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ABSTRACT This paper starts with the proposal of an enhanced version of a planar rectangular slot antenna fed by the quasi‐TEM printed ridge gap waveguide (PRGW), attended with a numerical study of a miniaturization procedure showing the limitations of the conventional PRGW‐based antennas. Then innovative solution is introducing a new miniaturized pure TEM wide‐band slot antenna utilizing double PRGW (D‐PRGW) technology; the proposed approach is self‐packaged and shows high potential for enhancing antenna performance, particularly in terms of bandwidth, gain, and compactness. This technology is featured with low loss, high performance, and compact size; it consists of surrounding the ridge area with a double layer of electromagnetic band gap (EBG) lattice instead of one to eliminate the surface waves effectively and keep the signal completely confined inside the ridge area with strict minimum rows of EBG. Therefore, a broad impedance matching bandwidth (|S11| ≤ −10 dB) of 33.33% is obtained from 50 to 70 GHz, which covers the unlicensed NR parts (n262; amp; n263) of the V band. Furthermore, the antenna achieves a peak gain of approximately 16 at 65 GHz while the overall efficiency remains above 90% across the entire operating frequency band. The high performance along with the compact size of this novel design makes it a good candidate for 5G wireless communications applications centered around 60 GHz. [ABSTRACT FROM AUTHOR]

Dielectric resonator antennas have been demonstrated to be an efficient radiator, especially with the possibility of fabricating it at low cost based on 3-D printing technologies. However, they have two main limitations which are: their relatively small gain (about 5dBi) and narrow bandwidth. To enhance the gain of DRA, higher-order mode excitation can be utilized; however, typically this has a limit of a few dB increments besides its negative effects on the bandwidth. This study employs a cavity-backed slot to provide an appropriate feeding method for a cylindrical dielectric resonator antenna (CDRA). This design effectively facilitates the excitation of higher-order modes, resulting in a significant gain of up to 15 dBi, which is essential for many wireless systems that are unable to support larger aperture sizes through the standard use of arrays. Additionally, two modes are excited to keep a relatively broadband of about 15 %. The proposed design consists of a cylindrical dielectric placed on top of a cavity-backed slot that is excited by a coaxial probe soldered to the top patch of the cavity. With this feeding, a good matching is achieved for different dielectric resonator heights, hence, the gain can be adjusted easily without the need of reoptimizing the antenna or the feed structures. The design process is explained in addition to performing a sensitivity analysis of fabrication tolerances which confirms that the 3-D printer provides enough accuracy with a negligible effect on the antenna's performance. Then a prototype with a medium length is fabricated and measured to provide high realized gain and impedance bandwidth of 11 dBi and 14.5 %, respectively. The measured data demonstrate the good performance of the antenna with great matching compared to the simulated ones. Furthermore, the antenna presents a good performance in terms of sidelobes and polarization. This proposed design outperforms other DRA designs based on higher-order modes. [ABSTRACT FROM AUTHOR]

Summary: This article presents a quad element wideband multiple‐input multiple‐output (MIMO) antenna consisting of human face‐shaped patch radiators with defected ground structure (DGS) having rectangular split ring resonator (RSRR) in ground surface. The measured bandwidth of the proposed MIMO antenna is 3.0–6.5 GHz, and the isolation between the ports is more than 16 dB. Additionally, simulated diversity characteristics like the channel capacity loss (CCL), channel capacity (CC), total active reflection coefficient (TARC), mean effective gain (MEG), and envelope correlation coefficient (ECC) are investigated with the measured value and observed to be within the acceptable ranges over the operating frequency band. The suggested antenna can be used in the wireless local area network (WLAN) (i.e., 4.9–5.725 GHz), wireless fidelity (Wi‐Fi) (i.e., 5.15–5.85 GHz), and 5G under 6 GHz (3.3–5.0 GHz) frequency ranges. [ABSTRACT FROM AUTHOR]

A dual-frequency antenna based on substrate integrated waveguide (SIW) for unmanned aerial vehicle (UAV) applications is proposed, which provides a new idea for the design of multi-frequency antennas by stimulating multiple high-order modes. A group of fan-shaped patches are added to the circular slots on both sides of the dumbbell slots to form modified dumbbell slots. Two resonant modes are excited by this slot structure, and a dual-frequency response is achieved. Different opening angles and offset angles of fan-shaped patches can cause the deviation of the dual-frequency response bands. Therefore, the antenna working frequency band can be freely designed within a certain frequency band, which improves the flexibility of antenna design. The designed antenna is analyzed theoretically and optimized by simulation. Finally, the antenna was manufactured, and the experimental results were basically consistent with the simulation optimization results. The antenna worked in the X-band and the Ku-band, and the relative working bandwidth of the two bands was 6.06% (9.6–10.2 GHz) and 1.41% (14.06–14.26 GHz), respectively. The maximum gain of simulation in low frequency and high frequency operating bands is 5.9dBi and 6.13dBi, respectively. [ABSTRACT FROM AUTHOR]

