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In this article, a novel printed dipole antenna is proposed with gain enhancement by using the newly emerging substrate-integrated double line (SIDL) technology for potential 5G millimeter-wave (mm-wave) applications. As a three-wire transmission line, the SIDL incorporates two parallel inner strips and one grounded outer conductor. The inner strip pair protrudes and is bent bilaterally to form the dipole’s arms. The outer conductor is stretched out and splits into four strips in a fourfold symmetry along the longitudinal axis to boost the gain. A bilateral slotline technology is used to couple the energy from the feed to the SIDL structure, providing a broadband transition. The shaped SIDL and the transition contribute to the proposed dipole element and then are expanded to a $1\times 2$ array, both of which are designed and fabricated by using the standard printed circuit board (PCB) process. The measurement discloses that the element has an actual −10 dB impedance bandwidth from 33.5 to 47.4 GHz (34.4%@40.4 GHz) with a practical peak gain of 7.00 dBi, which for the array are 32.0–45.1 GHz (34.0%@38.6 GHz) and 8.88 dBi, respectively. Good agreement between the simulated and experimental results demonstrates the feasibility of SIDL’s utilization in designing the printed dipole antenna for high-gain and wideband mm-wave applications. [ABSTRACT FROM AUTHOR]

This communication presents a unique design of a dual-polarized wideband passive beam-switching antenna at millimeter-wave (mm-wave) bands for multiple-input–multiple-output (MIMO) pattern diversity applications, which exhibits low correlation between the ports and a broad tilt bandwidth (BW). A magnetoelectric (ME) dipole fed by a printed ridge gap waveguide (PRGW) as a quasi-TE source is considered as the elementary antenna in the Ka-band. To achieve beam deflection in each quadrant, a four-port MIMO prototype consisting of four ME-dipoles, positioned perpendicular to each other, is integrated with a meta-lens that consists of three layers of $12\times12$ dual-polarized split-ring resonators (SRRs) offset from the center of each antenna. The beamforming structure is able to generate four fixed beams, one in each quadrant at an elevation angle of $\sim 40^{\circ }$ with respect to the broadside direction by exciting each port sequentially, while the other ports are terminated. Moreover, the proposed orthogonal structure contributes to low correlation between the four ports, while achieving dual-polarization, which highlights the suitability of the antenna for 5G mm-wave applications. The measured results from a fabricated prototype demonstrate a −10 dB impedance BW of 40% over 24–36 GHz, tilting BW of 32.2%, and a peak gain of 13.4 dBi at 29 GHz, while an isolation better than 30 dB is achieved over the whole frequency band. Moreover, a measured radiation efficiency in excess of 85% is obtained, due to the use of the low-loss PRGW feedlines. [ABSTRACT FROM AUTHOR]

A substrate integrated waveguide (SIW) H-plane horn antenna loaded with tapered multistrip transition and dielectric slab is proposed for broadband high-gain operation. The broadband characteristic of the proposed antenna is obtained by loading a tapered multistrip transition. The theory of coupled resonator is introduced to reveal the mechanism of bandwidth enhancement. On the other hand, a dielectric slab is used to enhance the gain of the proposed antenna. The optimal length of this dielectric slab is determined based on the design principles of a dielectric rod with maximum gain. Besides, the tapered multistrip transition also contributes to the gain improvement by suppressing the feed radiation and prompting the transverse expansion of the surface wave. To verify the design theory and concept, a prototype operating at the K- and Ka-bands is fabricated and measured. The measurement results show that the impedance bandwidth of the proposed antenna is from 20.6 to 38.4 GHz (60%). Within the operating band, a peak realized gain of 19.1 dBi and excellent endfire radiation patterns with low cross polarization (<−30 dB) and high front-to-back ratio (FBR >20 dB) are achieved simultaneously. With its broad bandwidth, high gain, low cross polarization, and high FBR, the proposed antenna is promising for various millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A reconfigurable 1 bit millimeter-wave array antenna for mobile terminals is investigated. The reconfigurable array antenna consists of four reconfigurable 1 bit microstrip patch antenna elements. Each patch antenna element is fed by a slot on the ground. The 1 bit patch antenna element with phase values of $-\pi $ and 0 is achieved by selecting the feeding direction of microstrip line. After analyzing the performance of the 1 bit four-element array, a fixed phase is applied to mitigate the negative effects of the 1 bit phase quantized error. The 1 bit four-element arrays with and without the fixed phases are compared in detail. The overlapped −10 dB impedance bandwidth of a prototype array at different beam directions reaches 3 GHz (25–28 GHz). Within the frequency range of 26–28 GHz, the array with the fixed phases can steer the main beam from −34° to 35° without grating lobes. Within these steering beams, the performances of good array gain, moderate sidelobe level, and low cross-polarization level are achieved. [ABSTRACT FROM AUTHOR]

