This paper proposes and demonstrates a compact integrated filtering antenna built on a square ring resonator coupled with a capacitors loaded microstrip line filter. A microstrip filter module is connected to feeding line of the conventional patch without adding extra space. Thus, the combined configuration possesses radiating and filtering functions simultaneously. The proposed filtenna has a fractional bandwidth (FBW) of 3% at center frequency 2.4 GHz with 2.5 dB of maximum gain. The obtained result shows that the proposed design shows good stopband gain rejection, good selectivity at band edges, and smooth passband gain. Furthermore, the introduced filtenna has advantages of a small size and a simple structure, which makes it ideal for interconnection with different wearable devices operating within 2.4 GHz wireless system range.

A wide locking range injection locked frequency divider (ILFD) with a low power consumption for 60GHz applications is presented. The locking range of the ILFD is enhanced by reducing the parasitic capacitances of the transistors. The cross-coupled transistor and injected transistors are integrated to become a compact structure, which exhibits simple routing and induces less parasitic capacitances. To verify the proposed structure, the ILFD was fabricated using 65 nm CMOS technology. It has a measured locking range of 55.3 GHz to 67 GHz (19%) with 0 dBm input power. The circuit dissipates 1.98 mW at 0.5 V supply voltage without the output buffers.

We report the second-harmonic generation (SHG) from single GaN nanowire. The diameter of the GaN nanowire varies from 150 to 400 nm. We present a model for the SHG process in the GaN nanowire; the analysis shows quantitatively that the SHG is dominated by its surface area. The effective second order nonlinear optical susceptibility (χ⁽²⁾_eff) increases as the diameter of the GaN nanowire decreases. For 150-nm diameter GaN nanowire, χ⁽²⁾_eff reaches 136 pm/V.

In this paper, a wideband metasurface reflector that converts polarization of plane wave to the cross polarization with a double-square-shaped unit cell is presented, and the principle of polarization conversion based on polarization synthesis is also presented. The proposed structure has a unit cell with the longest dimension of 0.37 wavelength, a width of 0.23 wavelength, and a thickness of about 0.09 wavelength. 95% or more of the incident wave power is converted to cross-polarization covering a fractional bandwidth of 32.4% at 8.5 GHz.

A double-layer frequency selective surface (FSS) with dual rings is used as a reflector in the design of an Archimedean spiral antenna (ASA) with low radar cross section (RCS) and uni-directional characteristics. The proposed FSS presents a stopband in the range of 2 GHz to 4.7 GHz, which is applied to ASA to form a unidirectional radiation pattern with front to back ratio (FBR) values larger than 10 dB in the stopband, and the maximum FBR value is up to 25.26 dB. Compared with the reference antenna with the same-size metallic ground, the proposed FSS reduces the RCS about 2.5-38 dB in the frequency ranges of 4.8-30 GHz. And the FSS antenna also exhibits better axial ratio characteristics in the frequency range of 2.8-8.1 GHz. The composite structure is compact, with a total height of 0.18 wavelength at the lowest analysis frequency of 2 GHz. Measured results indicate that the proposed antenna reproduces the inherent wideband of the original ASA from 1.6 GHz to 8.1 GHz. Meanwhile, the gain of the ASA is increased by 3 dBi. Full-wave simulations and measurements prove that the novel FSS reflector can be employed to replace a metallic ground which realises a uni-directional ASA with broadband low RCS, high gain and good circular polarization (CP) performance.

A new miniaturized and ultra-thin non-resonant element-class of convoluted frequency selective surface (FSS) structure with reduced overall thickness is presented and empirically verified. The proposed FSS structure, which could be capable of providing a first order narrow band pass response for X band applications, is made up of three metallic layers separated from one another by two dielectric substrates. The outer layers are made up of convoluted inductive grids， and the inner layer is a non-resonant structure composed of convoluted square slot array. A first-order band pass response FSS with a centre frequency of 10.5 GHz and fast roll-off characteristics is presented. The overall element thickness of the proposed FSS is λ/56, which is smaller than previously proposed miniaturized structures. The comparison between all patch layers with the proposed structure which is not an all patch layers is explicated in detail with its convoluting effects. The validity of this design procedure is verified with an equivalent circuit model, and a sample is fabricated and measurement done using a WR 90 waveguide setting for experimental verification.

