This paper describes how information about the electromagnetic structure of targets can be obtained from direct detection radar techniques, where the relative phase of the transmitted and received signals is not measured. A comparison is made between the resolved structure of a simple test target from an ultra wide band, pulse synthesis direct detection radar system at 14-40 GHz and an equivalent heterodyne radar receiver where phase information is recorded. The test targets employed are wax sheet of thickness 20 mm and 80 mm which are illuminated alone and in contact with the human body. A vector network analyser is used as the radar system. The simplicity of constructing ultra wide band direct detection radar systems combined with their cost makes the use of such radar systems appealing for applications such as concealed threat detection and nondestructive testing, where absolute range to the target, if required, can be determined by other methods.

This paper proposes miniature radio frequency identification (RFID) tag antenna designed to operate on metallic objects, in the UHF frequency range (915 MHz), without significantly degrading its read range. The antenna structure is composed of two parts: Part 1 comprises two square patches electrically connected to the ground plane through vias while Part 2 is an unconnected inter-layer consisting of two square complementary split ring resonators to allow for capacitive reactance increase. Consequently, its self-resonant frequency will shift towards low frequency, which theoretically allows shrinking RFID tag antenna into smaller size. The antenna was simulated and measured to verify its conjugate matching with chip impedance. The results of experimental tests show that the proposed RFID tag offers a maximum read range of 0.82 m when placed on a metallic object. The tag's overall size is 36.7×18.1×3.2 mm³. Both simulation and measurement results are provided to validate the design.

Two improved circularly polarized microstrip planar antennas operating in 5 GHz-6 GHz are proposed in this paper. The Swastika slot and a circular feeding line are introduced into Ant.2 which exhibits wide impedance bandwidth and AR bandwidth during simulation and measurement than a basic truncated edge CP microstrip antenna. In further studies, a center circular slot is introduced into Ant.3, and the experimental results show a wider impedance bandwidth and AR bandwidth with high gain.

A miniaturized triple-band branch-line coupler based on the simplified dual-composite right/left-handed transmission line (S-D-CRLH-TL) is proposed in this paper. The electromagnetic characteristics of S-D-CRLH-TL are analyzed by the simulator and equivalent circuit model, and the results prove that there are three frequencies with phase of -90° in the passbands; this characteristic can be applied in designing triple-band quadrature microwave components. The proposed branch-line coupler is fabricated and measured, the measured and simulated results are in good agreement with each other, showing that the triple-band operating at 3.06 GHz, 4.00 GHz and 5.54 GHz, the useful bandwidths are 2.97 GHz-3.16 GHz, 3.82 GHz-4.12 GHz and 5.48 GHz-5.67 GHz. In addition, compared with the conventional branch-line coupler, the whole size of the proposed one is 17 mm × 14.4 mm (0.173λ × 0.147λ) (λ is the wavelength in low frequency), it realizes a 73% size reduction. Moreover, compared with the triple-band branch-line coupler based on the double-Lorentz transmission line metamaterial, the proposed branch-line coupler is more effective in the situation, which is sensitive to phase-changing, as the sign of phase difference in the two outputs at the three frequency points keeps the same.

Ultra wide band (UWB) impulse radio (IR) technology has different applications in different sectors such as short range radios and collision avoidance radar. A strong signal denoising method is needed for UWB-IR signal detection. One of the challenges of UWB-IR signal detection technique is the environmental interferences and noises. Wavelet Packet Transform (WPT) based multi-resolution analysis technique is suitable for this kind of signal denoising and detection. The paper describes a better method of denoising and detection technique of UWB-IR signal based on calculation of energies of the coefficients of each WPT terminal-node and by using an improved threshold calculation technique. The proposed technique is investigated through both simulation and experimentation.

The uniform expressions of scalar fringe waves which are based on the physical theory of diffraction (PTD) were obtained for the impedance half plane in terms of the Fresnel integrals. Asymptotic and uniform forms of the fringe fields were compared. The radiated fields of the fringe expressions were analyzed numerically.

