Electronic measurement systems in the THz frequency range are often bulky and expensive devices. While some compact single-chip systems operating in the high millimeter-wave frequency range have recently been published, compact measurement systems in the low THz frequency range are still rare. The emergence of new silicon-germanium (SiGe) semiconductor technologies allow the integration of system components, like oscillators, frequency multipliers, frequency dividers, and antennas, operating in the low THz frequency range, into a compact monolithic microwave integrated circuits (MMIC), which contains most components to implement a low-cost and compact frequency-modulated continuous-wave-radar transceiver. This article presents a single transceiver solution containing all necessary components. It introduces a $0.48\,\mathrm{THz}$ radar transceiver MMIC with a tuning range of $43\,\mathrm{GHz}$ and an output power of up to $-9.4\,\mathrm{dBm}$ in the SG13G3 $130\,\mathrm{nm}$ SiGe technology by IHP. The MMIC is complemented by a dielectric lens antenna design consisting of polytetrafluoroethylene, providing up to $39.3\,\mathrm d\mathrm B\mathrm i$ of directivity and half-power beam widths of 0.95∘ in transmit and receive direction. The suppression of clutter from unwanted targets deviating from antenna boresight more than 6∘ is higher than $24.6\,\mathrm d \mathrm B$ in E- and H-Plane.

An E-band Cassegrain switched beam high-gain antenna concept for 5G backhauling systems is proposed in this article. The antenna requirements target the compensation of small misalignments (within ±1 degrees in both azimuth and elevation planes) in E-band backhauling links due to adverse weather conditions or thermal deformations. The intended antenna is able to realize beam-switching operations by using a feed-array architecture based on a 7 × 7 array of cavity-backed magnetoelectric (ME) dipoles, where every element is capable of providing a steering of ±0.33 degrees in both the elevation and the azimuth planes. The ME dipole illuminators combined with a Cassegrain reflector provide a gain of 52 dBi within the whole scanning range. Besides, they can be easily integrable with the front-end modules, thus being an easily implementable and low-cost alternative to other more complex solutions based on horns or lens antennas.

With the increasing demand for smarter antenna design in advanced technology applications, well-designed antennas have been an important factor in enhancing system performance. Most traditional antenna design requires multiple iterations and extensive testing to produce a final product. Machine learning (ML) algorithms have been used as an alternative to predict the optimal design parameters, but the outcome depends highly on the ML model efficiency. With recent development in machine learning algorithms and the availability of data for antenna design, we investigated different machine learning algorithms for optimizing the output strength of three basic antennae by analyzing the signal strength of the antenna for various antenna parameters. Different regression-based ML models were used to learn the behaviors and efficiency of three different antennas and to predict the output strength (S11) for different ranges of frequencies. The experiment compared and analyzed these ML regression algorithms for three different antennas: shot antenna, patch antenna, and bowtie antenna. In addition, the paper also provides comparison of ensemble ML models for performance analysis using the best three ML algorithms from the preliminary study. This study optimizes antenna parameters and quicker and smarter antenna design procedure using ML algorithms as compared to traditional design methods.

This paper presents a broadband Butler-based slant ±45° dual-polarized omni-directional antenna working at the frequency band of 1.69–2.69 GHz for extending wireless communication network capacity in the limited service size. The proposed antenna realizes a 360° full coverage with wider bandwidth in a compact cylinder and increases the network capacity to 6 × 6 MIMO instead of using three traditional 2 × 2 MIMO omni-directional antennas. Theoretical analysis, simulation, and fabrication are conducted to validate the idea of the proposed omni-directional antenna. The measured results show 46% bandwidth with 15 dB return loss, 2.2 dB azimuth null and 8.9–10.5 dBi gain for port-C with 0° phase increment, and 14.1 dB azimuth null and 9.6–10.6 dBi gain for port-L/R (left/right) with ±120° phase increment, respectively.