A new antenna element type based on the open-ended ridge gap waveguide (RGW) is proposed for phased array applications. This element type is of a particular interest at high millimeter-wave frequencies ($\geq$ 100 GHz) owing to a contactless design alleviating active beam-steering electronic integration. The key challenge addressed here is a realization of a wide fractional bandwidth and a wide scan range with high radiation efficiency. We demonstrate a relatively simple wideband impedance matching network comprised of an aperture stepped ridge segment and a single-pin RGW section. Furthermore, the $E$ - and $H$ -plane grooves are added that effectively suppress antenna elements’ mutual coupling. Results demonstrate a wide-angle beam steering ($\geq \text{50}^\circ$) over $\geq {20\%}$ fractional bandwidth at the $W$ -band with $\geq {89\%}$ radiation efficiency that significantly outperforms the existing solutions at these frequencies. An experimental prototype of a 1 × 19 $W$ -band array validates the proposed design concept through the embedded element pattern measurements. [ABSTRACT FROM AUTHOR]

This letter presents a dual-band antenna with a large frequency ratio of 11.7 (2.4 GHz/28 GHz) by integrating an mm-wave Fabry–Perot cavity (FPC) antenna into a sub-6 GHz patch antenna. The patch with periodic slots functions as both the 2.4 GHz radiator and the partially reflective surface (PRS) of the 28 GHz FPC antenna. By properly tuning the length of the periodic slot, the PRS's reflection can be easily adjusted. As the periodic slot's length and width operating at 28 GHz are much smaller than the wavelength at 2.4 GHz, periodic slot operating at 28 GHz have little impact on the radiation of the patch. Furthermore, because of the Fabry–Perot resonance, the antenna can have a peak gain reaching 15 dBi at 28 GHz band with an easy feeding structure. For demonstration, a prototype is fabricated and experimentally verified. Note that the frequency ratio is not limited to the proposed design (11.7 for demonstration). It can be easily adjusted based on the same principle. [ABSTRACT FROM AUTHOR]

A novel antenna beam-steering technology is proposed for emerging millimeter-wave (mm-wave), broadband mobile technologies such as 5G and beyond. A high-gain (23 dBi) antenna with 30° beam steering is designed and tested at around the 38 GHz band. A Fabry–Perot type leaky-wave antenna (LWA) is employed as the main radiating structure, with a tunable high-impedance surface (HIS) used as the ground plane. The HIS phase tuning is accomplished by electro-mechanically varying the displacement between the HIS periodic metasurface layer and the ground plane using a flexure amplified piezoelectric actuator (PEA). The antenna exhibits very low loss (<1 dB) along with fast (in the order of ms.) and continuous beam steering. The measured and simulated results show close agreement and suggest that PEA-tuned, metasurface-based antennas offer a promising solution for use in future mm-wave communication systems. [ABSTRACT FROM AUTHOR]

A wide-beamwidth magnetoelectric (ME) dipole antenna for millimeter-wave (mm-wave) phased array applications is proposed in this letter. The antenna is fed by a substrate integrated waveguide. The electric dipole is formed by two patches, while the magnetic dipole consists of two apertures between the two patches. A short strip is introduced to connect the two patches, which can improve the impedance matching performance. The impedance bandwidth with |S11| < −10 dB for the antenna element is 19.9% (28.11–34.32 GHz), as shown in the simulated results. And its half-power beamwidth in the xoz plane and yoz plane is wider than 82.1° and 81.8° over the operating band. To test the scanning potential of the ME-dipole antenna, a 4 × 4 phased array is constructed in high-frequency simulation software. The simulated scanning range of the phased array is beyond −41°∼41° at two sampling frequencies. Besides, a 4 × 4 antenna array is designed, processed, and measured. The array demonstrates a −10 dB fractional bandwidth of 15.3% (27.7–32.3 GHz) with a peak gain of 17.79 dBi at 30.4 GHz. The proposed ME-dipole antenna demonstrates good potential for 5G mm-wave phased array applications. [ABSTRACT FROM AUTHOR]

