The major component for the effective functioning of airborne unmanned aerial vehicles (UAVs) is an antenna. The unified integration of an antenna with UAVs without disturbing the other components of UAVs, compact size, thin, and wideband antennas are preferred. Based on these prerequisites, a low-profile and a wideband antenna is presented for autonomous UAVs for C-band applications. The antenna is designed on an extremely thin substrate of size 0.01λ0 without compromising the antenna's broad bandwidth. The antenna structure comprises a corrugated U-shaped patch, a few parasitic patches along with the partial ground. Initially, only a single mode was excited using a U-shaped patch, then further on introducing a few more parasitic patches along with corrugations in a U-shaped patch other modes were also coupled leading to enhancement in the bandwidth of the antenna. The proposed antenna along with a 2 × 2 quad-port multiple input, multiple output (MIMO) antenna is designed and fabricated. The measured results are found to be in good agreement with the simulated results. A broad bandwidth of 74.5% (4.1–9.0 GHz) with 5.02 dBi peak gain at 6.6 GHz is exhibited by the fabricated MIMO antenna. Thus, the designed antenna proves to be an effective candidate for UAV-based C-band applications.

A novel concept of SIW cavity-backed dual inverted edge curved L slots antenna array with the defective ground plane is proposed in this paper. A linearly placed six-element inverted dual L slots array antenna is designed separated by a distance of 0.55λg to achieve high gain. Each pair of slots is separated by a column of the vias to form sub-cavities and those are fed individually. Defective ground structure (DGS) is introduced at the ground plane to manage the propagation of wave to the last slots in the array. The slots are enclosed by a SIW cavity of height 0.24λg in a single substrate. A measured peak gain of 8 dBi is achieved at 14.29 GHz. The antenna shows a front-to-back ratio of 24.9 dB. The design is also compared with various aspects to show the advantages of each element introduced in the design. The validity of the design is proved by the good agreement between the simulated and measured results. This novel design can be used to achieve the performance requirement of a satellite antenna working in Ku band.

A linearly polarized dual band reflectarray (RA) antenna designed, fabricated, and tested to operate in the Ku and K band frequencies is reported in this paper. The 24 × 24 cm2 size RA is developed using 1058 integrated elements etched over a 0.275 mm thick Rogers RT5870 substrate. The integrated elements include concentric circular rings distributed co-centric with the source and the Malta cross elements distributed offset from the source. The distribution of these elements is done based on the 590 and 360° phase change observed at 14.25 (Ku) and 22.5 (K) GHz by varying the size of the circular rings and the Malta cross respectively. The designed RA offers a simulated gain of 28.62 dBi at 14.25 GHz and 26.92 dBi at 22.5 GHz. These results are validated experimentally using the fabricated prototype. A measured peak gain of 28 and 26.4 dBi are observed with sidelobe levels (SLL) of −21 and −11 dB at 14.25 and 22.5 GHz respectively. The cross-polarization levels measured at the resonant frequencies are <−31 and <−28 dB. The proposed dual-band RA covers the entire Ku band uplink frequencies utilized for fixed satellite services and the K band downlink frequencies useful for earth exploration satellite services.

This paper presents a new design of a reconfigurable miscrostrip patch antenna based on a substrate-integrated waveguide (SIW). The antenna is resonant at the millimeter-wave (mmWave) 5G spectrum. The tuning technique consists of using a nematic liquid crystal (K15). An adjustable frequency band from 30.191 to 32 GHz is obtained, giving a tunable range of Δfr = 1.809 GHz. The maximum gain and efficiency reach the values of 7.61 and 9.07 dBi and 93 and 94%, respectively. The proposed SIW antenna loaded with liquid crystal was fabricated and tested. The experimental results correlated well with the simulation; however, the measured reflection coefficient plot shows a shift of the tuning range of 284 MHz, which is an acceptable outcome compared to simulation. A new approach of adopting the magnetic field as a technique to tune the resonance frequency has been used. The structure is characterized by its design simplicity, compactness, and fabrication process. The proposed antenna proves that the liquid crystal improves the performance of the antenna in the Ka band for 5G applications and satellite communication systems.

