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This letter shows a comparative analysis between the conventional and reverberation chamber (RC) measurements of error vector magnitude (EVM). The conventional methods, including direct link (DL) and anechoic chamber (AC), have been used to measure EVM for several years. However, the over-the-air testing of devices under test (DUT) is emphasized, and the EVM measurement in RC is a difficult question. For mass production testing, instead of using two chambers (RC and AC), it is expected to integrate EVM testing into the existing RC measurement system to give a pass/fail conclusion quickly. Hence, we measured EVM in 2 GHz (2412 MHz) and 5 GHz (5180 MHz) using RC, AC, and DL methods. From the measurement results, we find that the measured EVM is repeatable, stable, and insensitive to the location of DUT. Besides, the measured EVMs obtained from all scenarios deteriorate with the decrease of received power. Comparing the results from RC with that from the conventional methods, it could be concluded that with the reduction of multipath effect, the measured EVMs approach to the ideal values measured in AC. The differences among the methods could be used to calibrate the measured EVMs and give a pass/fail conclusion efficiently for mass production. [ABSTRACT FROM AUTHOR]

The scanning rate of a composite right/left-handed (CRLH) leaky-wave antenna (LWA) is usually determined by the dispersive behavior of the corresponding CRLH unit cell. In this letter, a novel CRLH unit cell with high dispersive behavior is proposed and investigated. The unit cell is formed by four stubs embedded in a rectangular ring patch, which is grounded with several metal vias. The right-handed characteristic is enhanced by the ring patch, while the left-handed characteristic is reduced by the vias and the gaps between the patch and the stubs. Then, the unit cell is applied to design an LWA with high scanning rate. The measured result shows that the seamless scanning angle of the antenna prototype is 130° (−65° to +65°) within a frequency range from 9.3 to 9.93 GHz (i.e., 6.6% for fractional bandwidth). Therefore, the proposed LWA antenna is with a high scanning rate up to 19.7°/%BW. [ABSTRACT FROM AUTHOR]

This letter presents the design, analysis, and measurement of a miniaturized ($\text{7}\!\times\!\text{7.5}$ mm) electrically small helical dipole antenna with the introduction of a flexible magnetic sheet of high permittivity and permeability for biomedical implants. The proposed helical dipole, operating at 402–405 MHz Medical Implant Communication Services (MICS) band, supports wider bandwidths (10 dB bandwidth: simulated 33 MHz; measured 49.5 MHz) compared to the state-of-the-art designs. In addition, as a hybrid between a magnetic loop antenna and an electric dipole antenna and operating in the normal mode with small radian (ka < 0.36), enhanced radiation efficiency has been achieved as a result of the magnetic sheet. Measured in-body to on-body transmission verifies the antenna performance. [ABSTRACT FROM AUTHOR]

A planar dual circularly polarized (CP) broadband array is proposed in this letter. The antenna consists of two semicircular patches and two suspended metal posts. According to the investigation of our previous work, the circularly polarized mode generated by combining the patches and the metal posts can achieve very wideband CP radiation. In order to achieve dual CP radiation with similar performance, a new antenna element is proposed with a centrally symmetrical configuration. The orthogonally crossed slot etched on the substrate-integrated waveguide cavity is used to excite the antenna element. A 4×4 array is designed, fabricated, and tested. Measured results show that a 3 dB AR bandwidth of 28.28% (26–34.6 GHz) and 30.61% (26–35.4GHz) is achieved for left-handed CP (LHCP) and right-handed CP (RHCP) radiation, respectively. The 3 dB gain bandwidth of 22.81% (26.4–33.2 GHz) and 24.50% (26–33.26 GHz) for these two polarizations is obtained. The proposed array demonstrates the feasibility of dual-polarized radiation. It features the advantage of wide bandwidth, easy integration, and low cost, which is very suitable for millimeter-Wave system applications. [ABSTRACT FROM AUTHOR]

A miniaturized, vertically polarized (VP), pattern switchable/beam-steering antenna based on a metamaterial radiator is presented for sub-6 GHz applications. Different from the traditional split-ring resonator (SRR), the proposed T-shaped SRR can work as a miniaturized VP omnidirectional radiator. To steer the radiation beam, a novel switchable mushroom reflector with a low profile and low loss is explored and utilized. Multiple switchable mushroom reflectors are loaded around the T-shaped SRR radiator to obtain various steerable beams. To verify the proposed design principle, a VP beam-steering SRR-based antenna with a compact size of 0.36 λ0 × 0.36 λ0 × 0.07 λ0 is designed by loading four mushrooms. By controlling the off/on states of four switches, the proposed reconfigurable antenna can realize beam-steering in the horizontal plane (eight states with 45°-step). The measured overlapped −10 dB impedance bandwidth is wider than 3.40–3.80 GHz (11.1%), and the realized peak gain is larger than 5.3 dBi. Therefore, the proposed antenna is a good solution for the widely deployed fifth generation (5G)-NR and smart antenna applications due to its compact size, flexible beam-steering capacity, broad bandwidth, and good scanning coverage. [ABSTRACT FROM AUTHOR]