Modern radar sensors are gaining more and more relevance for several industrial measurement applications. To achieve the required range resolution and measurement accuracy, the use of higher frequencies beyond 100 GHz is beneficiary. A commonly used signal generation concept in fully integrated radar transceivers is to use a fundamental oscillator with subsequent frequency multiplication. Depending on the overall system concept, this type of signal generation suffers from a fundamental feed-through signal which generates false targets in frequency modulated continuous wave operation. Additionally, those unwanted signal components radiated by the sensors might be problematic for legal conformity or electromagnetic (EM) interference compliance. This paper presents a novel concept for frequency filtering dielectric lens antennas, to suppress unwanted signal components at harmonic frequencies based on interference filtering effects. Besides the EM simulations to theoretically prove this concept, multiple prototypes of filtering lens antennas were fabricated by conventional mechanical and additive manufacturing. Using a self-developed, ultra-compact radar sensor, measurements were taken to compare the lens antenna prototypes in terms of filtering performance and how the material characteristics affect the filtering performance. Within these measurements, the successful suppression of false targets caused by fundamental feed-through signals is demonstrated.

In this communication, a compact flower shaped printed antenna for ultra-wideband communication is proposed. The “flower-shaped” structure is capable of transmitting UWB-band signals. The designed antenna exhibits a return loss ranging from 2.3 to 11 GHz with an 8.7 GHz central frequency and has 130% relative bandwidth. The suggested design includes a patch in the shape of a flower with several slots fed by a microstrip line. Multiple slots have been designed for better resonances at lower modes. The antenna is constructed with an FR4 substrate, and a 50 Ω A-type connector feeds it. The optimum dimensions of the designed antenna are 12 × 16 × 1.6 cubic-millimeters and 0.092λ × .12λ × 0.012λ in lambda. The proposed structure also demonstrates stable radiation patterns across the operating bandwidth. The proposed radiator has a high gain of 2.67 dBi, and an efficiency of 85%. It is compact, lightweight, and easy to make. Therefore, it can be used for UWB applications.

In this article, we present a simple, low-cost solution for the gain enhancement of a conventional pyramidal horn antenna using additive manufacturing. A flat, metamaterial lens consisting of three-layer metallic grid wire is implemented at the aperture of the horn. The lens is separated into two regions; namely epsilon-positive and epsilon-near-zero (ENZ) regions. The structure of the ENZ region is constructed accounting the variation of relative permittivity in the metamaterial. By the phase compensation property imparted by the metamaterial lens, more focused beams are obtained. The simulated and measured results clearly demonstrate that the metamaterial lens enhances the gain over an ultra-wide frequency band (10–18 GHz) compared to the conventional horn with the same physical size. A simple fabrication process using a 3D printer is introduced, and has been successfully applied. This result represents a remarkable achievement in this field, and may enable a comprehensive solution for satellite and radar systems as a high gain, compact, light-weighted, broadband radiator.

One of the current trends in the integrated circuit (IC) development is the integration of antennas on-chip or in the package of the IC. This poses challenges in the production testing process of the packaged IC, as the antenna functionality has to be included and at least one of the signal ports cannot be accessed at a conducted manner. In order to measure the reflection coefficient of an integrated antenna, a contactless characterization method (CCM) can be used. In this paper, the practicality of a CCM is assessed, having the application of a cost-effective high-volume testing procedure for integrated antennas in mind. It is shown that the CCM yields accurate results for different imperfections in the measurement setup. Moreover, measurement results around 33 GHz using a connectorized patch antenna are shown, which experimentally verify the validity of using the CCM under near-field conditions.

Phase retrieval algorithm is an effective method to reconstruct the surface distortions for reflector antennas. As the traditional Fourier iterative algorithms usually stagnate at local minima, we previously proposed a global phase retrieval algorithm, named CMAES-HIO, based on the hybridization of hybrid-input-output algorithm and covariance matrix adaptation evolution strategy. We address the problem of selection of the Zernike order used in the phase parameterization for CMAES-HIO algorithm in this paper. By introducing a hybrid evaluation parameter, which combines the algorithm accuracy and time consumption, we utilize the Monte-Carlo method to simulate the algorithm performance under different random surface distortions. Simulation results show that for an unknown surface distortion, a Zernike order of 5 or 6 is probably the optimum for the comprehensive algorithm performance with respect to time and accuracy.

