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This article presents a dual‐band shared aperture antenna array designed for ASAR applications. The antenna array comprises eight elements for Chebyshev array configurations in both X/Ku‐bands. The proposed array achieves a scanning angle of ±25° by employing an interelement spacing of 0.7 λ. The layout mitigates mutual coupling effects and provides good isolation performance between the X‐ and Ku‐band antenna arrays across all synthesis techniques. Adopting the open, short, and load antenna array achieves different side lobe level (SLL) performances, >−25 dB. The isolation between bands and between the three conditions is quantified as follows: S16 = S61 = −68 dB, S15 = S51 = −55 dB, S12 = S21 = −46 dB, S43 = S34 = −49 dB, and S56 = S65 = −43 dB. The SLL values for each synthesis technique in the X/Ku‐band are as follows: Chebyshev simulated and measured results for open‐ended (X/Ku‐band: −26/−24 dB/−27/−26.8 dB). Furthermore, the antenna array achieves maximum realized gains in different positions (0°, 5°, 10°, 15°, 20°, 25°) in the X/Ku‐band. The gains for each synthesis technique are as follows: Chebyshev (The measured gain of this X/Ku‐band is high around 16.2/16.5 dBi (open‐ended), 13.1/14.2 dBi (short‐ended), and 15.3/15.2 dBi (load‐ended). The antenna array exhibits a comparatively wide impedance bandwidth Chebyshev (X/Ku‐band: 100/230 MHz). [ABSTRACT FROM AUTHOR]

As theoretical research further develops, coding metasurfaces have been widely studied and applied due to their uniqueness in digital characterization and sequence arrangement. In this work, based on highly conductive graphene‐assembled film (GAF), an ultralight anisotropic broadband coding metasurface (ABCM) is proposed. The GAF ABCM consists of 16 units with specific phase responses and enables complete metal substitution. By arranging the unit cells in a specific order, the GAF ABCM realizes the functions of anomalous reflection, polarization conversion, and radar cross‐section (RCS) reduction. Results validate that the GAF ABCM has a measured 10 dB normal incidence backward RCS reduction within the working frequency band of 7–18 GHz, which fully covers the X‐band and Ku‐band for radar application. Furthermore, due to the lightweight property of GAF, the density of the GAF ABCM is only 0.06 g/cm3 (surface mass density of 0.038 g/cm2). All results indicate that the lightweight GAF metasurface is promising in radar stealth and communication fields. [ABSTRACT FROM AUTHOR]

A dual‐core voltage‐controlled oscillator (VCO) using harmonic resonance is presented in this letter. Without an additional switch capacitor bank, harmonic resonance implemented in VCO is realized by only a single control voltage, satisfying the requirement of frequency‐modulated continuous‐wave radar. Two pairs of varactors are added to the transformer‐based tank, which ensures a constant ratio between the two resonant frequencies of the tank in the entire tuning range. Robustly single‐frequency oscillation is obtained by increasing the coupling coefficient of the transformer and the coupling capacitor's capacitance. Implemented in a 28‐nm complementary metal–oxide–semiconductor, the VCO shows a 14.75% frequency tuning range covering 34.16–39.6 GHz. The measured results show it exhibits −102.13 dBc/Hz phase noise at a 1 MHz offset from the 34.16 GHz. The oscillator core draws 21–28 mA from a 0.9 V supply. [ABSTRACT FROM AUTHOR]

This paper presents a novel high‐gain, miniaturized, and ultra‐wideband tapered‐slot Vivaldi antenna (TSVA) for ice‐sounding radar applications. To miniaturize the antenna and improve the impedance matching and antenna gain of conventional TSVA, tapered slot edge, circular cavity, rectangular cavity, inner circular patch, and rectangular slit structures are newly designed and introduced. The simulation results show that the size of the designed Vivaldi antenna is reduced by 15% and increases the peak realized gain by up to 5.1 dBi, compared to the conventional Vivaldi antenna. The optimized Vivaldi antenna was fabricated and characterized for its antenna performance. The simulated results are in good agreement with the measured results. [ABSTRACT FROM AUTHOR]

The design and fabrication of low loss and wideband Magic‐T with 10 dB return loss (RL) bandwidth over 40% is proposed for X‐band application, which can be used in monopulse comparator network. The proposed Magic‐T is composed of WR90 waveguides include an exponentially conducting cone, metallic multistep l‐shaped septum, and some other conducting posts. By implementation of these optimized conducting cone, septum, and posts, the 20 dB RL bandwidth over 36% is achieved with very low insertion loss (IL) (<0.15 dB) at each port. Moreover, high isolation (>40 dB) across all port over X‐band is another feature of the proposed Magic‐T. The equal power division (in amplitude and phase) at H‐arm and phase cancellation of input power at E‐arm introduce the proposed Magic‐T as a good candidate for sum/difference comparator network for monopulse application. Validation of the simulation results by experimental ones proves the wideband RL, low IL, and high isolation coefficient of the proposed high‐power Magic‐T as well. [ABSTRACT FROM AUTHOR]