Leaky-wave antennas (LWAs) have been widely investigated for wireless systems. Most LWAs reported to date are open-path based, i.e., their guided traveling waves follow a non-closed path. A substrate-integrated (SI) toroidal waveguide-based LWA is developed in this article. A coaxial-fed probe structure effectively excites traveling waves that propagate along a closed path in the toroidal waveguide. Inverted L- and planar helical-shaped radiators, whose pickup structures extract power from the waveguide through its top wall, are introduced to radiate, respectively, linearly-polarized (LP) and circularly-polarized (CP) directed beams. The dispersion properties of the closed waveguide’s traveling wave are determined and the associated propagation phase along circular paths with specific radii guides the placement of these radiators to achieve a directive beam at a specified angle. Prototypes of both the LP and CP toroidal LWA (TLWA) systems were fabricated and tested. Good agreement between the simulated and measured results was obtained. The measurements of the compact, low-cost LP and CP prototype systems confirm they radiate beams pointed in their distinctly different, specified directions with realized gains of 13.2 dBi and 13.9 dBic, respectively, at 9.75 GHz. [ABSTRACT FROM AUTHOR]

This article presents a design methodology and a realization of an antenna radiating circular polarization (CP) for Frequency Modulated Continuous Wave (FMCW) radar at mm-wave frequencies on-chip, which combines antennas of different resonance frequencies to increase the operation bandwidth and allow for high-resolution radar. The antenna consists of four dipoles with an on-chip ground plane operating at two resonance frequencies combined with a matching and feeding network, which enables both frequency selectivity in advantage for the resonant antenna and radiation of circular polarization. The dipole arms are based on shorted ${\lambda }{/4}$ resonators, which are enhanced with series capacitances for increased radiation efficiency. A method for the broadband characterization of CP antennas and the measurement results of the designed CP antenna are presented. It is shown that the antenna covers a bandwidth between 220 and 260 GHz, indicating the feasibility of both the measurement method and the antenna concept. [ABSTRACT FROM AUTHOR]

This article presents the design and analysis of a dual-polarized low-profile circuit analog absorber with wideband absorption characteristics. A lossy frequency selective surface consisting of cross dipole with central resonant node element is used as the top layer, while there is a continuous copper ground as the bottom layer. The novelty of the design lies in the use of the resonant node as it improves the absorption bandwidth by providing an additional resonance without compromising the low-profile nature of the design. It has a thickness of 0.077 $\lambda_{L}$ (where $\lambda {\_}L$ is the wavelength corresponding to the lowest operating frequency). The absorber also exhibits a stable absorption characteristics up to 30 $^\circ$ angle of incidence and can avoid grating lobes within the operating bandwidth up to 40.79 $^\circ$ angle of incidence. An equivalent circuit model is proposed to discuss the operating principles of the design. The validation of the design is done experimentally using the time-gating technique, and a good agreement between the measured and the simulated results is observed. The 10-dB reflection reduction bandwidth and the thickness-to-bandwidth ratio of the absorber are obtained as 108.67% (from 3.58 to 12.10 GHz) and 0.104 from full-wave simulation and 115.67% (from 3.5 to 13 GHz) and 0.098 from measurement, respectively. [ABSTRACT FROM AUTHOR]

This article presents a novel and cost-effective vector network analyzer (VNA)-based phase-compensated channel sounder operating in the frequency range of 10–50 GHz using radio-over-fiber (RoF) techniques, which can support multilink/channel long-range phase-coherent measurements. The optical cable enables long-range channel measurements with a dynamic range of 115.7 dB at 30 GHz (for the back-to-back connection). The phase compensation scheme is utilized for stabilizing the inherent phase variations introduced by the optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. A novel optical delay line and combiner scheme is proposed and implemented to separate the signals, thereby saving the port resource on the VNA for multilink/channel measurements. The proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with the presence of thermal changes and mechanical stress. The phase change could be maintained within 3° at 10–30 GHz and 7° in 30–50 GHz compared to the over 80° phase variation introduced by the cable effects at 10–50 GHz, demonstrating the robustness and effectiveness of the developed channel sounder in practice. With the proposed optical delay line and combiner scheme, multiple channels can be measured simultaneously with minimal VNA ports, significantly reducing the measurement cost and time for multilink channel measurements. Two multilink indoor channel measurements are conducted and analyzed using a virtual uniform rectangular array (URA) at 28-GHz bands. The results demonstrate the capability of the proposed channel sounder to perform high-fidelity long-range ultrawideband multilink channel measurements. [ABSTRACT FROM AUTHOR]

A microstrip dual-split-ring antenna array for fifth-generation (5G) millimeter-wave dual-band applications is presented in this letter. The microstrip dual-split-ring structure is adopted to generate two resonance points operating at 28/38 GHz dual band, respectively. To improve the radiation characteristics at 38 GHz band, two branches are added to the middle of microstrip dual-split-ring structure. Finally, the proposed 1 × 4 microstrip dual-split-ring antenna array can achieve impedance bandwidths of 12.5% (26–29.5 GHz) and 5.3% (36.7–38.7 GHz), and peak gains of 12.7 and 14.9 dBi at 28/38 GHz dual band, respectively. The proposed antenna array with one signal chain has these advantages of simple structure, wider dual-band impedance and gain bandwidths, higher gain and lower sidelobe level. Therefore, the design scheme will be suitable for the 5G millimeter-wave dual-band applications. [ABSTRACT FROM AUTHOR]

An ultrawideband dual-polarized antenna for fifth generation (5G) customer premise equipment is investigated and designed in a compact environment by using a double-loop-dipole structure and a co-planar-slot feeding concept. First, the existing design of dual-polarized octagonal loop dipoles is introduced at first. Then, a novel double-loop-dipole structure and co-planar-slot feeding are proposed and demonstrated in detail from the current distribution and physical structure sides. Finally, the proposed antenna is designed, fabricated, and measured. The measured results present that the proposed antenna has a wide bandwidth of 86% from 2.2 to 5.5 GHz with the VSWR less than 1.8, high polarization isolation of 25 dB, and stable radiation patterns over the desired frequencies of 2.3–5.2 GHz. It is worth mentioning that the proposed ideas can effectively aid in impedance bandwidth improvement without adding additional cost for sub-6G 5G applications. [ABSTRACT FROM AUTHOR]

