ to the OCA in the transmitting mode. As the antenna has a small footprint and is analytically estimated to be capable of communicating at a high uplink bit rate of 1 Mb/s over a distance of 5.2 m with a 3 dB link margin, it is most suited as a minimally invasive implantable medical device. [ABSTRACT FROM AUTHOR]

Waveguide slot arrays are a widely used solution to attain linearly polarized high-gain antennas. In this article, an all-metal T-shaped radiating element is conceived with the aim to replace the usual rectangular slots and attain circularly polarized arrays, preserving their good properties. The polarization conversion is made possible due to the inclusion of a parasitic arm perpendicular to the main active slot. Due to the fact that this second arm is not directly fed by the waveguide but coupled to the active slot, the T-shaped element can be used in any array originally formed by metallic rectangular slots. The design of resonant shunt arrays has been addressed here for validation purposes. The experimental results of two sample linear arrays at 30 GHz demonstrate the design accuracy and manufacturing reliability, reporting an axial ratio below 2 dB within a bandwidth of 1.9 GHz and a peak efficiency around 98%. [ABSTRACT FROM AUTHOR]

A single-layered slot antenna system working at 5.8 GHz Industrial, Scientific and Medical (ISM) band is proposed for in-band full duplex (IBFD) operation applications without the use of a coupler. First, high isolation is achieved by strong separation of even- and odd-mode feeds. The microstrip-coupled coplanar waveguide (CPW) is used at Port 1 (TX port) to excite a stepped-slot antenna in the CPW odd mode. On the opposite side, a microstrip T-junction power divider is employed at Port 2 (RX port) to feed two offset-fed stepped-slot antennas in even mode. Second, isolation is further improved by 30 dB by using a lumped capacitor at the termination of the CPW. The measured isolation between the two ports is about 50 dB across the bandwidth. The measured −10 dB bandwidth of Port 1 is 0.49 GHz (8.5%), while that of Port 2 is 1.06 GHz (18.3%). The gains of TX and RX antennas are 5.4 and 5.8 dBi at 5.8 GHz. The proposed antenna can also be deployed as a dual-polarized antenna. Mathematical analysis and equivalent transmission line circuit models are provided to give physical insight into the working principals of the antenna with validation from ANSYS HFSS simulation. [ABSTRACT FROM AUTHOR]

A novel electrically small, wide beamwidth circularly polarized (CP) antenna using two orthogonal smaller hybrid magnetic dipoles (HMDs) for radio frequency identification (RFID) reader application is presented, which achieves a quality factor ($Q$ -factor) approaching the Chu-limit. First, a HMD is implemented by the combination of two single-slit magnetic dipoles (S-MDs) and one dual-slit magnetic dipole (D-MD), which is carefully analyzed by equivalent circuit models and field distribution. Then, by implementing two orthogonal HMDs with slightly size difference and a 45° angle tilted coupling feeding line, two orthogonal magnetic components with equal magnitude and 90° phase difference are obtained, which lead to a CP radiation. Finally, an electrically small CP magnetic dipole antenna with a size of $0.12\,\,\lambda _{0} \times 0.12\,\,\lambda _{0} \times 0.04\,\,\lambda _{0} (ka< 0.55)$ ($\lambda _{0}$ is the free-space wavelength at its center frequency) is fabricated and measured. The measurement shows that a −10 dB impedance bandwidth of 3.17% (cover 902–928 MHz UHF band well), a half power beamwidth (HPBW) of 104°, and a peak radiation gain of 4.57 dBic are achieved. Generally, it features a small size, wide beamwidth, simple design, and good radiation performance, exhibiting good application potential usage in internet of things (IoTs) systems. [ABSTRACT FROM AUTHOR]

Waveguide arrays comprise slot radiators cut into hollow, single-mode, standing wave structures. Their impedance bandwidth and compactness are limited by the waveguide cutoff. By using the TEM mode of a coaxial waveguide, a more compact structure with a larger bandwidth is possible at the expense of increased ohmic loss in the waveguide. Using this basis, a new type of slotted coaxial waveguide antenna is presented. A compact waveguide array means that the element and array aspects are not independent, and with no accurate transmission line models for the structure, the design is from a parametric study by simulation. Two basic designs are demonstrated: the first with no constraint on the azimuthal extent of the slots, and the second where some mechanical strength of the waveguide is maintained by constraining the azimuthal extent of the slots to be 90° or less. The parametric studies provide insight for realizing the high bandwidth, and measurements of prototypes confirm the performance. These antennas are useful for integration with cylindrical structures such as masts or bicycle and drone frames. [ABSTRACT FROM AUTHOR]

A fully metallic partially open corrugated waveguide (CW) is employed to construct the Ka-band linearly polarized (LP) and circularly polarized (CP) frequency-scanning (FS) periodic leaky-wave antennas (PLWAs) with the spatial coverages from backward ($\theta < 0$) to forward ($\theta > 0$). The waveguide structure is obtained by cutting a conventional CW in half along its longitudinal symmetry plane. The $n =-1$ space harmonic is generated effectively by the half-wavelength radiating slots on the corrugations. The broadside frequency is about 31.5 GHz. The LP and CP radiations are realized by rotating the radiating slots to different angles. The measured scanning ranges of the LP and CP PLWAs are from −42.7° to 16.5° in the band of 26.5–33.5 GHz and from −48° to 22.7° in the band of 26.5–34 GHz, respectively. The measured axial ratio of the CP PLWA is below 3 dB in the mainlobe directions varied with frequency. The prototypes and experimental results make contributions to the polarization control, scanning rate improvement, and profile reduction in the frequency-controlled millimeter-wave imaging and radar systems. [ABSTRACT FROM AUTHOR]