This study proposes a novel method, that is, synthesized pattern null (SPN) method. The SPN method has very low computational complexity, which can be fully applied to all range‐azimuth resolution cells of the actual radar system. It does not depend on the multipath propagation model and has good robustness. This study presents the derivation process, the simulation results, and comparative experimental results of the actual radar system. The results reveal that the SPN method can significantly reduce the elevation angle error for low‐angle targets, and the root mean square error (RMSE) can be reduced to about 1/15 beam width. Moreover, compared with the synthesized vector maximum likelihood method, this method has similar angle measurement performance, much lower computational complexity and better robustness. [ABSTRACT FROM AUTHOR]

In this study, we introduce a radar sensor that we have developed for the micro‐Doppler signature measurements together with three consecutive signal preprocessing routines that are to be used for primary detection and classification of human gait and movements. The developed C‐band radar sensor has been used in a series of human walking and running experiments that were conducted at Mersin University facilities. First, the raw data collected in time domain are transformed to two‐dimensional (2D) time‐frequency plane to investigate the Doppler characteristics of human movements. To detect and extract the main body signature of the human, a Kalman filter‐based torso signature detection methodology is introduced as the first preprocessing tool. Then, to be able to better detect the other body parts' signatures, the torso's response is thoroughly extracted from the 2D time‐Doppler image as the second preprocessing routine by applying a circular shift procedure along each time‐bin. As the last procedure, envelopes of the micro‐Doppler signatures on the 2D time‐Doppler image plane are determined by another routine based on human Doppler threshold method. To assess the success and the validity of the proposed pre‐signal processing tools, they are applied to the measured data collected via different experiments of human movements. After applying all these steps, the torso signature and envelopes of all other body parts' signatures are marked and determined with good fidelity. [ABSTRACT FROM AUTHOR]

This study proposed a method for distinguishing the baseband signal for each frequency in two‐tone radar systems using the difference in the number of peaks of the envelope detected signal. The proposed method is based on the characteristic that the baseband signal for each frequency exhibits a different number of peaks, depending on the operating frequency, at a fixed sampling frequency in data acquisition. The phase difference between the transmitting and receiving signals for each frequency can be obtained using envelope detection of the baseband signals in two‐tone radar systems, and the proposed method can effectively match the phase difference and operating frequency without using additional controls and synchronization. This simplifies the procedure to estimate the absolute range up to the maximum unambiguous range, corresponding to a phase difference of 2π. Measurement results demonstrate that the absolute range, using a two‐tone radar with a frequency spacing of 150 MHz, can detect the distance with an accuracy of 97.8% up to the maximum unambiguous range using the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, digital parallelization and fractional delay‐based novel methods are proposed for the realization of high bandwidth, high‐resolution Ku‐band radar target simulator with 2.5 GHz intermediate frequency. High bandwidth waveform from radar is sampled by high‐speed Analog to Digital Converter, and samples are parallelized in Field Programmable Gate Array (FPGA) to work at the nominal clock frequency. In Digital RF Memory‐based target simulator, for finer range resolution, the FPGA clock frequency needs to be increased, which leads to increased system design complexity. The finer range resolution is accomplished without altering the system clock frequency using variable fractional delay filters and the digital parallelization methodology is proposed in this paper. The maximum target range that can be simulated is 20 km. As a result, memory requirements, computational complexity, and power dissipation are reduced. Finally, simulation and implementation results are presented. [ABSTRACT FROM AUTHOR]

This letter provides a detailed explanation of a novel high‐gain cross slot substrate integrated waveguide (SIW) rectangular cavity‐backed antenna. The main SIW cavity is further divided into seven small linearly placed cavities at a distance of 0.9λg ${{\rm{\lambda }}}_{{\rm{g}}}$. Each cavity contains a cross‐slot at an equal distance from each other. The defective ground structure is placed at the bottom layer of an antenna with two metallic vias to divert the wave towards edge slots for further gain improvement. The antenna shows a measured gain of approximately 12 dBi from 11.37 to 11.78 GHz. The radiation efficiency of 92% and the front‐to‐back ratio of 28 dB is achieved. The proposed antenna provides a very high directive fan‐like pattern which can be utilized for satellite and radar applications in the X‐band. [ABSTRACT FROM AUTHOR]

