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.

With the rapid development of communication technology, the researches of multi-band filtering circuits have become more and more important. Multimode resonator (MMR) is one of the vital methods to provide multi-resonant modes within a single design. In this paper, a dual-band ultra-wideband bandpass filter (UWB-BPF) using stepped impedance stub-loaded resonators (SI-SLR) is presented. The main advantage of using SI-SLR is to have better performance with multimode behavior and more parameters to control resonant modes. SI-SLR combines the advantages of SIR and SLR structures, which gives a compact, high-performance multiband filter. The proposed filter design has compact size, sharp and flat response with low insertion loss (IL), low return loss (RL), and high band-to-band rejection. The filter is designed for UWB communication in wireless body area networks and fabricated on Arlon substrate with relative permittivity ${\varepsilon_{\textrm{r}}} = 3.25$, thickness $0.8\;{\textrm{mm}}$. The resulted dual-bands are centered at $4{\textrm{ GHz}}$ and $8.3{\textrm{ GHz}}$ with fractional bandwidths $37{\textrm{% }}$ and $48{\textrm{%}}$. The simulation was carried out using CST Microwave Studio. The filter provides good passband performances, with IL 0.49 dB and 0.31 dB at the center frequency of lower and higher bands, respectively. The band-to-band 40 dB rejection is realized by adding circular spiral at the input/output of the filter.

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.

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.

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 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, the patch-type frequency selective surfaces (FSS) based on substrate-integrated waveguide (SIW) technology is proposed to improve the bandwidth (BW) and angular performance. The proposed FSS configuration overcomes the limitations of both conventional 2D and 3D FSS structures. A closely coupled cascaded mechanism is employed to combine two identical FSS elements separated by thin dielectric substrate results in incorporation of SIW technology; hence, named as 2.5D FSS. A derived equivalent circuit model is used to estimate the basic performance of proposed FSS–SIW elements, and the response of analytical expressions has been validated and final design is obtained using full-wave simulations. Two basic FSS elements viz. single square loop and a Jerusalem cross have been investigated to prove the enhancement in their BW and angular stability. The proposed technique evidently improves the BW and angular stability of FSS structures than in its established form. Besides, various important parameters that influence the performance characteristics of reported 2.5D FSSs are also studied. The important observations made on the thickness, as the thickness increases the bandstop FSS, can change to bandpass FSS. Finally, the proposed FSS structure has been fabricated and measured using free space measurement setup, to show the effectiveness of theoretical results. The measured results show good agreement with simulated results at normal and oblique incidence angle.

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.

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.

A planar inverted F-Antenna with the dual band-dual polarization property is presented for medical body area networks applications. The designed antenna covers the 2.45 GHz industrial, scientific and medical, 4 G long term evolution (2.5–2.69 GHz) bands for ON body communication and Wi-Fi and WLAN (3.5–3.6 GHz) bands for OFF body communication. At the lower band, an equivalent offset fed magnetic microstrip type dipole has been utilized that generate field parallel to the surface of the body for supporting ON body communication. The broadside radiation pattern has been realized using the slotted patch counterpart for supporting OFF body communication. This technique has resulted in a design of dual band dual mode property using a single radiator. The footprint of the antenna is only 0.35λg × 0.17λg × 0.08λg. Owing to its compactness, lightweight, and easy mountable property (due to foam substrate), the proposed antenna is found to be robust for MBAN applications. The maximum permissible transmitted power for the 1st band is 25.78 and 20.3 dBm for the 2nd one to maintain standard specific absorption rate limitations of 1.6 W/Kg. Experimental investigations over human body showed minimal deviations from the free space conditions which makes it a potential candidate for body-centric communications.

Frequency- and time-domain characteristics as well as indoor propagation channel impulse response of a compact dual band-notched ultra-wideband (UWB) slot antenna are investigated in this paper. The antenna consists of a narrow rectangular radiation patch and a rectangular wide slot in the modified ground plane. A pair of L-shaped stubs are connected to the radiation patch to obtain band-notched property in WLAN band and a narrow straight stub is placed on the back side of the substrate to create band-notched characteristics in X-band downlink satellite communication system. Moreover, two small parasitic strips are added to the radiation patch to enhance the bandwidth (BW) of the antenna up to 14 GHz. A comprehensive study on time-domain and indoor propagation channel characteristics of the proposed antenna is also presented throughout the paper. A ray-tracing approach based on geometrical optics is applied to analyze the indoor channel characteristics. The designed antenna not only has a wide BW and compact size but also has appropriate radiation and time-domain characteristics over the antenna operating BW. The measured and simulated results are in good agreement. These advantages make the proposed antenna as a desirable option for UWB impulse radio applications.