This letter proposes a co-designed millimeter-wave (mm-wave) and sub-6 GHz antenna system. The antenna system consists of four 28 GHz mm-wave arrays with reconfigurable radiation patterns and two sub-6 GHz antennas fed with two corner capacitive coupling elements (CCEs). Each corner CCE is formed by the connected ground planes of two mm-wave arrays in the shared-aperture configuration. The two CCEs are separately matched to cover two sub-6 GHz bands. Each mm-wave array consists of an active patch element and two parasitic patch elements loaded with PIN diodes, realizing 90° beam scanning range with two states of the PIN diodes. The measured results of the fabricated prototype show good agreement with the simulated ones. The prototyped mm-wave arrays cover the band 27.5–28.35 GHz, and each achieves 90° beam scanning at 28 GHz, with measured peak realized gain of 7.9 dBi. The CCE ports cover the two sub-6 GHz bands of 0.79–0.96 GHz and 1.7–5 GHz, with measured isolation of above 17 dB and 20 dB, respectively. The mm-wave band isolation is above 26 dB. [ABSTRACT FROM AUTHOR]

In this article, a radiant metal block structure is proposed for designing reduced-size cavity-backed filtering antenna. The method of characteristic mode analysis is used to investigate the characteristic current modes of the cubic metal block, one of which can maintain a high inherent radiation capacity over a wideband. In addition, the radiation quality factor of the utilized mode is described in detail. Based on this characteristic current mode, metal block antennas with different bandwidths can be designed to realize broadside radiation. The proposed metal block antenna element can maintain stable radiation characteristics in the passband and the realized gain is greater than 9 dBi. To design the filtering antennas, the proposed metal block is cascaded with traditional resonant cavities. A third-order metal block filtering antenna array is fabricated for verification. The measurement results are basically consistent with the simulated ones. The maximum measurement gain is 12.85 dBi and the gain in the passband is flat. [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]

This letter presents a novel design of an electrically small, circularly polarized (CP), capacitively loaded loop (CLL)-based antenna for UHF radio frequency identification (RFID) applications. A simplified CLL working as a magnetic dipole is proposed. It is analyzed by the equivalent circuit and field distribution. Owing to the strong LC-resonant character of the CLL structure, an electrically small size of 0.137 λ0 × 0.137 λ0 × 0.046 λ0 (ka = 0.67) is easily achieved. Two sets of CLL structures with different loop dimensions are orthogonally arranged, with the crossed slot and 45°-rotated coupling feedlines. As a result, the dual-mode operation is realized and the RHCP wave is radiated. A 3.71% measured −10 dB impedance bandwidth (899–933 MHz) is achieved, which is well poised for the 902–928 MHz UHF reader applications. The measured peak gain and radiation efficiency are 4.83 dBic and −1.26 dB (74.8%), respectively. The proposed electrically small CLL-based CP antenna exhibits excellent overall performance, including easy fabrication, good bandwidth, high gain and efficiency and wide beamwidth. Therefore, it is suitable for RFID reader applications and other Internet of Things (IoT) systems. [ABSTRACT FROM AUTHOR]

A compact, single- feed, dual band, circularly polarized annular ring patch antenna coupled to a cross slot is proposed in this letter for GPS-aided GEO-augmented navigation (GAGAN) receivers covering L band, centered at 1176.45 MHz (L5) and 1575.42 MHz (L1) frequencies. The antenna consists of two annular rings configured by two small strips, which is coupled to a cross slot in the ground plane for gain enhancement. Circular polarization in both the bands is produced by introducing perturbations in outer annular ring and two orthogonal strips in the center space of inner annular ring. The proposed CP antenna radiates LHCP in both the desired frequencies. Two shorting pins are introduced near the feed to improve impedance matching. The simulated and measured reflection coefficient, gain, circular polarization, and axial ratio are in accord with each other. The measured 10 dB bandwidth is 2.7% (1168–1200 MHz) for the L5 and 2.5% (1560–1600 MHz) for L1. The AR bandwidth below 3 dB for the designed antenna is 1.5% (1156–1174 MHz) for L5 and 1% (1556–1572 MHz) for L1. [ABSTRACT FROM AUTHOR]

In this letter, we design a circularly polarized (CP) waveguide aperture antenna with a wide axial ratio bandwidth. The unit is composed of three waveguides with different rotation angles and width. The reflected and transmitted orthogonal electric fields are superimposed on the asymmetric plane of the rotating structure in each layer, which not only reduces energy reflection but also promotes the decomposition of the electric field with the same amplitude and the phase difference 90 $^\circ$ in different rotating waveguides. Finally, a CP electric field is formed on the antenna’s surface. The phase difference and amplitude difference of orthogonal electric field are approximately 90 $^\circ$ and less than 1.2 dB, respectively. In addition, the different width of the waveguide plays a role in impedance matching. A 2 × 2 array is fabricated and measured to verify the validity of the design. The measured results show good agreement with the simulation. Measured impedance bandwidth of 37.9% (27.5–40.4 GHz), axial ratio bandwidth of 41.2% (27–41 GHz), and a gain of 15.7 dBi at center frequency have been obtained. [ABSTRACT FROM AUTHOR]

