This work presents a passive intelligent surface designed at 2.45 GHz that has the capability of transmitting and reflecting electromagnetic waves that are incident upon it. The proposed surface does not require any circuitry or power source to function. Therefore, it makes a cost-effective and simple intelligent surface. It is a simple metallic structure that has embedded waveguide slots on its surface, allowing the waves to couple for transmission. A prototype of the proposed surface is designed using an aluminum foil and analyzed for both transmission and reflection of the wave. Further, the designed surface is investigated for tuning the directionality of the radiated field from the antenna. For this purpose, a coplanar patch antenna is first designed and then combined with the surface to tune the directionality of the radiated field of this antenna. The outcome of the measured performance validates that the proposed surface has the potential capability of field reconfiguration in wireless communication for Wi-Fi, WLAN, and Bluetooth applications.

In this paper, a capsule endoscopy system with a sensing function is proposed for medical devices. A single-arm spiral antenna is designed for data transmission and is combined with the voltage controlled oscillator to achieve sensing capabilities. The designed antenna operates at a 900 MHz industrial scientific medical band. By establishing a three-layer cylindrical model of the stomach, it was concluded that the antenna in the stomach has a high peak gain of −1.1 dBi. Additionally, the antenna achieved a −10 dB impedance bandwidth of 5%. The capsule endoscopy was experimentally measured in both actual stomach and simulated environments. The maximum working distance of the capsule endoscope was measured to be 6.8 m. Additionally, the proposed capsule endoscope was tested for its sensing function using solutions with different dielectric constants. Finally, it was confirmed through link analysis that it has good communication capabilities. The results and analysis confirm that the proposed capsule endoscope can be used for examining gastric diseases.

This paper presents a dual-band bandpass filter with regular harmonic suppression. The proposed third-order filter consists of two microstrip stepped impedance resonators and single substrate integrated waveguide resonator. The mismatches in their higher order resonant frequencies are utilized to suppress the regular harmonics. The passbands are centered at f1 = 2.4 GHz and f2 = 3.5 GHz with fractional bandwidths of 5% and 7.5%, respectively. The measured midband insertion and return losses are better than 2.55 and 14.5 dB for the first, whereas for the second band, they are better than 1.95 and 14 dB. The filter offers at least 33 dB suppression of first three higher order regular harmonics of f1 and f2.

This paper presents the design and analysis of a compact eight-port multiband multiple-input–multiple-output (MIMO) antenna for 5G smartphones. The proposed antenna structure is designed using meandering elements, as radiator, on the FR4 substrate of 150 × 80 × 0.8 mm with loss tangent (tan δ) of 0.02 and relative permittivity (εr) of 4.4. The proposed antenna resonates at 2.4, 3.5, and 5.5 GHz, and it covers the bandwidth of 2%, 6.28%, and 2.53%, respectively. The measured results provide an omnidirectional radiation pattern with 58%–78% of efficiency in all operating bands. The eight-port multiband MIMO design provides a high isolation of 17.5 dB, envelope correlation coefficient < 0.04, diversity gain of 9.98 dB, total active reflection coefficient < −10 dB, and channel capacity loss of <0.25 bits/s/Hz. Also, the hand phantom is designed to analyze the reflection coefficients and efficiency of the proposed antenna.

The accuracy of electromagnetic (EM) exposure assessments depends mainly on the resolution of a voxel human body model. The resolution of the conventional human body model is limited to a few millimeters. In the millimeter wave (mmWave) frequency range, EM waves are absorbed by the superficial tissues in the human body. Therefore, resolution and skin thickness of the human body model are important for accuracy of the EM wave exposure metrics recommended by international human safety guidelines. Realistic thickness modeling of the skin tissue on the human body may provide greater accuracy in the EM exposure assessment, especially at mmWave frequency range. In this paper, effects of the skin thickness on the EM exposure metrics in one-dimensional multi-layered models obtained from different regions of the body model are investigated using the dispersive algorithm based on the finite-difference time-domain method over the frequency range from 1 to 100 GHz. Furthermore, effects of eyelid tissue in a human eye on the EM exposure metrics are studied over the frequency range. The EM exposure metrics such as absorbed power density, heating factor, and power transmission coefficient are calculated up to 100 GHz to evaluate the limits of EM wave exposure.