This study investigates the potential for significant enhancements in the gain and return loss of a microstrip antenna through the meticulous design of slits and a triangular slot in the radiation patch, coupled with precise dimensioning of these elements and careful selection of the feeding point. To this end, a microstrip patch antenna with multiple slits and a triangular slot was designed and simulated on an FR-4 with a dielectric constant (ε) of 4.4. In the initial configuration, the antenna exhibited a gain of 2.3 dB at 5.79 GHz for the maximum Eɵ at θ = 6º, with an S11 value of -16.5 dB. The antenna biasing and feed position were carefully optimized to achieve the desired performance improvements, in addition to meticulous design considerations for gain and return loss enhancements. The optimized antenna demonstrated a gain of 6.2 dB at 6 GHz for Eɵmax at θ = 0º, along with an S11 value of -24.3 dB. The final optimized configuration was fabricated and subjected to rigorous laboratory measurements for validation. The proposed antenna demonstrated an S11 value of -18.6 dB, along with a corresponding gain of 5.4 dB for Eɵmax at θ = 0º at 6 GHz. Furthermore, it was observed that the bandwidth increased by 330 MHz compared to its initial state. Finally, a comparative table is presented comparing the proposed antenna with other similar antennas found in the literature. Based on this table, it is evident that the gain enhancement can be achieved in a remarkable manner without altering the overall dimensions of the antenna and without the need for an expensive substrate with high permittivity. [ABSTRACT FROM AUTHOR]

Dielectric resonator antennas have been demonstrated to be an efficient radiator, especially with the possibility of fabricating it at low cost based on 3-D printing technologies. However, they have two main limitations which are: their relatively small gain (about 5dBi) and narrow bandwidth. To enhance the gain of DRA, higher-order mode excitation can be utilized; however, typically this has a limit of a few dB increments besides its negative effects on the bandwidth. This study employs a cavity-backed slot to provide an appropriate feeding method for a cylindrical dielectric resonator antenna (CDRA). This design effectively facilitates the excitation of higher-order modes, resulting in a significant gain of up to 15 dBi, which is essential for many wireless systems that are unable to support larger aperture sizes through the standard use of arrays. Additionally, two modes are excited to keep a relatively broadband of about 15 %. The proposed design consists of a cylindrical dielectric placed on top of a cavity-backed slot that is excited by a coaxial probe soldered to the top patch of the cavity. With this feeding, a good matching is achieved for different dielectric resonator heights, hence, the gain can be adjusted easily without the need of reoptimizing the antenna or the feed structures. The design process is explained in addition to performing a sensitivity analysis of fabrication tolerances which confirms that the 3-D printer provides enough accuracy with a negligible effect on the antenna’s performance. Then a prototype with a medium length is fabricated and measured to provide high realized gain and impedance bandwidth of 11 dBi and 14.5 %, respectively. The measured data demonstrate the good performance of the antenna with great matching compared to the simulated ones. Furthermore, the antenna presents a good performance in terms of sidelobes and polarization. This proposed design outperforms other DRA designs based on higher-order modes.

A metal‐loaded double‐layer unidirectional radiation slot antenna with flat gain is proposed for millimeter‐wave (mm‐wave) operations. Our presented antenna is constituted of a slot antenna with metal vias, an inner floating metal, a metal line, and ground patch. With the help of inner metal excited by the coupling of the slot antenna, an additional resonance point around 26 GHz could be obtained and the antenna gain is enhanced. To verify the design, the antenna has been fabricated with the prepreg technology. The whole fabricated size is only 0.62 × 0.62λ0² with a thickness of 0.057λ0 (λ0 is the free‐space wavelength at 26 GHz). The measured impedance bandwidth is from 25.1 to 26.55 GHz. Moreover, the proposed antenna obtains a wide flat gain (5.78 ± 0.48 dBi) within the bandwidth and stable one‐sided radiation patterns. The above characteristics show that the proposed antenna is a competitive choice for mm‐wave systems. [ABSTRACT FROM AUTHOR]

The microwave dielectric properties of NdTi(0.5-x)GexMo0.5O4 ceramics were examined using densification and X-ray diffraction (XRD) patterns. As x increased from 0 to 0.05, the unit cell volume decreased, indicating that Ge4+ ions were incorporated within Ti4+ ions. After sintering at 1425 °C for 4 h, Nd(Ti0.49Ge0.01Mo0.5)O4 ceramics achieved a maximum relative density of 98.9%. The unloaded quality factor (Qu × f) of the NdTi0.49Ge0.01Mo0.5O4 ceramic sintered at 1425 ℃ for 4 h was 33,400 GHz (at 17.6 GHz). Additionally, this ceramic exhibited a dielectric constant (εr) of 17.6 and the obtained temperature coefficient of resonant frequency (τf) was-30.8 ppm/℃. In addition, this ceramic was used as a substrate for slot antenna liquid sensor application. We demonstrated how to improve the measurement results as well as the methodology for obtaining the results. As the water content in acetone increased from 0 to 100%, the measured resonant frequencies shifted from 2.6 to 2.0 GHz. [ABSTRACT FROM AUTHOR]

Summary: An ultrawideband multiple‐input‐multiple‐output (MIMO) slot antenna with a small size and high isolation is introduced. Two multi‐stepped microstrip lines are used to feed the MIMO antenna and the ground plane is designed in a defective structure for achieving good impedance matching in an ultrawide frequency range. A 3T‐shaped strip is utilized to diminish the coupling between the two microstrip feed lines for isolation improvement over the operating band. Two open‐end rectangular slots are attached in the ground plane of the MIMO antenna to generate anti‐phase current for further enhancing the isolation. By using this novel method, a compact ultrawideband MIMO slot antenna is designed and measured. It obtains an ultrawide bandwidth of 162.0%, ranging from 0.63 to 6 GHz, and excellent isolation of beyond 20 dB. Additionally, our MIMO antenna achieves a very low envelope correlation coefficient (ECC) of below 0.005, indicating its good diversity performance. [ABSTRACT FROM AUTHOR]