A new 3-D-printed wideband circularly polarized (CP) dielectric resonator antenna (DRA) with two printing materials is investigated. The DRA has a multilayer comb-shaped structure at its top for generating CP fields. Three dielectric strips are embedded inside the DRA body to support multiple transverse-electric (TE) DRA modes to widen the DRA bandwidth. To slightly improve the axial-ratio (AR) performance, the DRA is twisted in the horizontal plane. For demonstration, a prototype operating in C-band was designed and printed with two different materials. The reflection coefficient, AR, radiation pattern, antenna gain, and efficiency of the antenna are measured, and reasonable agreement between the measured and simulated results is observed. The prototype has a measured 10 dB impedance bandwidth of 69.7% (4.80–9.94 GHz) and 3 dB AR bandwidth of 68.6% (4.52–9.24 GHz), achieving a wide overlapping bandwidth of 63.2% (4.80–9.24 GHz). Both the AR and overlapping bandwidths are record-high for a single-fed CP DRA. The prototype has a measured peak antenna gain of 8.3 dBic inside the overlapped passband. [ABSTRACT FROM AUTHOR]

The detuning owing to the complex in-body operating scenarios, environmental factors, and circuitry of the implantable medical devices (IMDs) are the primary concerns in integrating implantable antennas with their corresponding systems. The wide bandwidth achievement for avoiding the detuning challenges is constrained by device specifications and antenna miniaturization. This study presents an ultra-miniaturized antenna of only 10.66 mm3 volume with an ultra-wide bandwidth of 3040 MHz (0.79–3.83 GHz) for a leadless pacemaker (LP). The proposed antenna encompasses the five important bands: ISM (868–868.6 MHz, 902–928 MHz, and 2.4–2.48 GHz), Wireless Medical Telemetry Service (WMTS) (1395–1400 MHz), and the midfield (1.45–1.6 GHz) bands. To consider a practical operating scenario, the antenna was integrated with a battery and controlling electronics of an LP. In a homogeneous heart phantom (HHP), the proposed antenna showed a higher gain of −28.7, −20.02, and −16.7 dBi at 915 MHz, 1.4 GHz, and 2.45 GHz, respectively. The specific absorption rate (SAR) evaluation in the heart of a realistic model guaranteed patient safety by satisfying the IEEE C95.1-2005 and C95.1-1999 guidelines. The antenna is experimentally validated through measurements in minced pork. The strength of the received signal in the measurements confirms a stable biotelemetric link of the proposed ultra-wideband (UWB) antenna with an external monitoring system. The results obtained through simulations and in vitro testing emphasized that the proposed ultra-miniaturized and UWB antenna could operate more efficiently in the heart, thus establishing itself as a suitable candidate for the LPs. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) magnetoelectric dipole (ME-dipole) antenna with a wide impedance bandwidth and 3 dB axial ratio (AR) bandwidth is proposed. The antenna is fed by a microstrip line and coupled through a modified cross-slot on the ground plane. Based on the conventional linearly polarized (LP) ME-dipole, the proposed electric dipoles and the coupling slots are modified to generate the CP radiation. Simulated results of the antenna element show an impedance bandwidth of 72.8% from 16.35 to 35.08 GHz and a 3 dB AR bandwidth of 39.2% from 21.53 to 30.07 GHz. To enhance the gain of the antenna for practical application, a 4 $\times $ 4 antenna array with full-corporate feeding network is designed, fabricated, and measured. The measured results show that an impedance bandwidth of 66.95% from 17.26 to 34.63 GHz and a 3 dB AR bandwidth of 41.1% from 19.25 to 29.25 GHz are achieved. The proposed antenna can be applied to K-band, Ka-band satellite communications or fifth-generation (5G) millimeter wave (mmWave) communications at n257 (26.5–29.5 GHz) and n258 (24.25–27.5 GHz) bands. [ABSTRACT FROM AUTHOR]

This letter presents a simple and effective self-decoupling method for dielectric patch (DP) antenna (DPA) by choosing proper structural parameters, without adding extra components. By theoretical analysis, the attenuation constant of the employed fundamental TM01 mode outside the DP is controlled by the structural parameters of the DP resonator, which is crucial for the decoupling between the two adjacent DPAs. It is found that the larger the attenuation constant of the TM01 mode, the better the port-to-port isolation in broadband, and then the radiation pattern can be stabilized. Under the premise of satisfactory isolation, the operational bandwidth and boresight gain of the DPA are studied for ensuring good antenna performance, exhibiting high design freedom and flexibility of the DPA. For demonstration, 1 × 2 closely spaced DPAs with optimal parameters are fabricated and measured. The simulated and measured results show good agreement. [ABSTRACT FROM AUTHOR]

A compact, ultrawideband (UWB) dual-polarized Vivaldi antenna with radar cross section (RCS) reduction is proposed and demonstrated. The dual-polarized antenna is constructed by aligning two single-polarized Vivaldi elements into a crossshaped arrangement. By cutting symmetric rectangular inclined slots and curved metal potions out from the radiating surfaces, the RCS of the antenna can be suppressed over a broad frequency band. The antenna possesses a footprint of 0.58 λL × 0.5 λL, where λL is the free-space wavelength at the lowest working frequency. The antenna is fabricated and characterized, showing a measured Sii < −10 dB covering the UWB band ranging from 1.8 to 6 GHz. Moreover, the measured port isolation is higher than 23 dB, whereas the averaged monostatic RCS is smaller than −30.2 and −28 dBsm under the illumination of x- and y-polarized plane waves, respectively. The demonstrated antenna is useful in a wide variety of applications such as the near-field measurement systems. [ABSTRACT FROM AUTHOR]