This paper provides the details of a novel systematic design methodology for two-way in-phase filtering Gysel splitter/combiner networks with high selectivity, which finds application in high power amplifier modules. It simultaneously realizes a filtering function and a two-way splitter/combiner function. The proposed five-port filtering device, based on the Gysel topology, is transformed into a ring of coupled resonators. A rigorous coupling matrix describing the network is used to synthesize the integrated filtering and combining functions. This general network can be implemented in any of the available filter technologies. In this paper, a few design examples are provided, and a six-pole prototype utilizing compact combline coaxial resonators is demonstrated. The proposed design provides an integrated dual function module, reducing component counts and system complexity. A design was fabricated and tested demonstrating good experimental results.

This communication designs and investigates a twin-port microstrip antenna loaded with a metasurface (MS). The proposed MS works in two ways: (i) artificial ground plane for radiator and (ii) as an ideal absorber of normal incoming waves at the same time. A stair shaped slot is loaded on rectangular patch for creating circularly polarized wave in between 835–894 MHz. Antenna port slots oriented in a mirror manner increase isolation by 25 dB. To act as a validation tool, the suggested antenna was built and its executions in individually operating modes evaluated by statistical and experimental analysis. It is shown that combining the patch and absorber results in a well-matched antenna in between 710–980 MHz with improved gain (more than 3.0 dBi). The proposed antenna design effectively used for UHF (Ultra High Frequency)radio-frequency identification (RFID) applications, which is due to its ability to mitigate multipath reflection issues and incorrectRFID reading.

This study intends to provide a comprehensive review of the basic concepts, types, applications, and experimental studies of frequency selective rasorber (FSR) presented in the literature. Analyzing the characteristics of FSR became crucial for future adaptability when taking into consideration of immense development in RADAR, military, stealth, and electromagnetic interference applications. The rasorber was initially conceived as a radome for antennas and it was developed expeditiously in recent years. This survey is focused on evaluating the unit cell design (2D, 2.5D, and 3D), equivalent circuit model, polarization characteristics, fractional bandwidth, insertion loss, absorptivity, bandwidth enhancement for absorption, transmission, and their applications based on the FSR. Various techniques like exploiting lumped elements, magnetic materials, lumped components, dual/triple layer structures, varactor diodes, PIN diodes, and distributed elements (slots and stubs) are used to improve the novelty and performance of the FSR that are discussed in the works of literature. At last, these techniques, bandwidth, structures, and performances are compared based on their relative positions to feature the benefits and limitations.

This paper presents a new topology for a microwave active mixer using compact microstrip diplexer constituted from two dual-mode open loop resonators. The resonators are tuned to the radio frequency (RF) and local-oscillator (LO) frequencies, respectively, to effectively isolate the two input signals, while the diplexer output port is connected to the gate circuit of a commercial low cost GaAs pHEMT transistor. The drain circuit of the active device is connected to the load via an intermediate-frequency (IF)-modified Chebyshev low-pass filter to remove the unwanted RF and LO signals and reduce other spurious frequencies at the output of the mixer circuit. The circuit has been designed and constructed for an RF of 850 MHz, LO frequency of 1050 MHz, and an IF of 200 MHz. Experimental measurements show that the circuit provides a conversion gain of 18 dB at LO drive power of +2 dBm. It also operates satisfactorily over the RF range from 800 to 900 MHz with good image frequency rejection and stable operation.

This paper presents the radio frequency (RF) design and experimental validation of a multifunctional bandpass filtering (BPF) concept with center frequency tunability and RF codesigned isolator and impedance matching functionality. The multifunctional bandpass filter/isolator (BPFI) concept combines frequency-tunable reciprocal resonators and nonreciprocal frequency-selective stages (NFSs) to realize center frequency tunability and fully directional transfer characteristics. The NFS, as the core component of the BPFI concept, exhibits frequency-selective transmission response in the forward direction and signal cancellation in the reverse direction. Its tunability is achieved by combining a transistor-based network with a tunable capacitively loaded coupled-line section. Furthermore, the NFS facilitates matching of different source loads allowing for the BPFIs to be used as reconfigurable matching networks. For experimental validation, an NFS and two BPFIs were designed, manufactured, and measured at L band. Their features include (i) NFS: center frequency tuning from 1.55 to 1.9 GHz with maximum directivity from 20 to 52 dB and gain from 0.3 to 1.3 dB. (ii) BPFI (topology A): center frequency tuning from 1.52 to 1.9 GHz with maximum directivity from 20 to 44 dB and gain from −1.5 to −0.5 dB. (iii) BPFI (topology C): ability to match complex loads with 26 + j18 Ω and 26 − j14 Ω.