A wideband vertically-polarized end-fire magneto-electric (ME) dipole antenna fed by an asymmetrical substrate integrated coaxial line (ASICL) is proposed for millimeter-wave (mm-wave) applications. The proposed ME dipole antenna has an impedance bandwidth of 60% and produces an end-fire radiation with a stable gain between 5.8 and 6.9 dBi in simulation. To verify the design concept and its application in arrays, a 1 × 8 linear array with a fixed beam and a 1 × 4 linear array with multiple beams are designed, fabricated and measured. The fabricated fixed-beam array prototype exhibits an impedance bandwidth of 62%, a peak gain of 15.9 dBi and a radiation efficiency of 79%. The multi-beam array is fed by a 4 × 4 ASICL Butler matrix. Experimentally, excellent beam scanning radiation patterns with reasonably low side lobes and low cross polarizations are demonstrated at 24, 30 and 36 GHz. And an overlapped operating bandwidth of 28.6% is achieved by the fabricated prototype.

This communication presents a very thin metasurface (MS) planar lens for millimeter-wave (mm-wave) MIMO applications. The MS planar lens consists of array of mm-wave resonators providing varying phase response to transform the phase profile of the electromagnetic wave propagating through this array. Each resonator consists of two identical layers having substrate separated by an air gap of ${h=0.8}\,\,{\text {mm}}$ and is ${4} \,\,{\text {mm}}{\times } 4\,\,\text {mm}$ in size. The MS lens having a focal length of $f=12\,\,\text {mm}$ is loaded to a three-port proximity fed antenna array to operate at 27.5–32 GHz. The designed lens is polarization-insensitive and can be used with any polarization. The three-port antennas with the MS lens is fabricated and tested, and the measured results have confirmed a beam scanning of ±15° with a peak gain of 20.2 dBi for port-2. [ABSTRACT FROM AUTHOR]

A wideband circularly polarized (CP) endfire planar magneto-electric dipole antenna based on substrate integrated waveguide (SIW) is proposed for millimeter-wave (mm-wave) applications. The antenna mainly consists of an open-ended rectangular SIW radiating like a magnetic dipole, a parallel electric dipole, and a double-sided parallel-strip line which connects the two dipoles and provides 90° phase difference between them to generate CP radiation. To increase the axial ratio (AR) bandwidth, a pair of triangular slots are etched at the end of the upper and lower broad walls of the SIW, and moreover, a specific bowtie-shaped electric dipole is used instead of the traditional linear one. It has been shown that both the slots and the bowtie-shaped electric dipole can regulate or tune the magnitude of the radiation field of the electric dipole, making it tend to balance with radiation field generated by the magnetic dipole, and hence, leading to a good CP performance. The antenna has a single-layer planar structure, and it shows a −10 dB impedance bandwidth of over 50%, a 3 dB AR bandwidth of 36.6%, and a peak gain of 9.3 dBic. [ABSTRACT FROM AUTHOR]

To maintain the compactness of future 5G smartphones, integration of sub-6 GHz and millimeter-wave (mm-wave) bands is a challenging task due to the large frequency ratio. We, therefore, propose a single-fed triple-band antenna with a large frequency ratio. The proposed antenna is composed of a microstrip patch radiator with an inverted U-shaped slot for dual-band operation in the mm-wave frequencies (28 and 38 GHz). A meandered radiating structure is linked to the microstrip patch radiator through a compact microstrip resonant cell (CMRC) low-pass filter (LPF), which is used for the integration of these structures to be operated at 3.5 GHz. A compact size of 22 mm $\times10$ mm $\times0.508$ mm for the proposed antenna was realized by incorporating the radiator slot, an LPF, the truncated ground, and a meandered line structure. Wide, decoupled −10 dB bandwidths of 12.9%, 5.8%, and 2.4% at 3.5, 28, and 38 GHz, respectively, were realized for the proposed MIMO antenna without utilizing an external decoupling structure. A detailed safety study with respect to specific absorption rates and power densities was analyzed in data, reading, and talking modes. Finally, the measurements were performed in an anechoic chamber, and the measured results were in a good correlation with the simulation results. [ABSTRACT FROM AUTHOR]