This paper proposes a co-planar waveguide-fed circularly polarized L-band antenna for GNSS Applications. The Fibonacci series inspired us to decide the physical dimensions of the radiating structure. The proposed antenna with the dimensions of 60 × 40 × 0.8 mm3 is fabricated by etching out several slots from the patch and ground plane as well. The circular polarization (CP) behavior is observed from different shaped slots in the ground plane as well as in radiating patches. The experimental and simulation results revealed good agreement over the entire operating frequency range. [ABSTRACT FROM AUTHOR]

A simple technique for gain enhancement of irregular hexagonal shaped ultra-wide band (UWB) slot antenna by inclusion of closely packed tessellated rhombic loop (TRL) based FSS is presented in this paper. The slot antenna is designed to cover entire UWB (3.1–10.6 GHz) frequency range with stable bi-directional radiation pattern. Also, it exhibits non-uniform boresight gain in zenith (θ = 0°) and nadir (θ = 180°) directions. The slot antenna is further loaded with TRL FSS at both slot and feed side separately to study distinct configurations of antenna integrated with FSS and evaluate the impact of the configurations of FSS on antenna performance. Later, an antenna and antenna loaded with TRL FSS prototype are developed for experimental validations. Through measurements it is found that the slot antenna covers entire UWB frequency band and provides a maximum of 4.31 dB gain in zenith direction while 4 dB gain in nadir direction. A gain enhancement of 2.44 dB in zenith and 3.8 dB in nadir directions are achieved when the slot antenna is integrated with TRL FSS along feed side and slot side separately. The measured results confirm the simulated results well. [ABSTRACT FROM AUTHOR]

A slot antenna has been widely used for multifunction in modern wireless communication technologies such as WLAN, WiMAX, IoT, and GSM. Generally, slot antennas can operate in wideband. Nevertheless, this antenna type was limited in terms of lower gain because of wideband operation. Therefore, this paper presents a slot antenna designed for operation frequencies between 1.8 GHz and 6.5 GHz and a study of the performance improvement of slot antennas with metamaterials to increase antenna quality. The utilization of metamaterials can improve the performance of slot antennas by increasing gain levels, reducing sidelobe levels, and optimizing reflection coefficients (S11). As a result, determine the metallic hole structure and wire medium structure put behind the slot antenna for comparing performance. All of them act like reflectors for reflected radiation from the back to the front, which improved the average gain of all operating frequencies from 3.41 dBi to 7.33 dBi for metallic hole structure and 7.42 dBi for wire medium structure. Moreover, the simulation and measurement gave great results. These proposed metamaterials provided enhanced gain and reduced sidelobe level.

AbstractThis paper introduces a compact, circularly polarized spidron-fractal slot antenna with a rectangular island. The reflection-coefficient |S11| of the proposed antenna covers the band from 7 GHz to 10 GHz. The proposed antenna is circularly polarized with an axial-ratio (AR) bandwidth that extends from 7 GHz to 10 GHz. It offers simultaneous dual circular polarization (RHCP and LHCP). The gain of the proposed antenna varies between 4 dBi and 6.9 dBi. The simulated efficiency reaches 97%. The overall dimensions of the antenna are 19.7 x 23 x 0.508 mm3 (0.55λ0 x 0.65λ0 x 0.014λ0), making it suitable for CubeSats with limited surface area. The proposed antenna can be employed for both the X-band satellite downlink (from 7.25 GHz to 7.75 GHz) and uplink (from 7.9 GHz to 8.4 GHz) frequency bands. Additionally, the antenna can be utilized in small satellite Synthetic-Aperture-Radar (SAR) systems operating from 9 GHz to 10 GHz, military applications, and RFID tag tracking-equipment. A prototype of the proposed antenna has been fabricated and then measured using Vector-Network-Analyzer (VNA) and inside an Anechoic chamber. The measurement results of the proposed antenna are in excellent match with the simulated results.

In this paper, a compact size, high gain, narrow beam array antenna is proposed for RFID application. A suitable compact size antenna with a gain of 7 dBi is designed as basic element for the array. This base antenna is designed using three slots. Unlike other works, all the three slots are different in shape. Electrical equivalent for this antenna is also proposed to understand antenna working. The same compact antenna is used as basic element to design a 2 x 2 antenna array. A 4:1 feeding network is designed and electrical equivalent of the same is proposed to show power division among the four-radiating patches. Overall size of antenna array is 1.04 λ0 x 1.04 λ0 x 0.029 λ0 mm3. Array's radiation beamwidth is 530 and gain of the antenna array is 10.3 dBi. All the measured results are in good agreement with simulated results. The proposed work is compared with other existing works and is found to be highly compact with excellent gain for the same size. [ABSTRACT FROM AUTHOR]

This paper presents novel approaches used to achieve compactness of printed circular antenna and circular polarization. Size reduction is achieved using three different shapes of slots unlike the conventional technique which uses similar slots. Overall dimension of the antenna is 0.52 λo x 0.52 λo x 0.029 λo mm3 and achieved by combining two circular sector slots of length 900, circular slot of radius 25 mm and a diametric slit of length 15 mm to the patch. Finally, circular slot is replaced by elliptical one to achieve circular polarization. Electrical equivalent of antenna is discussed at each design stage. The antenna is designed to cover UHF RFID application band and bandwidth obtained is 41 MHz with antenna gain of 7.3 dBi at 866 MHz. The proposed work is compared with other existing work and is observed that the proposed antenna not only is compact in size but has higher gain. All the measured results are in close agreement with the simulated results and proposed antenna is a very suitable candidate for making high gain compact array antenna. [ABSTRACT FROM AUTHOR]