This paper presents an analysis of the radiated susceptibility of multiconductor shielded cables within complex structures following a hybrid method using moments (MoM) circuit models. The MoM code was used to compute the currents on the shielding induced by an external electromagnetic field and incorporated into a circuit model. The proposed method can be employed for nonlinear loads. The method was tested on two cases: coaxial shielded cables inside a cavity and a car with complex wiring, including a coaxial cable, a twinax cable (a cable with two parallel wires), and a triaxial cable (a cable with three parallel wires), all of which are excited by an incident plane wave. The proposed method provides high accuracy and significant speed gain, and its results are in good agreement with those obtained in other studies.

The distorted Born iterative method (DBIM) is a widely used quantitative reconstruction algorithm to solve the inverse scattering problems of microwave imaging. The major mathematical challenges in solving such problems are non-uniqueness, non-linearity, and ill-posedness. Due to these issues, the optimization algorithm converges to a local minimum. This drawback can be overcome by selecting the correct initial guess solution, which helps to escape local minima and thus guides the inversion algorithm to a satisfactory result. This study uses a back-propagation algorithm to calculate the initial estimate, which significantly accelerates the rate of convergence and improves the accuracy of the standard DBIM approach. The results of this method are compared with zero initialization and Born-approximated initialization. For comparison, weak as well as strong scattering profiles of synthetic and experimental dataset are considered. The results suggest that the proposed method provides a significant improvement in terms of computing cost and efficiency. Furthermore, the proposed technique has the potential to successfully push the limits of reconstructible contrast.

A low-profile slant ±45° polarized antenna for a 4G/5G base station with a dominant path wave propagation model (DPM) is reported in this paper. For dual-polarization and wide impedance bandwidth, the two dipole radiators are crisscrossed and a square metallic ring is integrated with the dipole arms and screwed with the four shorting vias. The antenna operates in Band 40/41/42/43 with strong isolation and low ECC (Envelop Correlation Coefficient). Fabricated antenna results show that the predicted wideband antenna has 13.38% bandwidth in 4G, which is Band 40/41, and 29.33% bandwidth in 5G sub-6 GHz Band 42/43. The antenna has a consistent radiation pattern, a 40 dB XPD (Cross Pol Discrimination), and a beam width of 69.5° ±1.5° in the entire frequency band. Three base station sites were explored to deploy the radiation pattern of a dual-polarized antenna in the 3D EM (Electromagnetic Analysis) tool. To evaluate signal quality, strength, radio network planning, and wave propagation analysis by analyzing antenna performance in real-time scenarios with 64 and 256 QAM (Quadrature Amplitude Modulation) techniques. For the proposed four-stream MIMO (Multiple-Input-Multiple-Output) antenna arrangement at deployed cell sites for 4G/5G base station applications, the maximum downlink and uplink data rates are 3.826/2.8 Mbps and 1044/800 Mbps respectively.

Dielectric resonator antennas (DRAs) are developed antennas that are lightweight, wideband, small-sized and have high radiation efficiency. A DRA is an appropriate candidate for any radio communication including radar applications mainly because of its high efficiency and wideband performance. As the development of DRAs has been a continuous process for more than five decades the plethora of the same has become magnificent in all possible ways. Scientists have walked the technical path for more than centuries and tried to meet the various challenges in the most graceful ways. Reduction of loss, lightweight, and desired radiation patterns are some of the issues which are effectively met by DRAs. This paper presents a brief comprehensive review of the state of art techniques, giving an exhaustive idea of achieving broadband and multi-frequency operations in the areas of DRAs. The paper associates the references of the past and correlates with the current and future trends of research in DRAs that could be of immense help to the young upcoming researchers interested in this field.

The study aimed to present a dual-band 5G multi-input multi-output monopole dual-antenna system, which was configured on the upper edge of the display ground plane for laptops. The dual-antenna unit is a 29 × 2 × 3 mm3 three-dimensional structure with two antennas of the same structure and size, consisting of a fed monopole antenna and a shorted monopole antenna. The antennas are arranged 4 mm apart, side by side in the same direction, to form a dual-antenna unit. Such a configuration allows the feeding points of the two antennas to be separated by the shorting point of the shorted monopole antenna, and the shorting point of the low-frequency resonant path (the shorted monopole antenna) of the two antennas to be larger than a quarter of the wavelength of the low frequency with appropriate bending. The strong current will be concentrated near the shorting point of the shorted monopole antenna when the low-frequency mode is excited, and the current flow from the ground to the feeding point of the other antenna will be reduced, achieving the isolation which is better than 10 dB in measurement between the two antennas without adopting any isolation element. The envelope correlation coefficients calculated from the measured complex E-field radiation patterns are all smaller than 0.12, which can cover the 5G dual-band operations of 3300–3600 and 4800–5000 MHz, and the measured antenna efficiencies can reach more than 40%, which are well suited for multiple antenna applications.