A flexible broadband antenna with high radiation efficiency for the Internet of Things (IoT) applications is presented. The design is based on a U-shaped and a triangular-shaped radiator with two tuning stubs. A 50 Ω coplanar waveguide (CPW) transmission line is employed to feed the antenna. The proposed antenna is fabricated on a flexible substrate from a composite synthesized by mixing natural rubber with SiO2 as a filler. The radiating elements, along with the CPW, are built using a highly conductive woven fabric. Results show that the antenna has a simulated and measured impedance bandwidth of 0.856–2.513 GHz and covers the most commonly used wireless communication standards and technologies for IoT applications. The radiation efficiency of the antenna reaches over 75% throughout the operating frequency band with satisfactory radiation patterns and gain. The flexible antenna was also tested under bending conditions. The presented results demonstrate that bending has a minor effect on the antenna performance within the target frequency range. The measured results show a good agreement with simulations.

A novel 1 × 4 phased array elliptical inverted T-shaped slotted sectored patch antenna with defected ground structure (DGS), resonate at proposed ultra-wide tetra band at 28, 43, 51, and 64 GHz with high gain and beam-steering capabilities is presented. An inverted T-shaped slotted stub is used with the sectored patch to achieve ultra-wideband properties. In order to resonate the antenna at four different bands, DGS of round bracket slot is etched on the ground. The 1 × 4 phased arrays are used at the top edge and bottom edge of mobile PCB with high gain. The simulation results show that the antenna has four ultra-wide bands: 25.8–29.7, 40.6–44.6, 49.2–53.1, and 62.2–74 GHz with a maximum gain of 16.5 dBi at 51 GHz. The phased array antenna is capable to steer its main beam within ±30° at the 26, 28, and 43 GHz, using appropriate phase shifts of each antenna element. The proposed millimeter wave antenna is particularly suitable for cellular infrastructures and can be a candidate for emerging 5G mobile applications. The availability of an additional 11.8 GHz (62.2–74 GHz) of contiguous unlicensed spectrum will allow the launching of new exciting wireless services.

This paper deals with a near-field to far-field transformation able to predict the radiation of UHF antennas located over a lossy ground. From in-situ near-field measurements, an equivalent set of dipole sources is obtained as a model of the characterized antenna. The paper details the main steps of the transformation and describes the specific experimental set-up designed for the application. Simple directional antennas (monopoles array) as well as more complex omnidirectional antennas (like a biconical antenna as a scaled-down model of a HF antenna) have been tested in realistic environments. This approach is very efficient for separating the contributions of the radiated waves: the sky wave and the surface wave.

In this paper, a flexible CPW fed ultrawide band (UWB) antenna with mu-negative (MNG) metamaterial is designed, fabricated, and tested for wearable applications. Initially, a UWB antenna of size 50 mm × 43 mm is fabricated on two different substrates, viz. flexible FR4 and semi-flexible Rogers RT/duroid 5880. A metamaterial structure fabricated on flexible FR4 shows a magnetic resonance from 7.2 GHz to 9.2 GHz with maximum stop band attenuation (−49 dB) and high MNG value (−2121.6) at 7.87 GHz. Then a (3 × 3) array of designed MNG metasurface is used as ground plane with flexible UWB antenna, which improves its overall gain and radiation pattern. The performance of the flexible antenna with/without metamaterial at various distances from flat and cylindrical three-layered human phantom of skin, fat, and muscle is studied. Further, the bending characteristics at different angles and performance over thin metallic sheet is also evaluated. Additionally, the peak specific absorption rate value averaged over 1 g of tissue at three chosen frequencies from UWB range (3, 5, 10 GHz) with/without metamaterial using 0.3 and 0.1 W of input power is also analyzed. The simulated and measured results are in good agreement which confirms that the designed antenna is a good candidate for wearable applications.