Diagnosis of neural diseases can be performed using microsystems that record neural signals collected simultaneously after neural simulations. Headstage and homecage-based recording systems can be implanted on small freely-moving animals to test such system which requires miniaturized, lightweight, and high gain antennas in order for the small animals to carry them easily while also decreasing loss during data transmission. This paper proposes a $15\times $ 15 mm2 slot antenna with a $50~\Omega $ microstrip excitation line. The slot antenna is created by the addition of slots in the ground plane which is a common miniaturization method as it results in ultrawideband operating frequency. A lumped component-based model along with a 3D EM model of the modified SMA connector used for the measurement and headstage model is also developed to observe the effect on the antenna performance. The antenna achieved an operating frequency of 4.25 - 9.4 GHz and a bidirectional radiation pattern with gain ranging from 2.24 to 4.35 dBi. The proposed antenna is also circularly polarized and achieves 80.6% - 90.8% radiation efficiency over the operating BW. It can transmit a maximum of 20 dBm of power over the operating frequency without exceeding the FCC-imposed SAR limit. Based on the performance, the antenna is suitable for headstage and homecage-based neural signal recording systems with IR-UWB transmitter for high data rate transmission.

In this study, a dual-feed polarization diversity antenna with a broadside or conical radiation pattern is proposed for fifth-generation (5G)-NR applications. The antenna’s design incorporates a radiator created using a circular slot, segmented into two semicircular slots by a protruding stub. By adjusting the phase difference applied to these two semi-circular slots, different radiation patterns within the same frequency band can be achieved. A modified 180° rat-race coupler served as the feed structure. By analyzing current distribution and E-field distribution, the phase difference formed in the two semi-circular slots according to the input terminal is confirmed. The measurement results showed that the proposed antenna exhibited polarization diversity characteristics across a bandwidth of 12.7% ( $3.24\sim 3.7$ GHz), with isolation exceeding 25 dB between the two input terminals. In this case, the measured gains are 5.2 dBi for Port 1 and 3.5 dBi for Port 2.

This paper presents three prototypes of cavity-backed slot antennas integrated with solar panels. The antenna design is straightforward and requires minimal alteration on the solar panel’s geometry. The antennas and solar cells are on the same surface and are effectively independent of each other. This eliminates the need for custom designed solar cells required in previous studies. The integrated solar panel antennas were demonstrated using all commercial-off-the-shelf space-qualified components and printed circuit board technology. The presented modular design method is valuable for CubeSats primarily built with standardized commercial components and where the surface area is limited to house solar panels and antennas separately. The integrated solar-antenna panels include a circularly polarized antenna, a linear two-slot antenna, and a dual band antenna. Measurements were performed to validate both antennas’ and solar panels’ functionality and the results are outstanding when compared to the antenna design data and solar cells’ specifications.

In this work, a slotted wideband eight-element multiple-input multiple-output (MIMO) antenna system is presented, which covers the N77 (3.2-4.2 GHz) frequency band. The MIMO antennas are printed on a 0.8-mm-thick FR-4 substrate with dimensions of $150\times75$ mm2. The antennas are placed along the length and width of the printed circuit board (PCB). The arrangement of antenna elements offers pattern and polarization diversity, enhancing the smartphone’s ability to receive signals from various directions. The wideband characteristics in the frequency range of 3.25-4.49 GHz are achieved by utilizing a T-slot and an inverted C-slotted stub together. The radiation and total efficiency are found to be >60% for all the MIMO elements. For enhanced isolation between antenna elements placed along the width of the PCB, a slot is introduced, which ensures an isolation of 14.5 dB. This helps achieve an envelope correlation coefficient (ECC) < 0.025, diversity gain (DG) >9.95 dB, and a maximum channel capacity (CC) of 40 bps/Hz. The performance of the MIMO antenna is also assessed in the presence of a human, and comparable results are observed. In addition, the examination of the specific absorption rate (SAR) confirms that it remains well within the safety margins when in proximity to humans.

This manuscript presents comprehensive modal analysis of a compact, half-mode SIW-fed slot-coupled dual-band antenna. The Characteristic Mode Analysis (CMA) is investigated in detail and presented for the first time to analyze the radiation behavior and frequency domain characteristics of the proposed structure. The number of dominant operative modes supported by the antenna is decided based on the number eigen factors, its corresponding values, and the characteristic angles. The antenna operates at 33 and 38.14 GHz with a return loss of 20.5 and 19.5 dB, a gain of 7.9 and 6.7 dBi, and an efficiency of 90% and 88%, respectively. Measured results are in close resemblance with the CMA, considering the difference between the conventional cavity modes and the characteristic modes of the proposed planar cavity configuration. The methodology can be extended to characterize any arbitrary shape radiating geometry. [ABSTRACT FROM AUTHOR]

In this paper, two new compact halved-size single and UWB antennas are proposed for WiFi and UWB applications. The single-band compact halved size slot antenna is proposed for WiFi applications at 2.4 GHz. The resonant frequency of the conventional slot antenna can be reduced by cutting the antenna into two halves and without using any lumped elements inside the slot. Moreover, the impedance and radiation characteristics of the proposed halved-size antenna are suitable for WiFi applications at 2.4 GHz. The proposed WiFi antenna has a miniaturised size of 25 × 16.5 × 0.813 mm3. Then, an octagonal blended-shape antenna (OBSA) for UWB applications is proposed. The UWB band from 3.1 GHz to 10.6 GHz is encompassed by the halved-size OBSA using the same cutting concept. Furthermore, a grounded L-stub is added on the top side to improve the reflection coefficients. The proposed OBSA has a compact size of 28 × 13 × 0.813 mm3 with stable omnidirectional radiation patterns. Simulation and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