A high gain antenna with Mu-near-zero metasurface (MNZ-MS) is introduced in this work. The proposed antenna can be utilized for future 5G applications. The patch antenna is designed on the upper face of the square substrate with a ground plane at the bottom face. To improve the antenna gain, a layer of MNZ-MS unit cells is placed above the antenna substrate with 0.48λ0 air space between the two layers, where λ0 is the wavelength in free space at the resonance frequency of 26.3 GHz. The MNZ-MS layer consists of four double-sided split square resonators. The overall thickness of the proposed antenna is 0.66λ0. To approve the execution of the proposed antenna, a prototype model is manufactured and tested. The outcomes fulfill a reflection coefficient lower than −10 dB over the frequency spectrum of 26–28 GHz. A gain improvement better than 5 dB is obtained compared to the gain of the reference patch at the center frequency of 26.3 GHz.

A small-size multiband antenna with 14 bands is presented in this paper for wireless applications. The studied antenna mainly consists of a folded monopole antenna and an M-shaped structure. Furthermore, the antenna has a simple design with a compact dimension of 26.8 × 10.8 mm2. The studied antenna is printed on FR4 substrate with a depth of 0.8 mm and fed by a coaxial cable. The −10 dB bandwidths measured are 210 MHz (1200–1410 MHz), 100 MHz (2200–2300 MHz), 193 MHz (3000–3193 MHz), 180 MHz (3330–3510 MHz), 390 MHz (4110–4500 MHz), 4971 MHz, 577 MHz (5300–5877 MHz), and 700 MHz (7100–7800 MHz), which can cover 3G/4G/5G/Wi-Fi/WiMAX, C, and S bands. The gain and efficiency of the presented antenna are 1.3–4.00 dBi and 46%–60.2%, respectively.

As the demand for high data rates is increasing day by day, fifth-generation (5G) becomes the leading-edge technology in wireless communications. The main objectives of the 5G communication system are to enhance the data rates (up to 20 Gbps) and capacity, ultra-low latency (1 ms), high reliability, great flexibility, and enhance device to device communication. The mentioned objectives lead to the hunting of the millimeter-wave frequency range which lies from 30 to 300 GHz for 5G wireless communications. To design such high capacity, low latency, and flexible systems, antenna design is one of the crucial parts. In this paper, a survey is presented on various antenna designs with their fabrication on different types of substrates such as Rogers RT/duroid 5880, Rogers RO4003C, Taconic TLY-5, etc., at different 5G frequency bands. The different configurations of antennas that covered antenna arrays, multiple-input multiple-output (MIMO) antennas, phased antennas, and beamforming antennas are discussed in detail with their applications. The design of MIMO antennas in the 5G frequency band occupied less space so mutual coupling reduction techniques are required for maintaining the required gain, efficiency, and isolation. This paper is also focused on the mutual coupling reduction techniques and diversity in MIMO antennas.

A compact microstrip to substrate integrated waveguide transition feed tapered slot antenna array (1 × 4) with the elliptical patch is proposed and analyzed. The new approach is presented, employing a parasitic patch in the flared aperture to generate more radiation in the end-fire direction and improve field coupling between the arms. It boosts gain while maintaining overall size and low-frequency performance without using electrically thin dielectric substrates. To validate the designed approach, the proposed structure is fabricated and measured. The measured results show that the array provides impedance bandwidth of 40%, peak measured gain of 9.14 dBi, and radiation efficiency is 90% over the 8.5–12.5 GHz frequency band. A four-way feed network is also fabricated with the insertion loss of −6 ± 0.9 dB; the reflection coefficient is below −15 dB over the desired frequency range and only ±4° phase imbalance. The overall dimension of antenna array is 50 × 54 × 0.813 mm3 or ~1.6λ × 1.8λ × 0.027λ at 10 GHz.