This paper describes the design and characterization of a compact substrate integrated waveguide (SIW) fed antenna for the 122 GHz industrial, scientific, and medical band. The use of a single RO4350B substrate layer and the SIW feeding ensure a low-cost fabrication. Two versions of the antenna are presented differing in antenna gain and size. For measurement purpose, a transition from rectangular waveguide to SIW is introduced. Measurements of the radiation pattern have been performed and show good agreement with the numerical results for both antennas and an antenna gain up to 7.14 dBi.

Though compact polarimetric approaches have been developed and applied in space and geo researching systems they have not been taken into consideration in automotive applications, yet. A sensor system has been designed to conduct polarimetric measurements in the 77 GHz frequency band, which is permitted for automotive usage. This system is able to transceive linearly as well as circularly polarized electromagnetic continuous waves. Depending on the case of application, the frequency output can be set statically or modulated over time within adjustable parameters. Hence, a variety of compact polarimetric modes can be performed and compared with full polarimetric approaches. Two compact polarimetric modes, dual-circular polarimetric mode, and circular-transmit-linear-receive, will be introduced and applied in this contribution. Their operability in this frequency range will be investigated after the microstrip antennas as well as the beam focusing dielectrical lense are characterized. Finally, results of a realistical measurement set-up will confirm the practicability of compact polarimetric approaches for double bounce recognition.

The paper describes the design and development of a low profile wide scanned conformal active 1 × 32 phased array antenna for Ku-band SATCOM applications. The realized antenna is diagonally polarized and covers full transmit frequency band (i.e. 13.75–14.5 GHz) of Ku band SATCOM. All the developed sub-systems of the antenna, i.e. conformal radiating array, conformal transmit module, manifold network, and beam steering unit are described. The VSWR of the antenna is better than 1.65 over the complete transmit frequency band. The antenna has the beam steering capability of ±60° in the array plane. Designed antenna is best suited for airborne applications, where antenna profile contributes considerable aero drag and RCS to the host platform.

In this paper, a compact wideband tightly-coupled dipole antenna array has been developed. Dipole elements are placed in the triangular lattice to reduce the side lobe level in the radiation pattern of one of the planes. To obtain the initial dimensions, 1-D infinite array analysis of the proposed array is carried out. The infinite array is designed to operate in 5–14.3 GHz (96.3% impedance bandwidth) frequency band. The antenna array can be used in C and X band applications. Inter-element coupling is utilized to achieve ultra-wideband performance in the proposed array. A 2 × 8 elements finite array is designed with the feed network. An ultra-wideband parallel strip to microstrip transition is used to feed the array elements. A metallic shielding for the feed network helps in reducing the back lobes. The overall size of the array with the reflector and the feed network is 148 mm × 224 mm × 54.5 mm. To validate the proposed concept, the antenna array is fabricated and tested. Impedance bandwidth of 2.8:1 along with broadside radiation pattern throughout the band of interest is observed.

The measurement accuracy of low-frequency narrow-band antenna is heavily influenced by its environment, which is also difficult to remove the clutter with a time gating. This paper proposes a method to improve the measurement accuracy of low-frequency narrow-band antenna using signal processing technique. The method is to predict the unknown value out of received original signal with an auto-regressive model (AR model) based on modern spectral estimation theory, and the parameters in AR model are calculated by maximum entropy spectral estimation algorithm. Thus, a wideband signal compared with the original band is obtained, and then the time-domain resolution is enhanced. The time gating is more exactly to separate the antenna radiation signal from multipath signals. The simulation and experimental results show that about 50% extended data for each ends of original band can be obtained after spectral extrapolation, and the time-domain resolution after extrapolation is twice than the original narrow-band signal, and the influence of measurement environment can be eliminated effectively. The method can be used to improve accuracy in actual antenna measurement.