A dielectric‐loaded slot antenna with the characteristic of broadband, low profile, and low cross‐polarization is presented. The antenna incorporating a low permittivity (εl=4.1 ${\varepsilon }_{l}=4.1$) and multiple high permittivity (εh=22 ${\varepsilon }_{h}=22$) rectangle dielectric is fed by two rectangle slot, which generates three slot modes and achieves measured 10 dB impedance bandwidth of 88% $ \% $ from 1.57 to 4.04 GHz covering the long term evolution (1.71–2.69 GHz) and sub‐6G (3.3–3.6 GHz). Furthermore, the presented slot antenna with a footprint of 0.81 × 0.56λ02 ${\lambda }_{0}^{2}$ and a low profile of 0.09λ0 ${\lambda }_{0}$ (λ0 ${\lambda }_{0}$ is the wavelength in the air region at the center frequency) appears the performance of measured peak gain of 9 dB without using any dielectric resonator mode. On the basis of the single‐polarized design, the dual‐polarized design with a profile of 0.09λ0 ${\lambda }_{0}$ is investigated and fabricated. According to the measured results, the dual‐polarized prototype achieves a 10‐dB impedance of 60% $ \% $ from 1.6 to 3 GHz. [ABSTRACT FROM AUTHOR]

The focal plane of a telescope for cosmic microwave background (CMB) observation typically contains a large-scale array of transition-edge sensor (TES) bolometers. Polarized planar antennas are easy to fabricate and integrate, compared to commonly used horn antennas in receiving modules. In order to enhance the directivity and coupling efficiency, a planar antenna is generally equipped with a hyper-hemispherical silicon lens. However, a Si lens has a large volume, and the fabrication and assembly processes are complex. A flat all-dielectric metasurface lens is proposed to replace Si-lens to converge beam and increase gain of a slot antenna. The all-dielectric structure of silicon holes with sub-wavelength thickness can change the volumetric fill factor to adjust the local effective refractive index, and thus manipulate the shape of wavefront while ensuring high transmission efficiency. The meta-lens was found to exhibit high gain, low cross polarization and good beam symmetry, as verified by simulated electric field amplitude distribution and far-field patterns at 225 GHz using CST microwave studio suite. The detector array and the meta-lens array can both be fabricated using standard planar photolithography technology, and the combination has the potential to achieve larger scale arrays. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: An ultra‐wideband dual circularly polarized (CP) slot antenna with high isolation is presented. Two L‐shaped probes are on the upper layer, both a ladder strip outside and a bent strip in the center on the bottom layer. The L‐shaped probes and the ladder strip result in four impedance resonance modes, and the bent strip moderates real and imaginary impedances to achieve an ultrawide impedance bandwidth. Furthermore, two L‐shaped strips on the ladder strip make two linear polarized Modes 1 and 2 into two CP modes at the low‐ and mid‐frequency bands. Meanwhile, the bent strip combined with the L‐shaped probes creates the third CP resonance mode at the high‐frequency band. The cutting corner and bent slots on the ladder strip change the amplitude and the phase of the electric fields Ex and Ey to realize ultra‐wideband CP radiation. In addition, the port–port isolation is enhanced because the currents are concentrated on the bent strip, and the coupling current path is cut off with the bent slot. The fabricated antenna achieves a −10‐dB impedance bandwidth of 111% (1.7–5.94 GHz), a 3‐dB axial ratio bandwidth of 101% (1.7–5.2 GHz), and a port–port isolation of better than 20 dB. Besides, our antenna obtains a high peak gain of 8.1 dBi and a lower profile of 0.004 λL, where λL is the lowest frequency wavelength of the operating bands in vacuum. These performances make the proposed design competitive for wireless communications. [ABSTRACT FROM AUTHOR]

Here, a single‐layered single‐fed slot antenna is realized with low cross‐polarization over the full operating bandwidth. This design consists of a circular‐shaped cavity resonator, employed by using substrate integrated waveguide (SIW) technique and a square‐ring slot on the upper metal cladding of the cavity. The antenna is fed using a probe feed which excites the design in dual mode, that is, slot mode and inset patch mode. Due to the proximity of these dual resonances, the antenna operates over a relatively wider bandwidth than previously suggested designs with the claim of low cross‐polarization. The proposed design helps to realize more than 35 dB of co‐to cross‐pol isolation in both E and H planes. Overall experimental results demonstrate a good radiation performance, it is confirming up to 15–20 dB improvement in cross‐polarization level with enhanced enhancement bandwidth which makes it appropriate for a modern wireless application. [ABSTRACT FROM AUTHOR]