This communication presents the significance of a four-port 2×2 multiple input multiple output antenna operating in mid-band frequency for 5G handheld device application. A microstrip-fed reference truncated decagonal monopole antenna operating at 3.9 GHz and a modified split-ring resonator (SRR)-based low-pass filter that excites at a cut-off frequency of 6.5 GHz are designed. On introducing a stub line in the SRR structure, the proposed filter shows a good out-of-band rejection beyond 6.5 GHz. By integrating the filter into the reference monopole, a wideband filtering monopole with improved stopband performance is obtained. A four-port MIMO array is constructed by orthogonally positioning the antenna with a center-to-center separation of 0.25λ0. To improve isolation, a pair of inverted L-stubs of varying lengths is introduced. The closed loop formed by the interconnection of stubs enhances isolation within the frequency range of 3–3.5 GHz. The fabricated prototype fosters an impedance bandwidth of 66.67%, isolation >18.5 dB, an average suppression of 15 dB, an average peak gain >3.7 dB, envelope correlation coefficient < 0.015, Actual Diversity Gain (ADG) > 9.9 dB, Effective Diversity Gain (EDG) > 8.8 dB, and efficiency >88%. The proposed design is suitable for 5G sub-6 GHz applications such as n48, n77, n78, n79 bands, WiMAX, and LTE bands 42, 43, 46, 47, 48.

This study presents a dual-circularly polarized (CP) Fabry–Pérot (FP) antenna, employing a novel receiver–transmitter (RT) metasurface (MS). The RT-MS unit cell consists of two identical neighboring substrates, with a three-layer metal coating printed on their surfaces. The bottom patch is adopted as a receiver to transfer electromagnetic waves to the top-corner cut patch, passing through the coupling cross-slot sandwiched in the middle. The RT-MS has high reflectivity to achieve a high gain. Through energy and a cross-slot, high aperture efficiency can be realized. A conventional corner cut patch can excite a CP mode of equal magnitude and a 90° phase difference. The RT-MS is arranged in 12 × 12 unit cells and used as a superstrate for a dual-CP antenna. Two orthogonally etched slots fed by two branch-matched orthogonally arranged feed lines are used as feeders to produce perpendicular linearly polarized waves. To enhance the bandwidth and improve the gain, double identical stack substrate patches are placed at the top side of the slot with no air gap, for a wide impedance band and high gain. Two wide CP bands, left-hand circular polarization and right-hand circular polarization, of 12.21–13.1 GHz (7.03%) and 12.35–13.1 GHz (5.89%), respectively, have maximum high gains of 16.5 and 15.97 dBic at 12.58 and 12.7 GHz, respectively, with a compact size of 2.6λ0 × 2.6λ0, suggesting better properties than recent antennas. The aperture efficiency can reach 63.2%. Thus, the RT-MS-based FP antenna is a good candidate for commercial and military communication systems.

This paper presents a novel method to improve the working bandwidth and radiation intensity of piezoelectric antenna by using external circuit. This method makes the piezoelectric antenna combined with roles of high radiation intensity and multiple resonant frequencies without changing the structural size of the piezoelectric antenna. The experimental results show that, compared with the original piezoelectric antenna, the tuning range of the resonant frequency of the piezoelectric antenna caused by the series capacitance and inductance is +13.6 and −24%, respectively. The series inductance will produce new resonance frequency, which provides a new method for the multi-band operation of the piezoelectric antenna. The LLC (series and parallel circuit) composite circuit can increase the number of resonant frequencies of the piezoelectric antenna from 1 to 3, and the S11 at the resonant frequencies are all lower than −10 dB, and the radiated magnetic field of the piezoelectric antenna is increased by 42.3% at least. This method makes the piezoelectric antenna have the dual functions of high radiation intensity and multi-band, which has great significance for broadening the application field of piezoelectric antenna.

This article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18λ0 is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186° and 188° in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S11 ≤ −10 dB) of 2.6% (2.283–2.342 GHz), CP bandwidth of 0.9% (2.294–2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.