This article presents a portable system for freehand antenna diagnosis and characterization based on amplitude-only data. The amplitude-only samples are acquired by moving a handheld probe, which is tracked by a motion capture system, in front of the antenna under test (AUT) aperture. The acquired measurements are processed using the phaseless sources reconstruction method to compute an equivalent current distribution on the AUT aperture. Finally, the radiation pattern of the AUT can be obtained by evaluating the corresponding radiation integrals. Unlike previous work, the use of amplitude-only data avoids the need of a phase reference, paving the way to the diagnosis and characterization of antennas under operational conditions. This fact, together with the handheld capabilities, makes the system very convenient for measurements of already deployed and onboard antennas. Moreover, these amplitude-only acquisitions also simplify the required hardware. The system has been validated through measurements in a wide frequency range from Ka-band up to 300 GHz. Despite that one cannot expect the same degree of accuracy that can be achieved under laboratory conditions (including an anechoic environment and highly accurate positioners), the system shows excellent capabilities to detect malfunctions, such as wrong amplitude/phase distributions, as well as a fair estimation of the far field. [ABSTRACT FROM AUTHOR]

A millimeter-wave (mm-Wave) wideband dual circularly polarized (CP) antipodal septum antenna is proposed. By introducing two antipodal septum blames in widened rectangular waveguide and the corresponding feeding network, the operating bandwidth of the septum antenna is enhanced. The working principle of the generation process of dual CP is explained by a three-port model with three excitation conditions. In addition, the asymmetrical radiation pattern of the classical polarizer consisting of square waveguide and single septum caused by the high-order modes is explained and eliminated. To verify the design, the proposed antenna has been fabricated and measured. An operating bandwidth of 37.4% for reflection coefficients less than −13.8 dB, isolation better than 22 dB, and axial ratio (AR) value less than 3 dB is achieved. [ABSTRACT FROM AUTHOR]

This letter presents the design of a single point-fed, geometrically simple circularly polarized (CP) antenna for 28 GHz Ka-band applications. The proposed antenna is based on a straight microstrip line printed on one side and coupled with the nearly square patches through a 45° inclined V-shaped slot aperture on the other side. In order to generate circular polarization, the fundamental radiating mode is degenerated at a slightly different frequency by aligning the patch edges parallel to each arm of the V-slot with orthogonal arms. This configuration yields a relatively small size (10 mm × 27.7 mm), wideband, and high-gain right-hand CP antenna operating at 28 GHz. The impedance bandwidth of the proposed antenna is from 27.2 to 30.35 GHz and the 3 dB axial ratio (AR) bandwidth from 27.3 to 29.7 GHz with excellent directional characteristics in the broadside direction. The peak gain is approximately 11.65 dBic. The performance characteristics in terms of the impedance matching, AR, gain, and efficiency of the antenna for wearable applications are also investigated both numerically and experimentally. For practical applications, the small size of the structure allows for implementing the systems that consist of more than one antenna to account for user mobility. [ABSTRACT FROM AUTHOR]

In this letter, dual-polarized cavity-backed bow-tie slot arrays are designed and integrated on the frame of the mobile handset. The bandwidth is firstly enhanced for the cavity-backed slot antenna using hybrid modes, with a wide band of 4.1 GHz achieved by dual resonances. However, the hybrid modes result in poor isolation between the orthogonally placed antennas, and a tradeoff between bandwidth and mutual coupling is made, which provides an isolation of above 13 dB between the ports. Two antenna arrays, with each composed of four dual-polarized cavity-backed slot units, are then utilized on the longer metal frames of the handset. The scanning beamwidth for each array is 138° for the gain of above 7 dBi. The 3-D coverage efficiency of the antenna reaches 52% for a threshold gain of 5 dBi. Thus large coverage area and high gain are achieved simultaneously by the dual-polarized frame integrated slot arrays. The proposed antenna arrays are suitable for mobile handsets for their simple structure, high integration, dual polarizations, high gain, and large coverage area. [ABSTRACT FROM AUTHOR]