The article proposes methodology to use circularly polarized (CP) ultra-wideband (UWB) signals for simultaneous measurement of orientation and distance changes between transmitter and receiver. The proposed technique uses the rotational Doppler effect on CP pulsed communication. The amplitude of a CP signal is immune to polarization misalignment in the presence of rotation; however, the phase is subjected to a frequency-invariant shift proportional to the rotation angle. This significantly distorts the pulse shape in the time domain and can be used for the measurement of the rotated angle. By combining the technique with the well-known localization capability of UWB systems, one can precisely measure not only the distance but also the orientation. This is demonstrated by both numerical and experimental studies presented in this article. [ABSTRACT FROM AUTHOR]

Due to the great demand of throughput and reliability for multimedia applications in Fifth Generation (5G) networks, many broadcasting systems adopt the Millimeter Wave (mmWave) technology to address the lack of the spectrum resources. As one of 5G-PPP projects, Internet of Radio Light (IoRL) project adopts 40GHz mmWave band to support a high-speed and stable Ultra-High-Definition (UHD) television broadcasting service in the indoor environment. Because of the high frequency property, mmWave bands usually suffers from the high path loss and the penetration loss. Thus, in order to overcome these issues, directional antennas are employed to provide additional power gain while increasing transmission distance. However, the mmWave with directional antennas brings additional problems, such as limited transmission angle and more multipath effects. Therefore, in this paper, for better understanding of impact factors on the signal quality and transmission coverage of the directional 40GHz mmWave band in the indoor environment, a measurement campaign is introduced in detail and the channel characteristics are measured and analysed in varying cases. The mainly concerned characteristics are path loss, shadow fading, average Power Delay Profile (PDP), Root-Mean-Square (RMS) delay spread, arrival rate and coherence bandwidth. All Measured characteristic values are summarised in three tables at the end of this paper. Besides of these, as a reference of channel analysis and a metric of signal quality and effective coverage, Error Vector Magnitude (EVM) of received signal in each case is measured and discussed. Moreover, a simulation is performed based on a statistical channel model to validate the measured results. [ABSTRACT FROM AUTHOR]

In this letter, a wideband three-dimensional (3-D) isotropic antenna is proposed with improved 3 dB coverage ratio. Based on the investigation about the effect of the metallic ground size on isotropic radiation, a compact sequential-phase feeding network made of lumped components with miniaturized ground is elaborately designed for wide operating bandwidth and enhanced 3 dB coverage ratio in 3-D space. In the measurement, the antenna prototype is with the size of 70 × 70 × 0.5 mm3 (0.23 × 0.23 × 0.0017 λ03). The measured result shows that the proposed antenna provides the 6 dB gain variation fractional bandwidth of 4% and the 3 dB coverage ratio of more than 80%, leading to promising usage for wideband isotropic radiation applications. [ABSTRACT FROM AUTHOR]

A frequency-reconfigurable antenna with a compact size of 32.5 × 4 mm2 suitable for high screen-to-body ratio smartphones is proposed to work in the full LTE band of 698–960 MHz and 1710–2690 MHz. The antenna is physically realized on the metal frame by inserting gaps on the top of metal frame and introducing a shorting stub. The practical environment including the surrounding components and modules is fully considered throughout the antenna design process. The low and high frequency band of this antenna is achieved by activating four and six different SP4T switch states, respectively. The effect of the switch's position on the antenna performance is also investigated. The proposed antenna maintains radiation efficiencies higher than −7 dB at the low frequency band and higher than −5 dB at the high frequency band. The OTA results demonstrate the antenna can be a good candidate in smartphones. [ABSTRACT FROM AUTHOR]

Based on an interlaced grid arrangement, a dual-band dual-polarized bandpass frequency selective structure (FSS) with a large band ratio (BR) is proposed in this letter. The FSS is assembled from vertical layers arranged along x- and y-directions, and the vertical layers arranged along the two orthogonal directions are polarization independent. The grating structures printed on the vertical layers form a higher frequency passband, and by having additional wire-grid polarizers with a high-pass response, a lower frequency passband is formed. The proposed interlaced grid FSS is a combination of two square grid FSSs. Since the distance between adjacent vertical layers is smaller than that of the square grid FSS, the proposed FSS has a wider bandstop response to achieve the design of a large BR. The measured results show that for both TE and TM polarizations, the center frequencies of the two passbands are 2.5 GHz and 15.5 GHz, respectively, with a corresponding BR of 6.2. [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]

Polarization reconfigurable antennas at millimeter-wave (mm-wave) frequencies are important technologies for 5G and beyond wireless communications systems. This article presents an mm-wave multi-linear polarization (LP) reconfigurable antenna. It employs a resonant TM510-mode air-filled cavity as the base, and a circular array of slots is uniformly etched on its top surface to provide a rotationally symmetrical “excitation” for the multi-LP antenna. An upper substrate printed with engineered patch layers is introduced above the slots for an in-phase high-gain composition, and it is mechanically rotated to facilitate the multi-LP reconfiguration. Each slot radiation is separately monitored and analyzed by using single-slot cavity models. A final multi-LP antenna that can switch among five LP states at mm-wave band was constructed. To overcome the classic high sidelobe problem associated with circular arrays, a modified bottom layer is introduced to the multi-LP antenna. The measured overlapped bandwidth of the optimized multi-LP antenna ranges from 28.58 to 28.99 GHz. For all of the five LP states, the simulated and measured sidelobe levels are −13 and −10 dB, respectively. The measured realized gains are varied from 15.5 to 16.8 dBi in the overlapped operating bandwidth. This is the first time to report an mm-wave multi-LP reconfigurable antenna. [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]