This communication presents a compact leaky-wave antenna providing circular polarization from a dual-mode hollow waveguide (WG). The monolithic structure is based on a rectangular metallic guide that is perforated with crossed slots. The antenna is fed by a standard WR42 port, which is connected to the leaky WG by a transition that allows for dual-mode excitation. The axial ratio (AR) is determined by the size of the WG section and the dimensions of the crosses. In order to preserve the polarization purity, the geometry of the first radiating elements is modulated. Designed at $K$ -band, the present proposal is suitable for space applications since it relies on a full-metal structure. A design methodology is proposed based on the dual-mode dispersion analysis. Selective laser melting is used to monolithically 3-D print the antenna. Measurements are in good agreement with simulations and the AR is 0.92 dB at 20.5 GHz. [ABSTRACT FROM AUTHOR]

In this article, a four-element circularly polarized series-slot-fed multiple–input-multiple-output (MIMO) antenna array with circular polarization (CP) diversity is presented. The proposed design utilizes a combination of 45° inclined slots and a straight microstrip line feeding technique. The two antennas are designed to operate with the opposite sense of CP. CP is achieved by placing a patch of just about square dimensions on the top of the V-slot with orthogonal but unequal arms. The unequal arm of the slot degenerates the fundamental mode at a slightly different frequency with a 90° phase difference occurring at the center frequency of each arm. Proper positioning of the patch on the top of the slot ensures excitation of CP. For realizing a MIMO antenna with a different sense of polarization, both the slots and the patches are flipped with respect to the feedline. Following optimization at the full-wave level of description, the antenna is prototyped and validated experimentally. The realizable antenna footprint is 20 mm $\times27.7$ mm. The simulated and measured results indicate that the proposed antenna features a wide impedance bandwidth ($\vert \text{S}_{11}\vert < -10$ dB) from 26.9 to 30.7 GHz, 3 dB axial ratio bandwidth from 27.31 to 29.65 GHz and the peak realized gain of 11.86 dBic. Moreover, it exhibits a low level of in-band isolation $\vert \text{S}_{21}\vert > -37$ dB and an almost negligible envelope correlation coefficient (ECC), less than 0.00025. The highly directional beams, high gain, and compact size of the proposed antenna permit implementation of multiple antennas for indoor applications in the 28 GHz band. [ABSTRACT FROM AUTHOR]

This article proposes a novel design of the dual-band antenna pair. Starting from the single-band antenna pair composed of T-shaped monopole and T-shaped slot that are intersected with each other, orthogonal T-monopole and odd-symmetrical slot modes are excited. By adding symmetrical low-pass high-stop filters into the horizontal stub of the T-monopole and high-pass low-stop filters into the gap of the T-slot, an extra mode is introduced for each antenna, producing dual-band operation. Impedance bandwidths and radiation efficiencies of both bands can be adjusted flexibly using the filters. A detailed design guideline is given. The dual-band antenna pair operating at partial N78 (p-N78, 3.4~3.6 GHz) and partial N79 (p-N79, 4.8~4.9 GHz) is with a footprint of $15\times 6$ mm2. The measured results show that the average efficiencies are both −3.4 dB at p-N78/p-N79 for the odd-symmetrical slot and −2.8 dB/−3.7 dB at p-N78/p-N79 for the T-monopole, isolations are better than −16.8 dB at p-N78 and −11.8 dB at p-N79, and ECCs are lower than 0.1 at p-N78 and 0.2 at p-N79. The proposed dual-band antenna pair exhibits great potential to be applied in the fifth-generation (5G) multiple-input multiple-output (MIMO) terminal. [ABSTRACT FROM AUTHOR]

A wide impedance-bandwidth and gain-bandwidth terahertz (THz) on-chip antenna (OCA) with chip-integrated dielectric resonator (CIDR) backed by a ground plane is proposed in this article. The antenna uses the inherent silicon substrate in complementary metal–oxide–semiconductor (CMOS) technologies as a rectangular dielectric resonator (DR), that is, the CIDR. This CIDR can be seen as a standard dielectric resonator antenna (DRA) or a magnetic wall cavity with in-phase reflected waves from the ground. A versatile comb-shaped dipole antenna is designed above the silicon CIDR, functioning both as a feeder for the DRA and an independent radiator. With the proper design of the CIDR and the dipole, multiple higher order DR modes and the cavity mode are simultaneously excited, namely, hybrid DR–cavity modes. The hybrid modes greatly expand the bandwidth and improve the gain. Simulations show that the −10 dB impedance bandwidth and 3 dB gain bandwidth are 50% and 34.5%, respectively, while a peak gain of 6.5 dBi is achieved at 305 GHz. For validation, the antenna is fabricated using the Taiwan Semiconductor Manufacturing (TSMC) 65 nm CMOS technology and tested by dedicated THz measurement setups. The fabricated sample shows a peak gain of 8.6 dBi and a maximum radiation efficiency of 44% at 295 GHz. Meanwhile, low cross-polarization levels and stable patterns are also observed. The features of wide bandwidth, high gain, and low profile make the antenna a good candidate in fully integrated THz transceiver systems. To the best of the authors’ knowledge, this is the widest fully integrated OCA working at THz frequencies. [ABSTRACT FROM AUTHOR]