This paper proposes an Extended Inverse Chirp-Z Transform (EICZT) algorithm to handle the high squint FMCW SAR data, where the conventional Inverse Chirp-Z Transform (ICZT) cannot work due to the failure in dealing with the range-variance of second- and higher-order range-azimuth coupling terms. A pre-processing operation is implemented in the azimuth-Doppler and range-time (Doppler-time) domain, where a perturbation function consisting of second-order and third-order range time variables is implemented to compensate the range variance of the second order range terms. Moreover, a new scaling factor is formulated to represent the Range Cell Migration (RCM), and further corrected by the presented EICZT approach. The proposed approach is analyzed and compared with the conventional ICZT. The simulated high squint SAR scene with nine targets is well focused by the proposed approach and the quality is greatly improved with respect the conventional ICZT. The proposed algorithm is also validated by the X-band high-resolution real SAR data.

State-of-the-art radomes exploit frequency selective media so as to be transparent for the frequencies of the antenna protected by them and opaque to other frequencies. This feature helps in reducing the radar cross section of the antenna and in protecting it from interference. The study of a frequency selective radome is a daunting task, since the radome is usually large in terms of wavelengths, hence full wave analyses are prohibitive. In this paper an approximate technique, based on the physical optics concept, is proposed to attain an estimation of the behavior of a radome shielded antenna in a short time with a commonly available computer. Results are validated against a full wave technique over a relatively small radome.

With rapid development of satellite technology in monitoring the ocean, a good understanding of the physical processes involved in the electromagnetic ocean-surface interaction is required. The composite surface models are usually applied in the analysis of the interaction, hence a systematical check of their region of validity is desirable. Based on a generalized minimal residual procedure which is right preconditioned (GMRES-RP) that we have recently developed which has demonstrated the desirable properties of a numerical algorithm: robust and efficient, in this paper, for bistatic scattering from one dimensional ocean surfaces, we carry out a systematic assessment of the performance of the popular two-scale model and the advanced three-scale model under different conditions of ocean surface wind speeds, polarizations, frequencies, and incidence angles. It is found that the two-scale model in general captures the bistatic scattering pattern, yet the accuracy of geometrical optics (GO) for the large scale wave brings considerable impact on the overall accuracy. If the evaluation of the contribution of the large scale wave is instead using direct numerical integration for the corresponding Kirchhoff integral, impressive improvements are frequently observed, especially at low frequency (L and C bands) and low wind speed (3 m/s). But care should be taken when apply two-scale method with numerical integration, since there are cases where visible discrepancy with method of moment (MoM) are observed. On the other hand, the three-scale model is found in very good agreement with MoM across the considered ocean surface wind speeds, polarizations, frequencies, and incidence angles, hence represents a much advanced model over the two-scale model.

This paper presents an effective method for reconstructing the rotation-induced micro-Doppler (m-D) from a signature corrupted by noise. An adaptive low-pass filter is employed as a preprocessor of empirical mode decomposition (EMD) in order to effectively extract the first chopping harmonic component of the rotation-induced m-D. Then the extracted component is used for reconstructing the original m-D signature in the joint time-frequency domain. Although it is difficult to interpret the time-frequency representation of the noise-corrupted signature, the reconstruction of the m-D enables the acquisition of related information and can be used for complementing other traditional analysis methods. By validating the applicability of the proposed method with measured jet engine modulation (JEM) signatures, we demonstrate that the reconstruction process presented in this paper is expected to be significantly helpful for radar target recongnition in real environments.

This paper presents a high-efficiency ferrite meander antenna (HEMA), which can be used to realize a 2×2 multiple-input-multiple-output (MIMO) communication system when it is used at both the transmitter and the receiver ends. This antenna is designed to operate at 2.45 GHz center frequency (fc). It consists of two spatially separated half-cycle microstrip meander structures. Ferrite material is not used for the entire substrate, only beneath each meander structure. A standard FR-4 substrate is utilized as a system board. Impedance bandwidth and radiation patterns of the fabricated antenna are measured and compared with those of the simulation results. The -10 dB impedance bandwidth of the fabricated antenna is 262 MHz, whereas the simulated bandwidth is 235 MHz. According to the simulations, the gain and efficiency of the antenna are 2.2 dB and 81%, respectively. The efficiency of the antenna is confirmed by measurements. By using the simulated radiation patterns, correlation between the radiation patterns is calculated and employed in the generation of the channel matrix. Mutual impedance of the antennas and antenna efficiency are also included in the channel matrix, which in turn is used in bit error rate (BER) and ergodic capacity simulations. BER and ergodic capacity are utilized as performance metrics. The effect of antenna efficiency, mutual impedance of the antennas, and correlation between radiation patterns on system performance are presented.