This paper introduces a compact, circularly polarized spidron-fractal slot antenna with a rectangular island. The reflection-coefficient |S11| of the proposed antenna covers the band from 7 GHz to 10 GHz. The proposed antenna is circularly polarized with an axial-ratio (AR) bandwidth that extends from 7 GHz to 10 GHz. It offers simultaneous dual circular polarization (RHCP and LHCP). The gain of the proposed antenna varies between 4 dBi and 6.9 dBi. The simulated efficiency reaches 97%. The overall dimensions of the antenna are 19.7 x 23 x 0.508 mm³ (0.55λ0 x 0.65λ0 x 0.014λ0), making it suitable for CubeSats with limited surface area. The proposed antenna can be employed for both the X-band satellite downlink (from 7.25 GHz to 7.75 GHz) and uplink (from 7.9 GHz to 8.4 GHz) frequency bands. Additionally, the antenna can be utilized in small satellite Synthetic-Aperture-Radar (SAR) systems operating from 9 GHz to 10 GHz, military applications, and RFID tag tracking-equipment. A prototype of the proposed antenna has been fabricated and then measured using Vector-Network-Analyzer (VNA) and inside an Anechoic chamber. The measurement results of the proposed antenna are in excellent match with the simulated results. [ABSTRACT FROM AUTHOR]

Soft robotics is an emerging technology that provides robots with the ability to adapt to the environment and safely interact with it. Here, the ability of these robots to identify the surface of interaction is critical for grasping and locomotion tasks. This paper describes the capability of a four-limb soft robot that can identify background materials through the collection of reflection coefficients using an embedded antenna and machine learning techniques. The material of a soft-limb robot was characterized in terms of the relative permittivity and the loss tangent for the design of an antenna to collect reflection coefficients. A slot antenna was designed and embedded into a soft limb in order to extract five features in reflection coefficients including the resonant frequency, −3 dB bandwidth taken from the lowest S11, the value of the lowest S11, −3 dB bandwidth taken from the highest S11, and the number of resonant frequencies. A soft robot with the embedded antenna was tested on nine different background materials in an attempt to identify surrounding terrain information and a better robotic operation. The tested background materials included concrete, fabric, grass, gravel, metal, mulch, soil, water, and wood. The results showed that the robot was capable of distinguishing among the nine different materials with an average accuracy of 93.3% for the nine background materials using a bagged decision-tree-based ensemble method algorithm. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a directivity‐enhanced planar slot antenna (PSA) backed by substrate integrated waveguide (SIW) cavity is proposed to solve the problem of maximum gain direction bias. According to the radiation principle of slot antenna, the reason for maximum gain direction bias is explained and the solution has been given. Ulteriorly, the problem of frequency bias caused by changing the directivity is also explained by resonance modes and solved by introducing the metal via. An example with 5.8 GHz which has the maximum gain of 5.28 dBi and the total thickness less than λ/4 is given. After structural optimization and measurement, the maximum radiation direction of improved antenna is 0° from the normal direction of antenna surface, and it maintains the good radiation performance and small size of the traditional PSA backed by SIW cavity. [ABSTRACT FROM AUTHOR]

In this work, a compact size 4 ports multiple input multiple output (MIMO) slot antenna with the connected ground for Ultra-Wide Band (UWB) and X band applications is introduced and discussed. The single antenna is a cross-shaped slot antenna in the ground plane and a 50 Ω microstrip line with a small L-stub is used to feed the antenna on the other side. The suggested MIMO antenna has four identical elements arranged to be orthogonal to each other to enhance the MIMO system performance. The antenna elements are connected with a small strip to compose the proposed connected ground antennas. The suggested MIMO antenna has an overall size of 47 mm × 47 mm. The antenna has tested and simulated bandwidth with S 11 < −10 dB extended from 4– 14 GHz and has isolation greater than 20 dB between ports without utilizing the decoupling elements and with good consistency between results. The MIMO antenna has peak gain and efficiency, envelope correlation coefficient, diversity gain, and channel capacity loss of 5.6 dBi and 80%, <5 × 10–3, 10 dB, and <0.4 bit/s/Hz, respectively which prove that our antenna can be suggested for the UWB MIMO applications. [ABSTRACT FROM AUTHOR]

Aَ Numerical study of hyperthermia was performed using a microwave slot antenna in the treatment of liver cancer. The modeling of the problem in Comsol software is done symmetrically and two-dimensionally and the electromagnetic equation is coupled with the biothermal transfer equation. Temperature distribution, cancer tissue destruction, microwave absorption in liver tissue and specific absorption rate (SAR) are presented as results. The results showed that the two-hole antenna has a wider distribution of the amount of microwave absorbed than the single-slot antenna. The SAR distribution along the longitudinal axis of the antennas gradually increases and reaches its maximum point where the slot is located, and then the SAR distribution decreases rapidly and reaches its minimum at the end of the antenna. According to the results, changes in temperature in liver tissue also depend on the type of antenna and penetration depth, and temperature distribution and SAR distribution have a similar trend. Also, single-slot antenna is suitable for elliptical tumors and double-slot antenna is suitable for spherical tumors. [ABSTRACT FROM AUTHOR]

This paper proposes a planar wideband microstrip feedline to a slot-line-based patch antenna for high-frequency pattern diversity applications. The antenna consists of two adjacent rectangular patches separated by the ground slots, with a directive patch slot along the edge of the substrate. A compact common feedline-to-slot configuration is used to miniaturize the antenna. The antenna is designed in stages, starting with an in-phase feedline, followed by a slot line structure, with two radiating patches on top and a director on the side. This creates radiation diversity with directive radiation patterns. The antenna was fabricated and analyzed inside a far-field anechoic chamber. The experimental results validate the return loss, gain, and radiation performance. The measured results of the antenna within a frequency range of 8.5 to 11 GHz show good agreement with the simulation. The antenna has a maximum gain of 9.2 dBi and has the potential to be beneficial for beam steering and X-band applications due to its low profile, broad bandwidth, high gain, and good directivity. [ABSTRACT FROM AUTHOR]