In this paper, the soft and hard composite patterns for electromagnetic scattering control at both normal and grazing incident angle is proposed. The soft and hard parts are composed of dielectric substrate sandwiched by transverse or longitude metal strips with metal via and the perfect electrical conductor ground, and these two parts are combined at a certain inclination angled to form the soft and hard composite patterns. The simulation results demonstrate that the proposed composite patterns have the monostatic radar cross‐section (RCS) reduction of 20.79 and 18.36 dB at 11.24 GHz under normal incidence for transverse electric polarization and transverse magnetic polarization, respectively. Also, this structure achieves 2.78 and 5.43 dB monostatic RCS reduction under grazing incidence from 60° to 90°. The simulation results are in good agreement with the experimental ones. The physical mechanisms of the proposed composite patterns can be elucidated by the equivalent impedance method based on its near‐field distribution. The proposed composite patterns can be functionalized by changing the electromagnetic parameters of the soft and hard surfaces, which has a great potential to be used as the traveling wave antenna enclosure for scattering control. [ABSTRACT FROM AUTHOR]

In this letter, we present the novel design of a near‐high frequency antenna for a small unmanned aircraft systems helicopter for the intended purpose of sounding and imaging temperate glaciers. The antenna leverages concepts in the areas of efficient electrically small antennas, structural antennas, and impedance matching to create a versatile design that is small and lightweight yet robust for airborne operations and has wider bandwidth than existing designs. [ABSTRACT FROM AUTHOR]

In view of the fact that the traditional radar system follows the Nyquist sampling theory and have the constraint of high sampling rate, we analyze a low‐speed sampling radar imaging based on compressed sensing. In compressed sensing, it uses the low‐rank characteristics of the signal to make it non‐adaptively sample the signal at a rate of far lower than the Nyquist sampling rate, so that it can reduce the requirements of hardware. Therefore, it not only can help to solve the problems of power, size, weight, reliability, and cost, but also can be seen as an upgrade and supplement of the traditional radar. [ABSTRACT FROM AUTHOR]

In this article, a new Swerling‐chi/inverse generalized gamma composite distribution model is proposed for modeling the monostatic radar cross‐section (RCS) statistical characteristics of stealth aircraft. Under some conditions, the proposed distribution model can be reduced to the Fisher‐Snedecor ℱ distribution model and the Swerling‐chi distribution model. A typical stealth aircraft without radar absorption materials (RAM) is selected as an application for simulation using the adaptive cross approximation (ACA) technique. Based on the nonlinear least‐squares criterion, monostatic RCS statistical characteristics of the front sector of this aircraft are fitted using the proposed composite model. For the comparison purpose, monostatic RCS statistical characteristics of this aircraft are also fitted with the conventional RCS distribution models. Goodness‐of‐fit tests of the proposed distribution model and the conventional distribution models are analyzed in terms of the error‐of‐fit results and the R2 test results. Simulation results validate the efficiency and robustness of the proposed distribution model. [ABSTRACT FROM AUTHOR]

A sparse phased array with 4% sparsity is developed for advanced low‐cost W‐band radar applications. A high‐order radiation mode‐based substrate‐integrated waveguide antenna featuring waveguide feeding is employed as the antenna element to achieve feeding loss reduction and antenna gain enhancement. An improved optimization technique is adopted to optimize the antenna element distribution. The combination of the element distribution and the antenna element radiation pattern achieves grating lobe suppression. Both the simulation and measurement results show that a ±15° beam scanning range can be achieved, and the level of the measured normal and scanning sidelobes is lower than −18 dB and −13 dB, respectively. [ABSTRACT FROM AUTHOR]

This article presents a concurrent X‐ and K‐bands low noise amplifier (LNA) for a radar detection system. A dual‐band matching and direct current bias circuitry were configured using surface‐mount device lumped capacitors and distributed transmission lines for the compact size. The designed LNA has dual‐pass band operation and a notch between the X‐ and K‐bands. The proposed LNA was implemented in hybrid integrated circuit technique on the microwave substrate. The measurement has showed the gains of 18.6 and 22.4 dB and noise figures of 3.29 and 1.67 dB at 10.525 and 24.1 GHz, respectively. [ABSTRACT FROM AUTHOR]

Tracking low‐angle targets over an uneven surface are challenging because of the highly correlated, complicated, and volatile multipath signals encountered in radar. Especially, in the context of irregular reflector modulated by rough sea, which results in performance depravation of the existing direction‐of‐arrival (DOA) estimation methods. An effective DOA estimation approach is based on maximum likelihood (ML) estimator which is referred to as optimal synthetic vector maximum likelihood (OSVML) method. The approach is essentially different, multipath signals are present that without known prior information of ideal model. The optimal projection space in estimator banks is spanned with direct subspace and indirect subspace to match the signals received by S‐band radar. Then, the performance of the proposed method is evaluated by simulations in terms of the signal‐to‐noise ratio (SNR) and snapshot. Finally, field data sets acquired from S‐band radar are carried out to verify the practicability of the proposed method in a naval environment. [ABSTRACT FROM AUTHOR]