In this paper, a new super-resolution and highly stable DOA estimation technique of coherent sources is introduced. Furthermore, the proposed technique is applied to the data collected from the AWR1243 mm-wave 76-81 GHz frequency modulated continuous wave (FMCW) radar to estimate the DOAs of real targets. A virtual antenna array is proposed to increase the array aperture size and the dimension of the data covariance matrix which effectively helps in de-correlating the received signals and in increasing the number of detectable sources and hence improving the detection resolution. Moreover, a significant improvement in the DOA estimation capability is achieved by handling the frequency domain of the received signals instead of their time-domain representations. That is because the signal to noise ratio (SNR) is increased by a multiplication factor when it is transformed using FFT which acts as a filter for the noise. The simulation results proved the superiority of the proposed technique compared to the state of the arts in this field, especially at low SNR that approaches -35 dB.

A new class of the wideband series-fed microstrip array antenna is presented for X-band applications. A novel configuration of the reflector-slot-strip-foam-inverted patch (RSSIP) is proposed to provide high efficiency and wide operating frequency band. To improve the front to back ratio (FBR) and enhance the gain, a reflector is used. The series-fed configuration is selected for the array to simultaneously provide a very high efficiency and reduce the side lobe level. To experimentally verify the performance, a prototype of the array antenna is fabricated, and measurement is performed. This array consists of 12 sub-linear arrays with series-fed microstrip excitation. Also, each of these subarrays consists of 16 RSSIP antennas. An excellent agreement exists between measurement and simulation. The measured gain and efficiency of the fabricated antenna are 28.5 dB and 67% at 10 GHz, respectively. The measured impedance matching bandwidth (S₁₁<-10 dB) is 24% which confirms the wideband characteristic of the antenna. The series-fed configuration results in very low measured SLL of -24.5dB at H-plane. The proposed 16 x 12 array antenna is a proper candidate for applications in MIMO systems and synthetic aperture radars (SAR).

Double Elliptical Micro-strip Patch Antenna (DEMPA) is a newer family of patch antennas which possesses higher design flexibility and has greater potential for getting miniaturized than Elliptical Micro-strip Patch Antenna (EMPA). The DEMPA is made out of a Double Elliptical Patch (DEP) which is designed as a combination of two half-elliptical patches either with a common minor axis and two different semi-major axes or with a common major axis and two different semi-minor axes. There are only two design parameters for an EMPA, its semi-major axis and semi-minor axis, whereas a DEMPA has three because of either two different semi-major axes or two different semi-minor axes. A parametric study is required to understand the relationship among these three design parameters and antenna characteristics such as return loss, impedance, resonant frequency and gain. The present work is a statistical study, using the concept of Design of Experiments (DOE), of the impact of these design parameters on the return loss at resonant frequency within the frequency band of 8.50 GHz-10.55 GHz which has been earmarked for radiolocation applications by regulating agency. The Central Composite Design (CCD) technique in the Response Surface Methodology (RSM) of DOE has been employed here to develop empirical relationship between the design parameters and response variable. Numerical models were developed using Ansoft's HFSS as per the design matrix provided by Minitab. The concept of DOE helped to establish statistically significant parametric relationship between the design parameters and antenna return loss with the minimum amount of design effort. The predictive ability of regression model was confirmed by using numerical models of two DEMPAs that were not utilized to build the empirical relationship, one among which had been fabricated, tested and reported in literature.

In order to reduce the cost and blindness of antenna design, the application of electromagnetic field similarity principle in the working environment of underwater receiving antenna was studied and verified. The field distribution and electrical parameters of the underwater receiving antenna and its reduced-scale model were calculated and proved to be in accordance with the similarity principle. The simulation analysis of the receiving antenna and its reduced-scale model for receiving the airborne electromagnetic wave signal in the seawater shows that the underwater receiving antennas before and after the scale-down are similar. The simulation is verified by measuring the receiving signal amplitude of the underwater receiving antenna and its reduced-scale model. The results of theoretical derivation and simulation analysis show that the electromagnetic field similarity principle can be applied to the underwater receiving antenna system.