This article presents a novel dual-polarized millimeter-wave (mm-Wave) patch antenna with bandpass filtering response. The proposed antenna consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches. The combination of the stacked patches and the driven patch can be equivalent to a bandstop filtering circuit for generating a radiation null at the upper band edge. Besides, four additional shorted patches are added beside the cross-shaped driven patch to introduce another radiation null at the lower band edge. Moreover, by embedding a cross-shaped strip between these four stacked patches, the third radiation null is generated to further suppress the upper stopband. As a result, a quasi-elliptic bandpass response is realized without requiring extra filtering circuit. For demonstration, a prototype was fabricated with standard PCB process and measured. The prototype operates in the 5G band (24.25–29.5 GHz) and it has an impedance bandwidth of 20%. The out-of-band gain drops over 15 dB at 23 and 32.5 GHz, respectively, which exhibits high selectivity. These merits make the proposed antenna a good element candidate for the 5G mm-Wave massive MIMO applications to reduce the requirements of the filters in the mm-Wave RF front ends. [ABSTRACT FROM AUTHOR]

This article presents a wideband beam-steering antenna system for high-mobility millimeter-wave (mm-wave) systems. It can provide both continuous and discrete beam steering in two dimensions (elevation and azimuth) at a speed that is sufficient for various applications including some in defense. The antenna is completely passive and beam steering is achieved using near-field phase transformation by employing a pair of distinct rotatable stepped-dielectric phase transformers (SPTs) placed in the near-field region of a fixed radiating source. The antenna system has a steering and impedance-matching bandwidth of 40.6% from 26.5 to 40 GHz. A prototype of the beam-steering antenna system including a mechanical system to rotate each of the SPTs around the antenna axis has been fabricated and tested. The rotating SPT pair introduces a predetermined phase gradient to the input near-field and creates an output near-field that will radiate in an arbitrarily selected direction, which can be varied within a large conical region with a maximum apex angle of 104°. The system exhibits predicted and measured peak gains of 21.5 and 21.25 dBi, respectively, and the measured gain variation over 2-D beam steering is less than 3 dB except at 36 and 39 GHz, where it rises to 3.6 and 3.1 dB, respectively. This beam steering method obviates the need for expensive phase shifters and distribution networks, which are also lossy at mm-wave frequencies. The measured results validate the predicted wideband matching and steering performance of the system with close agreement. [ABSTRACT FROM AUTHOR]

A singly fed wideband circularly polarized (CP) substrate-integrated dielectric resonator antenna (SIDRA) is proposed for millimeter-wave (mm-wave) applications. The SIDRA consists of an inner cylindrical dielectric resonator (DR), an outer ring DR, and a substrate-integrated waveguide (SIW) cavity. To generate CP fields, a cross-slot formed by two rectangular slots with different lengths is utilized to feed the DRA at its bottom. It has been found that owing to the embedded structure, the fundamental HEM $_{11\delta }$ mode of the inner DR and the higher order HEM $_{12\delta +1}$ mode of the entire DR can be excited simultaneously, at adjacent frequencies. Moreover, owing to the different loading effects of the two feeding slots, the resonance frequencies of the nearly degenerate DR modes excited by the two slots are slightly different from each other. The two nearly degenerate modes lead to the wide impedance and axial ratio (AR) bandwidths of 34.6% and ~30%, respectively. In addition, due to the surrounding SIW cavity, the directivity of the antenna is greatly improved as compared with that of the isolated counterpart, with the maximum gain given by 8.15 dBic. [ABSTRACT FROM AUTHOR]

In this letter, a compact circularly polarized horn antenna is presented. By cutting a slot along the 45° direction at the end of the circular waveguide, the proposed antenna achieves the wideband circularly polarized radiation. A prototype working at W-band is fabricated. Both the impedance bandwidth (S(1, 1) <−10 dB) and the circular polarization bandwidth (AR < 3 dB) of the processed antenna are measured as 37.8% (75–110 GHz). The proposed antenna exhibits a simple structure, and it is easy to design, so it can be extensively applied in millimeter-wave (mm-wave) and submillimeter-wave systems. [ABSTRACT FROM AUTHOR]