In this research work, a wideband metamaterial‐inspired circularly polarized antenna array is designed. The designed antenna array has a low radar cross‐section (RCS) but high gain. The basic element of the planar array is analyzed as a dual‐band electromagnetic absorber. Under normal incidence, the designed basic element has two absorbing peaks at 3.6 and 11.2 GHz. Further, four elements of the 4 × 4 elements array are connected to the feeding network through metallic vias. The feeding network is designed on the bottom layer. The circular polarization is archived by feeding the cross shape metallic resonator at two feed points, in a manner that there is a 90° time phase difference between the fields of two. It is shown that a good axial ratio is obtained over a wideband. This design method simultaneously validates high gain antenna performance and also meets the conditions of low‐RCS. [ABSTRACT FROM AUTHOR]

Designing a low frequency broadband absorber is a nontrivial task in terms of establishing a trade‐off between overall absorber thickness, wide absorption bandwidth, and miniaturized unit cell size. To address the issue, we propose a novel broadband absorber design based on multilayered configuration, which covers the lower bands of the radar spectrum. The design is implemented using resistive ink patterns that are printed on an economical FR4 substrate. The reflectivity response of the proposed broadband absorber is less than −10 dB in the frequency range 1.26 to 4.38 GHz, covering the L and S bands of the radar spectrum with a fractional bandwidth of 110.63%. Furthermore, the structure has a miniaturized unit cell of dimension 0.057λL and a notable small thickness of 0.079λL. The implementation of the equivalent circuit model further validates the proposed design. The design is fabricated and experimentally verified. The simulation and measured results are in good congruence with each other. [ABSTRACT FROM AUTHOR]

A quaternary artificial magnetic conductor (AMC) is proposed in this letter, and we design broadband circularly polarized antenna on this basis. The main innovation of this work resides in the way of realizing ultra‐wideband radar cross‐section (RCS) reduction. The quaternary AMC has different scattering mechanisms in the low and high bands. In low band, since the AMCs' reflection phases in diagonal are very close, the quaternary AMC can be regarded as a conventional binary checkerboard AMC. But with the variation of frequency, the different reflection phases in the high band will cause the quaternary AMC to be a surface structure like a coding diffuse metasurface. Ultimately, RCS reduction of more than 10 dB is realized from 7.5 to 21.3 GHz, where the bandwidth approximately accounts for 95.83% of the center frequency. Thanks to the proximity coupling, the AMC array around the original antenna, as the parasitic patch, plays a significant role in regulating and improving the axial ratio. The measurement and simulation results demonstrate that the proposed antenna obtains an axial ratio of <3 dB from 8.95 to 11.07 GHz, the impedance bandwidth (ie, VSWR ≤2) ranges from 8.45 to 11.80 GHz. [ABSTRACT FROM AUTHOR]

This article indicates a thus far unexplored area of applied research and development to the application and system engineers and researchers from broad engineering backgrounds. Results of a study are presented for measurement of calibrated Radar Cross Section (RCS) of a 9‐mm bullet (projectile) model by using a commercial‐of‐the‐shelf (COTS) millimeter wave Frequency Modulated Continuous Wave (FMCW) radar system operating in 77 to 81 GHz frequency range. The calibrated RCS variation against the aspect angle is measured experimentally, analyzed, and compared with the simulation results which shows fair matching between the two. The opportunities and challenges attached with the use of such COTS systems for development of Hostile Fire Indication (HFI) systems are discussed. This bullet type and this mmwave frequency has not been thus far studied and reported in literature. This may motivate interested individuals/entities to try to measure (at acceptable accuracy before anechoic chamber measurements) RCS of similar low‐size objects by using such low‐cost COTS platforms. [ABSTRACT FROM AUTHOR]

We demonstrate a 24 GHz hydrology radar system. The continuous‐wave Doppler radar is capable of noncontact and wide‐range surface‐flow velocity detection in various scenarios. The radar receives the reflected echo signal through a directional narrow‐beam antenna. After amplification and demodulation by the proposed low‐noise amplifier and the subharmonic down‐conversion mixer, respectively, the Doppler frequency‐shift is analyzed by the digital signal processing (DSP) module for estimation of the water flow velocity. Moreover, for water level detection, a phase‐locked loop with micro control unit (MCU)‐controlled division ratio is included in the RF module for generating a stable and tunable (or frequency modulation) 24‐GHz‐band transmitting signal with low phase noise. To verify the radar system, outdoor field tests have been conducted. The measured results are consistent with the theoretical values, and the results of both the float method and the commercial handheld (Stalker Pro II) surface velocity radar. In the condition of water ripple lower than 3 cm, the radar functions well for flow speed range of 0.3 ~ 34.6 m/s. Overall, the hydrology radar is suitable for surface‐flow velocity detection (especially in bad weather) and water resource management (such as water‐level detection). [ABSTRACT FROM AUTHOR]