Low-profile shared-structure dual-polarized (DP) Yagi–Uda antennas are proposed, which are formed by three kinds of basic components, namely DP driven element, DP director, and DP reflector. An open-cavity dipole is utilized as the DP driven element to generate DP endfire radiations. The quarter-wave resonance mode for vertical polarization (VP) and half-wave dipole resonance mode for horizontal polarization (HP) are excited by differential feeding structures in the DP driven element. The open-cavity element is adopted as the DP director or reflector to enhance endfire gain. For the proposed design, two polarization radiators are integrated into one structure, realizing structure sharing, and thus a low profile. Three-element (Ant. 1) and seven-element (Ant. 2) antennas with a profile of 0.1 λ0 are designed, fabricated, and measured. The measured overlapped bandwidth of the Ant. 1 is from 4.11 to 4.83 GHz (16%) with ports isolation higher than 30 dB, and the measured VP and HP gains are from 5 to 6 dBi and 5 to 7 dBi, respectively. The Ant. 2 further increases the DP endfire gain by 2–3 dBi at the overlapped bandwidth of 16.3%. [ABSTRACT FROM AUTHOR]

An improved method of wideband performance is demonstrated by being applied to a miniaturized four-arm log-periodic toothed antenna with an integrated balun. The required minimum length of the integrated balun is reduced through the input impedance reduction structure on thin dielectrics with a low relative dielectric constant. In addition, destructive currents arising from the combination of the antenna structure and miniaturization structure are solved by modeling them as an equivalent circuit structure from an impedance perspective. The proposed antenna represents a voltage standing wave ratio of less than 2:1 in the 1.25–18 GHz bandwidth range and has a realization gain of more than 2 dBi in the overall operating band with a diameter of 0.325 $\mathbf{\lambda}_{\mathbf {L}}$. [ABSTRACT FROM AUTHOR]

We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occur due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms’ angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point dipole models are used which incorporate different aspects of the meta-atoms’ angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modeling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations. [ABSTRACT FROM AUTHOR]

This communication presents a low-profile and efficient low-very high-frequency (VHF) antenna designed for compact unmanned ground vehicles (UGVs). An effective miniaturization strategy for a top-loaded multielement monopole antenna is proposed to improve its gain while maintaining a low profile. The approach introduces multiple closely spaced short vertical radiating elements and a structurally constructed 180° phase shifter connecting the elements on a small ground plane. The phase shifter enables electric currents flowing through the vertical elements to be in phase, resulting in enhanced radiation without increasing the antenna profile. In order to improve the antenna bandwidth, a monopole configuration with a sleeve feed and capacitive top loading is adapted. The proposed antenna optimized for a compact UGV via parametric analysis has a height of $0.028\lambda $ at 42 MHz (the corresponding electrical size $ka=0.24$). The measured performance of an antenna prototype shows the 3 dB bandwidth of 0.67 MHz and the peak gain of −2.5 dBi. The proposed design can achieve more than 16% reduction in lateral dimensions and 1 dB improvement in gain compared to the state-of-the-art design with similar topology. The performance of the antenna integrated on an actual UGV system is also evaluated by experiments. [ABSTRACT FROM AUTHOR]

In this article, we study closed-loop digital predistortion (DPD) systems and associated learning algorithms. Specifically, we propose various low-complexity approaches to estimate and manipulate the inverse of the input data covariance matrix (CM) and combine them with the so-called self-orthogonalized (SO) learning rule. The inherent simplicity of the SO algorithm, combined with the proposed solutions, allows for remarkably reduced complexity in the DPD system while maintaining similar linearization performance compared to other state-of-the-art methods. This is demonstrated with thorough over-the-air (OTA) mmW measurement results at 28 GHz, incorporating a state-of-the-art 64-element active antenna array, and very wide channel bandwidths up to 800 MHz. In addition, complexity analyses are carried out, which together with the measured linearization performance demonstrates favorable performance–complexity tradeoffs in linearizing mmW active array transmitters through the proposed solutions. The techniques can find application in systems where the power amplifier (PA) nonlinearities are time-varying and thus frequent or even constant updating of the DPD is required, good examples being mmW adaptive antenna arrays as well as terminal transmitters in 5G and beyond networks. [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]

By utilizing the quadruple-ridged waveguide (QRW), a high-gain dual-polarized all-metallic transmitarray (TA) antenna with wide gain bandwidth is proposed. The QRW has a fixed height with four identical ridges symmetrically located inside a square waveguide. The phase compensation is obtained by simultaneously controlling the length of the four ridges. The fully symmetrical structure of the QRW enables the proposed TA to achieve dual-polarization and two-dimensional (2-D) beam scanning. The proposed TA antenna with an aperture of 112 × 112 mm is designed and fabricated by utilizing 3-D metallic printed technology. The measured broadside gain at 30 GHz for the two orthogonal polarizations is 28.2 dBi and 28.1 dBi, corresponding to an aperture efficiency of 41.9% and 40.9%, respectively. The measured 1 and 3 dB broadside gain bandwidth is 27.3% and 34.8%, respectively. The 2-D beam scanning range at 30 GHz for the dual polarized radiation covers ±18°, with a maximum scan loss of 2.3 and 3.2 dB, respectively. [ABSTRACT FROM AUTHOR]

A single-feed, circularly polarized, log-periodic dipole array (CPLPDA) with size-reduced cross-dipole elements is proposed. Size reduction in elements is achieved with curved, T-shaped top loading. Compared with the full-sized CPLPDA elements, the achieved element-length reduction is 50%. With six elements, the antenna shows a −10 dB impedance bandwidth (IBW) of 87.0% and a 3 dB axial ratio bandwidth (ARBW) of 50.0% in measurement. The common bandwidth (CBW) between the −10 dB IBW and 3 dB ARBW of the CPLPDA is 50.0%. The peak realized gain in the direction of the shortest element is 6.60 dBi over the CBW. [ABSTRACT FROM AUTHOR]