In this paper, two different architectures based on fully and partially clustered arrays are proposed to optimize the array patterns. In the fully clustered arrays, all the elements of the original array were divided into several equal subarrays, while in the partially clustered arrays, only the side elements were grouped into subarrays, and the central elements were left individually. The second architecture enjoys many advantages compared to the first one. The proposed clustered arrays use quantized amplitude distributions, thus, their corresponding patterns were associated with high side lobes. To overcome this problem, a constraint mask was included in the pattern optimization process. Simulation results show that the peak sidelobe level and the complexity of the feeding network in the partially clustered arrays can be reduced to more than -28 dB and 70.833% respectively, for a total of 48 array elements, number of individual central elements = 24, number of clusters on both sides of the array Q = 4, and number of elements in each side cluster M=6. Finally, the principles of the proposed clustered arrays were extended and applied to the two dimensional planar arrays.

The aim of this work is to discuss the possibility of resistive thin-film coatings used for vacuum electron devices. Following a short review, results on radiophysical parameters studies in millimeter-band of such coatings are presented. Resistive Sn-O coatings with varied oxygen content were fabricated on quartz substrates by reactive magnetron sputtering. Morphology and elemental composition of prepared coatings were studied by means of scanning electron microscopy and secondary ion mass spectrometry, while four-probe method was utilized to study the resistivity of those. Dielectric properties were measured in the V-band (50-70 GHz) in free space using vector network analyzer. It was demonstrated that resistivity and the dielectric properties of coating in millimeter-band can be widely varied by controlling coating composition.

This letter presents a uniplanar two-port UWB-MIMO antenna with high isolation for wireless communication applications. The designed antenna is composed of a single metal layer and a thin substrate. The single metal layer acts as radiators and a ground plane. The radiator of each element consists of a modified dual-L-shaped feeding structure and a defected rectangular patch, which is shared by the ground plane. The modified dual-L-shaped feeding structure is introduced to broaden the bandwidth. Furthermore, two fork-shaped slots and bent slots are embedded in the rectangular shared structure for further improving the bandwidth and decreasing the mutual couplings without any other additional decoupling structures. The experimental results show that the proposed antenna achieves the ultra-wide impedance bandwidth (3.0-12.4 GHz), high isolation ( > 20 dB at entire impedance bandwidth), very small ECC (< 0.01), high multiplexing efficiency (> -1.9 dB), stable realized gain and radiation patterns. Therefore, the designed antenna is suitable for most wireless UWB communication applications.

In this paper, a planar, compact, and low cost printed microstrip line fed pentagon-shaped ultra-wideband antenna offering dual band notched characteristics response is proposed and investigated. By introducing modified V-shaped slots in the pentagonal patch and hexagonal electromagnetic band gap structures near the feedline, dual band notched response can be realized. The proposed antenna is successfully simulated, designed, and fabricated on an FR-4 substrate. The measured results show that the proposed antenna having dimensions of 35 × 33 × 1.6 mm³ has a bandwidth over the frequency band 2.7-10.6 GHz with magnitude of S₁₁ ≤ -10 dB (VSWR ≤ 2), except 3.7-4.6 GHz (C-band Satellite Communication) and 5.16-6.08 GHz (WLAN) frequency bands. The presented antennas show small group delay variation, nearly omnidirectional radiation pattern and stable gain at working frequencies. Satisfactory results have been obtained in frequency and time-domain analysis of the proposed antenna. The formulation of the center frequency of dual notched frequency band is also proposed.

The Ultra-Wideband Software defined microwave radiometer (UWBRAD) was developed to probe internal ice sheet temperatures using 0.5-2 GHz microwave radiometry. The airborne brightness temperature data of UWBRAD show a significant reduction due to reflections of surface layering of density fluctuations making difficult the retrieval of subsurface temperature in the kilometer range of depth. Such reflections can be measured by the ultra-wideband radar in the same frequency range suggesting a combined active and passive remote sensing of polar ice sheets. In this paper, we develop a coherent reflectivity model for both ice sheet thermal emission and backscattering. Maxwell equations are used to calculate the coherent reflections from the cap layers, and the WKB approximation is used to calculate the transmission for the slowly varying profile below the cap layers. Results are then shown to demonstrate the use of radar measurements to compensate reflection effects on brightness temperatures. It is shown that the reflections corrected brightness temperature is directly related to the physical temperature and absorption profile making possible the retrieval of subsurface temperature profile with multi-frequency measurements