The frequency diverse arrays (FDAs) have been extensively investigated since it can provide a unique angle‐range‐dependent beampattern. This range‐dependent characteristic can suppress the range ambiguous clutters, leading to many novel potential Radar applications. Two issues, however, exist in conventional FDA (CFDA) beampatterns, that is, range‐angle coupling and range periodicity. Therefore, for a CFDA Radar, target range information cannot be obtained directly from the beampattern peaks and target ambiguity occurs in the range domain. In this work, a new frequency diverse array (FDA) transmitter architecture with random logarithmically increasing frequency offset (log‐RFDA) is presented. It is shown that the proposed strategy provides a nonperiodic thumbtack‐like beampattern, eliminating the ambiguity in range domain, suffered in the CFDA Radar. Furthermore, reduced side lobe and higher detection resolution can be achieved, compared with the previously reported log‐FDA. [ABSTRACT FROM AUTHOR]

A new subspace method applied to through‐the‐wall radar for clutter mitigation is presented. The pseudo‐random code continuous wave radar is used and the wall subspace selection algorithm is introduced. The performance of this method is demonstrated and compared with the singular value decomposition‐based clutter mitigation methods. Results confirm that the new subspace method suppresses the wall clutter more thoroughly under the same conditions. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate and evaluate the effectiveness of broadband radar cross‐section (RCS) reduction using a radar‐absorbing structure combined with geometric control of edges. The proposed novel design uses a radar‐absorbing structure combined with a serrated edge structure to efficiently improve the absorbing performance of the edge. The primary principle of the RCS reduction in the proposed novel structure is multiple scattering inside the corner reflector shape formed between the serrated edges. Although the absorbing performance of the designed planar absorber has narrowband absorption, the absorber combined with a serrated edge exhibits broadband RCS reduction. In designing a serrated edge shape, a foam core, which is a low‐density and lightweight material, is used to minimize the weight increase. The edge return becomes important for the low observable aircraft platform; hence, the proposed design can be a promising structure for further RCS reduction. [ABSTRACT FROM AUTHOR]

Radar‐based human micro‐Doppler analysis has been the subject of much investigation in recent years. Apart from the conventional activity classification task, person identification based on human movement signal has emerged as a research interest. This paper presents a method to recognize a person's identity from varied human motions using an ultra‐wideband radar. The human movement data is captured in an indoor environment and is then transformed into micro‐Doppler spectrograms for identification. Moreover, as it is always challenging to construct large scale radar datasets in practice, we adopt a plain convolutional neural network with a multi‐scale feature aggregation strategy to address the identification problem. Experimental results show that the micro‐Doppler signatures have great potential in person identification, and our model presents relative satisfying performances limited training set. Especially, when "walking" is used for identification, our approach achieves a person identification accuracy of 96.8% for the four targets used. [ABSTRACT FROM AUTHOR]

A new approach for in‐band radar cross section (RCS) reduction of microstrip patch antenna with preserved radiation features is presented. This aim is achieved by the application of highly absorbing unit cells optimized by particle swarm optimization around the radiating patch of the reference antenna. More than 10 dB in‐band RCS reduction is observed from 2.5 GHz to 3 GHz for both x‐ and y‐polarizations with a −26.4 dB maximum RCS reduction at 2.8 GHz, according to measurement results. A close agreement between the measured and the simulated results shows that the proposed absorbing unit cell is a good candidate to enhance antenna in‐band stealth performance. In addition, with a comparative table, it has been shown that the proposed antenna has much lower in‐band RCS and is more compact than the other antennas proposed in previous literature. The basic benefit of this study is to achieve maximum in‐band RCS reduction, especially at the exact desired frequency without long‐term simulations and time‐consuming design studies. [ABSTRACT FROM AUTHOR]

Fully autonomous vehicles and the need to improve road safety have led to increased demands on the reliability of various advanced driver assistance systems (ADAS). Automotive radar is a key component of ADAS as it adds both safety and comfort features in vehicles. A key challenge in developing automotive radar is demonstrating reliability especially in corner cases. Building and testing radar systems for corner cases is time‐consuming, costly, and impractical. Simulation is the only practical way of investigating the countless possible automotive radar corner cases. An interesting corner case is the reduction of radar returns due to sharp road bends. Specifically, crucial targets with low radar cross sections (RCS) such as pedestrians can become invisible to radar when driving around sharp road bends. In this article, a high fidelity, full physics‐based simulation of a 77 GHz automotive radar scene will be used to investigate this corner case. The dependence of radar returns on the position of an ego vehicle negotiating a sharp bend will be presented. Results from these simulations show a pedestrian disappearing from view at an approaching angle of 60∘ with a degradation of over 40 dB in pedestrian radar returns. Using results from this study, a terrain‐adaptive technique for improving radar target detection capabilities is proposed. This technique is shown to improve pedestrian radar returns by over 26 dB. Improved radar returns can help in early detection of pedestrians and other relevant targets. Early target detection can help reduce accidents while potentially saving pedestrian lives. [ABSTRACT FROM AUTHOR]