In this work, an UWB/narrow band reconfigurable elliptical-shaped monopole antenna for cognitive radio applications with sequential perception and operation modes is presented. The proposed approach consists in integrating a reconfigurable filter, in an UWB antenna ground plan, by the mean of four horizontal slots and integrated switches that allow inserting/removing/varying zeros and poles in the frequency response. By acting on the slot lengths in order to alter their resonance frequencies, the different switch configurations allow the antenna to switch between an UWB mode that could be used for the perception (sensing) and different narrowband modes, mono-band and dual-band, that could be used for the operation at 2.4 or/and 3.5 GHz. To validate the concept, an experimental prototype has been fabricated and a good agreement between the simulated and the measured S-parameters has been obtained. While the presented work uses the presence/absence of a perfect conductive strip (PEC) to model real switch operation, it is believed that the obtained results conjugated with previous work using real switches on a very similar structure allows validating approach.

In this study, a new microstrip patch antenna with wideband radar cross-section (RCS) reduction is presented. The RCS of the proposed antenna was reduced by subtracting the current-direction slots of the patch, with the radiation performance sustained not only for the current-direction subtraction, but also for the no modification in the ground plane. Modified and reference antenna were fabricated and measured. The simulation and measurement results showed that the modified antenna reduced the in-band and out-band RCS simultaneously with no detriment to the radiation performance. In the frequency band from 3.9 to 8.1 GHz, the RCS of the modified antenna was reduced in the whole band compared with the RCS of the reference antenna. The maximum RCS reduction was 7 dB at a frequency of 6.7 GHz.

This paper aims at investigating the dependence of the impedance and the radiation characteristics of a cylindrical dielectric resonator antenna (DRA), on the feed point of the DRA. It is demonstrated that the resonant frequency, bandwidth, radiation pattern symmetry, and cross-polarized radiation levels depend highly on the feed point. Three standard single-ended feed mechanisms such as the microstrip line, the microstrip slot, and the coaxial probe are taken as examples, to demonstrate the feed-point dependence of the DRA performance. Standard commercial EM simulation tools (ANSYS HFSS and CST Microwave Studio) are used for generating insightful results to help the discussion. This analysis also provides a functional comparison among the above said three feed mechanisms with respect to the feed-point dependence, which is further verified through measurements of DRA prototypes employing the three feeds.

In this paper, we present a novel dual-band wearable compact flexible antenna for body-centric wireless communications (BCWCs). The design is based on a modified planar dipole with parasitic elements, meandered lines, and a rectangular reflector embedded into a hydrophobic rubber-textile multilayer substrate in order to get both good antenna performance and mechanical properties. The antenna's structure is analyzed and optimized in free space (FS), on a numerical and an experimental homogeneous flat phantom. The overall dimensions of the antenna are 50 mm × 40 mm × 4.6 mm and a prototype mass of 11 g, which makes it suitable for practical applications in BCWCs. The built prototype resonated at 2.47 GHz with a |S11|−26.90 dB and at 5.42 GHz with a |S11|−24.60 dB in the FS. The measured bandwidths are 500 MHz (2.2–2.7 GHz) and 1000 MHz (4.65–5.75 GHz) at lower and higher bands, respectively. The antenna exhibits a measured maximum gain of 1.17 dBi at 2.66 GHz and a radiation efficiency of 28.44% in FS. The 10 g average maximum specific absorption rate is 0.165 W/kg at 2.70 GHz and 0.520 W/kg at 5.24 GHz when the antenna is placed on the numerical phantom at net input power 0.1 W.

In recent years, millimeter wave (MMW) has received tremendous interest among researchers, which offers systems with high data rate communication, portability, and finer resolution. The design of the antenna at MMWs is challenging as it suffers from fabrication and measurement complexities due to associated smaller dimensions. Current state-of-the-art MMW dual-band antenna techniques demand high precision fabrication, which increases the overall cost of the system. Henceforth, the design of an MMW antenna with fabrication and measurement simplicity is quite challenging. In this paper, a simple coplanar waveguide (CPW) fed single-band MMW antenna operating at 94 GHz (W band) and a dual-band MMW antenna operating concurrently at 60 GHz (V band) and 86 GHz (E band) have been designed, fabricated, and measured. A 50 Ω CPW-to-microstrip transition has also been designed to facilitate probe measurement compatibility and to provide proper feeding to the antenna. The fabricated single frequency 94 GHz antenna shows a fractional bandwidth of 11.2% and E-plane (H-plane) gain 6.17 dBi (6.2 dBi). Furthermore, the designed MMW dual-band antenna shows fractional bandwidth: 2/6.4%, and E-plane (H-plane) gain: 7.29 dBi (7.36 dBi)/8.73 dBi (8.68 dBi) at 60/86 GHz, respectively. The proposed antenna provides a simple and cost-effective solution for different MMW applications.

A coplanar waveguide slot antenna is herein presented. A rectangular slot is excited by a Y-shaped monopole etched on a single FR4 substrate. This structure exhibits two resonances due to the presence of the slot and the central monopole which can be used to design a dual-band or a wideband antenna. A parametric analysis is presented to describe the impedance matching mechanism for the two impedance bandwidths (BWs), as well as for the wideband antenna. The latter is fabricated and provides a measured impedance BW from 2.28 to 3.6 GHz, and gain larger than 2 dBi, yielding an outstanding BW/size trade-off. Finally, a 60 mm × 60 mm back metallic reflector is used to achieve a directive antenna with 6 dBi of measured gain, and an impedance BW from 2.16 to 3.59 GHz.