A compact planar fixed-beam leaky-wave antenna that radiates its main beam at broadside is presented, that consists of two folded branches of periodically distributed series-fed microstrip patches. The antenna is fed from the center through a 50 Ω transmission line that subsequently feeds two constituent 100 Ω parallel branches, each consisting of eight series-fed microstrip patches. Fixed-beam operation is achieved by the combination of the two oppositely directed beams that are generated by the two branches. The proposed structure achieves a significant reduction of the longitudinal size by incorporating a 180° bend at the center of each branch, thus effectively folding the antenna in half. This results in a longitudinal size that is 1.8 times smaller than the analogous unfolded antenna. The antenna maintains a measured fixed beam at broadside over a wide zero beam-squinting bandwidth of 3 GHz in the 28 GHz band, with a radiation efficiency above 60% and a maximum measured gain of 14 dBi at 27.4 GHz, with an overall compact size of 5.8 × 1.1 cm. [ABSTRACT FROM AUTHOR]

In this brief, a low-profile wideband quad-element MIMO antenna with high isolation is designed, which is utilized to propose a 20-elements MIMO system. Each element of the MIMO antenna covers a wideband occupying a small area of $15\times 15$ mm2. The orthogonal symmetric arrangement of a single antenna forms an extremely compact quad-element MIMO antenna having shared ground, and its occupied volume is $0.84\lambda _{\mathrm{ g}} \times 0.84\lambda _{\mathrm{ g}} \times 0.019 \lambda _{\mathrm{ g}}$ ($\lambda _{\mathrm{ g}}$ at 3.95 GHz) with a minimum ($0.155 \lambda _{\mathrm{ g}}$) edge to edge distance between elements. The proposed antenna has a −10 dB ($S _{ij} \in i=j$) impedance bandwidth of 77.52% (3.95–8.95 GHz) and a minimum isolation ($S _{ij} \in i \ne j$) value of 17 dB. The measured and simulated results are found in good agreement that confirms the proposed antenna is appropriate for extending a higher-order MIMO system. Further, a low-profile quad-element MIMO antennas are arranged orthogonally at the four-corners and a quad-element MIMO antenna at the center of form a 20-elements planar MIMO antenna. It can be utilized as a localization system where different user’s devices are connected to the primary host. [ABSTRACT FROM AUTHOR]

A novel design concept to reshape radiated fields of a slot antenna for improved bandwidth and stable radiation pattern is proposed. Initially, the radiated fields of the traditional slot antenna are theoretically studied using characteristic modes (CMs). The results demonstrate that its CM1, CM2, and CM3 are resonated around 2.39, 4.78, and 7.17 GHz, respectively. Both CM1 and CM3 maintain the bidirectional radiation patterns, whereas CM2 generates a radiation null in the broadside direction. Then, in order to utilize the nearby CM1 and CM2 for wide bandwidth, the linear slot is properly folded so as to transform the nonbidirectional pattern of CM2 into the bidirectional one. After that, the narrow slot is reformed as the stepped scheme, thus reallocating these dual modes in proximity to each other. With these arrangements, the impedance bandwidth of the antenna is dramatically widened with two attenuation poles, while keeping a compact size and stable radiation pattern. Finally, the proposed antenna is fabricated and tested. Measured results show that the antenna without any extra feeding network has gained a wide bandwidth ($\vert S_{11}\vert < -10$ dB) of around 31.4% ranging from 3.22 to 4.42 GHz, which is about 2.24 times wider than its traditional counterpart (14%). Besides, the overall size of the slot radiator is kept as small as about $0.42\lambda _{0} \times 0.06\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength). Particularly, the bidirectional radiation pattern, stable gain of around 5 dBi, and low cross-polarization of below −12.3 dB are all satisfactorily generated during the operating band. [ABSTRACT FROM AUTHOR]

A compact printed-circuit leaky-wave antenna is designed to synthesize frequency-scanned monopulse patterns in the UHF RFID band from 902 to 928 MHz. A high-permittivity ceramic substrate is used to maximize the angular scanning range in such a narrow band. Two operating modes, i.e., narrow-field and wide-field modes, can be chosen by properly selecting the frequency channels and antenna ports. This allows to adapt to different fields of view while maximizing the maximum reading distance, as demonstrated with a fabricated prototype. [ABSTRACT FROM AUTHOR]

A planar dual-band dual-mode antenna with omni-/unidirectional radiation is proposed for 2.45/5.8 GHz bands. The lower-band antenna consists of four modified quarter-mode substrate-integrated waveguide elements, which are excited in-phase and with same magnitude to obtain vertically polarized omnidirectional radiation. The upper-band antenna is based on a four-port square patch with differential feeds to achieve highly isolated dual polarization with broadside radiation. In addition, the square patch is loaded with four overlapped-corner-mushroom structures to broaden the upper bandwidth. The final design with an overall size of 90 × 90 × 3.66 mm $^3$ (0.735 $\lambda$ × 0.735 $\lambda$ × 0.03 $\lambda$ at 2.45 GHz) was fabricated and measured. The measurements show a 10-dB return loss bandwidth of 160/400 MHz and a gain of 3.4/8.5 dBi at 2.45/5.8 GHz bands, respectively. Furthermore, the antenna prototype demonstrates an isolation of more than 30 dB among all ports. Especially, the isolation among the two ports of the upper-band elements is better than 40 dB. [ABSTRACT FROM AUTHOR]

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λo × 0.022 λowith a thickness of 0.006 λo and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems. [ABSTRACT FROM AUTHOR]