Abstract: In this article the concept of a fully electronic beamforming antenna array for radar systems based on a SDR architecture is proposed and experimentally evaluated in an anechoic chamber. The system uses 2 software defined radio (SDR) transceivers with 4 independently controlled transmitters, allowing an individual digital control of both amplitude and phase of the signal fed to each element of an antenna array. It is also proposed a beamforming method that greatly reduces the sidelobes of the radiation pattern and it was compared to traditional beam steered radiation patterns. Moreover, the proposed architecture has the advantage of being modular, and therefore easily scalable, for larger and more powerful solutions based on the presented antenna array system. [ABSTRACT FROM AUTHOR]

Abstract: This article presents a microwave imaging method based on the time‐reversed finite‐difference time‐domain method (FDTD‐TR) that enhances immunity to undesired interference and jamming signals. The method uses random noise as the source waveform that illuminates the imaging area. Signals scattered by objects in the imaging area are collected on a planar grid, followed by processing through a correlation operation, and then used in the FDTD‐TR algorithm to construct images on any desired plane in the computational domain. The method capability in suppressing interference noise is demonstrated through successful reconstruction of images for a test case consisting of a dielectric object behind a wall. The method is compared to conventional FDTD‐TR methods that fail the same image reconstruction test. [ABSTRACT FROM AUTHOR]

Abstract: We propose a low‐profile tilted‐beam waveguide slot antenna using corrugations for unmanned aerial vehicle (UAV) applications. The proposed antenna consists of a WR‐90 rectangular waveguide with a central slot on top and two asymmetric corrugations. The antenna satisfies a 10‐dB return loss from 9.82 to 10.18 GHz. To realize the low‐profile characteristic, the proposed antenna is fed from the flank instead of the bottom of the waveguide. In addition, the proposed antenna attains a tilted beam pointing 45 degrees from the broadside direction due to the asymmetric corrugations on the conducting plate. The antenna has a measured peak gain of 6.95 dBi at the center frequency of the operation band, which satisfies the gain requirement for UAV applications. The experimental and simulated results of the proposed antenna are in good agreement. [ABSTRACT FROM AUTHOR]

Abstract: This article presents the design of an ultrawideband active integrated antenna based on an electric dipole and the results of its testing. The antenna is intended to perform low‐distortion measurements of the instantaneous electric field strength of short pulses whose spectra lie within the frequency range from 0.05 to 3 GHz. The antenna is fabricated using the technology of printed circuit boards on a 1‐mm thick FR4 plate of dimensions 60 × 28 mm. It has a built‐in balancing‐to‐unbalancing unit and an unbalanced output. The difference in output voltage pulse waveform between the proposed antenna and a reference TEM‐antenna is insignificant. [ABSTRACT FROM AUTHOR]

This research article presents a novel design of printed antenna for 24 GHz ultra-wideband (UWB) applications. This research develops an antenna having dimension of 5 × 6 × 0.8 mm3 which operates from 24 to 30 GHz. This is achieved using techniques such as truncation of patch edges and inclusion of complementary split ring resonator metamaterial (MTM). This antenna can be used for short range RADAR application at 24 GHz UWB for automotive appliances. This article includes the detailed investigations such as surface current distribution on antenna, far field patterns, gain, group delay and radiation efficiency over frequency, as well as measurement details. Simulation and measurement data on return loss have shown good equality which proves the feasibility of the proposed antenna. [ABSTRACT FROM AUTHOR]

In this article, we present new two-layer and light-weighted grid wire metamaterial lens implemented on the aperture of conical horn antenna to manufacture a small-sized and high-performance antenna applied in 77 GHz radar system. It could shorten half-length of horn antenna without deteriorating its gain, broadband, and matching performance. The metamaterial lens is made by thin copper sheet whose thickness is only 0.1 mm. The measured results show that the metamaterial lens enhances the gain about 3.4 dB (@77 GHz) than short ordinary antenna with the same physical dimension, which equals to double its length. The high-performance and small-sized bulk make it suitable for 77 GHz radar system. [ABSTRACT FROM AUTHOR]