In this paper, a package concept based on low-temperature cofired ceramic (LTCC) technology is illustrated. The concept is specifically designed for frequencies beyond 100 GHz, taking into consideration the inherent LTCC manufacturing defects, e.g., shrinkage, layer misalignment, and warping. Simple techniques are used for package assembly which can be automated using standard industrial processes. The proposed concept is implemented by integrating a 122-GHz silicon-germanium (SiGe) radar transceiver chip in an LTCC-based package. The off-chip components of the package, operating at 122 GHz, include a transmit (Tx) and a receive (Rx) aperture-coupled patch antenna array, a stripline to grounded coplanar waveguide signal transition feeding each of the antenna arrays, and three parallel, self-matched ground-signal-ground wirebonds connecting the SiGe radar transceiver chip and the LTCC package on Tx and Rx side. The simulation and measurement results of the Tx and Rx antenna arrays along with the signal transitions in the frequency range of 110–140 GHz are shown. The radar front end (RFE) is encapsulated using an epoxy molding compound, Polytec TC 430-T with suitable dielectric characteristics in the desired frequency range. The encapsulated RFE is surface mounted on a baseband printed circuit board, thereby realizing a fully functional 122-GHz frequency modulated continuous wave (FMCW) radar. The FMCW radar is used to measure the distance of a target, and the measurement results are compared with those of a commercial 122-GHz RFE. [ABSTRACT FROM AUTHOR]

A simple decoupling method of using metallic vias to improve the isolation of millimeter-wave multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) elements is investigated. The vias are vertically added to the DRA elements, at appropriate positions. By means of the interaction with the electromagnetic fields, the vias can potentially affect the filed distributions and further reduce the coupled fields effectively. The isolation between the MIMO DRA elements can, therefore, be enhanced substantially. As the vias are placed inside the DRA elements, no extra footprint is needed, making the entire antenna system very simple and compact. Two typical examples, including an H-plane and an E-plane, coupled $1\times2$ MIMO DRA arrays, have been designed, fabricated, and measured to demonstrate the feasibility and universality of this method. The results show that by using the vias appropriately, the isolation of the H-plane coupled MIMO DRA array can be enhanced from ~15.2 to 34.2 dB, while that of the E-plane array can be improved from ~13.1 to 43 dB at 26 GHz. [ABSTRACT FROM AUTHOR]

In this letter, a differentially coplanar-fed filtering dielectric resonator antenna (DRA) is proposed for millimeter-wave applications. To realize a low-profile design, a novel coplanar feeding method is presented by incorporating a dielectric resonator and its feeding structure in the same layer, which minimizes the assembly errors. The DRA is shaped by hollowing out the substrate and can be manufactured with a single-layer laminate using standard printed circuit board technology. The DRA operates at TE111 mode that is excited differentially by a pair of microstrip lines with metallic vias. The filtering function is obtained by etching two pairs of slots with different lengths in the ground plane, resulting in two radiation nulls at both upper and lower band edges. For demonstration, a prototype is designed, fabricated, and measured. Good agreement can be observed between simulated and measured results. [ABSTRACT FROM AUTHOR]

This communication describes a novel concept of designing millimeter-wave (mm-wave) dielectric resonator antenna (DRA) arrays, in which the DRA element and part of its feeding network can be codesigned and cofabricated using the printed circuit board technology. Conventionally, the DRA and its feed are designed and fabricated using different dielectric materials. As a result, a large error might take place when mounting the DRA to its feed, which will result in significant influences to the performance of the antenna, especially to those operating in the mm-wave band. The proposed concept of the substrate integrated DRA provides a possibility to minimize the above mounting errors, by shaping the DRA and its feed together using the same material and fabrication process. Two kinds of antenna element, which separately exhibits linear and circular polarization, are designed at Ka-band. In order to demonstrate the feasibility of the proposed elements for array applications, two four-element antenna arrays in cooperation with different feeding networks and transitions are also designed, fabricated, and measured. Investigations show good agreement between simulation and measurement. The proposed substrate integrated DRA array can be easily extended to larger scales and has great potential to be integrated into mm-wave transceiver modules. [ABSTRACT FROM PUBLISHER]