This letter presents a compact wideband slot antenna for Wi‐Fi 6E application. It evolved from the full wave bow‐tie slot antenna, and four short slits are loaded on the metal plate with conjugate reactance to improve impedance matching at the extended 6 GHz band. The dimension of the proposed antenna is 39 × 39 mm, which is 0.32 × 0.32 λ at 2.45 GHz. The antenna has omnidirectional radiation at 2.45 GHz band, and it remains quasi‐omnidirectional radiation at 5 and 6 GHz bands with vertically polarized radiation. The prototype antenna is fabricated and measured for verification. The result shows that the wide bandwidth for return loss (RL) better than 10 dB is 104% from 2.35 to 7.44 GHz, and the radiation efficiencies are nearly 80% at the triple bands. [ABSTRACT FROM AUTHOR]

A novel wideband slot antenna with metasurface is presented. In order to achieve broadband, high-gain, and mechanical reconfigurable performance, a metasurface is adopted and combined with a new-type planar slot antenna The antenna and metasurface are designed on F4B substrate, and the overall dimension of the antenna is 1.48λ0×1.48λ0×0.2λ0 (λ0 is the free space wavelength at center frequency). Different from the traditional square metasurface, a structure with different properties in the x and y directions is utilized in the proposed antenna, which can be reconstructed by adjusting the relative position between the slot antenna and the metasurface. By introducing the metasurface, the maximum gain of the whole antenna is improved. The antenna works in two states with respect to the two locations of the metasurface. The impedance bandwidth of the proposed antenna in state A is from 5.49 to 9.40 GHz (52.5%), and the impedance bandwidth of the proposed antenna in state B is from 5.83 to 6.01 GHz (3%) and 7.05 to 9.62 GHz (30.8%). The gain of the whole antenna in both states is higher than that of the original slot antenna (without metasurface), and the maximum gain is 9.1 dBi. [ABSTRACT FROM AUTHOR]

Summary: A hexagonal shaped circularly polarized (CP) wideband slot antenna using multiple stubs has been proposed and investigated. A hexagonal slot is created in the ground plane with tapered sections improving the impedance matching. Two radiators are incorporated in the structure, which is responsible for generating orthogonal degenerate modes; hence, CP radiation is achieved for the proposed antenna. For enhancing the gain of antenna, one radiator is directly connected to feed line and another one embedded in the ground plane. An inverted L‐shaped arm is inserted in the slot to enhance and tune the circular polarized behavior. The presented radiator have input reflection coefficient ranges from 5.67 to 8.50 GHz (39.97%) and axial ratio bandwidth (ARBW) of 5.60–8.50 GHz (41.13%). The proposed antenna provides overlapping bandwidths of 5.67–8.50 GHz (39.97%) having average gains of 5.25 dBi within the entire frequency bands. The presented antenna is exceptionally good for the application of mobile and satellite communications. [ABSTRACT FROM AUTHOR]

A high-gain slotted waveguide antenna in substrate-integrated waveguide (SIW) configuration with enhanced bandwidth is proposed. Two different cases fabricated using Rogers RO 4003 substrate over a small area of 16 × 4.5 × 0.508 mm3 are discussed. SIW-based antenna having four longitudinally placed slots is studied with the help of simulation and experimental studies. Experimental results revealed that the proposed hourglass-shaped slot effectively enhanced the operation bandwidth without using additional complicated mechanisms. Improvement in bandwidth was achieved from the low-Q characteristics of the hourglass-shaped slots evidenced through the Z11 impedance analysis. The proposed hourglass-shaped slotted waveguide antenna exhibited 3.18% (37.09–38.29 GHz) impedance bandwidth with 5.8 dBi antenna gain at 38 GHz, where 1.08% bandwidth improvement was observed. Such low-profile planar structure resonating at mm-wave frequency band having high gain and improved bandwidth can be a suitable choice for integration with devices working in wireless network applications. [ABSTRACT FROM AUTHOR]

In this paper, modal analysis is used as a guide to design a circularly polarized open‐slot antenna. The design proposes an open wide slot that is fed electromagnetically by a modified feedline. Both open slot and feedline are asymmetrically placed to the edge of the substrate. The complete antenna without excitation is analyzed using characteristic mode theory to provide a physical insight into its circular polarization operation. The modal analysis proves that several nearly orthogonal modes can be generated at certain frequencies with 90° phase differences. The axial ratio (AR) corresponds to the modal analysis, which proves the validity of the modal analysis. An AR bandwidth from 3.2 to 6 GHz (61%) is achieved within an S11 bandwidth of 3.2–14 GHz (125%). The proposed antenna achieves a peak realized gain 4.3 dBi of within the AR band. [ABSTRACT FROM AUTHOR]