Recently, magnetic-resonance-based electrical properties tomography, by which the electrical properties (EPs), namely conductivity and permittivity, of biological tissues are reconstructed, has been an active area of study. We previously proposed an explicit reconstruction method based on the Dbar equation and its explicit solution given by the generalized Cauchy formula. In this method, as in some other conventional methods, the values of EPs on the boundary of the region of interest must be specified by the Dirichlet boundary condition of the partial differential equation. However, it is difficult to know the precise values in practical situations. In this paper, we propose a novel method that reconstructs EPs without the prior information of boundary EP values by deriving a new representation formula of the solution of the Dbar equation with the complex-derivative boundary condition. Numerical simulations and phantom experiments show that the proposed method can reconstruct EPs without knowledge of the boundary EP values. Therefore, the proposed method greatly enhances the applicability of the current EPT methods to practical situations.

A single-layer single-feed wideband omnidirectional microstrip antenna with rotating square patches is investigated in this paper. To obtain wide impedance band, the proximity-fed structure are introduced to the antenna to generate dual resonating modes. Two square patches with rotating angle of 90 degrees are used as the main radiator to improve the omnidirectional feature of the radiation pattern. For verifying the design, an antenna prototype with wide operation bandwidth is designed, simulated, fabricated, and measured. The results indicate that the impedance bandwidth (|S₁₁| < -10 dB) as high as 48.6% (3.02-4.96 GHz) is obtained. Meanwhile, the height of the antenna is only 0.11λ₀ (λ₀ is the free space wavelength corresponding the lowest frequency). What's more, omnidirectional radiation pattern is obtained over the operation band. The advantages ofwideband, low-profile and simple feed structure make the antenna good candidate in modern communication systems.

Enhancing the scattering of light from subwavelength structures is of both fundamental and practical significance. While the scattering cross section from each channel cannot exceed the single-channel limit, it is recently reported that the total cross section can far exceed this limit if one overlaps the contribution from many channels. Such a phenomenon about enhancing the scattering from subwavelength structures in free space is denoted as the superscattering in some literature. However, the scatterer in practical scenarios is not always in free space but may be embedded in environments with non-unity refractive index n. The influence of environments on the superscattering remains elusive. Here the superscattering from subwavelength structures in the isotropic environment with near-zero index are theoretically investigated. Importantly, a smaller n can lead to a larger total cross section for superscattering. The underlying mechanism is that a smaller n can give rise to a larger single-channel limit. Our work thus indicates that the scattering from subwavelength structures can be further enhanced if one simultaneously maximizes the single-channel limit and the contribution from many channels.

This article presents a metamaterial-based microwave sensitive sensor with a complementary split-ring resonator (CSRR) structure for nondestructive surface crack detection in pipelines. The CSRR resonator is etched in the ground plane of a microstrip line and is produced using printed circuit board technology. The novelty of the proposed sensor is its structure that allows it to be directly used for nondestructive crack detection in pipelines, based on frequency and Q factor variations, even for cracks under a coating. A measurement setup was used to test the proposed sensor in pipelines of different materials: steel, PVC, and aluminum. The sensor could detect cracks of 1 mm. For a crack of 1 mm, the frequency shift was 6.10 MHz in steel, 2.62 MHz in polyvinyl chloride (PVC), and 1.70 MHz in aluminum. In some conditions, the Q-factor shift measurements were 6.72, 5.18, and 7.15 for steel, PVC, and aluminum, respectively. The proposed sensor features high sensitivity, small dimension, simple design, and easy fabrication.

A novel high-gain polarization reconfigurable antenna composed of a polarization conversion metasurface (PCM) and a linearly polarized source patch antenna is presented in this article. The PCM is placed above the source patch antenna with an air gap. The proposed PCM can convert the linear polarization (LP) wave radiated by the source patch antenna to LP wave, right-hand circular polarization (RHCP) wave and left-hand circular polarization (LHCP) wave by rotating the PCM around the center of the antenna. Meanwhile, the proposed PCM can serve as the partially reflective surface (PRS) of a Fabry-Perot (FP) resonant cavity which can achieve gain enhancement. In order to validate the performance of the proposed design, a prototype antenna is fabricated and measured. Simulated and measured results agree well. From 10.43 GHz to 11.2 GHz, the polarization reconfiguration can be achieved by rotating the PCM to different angles while maintaining the high gain performance simultaneously.