A simple approach is proposed to design a new type of endfire antenna, which simultaneously possesses bidirectional and unidirectional radiation pattern in wideband. By the dispersion engineering, different frequency bands spoof surface plasmon polariton (SPP) modes are excited at the two ports of a proposed splitter structure, and the two ports of the splitter structure are directly connected with two radiator structures, which are utilized to decouple the different frequency bands spoof SPP to free space wave by dispersion mismatching, achieving bidirectional and unidirectional radiation pattern in different frequency bands. From 8.4 to 21.6 GHz, this designed spoof SPP antenna possesses bidirectional endfire radiation pattern, and from 21.6 to 45.0 GHz, this designed spoof SPP antenna possesses unidirectional endfire radiation pattern. This designed spoof SPP antenna has an average gain over 10.6 dB in the whole working bandwidth, and the relative bandwidth of this antenna is 137%. Both the simulation and measurement results verify that the stable bidirectional and unidirectional radiation pattern of this proposed endfire spoof SPP antenna in wide bandwidth are achieved. [ABSTRACT FROM AUTHOR]

Detailed detection of geological hazard sources is an important and yet challenging problem that remains unsolved. In this letter, we propose a whole closed space intrinsically safe Ground Penetrating Radar (GPR) system for geological hazard detection in coal mine roadway. Compared with many existing GPRs for half-space, this GPR system is characterized by achieving a stable radiation pattern and improved gain throughout the bandwidth. The improved performance for the system is achieved by the newly microwave front end design, adding round corners on the antenna radiation surface to improve radiation efficiency, designing resistive loading for better impedance matching, and optimizing shielding cavity dimensions to eliminate environmental interference. For design validation, a field experiment in mine roadway conditions is conducted, and the results show that the developed system has a good performance in mining roadway with depth detection accuracy at 0.5 m and direction detection accuracy at 1.5 m. [ABSTRACT FROM AUTHOR]

A compact log periodic planar dipole UHF array antenna from 500 MHz to 2.2 GHz for partial discharge measurement in power transformers is presented in this paper. The compactness of the designed antenna is achieved by shaping the arms and tuning selected dipole elements of the array to fill the unoccupied areas. Shaped dipole arrangement results in additional capacitance between the antenna elements enhancing the bandwidth. The designed antenna achieves a fractional bandwidth of 126% and the size is ($0.495\lambda _{0} \times 0.63\lambda _{0} \times 0.0144\lambda _{0}$) at center frequency of 1.35 GHz. The proposed antenna is experimentally validated on FR4 3.2 mm thickness substrate. The measured gain of antenna is 4 ± 0.5 dBi over 800 MHz to 2.2 GHz which provides lower variation in measured partial discharges. The effective antenna height of the proposed antenna is measured to be over 15 mm. The measured return loss is better than 10 dB over the frequency range. Moreover, partial discharge measurements with oil filled test objects demonstrate that the designed antenna can receive partial discharge signals effectively. [ABSTRACT FROM AUTHOR]

A novel wideband vertically polarized omnidirectional antenna is proposed in this letter. Two crossed bowtie slots are fed by a loop, which is arranged on the ground vertically. The loop works in the one wavelength mode together with its image with respect to the ground, and accordingly the quasi-omnidirectional radiation can be achieved. The bowtie slots are introduced to expand the working bandwidth. Afterwards, a top-loading patch is utilized to improve the impedance matching. Furthermore, the complete patch is replaced by the metasurface to suppress the lateral current so that the stable omnidirectional radiation can be maintained in the operating band. A prototype is fabricated and measured, and the –10 dB impedance bandwidth covers the long-term evolution band of 1.7–2.7 GHz. The proposed antenna is well tailored for Indoor ceiling base station applications. [ABSTRACT FROM AUTHOR]

In this letter, an 8 × 8 dual-polarized antenna array with high gain and broad bandwidth is proposed for $Q$ -band millimeter-wave (mm-wave) application. Metallic pillars and cavities act as magnetoelectric dipoles fed by a 1 to 4 backed cavity with cross-shaped slots. The cross-shaped slots are adopted to excite two orthogonal linear polarizations. A feeding network with shared vias is designed to construct the antenna array. An 8 × 8 dual-polarized antenna is fabricated and measured. The measured impedance bandwidths are 13.4% from 34.7 to 39.7 GHz and 14.4% from 34.6 to 40.1 GHz for the two ports, respectively. The 3 dB gain fluctuation bandwidth is 8% for the two ports. The maximum gain is up to 24.8 dBi due to less substrate loss in the radiation structure. Attributed to its high gain and high efficiency, the proposed antenna is a promising candidate for mm-wave applications. [ABSTRACT FROM AUTHOR]

A compact dual-polarized base-station antenna with filtering characteristics is proposed in this letter. The antenna is composed of a reflector, two balun structures, and two orthogonal half-wavelength radiation arms. The radiation arm mainly consists of multiple transmission lines of different widths, which can be equated to inductance or capacitance. The elaborately designed radiation arm not only ensures a wideband operation but also helps to achieve low-pass filtering characteristics, without using an extra parasitic structure. For demonstration, a $\pm 45^\circ$ dual-band dual-polarized antenna array operating at 690–960 MHz and 1710–2690 MHz are fabricated and measured. The implemented array (690–960MHz) achieves stable half-power beamwidth (HPBW) of 65 $^\circ$ $\pm$ 10 $^\circ$ and polarization isolation of 27 dB. Due to the filtering performance of the proposed antenna, stable high gain (17.5 $\pm$ 1 dBi) and HPBW of 65 $^\circ$ $\pm$ 6 $^\circ$ also can be realized at 1710–2690 MHz. The proposed antenna is suitable for the base-station application. [ABSTRACT FROM AUTHOR]