Purpose: Mitigating coupling effects between coil elements represents a continuing challenge. Here, we present a 16‐bowtie slot volume coil arranged in eight independent dual‐slot modules without the use of any decoupling circuits. Methods: Two electrically short "bowtie" slot antennas were used to form a "module." A bowtie configuration was chosen because electromagnetic modeling results show that bowtie slots exhibit improved B1+Pin$$ \frac{B_1^{+}}{\sqrt{P_{in}}} $$ efficiency when compared to thin rectangular slots. An eight‐module volume coil was evaluated through electromagnetic modeling, bench tests, and MRI experiments at 4.7 T. Results: Bench tests indicate that worst‐case coupling between modules did not exceed −14.5 dB. MR images demonstrate well‐localized patterns about single excited modules confirming the low coupling between modules. Homogeneous MR images were acquired from a synthesized quadrature birdcage transmit mode. MRI experiments show that the RF power requirements for the proposed coil are 9.2 times more than a birdcage coil. Whereas from simulations performed to assess the proposed coil losses, the total power dissipated in the phantom was 1.1 times more for the birdcage. Simulation results at 7 T reveal an equivalent B1+ homogeneity when compared with an eight‐dipole coil. Conclusion: Although exhibiting higher RF power requirements, as a transmit coil when the power availability is not a restriction, the inherently low coupling between electrically short slots should enable the use of many slot elements around the imaging volume. The slot module described in this paper should be useful in the design of multi‐channel transmit coils. [ABSTRACT FROM AUTHOR]

In this paper, a 12-port MIMO antenna system for 5G/WLAN applications is proposed. The proposed antenna system consists of two types of antenna modules: an L-shaped antenna module covering the C-band (3.4–3.6 GHz) for 5G mobile applications and a folded monopole module for the 5G/WLAN mobile application band (4.5–5.9 GHz). Each two antennas form a pair, six pairs in total, forming a 12 × 12 MIMO antenna array, and the elements between the antenna pairs can achieve an isolation of 11 dB or more without additional decoupling structures. Experimental results show that the antenna can cover the 3.3–3.6 GHz and 4.5–5.9 GHz bands with an overall efficiency greater than 75% and an envelope correlation coefficient less than 0.04. Finally, the one-hand holding mode and two-hand holding mode are discussed to demonstrate their stability in practical applications, and the results show that they still exhibit good radiation and MIMO performance when operating in both modes. [ABSTRACT FROM AUTHOR]

A wideband 8-element multiple-input multiple-output (MIMO) antenna for fifth-generation (5G) smartphones with a full-screen and a metal rim is presented. A single antenna element consists of two slots, open and closed, both placed solely on the metal rim. Wideband operation is based on the interactions of multiple slot modes, their simultaneous excitation, and overlapping resonance bands. The antenna occupies only the metal rim and does not have any matching circuits or decoupling structures. This simple zero ground clearance design enables a full screen which is a highly desirable property in modern mobile devices. A prototype of the proposed antenna design is manufactured and the measurements verify that the design covers a wide frequency band of 3.4–6.1GHz, isolation over 11.7dB, and good total efficiency of 57.6–84.9%. The performance of the antenna with the user’s hand is verified with simulations.

A dual-polarized paralle-plate waveguide slot array antenna operating at 24.5 GHz band is proposed in this paper. The radiating panel using a 5mm-thick expanded dielectric substrate ( $\epsilon _{r}=1.12$ ) consists of two orthogonally oriented $20\times 19$ radiating slot arrays, where the slots are positioned collinearly. The centered longitudinal feeding slots are introduced into the feeding waveguides, which offer improved aperture efficiency and higher cross-polarization discrimination (XPD) compared to the conventional tilted feeding slot approach. The antenna achieves a remarkable simulated radiation efficiency of over 95% within the operation bandwidth. A prototype antenna is fabricated and verified through measurements. The measured results demonstrate an impedance bandwidth of 13%, with reflection below -10 dB. Moreover, the antenna achieves a simulated peak aperture efficiency of 54% and a measured peak antenna efficiency of 40%. The measured XPD of the antenna prototype exceeds 26 dB.

This design proposes a self-grounding semi-circular gap dual-band flexible antenna in the context of the rapid development of wireless body area networks. The antenna combines the slit structure with the characteristics of traditional rectangular monopole antenna to realize dual-band. In addition, the antenna’s grounding structure adopts the self-grounding structure, which is less used nowadays, to extend the bandwidth. The antenna is designed on a dielectric board of polyimide material with a relative dielectric constant of 3.5. The overall dimensions of the antenna are 44 mm $\times 40$ mm $\times 0.2$ mm with two different sized gaps in a rectangular patch, similar to the geometry of an umbrella handle. Measured data shows that the structure has higher gain and efficiency in the bent state than in the flat state, making it ideal for wearable smart terminals. It can be combined with a smart armband for sports and medical applications or for a single soldier wearable wristband smartwatch. The article explores the effect of different slot sizes and different bending angles on the performance of the antenna, as well as the specific absorption rate values of the antenna for the human body. Finally, two frequency bands with good omnidirectional radiation characteristics are obtained: 2.38–2.81 GHz and 4.28–5.10 GHz. The antenna covers ISM, 4G, 5G, Bluetooth, WLAN, and other common communication frequency bands. The results of the study show that the design method is highly reliable.

In this article, a small aperture coupled SIW cavity-backed dual slot antenna is presented. It is demonstrated that, for a rectangular SIW cavity with dual slot, when the feed point is chosen properly, the structure can resonate at much lower frequency than that of the conventional SIW cavity mode frequency. An equivalent cavity model is formed; a formula for the calculating the operating frequency and a general design guideline are provided for this structure. The designed prototype antenna provides a gain of 8.41 dBi at 15 GHz. For high-gain applications, a $2\times4$ array of such element is demonstrated. An experimental validation of the array results in a gain of 16.01 dBi. The structure is compact, offers a broadside radiation pattern, easy to integrate with metallic surface, and has inherent property of reducing mutual coupling. As a result, it can find application in CubeSat/SmallSats where space is among the major constraints and components are very closely packed. It can be used in CubeSat missions for earth and planetary observations, intersatellite communications, and in MIMO systems for SmallSat swarms.