We report on the successful implementation of a photonic-based beam steering approach for point-to-multipoint terahertz (THz) communications. The frequency-agile radiation properties of a THz leaky-wave antenna connected to a photodiode are utilized in the remote transmitter for generating multiple individually steerable THz beams. The approach benefits from the ultra-wide frequency tunability of optical heterodyne systems for frequency-agile THz beam steering. Moreover, the approach allows to exploit high performance and mature optical modulation techniques for generating THz beams with a high data capacity. In the THz receiver, a carrier frequency insensitive envelope THz detector based upon a single Schottky-barrier diode is used. In detail, THz communications in the 300 GHz band (WR3.4) with a maximum steering angle up to 90° is reported. Experimentally, for single steerable THz beam operation, a record high data rate of 35 Gbit/s at a wireless distance of 30 cm is achieved using two-level pulse amplitude modulation. Also, longer wireless distances up to 110 cm with 5 Gbit/s are demonstrated. Furthermore, point-to-multipoint THz communications is reported using two individually steerable THz beams carrying 10 Gbit/s and 5 Gbit/s over 70 cm and 50 cm, respectively.

An isolated low-profile multilayer all-ports-matched broadside-coupled balun (BCB) with arbitrary isolation bandwidth is presented. Analytical relations are derived and provided for the isolation circuit (IC) design in terms of electrical and physical parameters. Accordingly, instructions are given on obtaining optimum bandwidth and isolation responses for the IC. Design procedure for the BCB is presented together with a case study for power amplifier application. The BCB is validated theoretically, analytically, and experimentally, and results are in good agreement. The fabricated balun has insertion loss of 0.27 dB, input and output return losses of 19 dB, isolation of 20 dB at fc, and phase and magnitude imbalance better than 2° and 0.2 dB across the Bandwidth (BW), respectively. The realized isolated balun has dimensions of 0.06λg × 0.03λg.

This work introduces a novel compact ultra-wideband (UWB) antenna designed for wearable applications, employing a bioinspired structure and machine learning (ML) techniques to achieve exceptional performance in the 3.10–10.42 GHz range. The antenna is fabricated by positioning conductive fabric on a polydimethylsiloxane polymer of 1 mm thickness to augment high flexibility and durability. Additionally, it pioneers integrating a complete ground plane to mitigate back radiation toward the human body, presenting a compact (35.5 × 30.5 × 1 mm3) UWB antenna design compliant with IEEE 802.15.6 standards. The design methodology includes using bandwidth enhancement techniques such as chamfering edges, slots, and adding stubs in the feed, along with applying ML to optimize the antenna’s dimensions for desired return loss characteristics. The proposed antenna demonstrates exceptional resilience to human body loading and physical deformation. The simulation and measurement results have good agreement. The K-nearest neighbour method beat the other ML algorithms maximum accuracy of 99.62% to predict the S11. According to the author’s best knowledge, this is the first compact UWB antenna with full ground specified by IEEE.802.15.6 with ML reported.

With the development of the communication field, more and more communication devices need multiple single-frequency antennas to work simultaneously. However, using multiple single-frequency antennas results in larger sizes. The miniaturized and dual-band communication system has become a new development trend. This paper designs a dual-band filtering patch antenna based on a multimode resonator, which is cascaded. The filter resonator part adopts step impedance resonance for branch shunt design, which can flexibly control the center frequency of two frequency bands. The filtering antenna utilizes a dual-layer substrate structure and achieves an integrated design through coupling probe feeding. This reduces the horizontal dimensions and improves miniaturization. Multiple radiation nulls are introduced outside the two-passband, and roll-off characteristics are evident. In addition, this design realizes high selectivity in the operating band. The antenna has large gains of 1.71 dBi and 6.25 dBi. It has good filtering and radiation characteristics.

This research proposes an inexpensive technique for wireless image transfer for security and surveillance applications. The technique uses a 5.8 GHz transmitter and receiver module, along with external antennas in the real-time image transfer within a radius of 100 m. The transferred images are stored in a laptop using a Python code-based graphical user interface application. Different antennas, dipole, circular split-ring resonators, hexagonal split-ring resonators, and metamaterial antennas are utilized for comparison. The Blind/Referenceless Image Spatial Quality Evaluator method is used to assess the picture quality of transferred images to quantify image transfer performance when no ground truth or reference photos are supplied. According to the presented results, images transferred using metamaterial antennas have higher quality than those transferred with other types of antennas. For security considerations, such a system can communicate and store the images in real time.