ABSTRACT Wireless monitoring of human vital signs such as breathing rate is a nonintrusive alternative to contemporary solutions relying on physical contact. To ease the installment, fiber optical transmission is used to extend the reach from the transmitter and receiver circuitry to the antenna subsystem. In this paper, a frequency modulated carrier wave radar, operating at 25.7-26.6 GHz and utilizing optical fiber extension, was experimentally demonstrated to accurately recover the breathing rate of a human placed 1 m away from the radar antennas. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:353-356, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we investigate the methods that can realize automatic target recognition and tracking by exploiting signal distribution of radar cross section (RCS) with frequency modulated continuous wave (FMCW) radar. In doing this we use the real RCS data measured from the short-range FMCW vehicle radar. We estimate the continuous valued degree of freedom and the mean of RCS distribution using maximum likelihood estimation (MLE) assuming that RCS follows gamma distribution. The experiments with real radar verify that parameterized gamma distributions for three targets of man, vehicle, and drone closely follow the empirical distributions. Then, we apply maximum a posteriori criterion (MAP) for target recognition. The average recognition probabilities for man, vehicle, and drone using MAP are 85%, 100%, and 92%, respectively. Since the vehicle has distinct RCS and thus perfectly recognizable, we apply a support vector machine (SVM) hoping to better classify the man and the drone. The man is recognized with similar accuracy, but the drone is not due to the lack of training samples, of which constraint is imposed by real implementation and experiment. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1745-1750, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents the design of a compact and low -cost single -stage narrow band low -noise amplifier (LNA) for atmospheric radar application. Active feedback technique is employed to improve linearity without affecting the noise figure and gain. The source -degenerated inductor topology is used along with the cascaded transistors to achieve stability with maximum gain and minimum noise figure simultaneously. High -pass input and output matching circuits are used to improve input and output return losses. The amplifier was implemented on a low -loss substrate RT/duroid with pseudomorphic high electron mobility transistor (pHEMT) technology at 1.3 GHz. The measured results of LNA exhibit a gain of 28 dB and noise figure of 0.39 dB. The input and output return losses are <10.8 dB and third -order input intercept point is 33 dBm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1618-1622, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT A compact dual band H-shape reactive impedance surface (H-RIS) metamaterial loaded Koch fractal antenna is presented in this paper. The array of H-shape unit cell resonators is used to form reactive impedance surface. Resonance occurred at 3.4 and 5.35 GHz frequency bands. These frequency bands are feasible to use at C- and S-bands synthetic aperture radar (SAR) applications. The geometry of proposed antenna is designed with low-cost substrate FR-4. Radiation patterns are measured and compared with the simulation results for testing the overall performance of the newly designed antenna. The measured results are well matched with simulation one. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1311-1314, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT A millimeter-wave (MMW) miniature planar dual balun (i.e. single-to-dual-differential four-way equal power divider) in 90 nm CMOS technology is reported. The dual balun can be applied to a star mixer for converting the single RF (or LO) input signal to dual differential RF (or LO) signals, or a four-way power amplifier (PA) for four-way equal power dividing. In contrast to the traditional four-way PA that uses three Wilkinson power dividers for four-way equal power dividing, the proposed PA achieves smaller chip area, higher output power and higher power-added-efficiency The dual balun occupies a small chip area of 0.14 mm×0.18 mm (i.e. 0.0252 mm2) and achieves S11 smaller than −10 dB for frequencies of 50-110 GHz. For frequencies of 55-65 GHz, the dual balun achieves S21 of −7.6 to −7.9 dB, S31 of −7.9 to −9 dB, S41 of −7.5 to −7.9 dB, S51 of −7.8 to −8.9 dB, magnitude of amplitude imbalance (MAI) of 0.34-1.1 dB and phase difference (PD) of 179.22-180.78° for ports 2-3, and MAI of 0.3-1 dB and PD of 178.83-180.48° for ports 4-5. For frequencies of 75-85 GHz, the dual balun achieves S21 of −9.1 to −10.5 dB, S31 of −10.7 to −12.7 dB, S41 of −9.1 to −10.5 dB, S51 of −10.7 to −12.6 dB, MAI of 1.7-2.2 dB and PD of 179.42-180.59° for ports 2-3, and MAI of 1.6-2.1 dB and PD of 179.93-180.73° for ports 4-5. The state-of-the-art results of the proposed dual balun indicate that it is suitable for 60 and 77 GHz communication systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:850-860, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article a RADAR scanning method, based on microwave photonics was presented. The operation principle was based on an antenna array radiating on a far-field target, where the radiation spectral curve was divided so that different spatial sub resolution segments within the target area were illuminated by a different microwave frequency. Thus, although the radiation that is back reflected from those spatially sub resolution segments was mixed in the detecting single small aperture antenna, due to the frequency encoding, their detector could back separate them and could reconstruct signal with higher spatial resolving capability. Experimental and simulation results were presented for one-dimensional and two-dimensional antenna array. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:831-835, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a novel phase shifter base on half mode substrate integrated waveguide (HMSIW) whose characteristics can be reconfigured electronically by simply loading it with electromagnetic bandgap (EBG) unit cells at 9.5 GHz is presented. The prototype of phase shifter contains a HMSIW as a transmission line and four metamaterial structure as a load on the one side of the transmission line. These loads with junctions (or PIN diode) can be connected to HMSIW. To obtain different radar bit-phases for S21, we change the situation of junctions (or PIN diode). For demonstration purposes, controllable phase shifters are designed, fabricated, and measured to give excellent performance for X-band applications. The phase shifter has bandwidth around 0.38% at 9.55 GHz. Design method is based on simulation of EBG cells in different position and changing reactance of the phase shifting elements which help us to modify our phase shifter for different phases. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2562-2567, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, an ultrathin penta-band polarization-insensitive metamaterial absorber has been presented, which consists of an array of a closed ring embedded in a tetra-arrow resonator. The proposed ultrathin ( ∼λ0/18 corresponding to the highest absorption frequency) structure exhibits five distinct absorption peaks at 3.4, 8.34, 9.46, 14.44, and 16.62 GHz with peak absorptivities of 98.6%, 96.6%, 90.1%, 97.8%, and 93.1%, respectively. Due to fourfold symmetry the structure provides nearly unity absorption for all polarization angles under normal incidence. The structure also exhibits high absorption peaks ( ∼80%) up to 45° incident angles for both TE and TM polarizations. Surface current and electric field distributions for different absorption frequencies have been analyzed to visualize the absorption mechanism of the structure. Finally, the structure has been fabricated and experimentally measured responses are in good agreement with the simulated ones. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2519-2524, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT Nowadays, the space target characteristics of terahertz steps into a crucial stage, and the research in radar cross-section (RCS) of large calibration objects is the foundation of it. This article gives the simulation and the tests of six conducting spheres of different surface characteristics. And the testing results show the variation of RCS calibrator. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2479-2482, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT The physical optics and shooting bouncing ray method are combined to rapidly compute the composite scattering from electrically large three-dimensional target on a dielectric rough surface. To avoid modeling the infinite rough surface, the image theory and its modification are used to account for the electromagnetic interactions between the target and the infinite ground with very minimal computation resources. Meanwhile, this proposed method can separate the overall multipath scattering into four main components, therefore, it is beneficial to quantify the scattering characteristics for the synthetic aperture radar imagery in this field. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1689-1695, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT This note describes a new material made of carboned foam glass. Shaped as a pyramid, its leads to great absorption levels. The computation of reflection coefficient is completely derived. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:18-22, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT This article describes a method to design an automotive radar frontend module that deals with the routing of 77-GHz signals on a low-cost printed circuit board including wire-bond and rectangular waveguide-to-microstrip transitions. The operation of the developed modules was successful in the first attempt, showing good model-to-hardware correlation. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:3015-3020, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a design and implementation of the electronically beam steering system for active electronically scanning array (AESA) radar. This beam steering system used look-up table (LUT) calibration method to calibrate an amplitude and phase errors of each T/R Modules. LUT contains the T/R Module characterization data and the antenna correction data. Performance of this beam steering system was verified with the X-band AESA radar demonstrator which has 1024 radiating elements and 504 T/R Modules. Beam steering angle is ±60° in each azimuth and elevation. Beam steering time is 3 µs using the precalculation method of the next steering position. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2769-2773, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents simulation and hardware implementation of a low cost radar that can be used as a speed sensor or a metal detector. The overall hardware costs only U.S. $25 and has maximum free space range of 3.65 m. Its underground range is 4.3 cm under wet soil conditions with free space distance of 50 cm above ground. The proposed model provides a basis for designing a mine detector based on the amplitude of the reflected wave. As the frequency of the wave or the water content of the ground increases, the amplitude of the reflected wave decreases making the detection difficult. A comparison between different attenuations offered to the signal under different soil conditions and different Target's materials is presented. The frequency selected for the design implementation was 10.525 GHz. A speed sensor module, HB100 miniature microwave motion sensor was used to sense the reflected wave and was interfaced with a frequency meter implemented using a microcontroller. The module transmitted a continuous wave with amplitude of 15 dBm. The wave reflected from the target was received by module's receiving antenna. It was amplified using a noninverting amplifier and was converted to pulses using a comparator. These pulses were fed to the in-house microcontroller-based frequency meter, and the speed of the target was observed on the LCD interfaced. Complete ground modeling for different water content and free space modeling was also done. The proposed model provides a low cost stand-alone implementation of the overall radar. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2484-2489, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT This article describes a highly efficient X-band CMOS power amplifier. To obtain high drain voltage for high power, instead of using the typical cascode structure, we use a common-source structure with a long channel length transistor. Generally, to enable high operating speed at high frequency, smaller transistor technology is used, but we demonstrate that using large transistor technology is also possible. The proposed power amplifier is designed with transistors of 300-nm channel length in a common-source structure using a differential structure of RFCMOS technology. Consequently, the maximum output power is 19 dBm with a power added efficiency of 40.5% at an input power of 5 dBm. This RFCMOS power amplifier includes all matching circuits and biasing circuits, and no external components are required. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2552-2557, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this work is to present a real experience on radar cross section (RCS) reduction using a radar absorbent material (RAM) made of microwire metallic fibers on a patrol ship of the Spanish Navy. The effectiveness of this RAM has been demonstrated, providing a drastic reduction in the number of significant scatterers or hot spots, together with a significant reduction (between 10 and 15 dB) in the global RCS pattern. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2270-2273, 2014 [ABSTRACT FROM AUTHOR]