A 3D-printed polarization-independent low-cost lightweight and flexible frequency selective surface based dual-band microwave absorber is presented in this paper. Two concentric square loops fabricated at different heights using 3D printing technology are responsible for exhibiting dual-band responses at 3.32 GHz (S-band) and 5.46 GHz (C-band) with more than 97% absorptivities. The corresponding full widths at half maximum bandwidths are observed as 230 MHz (3.21–3.44 GHz) and 450 MHz (5.27–5.72 GHz). The proposed topology is polarization-insensitive owing to the four-fold symmetry. The absorption phenomenon is explained with the analysis of current distributions at the surface and impedance curves at the frequencies of resonance. Further, the performance has been evaluated for both planar and curved surfaces with different angles of curvature, and the good agreement between the measured and simulated responses confirms the flexible behavior of the proposed structure.

A novel metasurface offering polarization conversion characteristic in five bands is studied and developed in this paper. To provide the anisotropic feature to the structure, a diagonally placed tapered rod is combined with two semicircular stubs. Due to the controlling ability to convert horizontal to vertical polarization and vice versa, and linear to circular polarization (CP), it serves as a multifunctional polarization converter. Simulation results suggest that the proposed polarizer functions as cross polarizer over 4.74−5.12 and 9.12−13.48 GHz. Additionally, it exhibits a distinct type of rotational sense across 4.24−4.68, 5.24−8.64, and 13.72–15.14 GHz in its linear to CP conversion behavior. The axial ratio of the polarizer is well below 3 dB throughout overall CP bands due to the minimum tolerance level in reflection phases with respect to acceptable limits. Moreover, it is noticed that the sense of CP is left-handed in the first band while right-handed in the remaining two bands. Thus, the suggested polarizer has potential to be integrated with antennas for satellite, defense, industry applications for getting the desired type of polarization in the distinguished bands.

In this article, a low phase noise signal source to be used as local oscillator in pulse Doppler radio frequency (PDRF) sensor is proposed. Innovative design techniques for realization of the low phase noise frequency source using phase-locked loop (PLL) and dielectric resonator (DR) are presented. Qualitative investigations have been carried out on the effect of phase noise in PDRF sensor performance. An X-band vibration resistant PLL-based frequency source with phase noise better than −95 dBc at 1 kHz frequency offset has been designed here. It also presents the design of a 7.6 GHz low phase noise, vibration resistant DR oscillator. Systematic analysis of the key design aspects, their thermal-vibrational stability, and ease of integration with hybrid microwave integrated circuits have been disclosed. A prototype board is fabricated, assembled in a compact mechanical enclosure of dimension 55 × 55 × 15 mm3. Finally, developed module is experimentally validated under 7.6 g rms magnitude random vibration test in three axes and compared results with other state of-the-art similar works. The comparison clearly shows the merit of present research work over other similar existing works.

Liquid crystal microwave phased arrays (LC-MPAs) are regarded as an ideal approach to realize compact antennas owing to their advantages in cost, size, weight, and power consumption. However, the shortcoming in low radiation deflection efficiency has been one of LC-MPAs’ main application limitations. To optimize the steering performance of LC-MPAs, it is essential to model the channel imperfections and compensate for the phase errors. In this paper, a phase error estimation model is built by training a neural network to establish a nonlinear relationship between the near-field phase error and the far-field pattern, hence realizing fast calibration for LC-MPAs within several measured patterns. Simulations and experiments on a 64-channel, two-dimensional planar antenna were conducted to validate this method. The results show that this method offers precise phase error estimations of 3.58° on average, realizes a fast calibration process with several field-measured radiation patterns, and improves the performances of the LC-MPA by approximately 4%–10% in deflection efficiency at different steering angles.

This paper proposes an air-filled substrate integrated waveguide (AFSIW) bandpass filter with a miniaturized non-resonant node (NRN). The NRN structure is introduced between the three resonators, and its size is smaller than the resonator size, which can realize the NRN structure’s miniaturization and reduce the model’s size. The NRN size of this filter is 41% of the NRN size of the existing AFSIW filter. This filter also introduces a transmission zero (TZ) above the passband. The measured results show that the filter’s center frequency is 20.73 GHz, and the bandwidth is 0.86 GHz. The insertion loss in the passband is 0.95 dB, and the return loss is better than 23 dB. Due to the TZ in the upper stopband, the AFSIW filter obtained good selectivity.