This paper presents a new approach to the electromagnetic inverse scattering formulation of the permittivity profile estimation. The proposed approach is particularly effective for the cases where unknown objects are made of a finite number of homogeneous regions. This approach prevents the need for the Born approximation initial guess and updating the internal total electric field iteratively. The solution to the inverse source problem and scattering problem is not unique. To address the non-uniqueness issue, we have defined the non-radiating objective functions. By minimizing this objective function and applying some constraints, we have been able to obtain a unique permittivity profile. The simulation results indicate that the low-contrast and high-contrast permittivity profiles are accurately estimated by the proposed method. The distinguishing feature of the proposed approach is that by including the non-radiating part of the equivalent source, the unknown permittivity profile becomes the solution to a minimization problem, which is much less computationally intensive as compared to existing methods using iterative field calculation over the entire domain, when applied to large (in terms of wavelength) objects. The high performance of the proposed method for noisy measured data has also been verified.

An electromagnetic band gap (EBG) waveguide using holes drilled in a dielectric substrate is investigated in this paper. A broadbanding technique is suggested and implemented through a detailed study of the modal behaviour of the guiding structure. The stop band of the EBG waveguide was adjusted by changing the width of the waveguide to increase its bandwidth. It is shown that the propagating mode is a quasi-TEM by examining the dispersion properties of the propagating mode. An EBG waveguide of 49.1 mm (equivalent to 19 EBG cells) was designed and fabricated. The simulation results show better than -10dB return loss performance from 27 GHz to 31.5 GHz with insertion loss of better than 2.5 dB over the same bandwidth, and also high isolation in the range of -20 dB with an adjacent similar EBG waveguide. There is a good agreement between the measured data and simulation results. A microstrip line was also fabricated and used as a benchmark for comparison with the designed EBG waveguide. The group velocity of this waveguide is nearly constant across its operating frequency band which implies low frequency dispersion and is also a confirmation of the quasi-TEM nature of the EBG fundamental mode. Also, using the physical insight gained from a careful study of the EBG guide, a simple method is suggested for the calculation of the dispersion characteristic of its fundamental mode.

The feasibility of realizing an all-optical AND gate for 320 Gb/s return-to-zero data by incorporating quantum-dot semiconductor optical amplifiers (QD-SOAs) in a Mach-Zehnder interferometer (MZI) is theoretically investigated and demonstrated. The proposed scheme employs the QD-SOA-based MZI in a configuration where the QD-SOA in one MZI arm is subject to the first data sequence, the QD-SOA in the other MZI arm receives no such input but is constantly held in the small signal gain regime, and the second data stream is inserted from the common MZI port acting as enabling or disabling signal. Compared to other approaches adopted for the same purpose this implementation is more general, direct, flexible and affordable as only one strong data signal is required to control switching. By conducting numerical simulation the impact of the critical parameters on the Q-factor is thoroughly assessed. The obtained results are interpreted with the help of a complete characterization of the QD-SOA response to an ultrafast data pulse stream. This allows to specify the requirements that the critical parameters must satisfy to achieve acceptable performance. The extracted design rules are technologically realistic and ensure AND operation both with logical correctness and high quality. The outcome of the numerical treatment extends the range of Boolean functions executed with the QD-SOA-MZI module at sub-Tb/s data rates.

A GPR object detection algorithm delivers a promising performance using the Hough transform through a high computational load. This paper presents a fast Hough-based algorithm. To reduce the parameter space of the Hough transform, first, two parameters for a reflection hyperbola were estimated using cross correlation between adjacent A-scans. Next, only a 1D Hough transform is necessary to detect an object compared with the 3D transform, which comprises the traditional Hough-based methods. Our method is compared with three other detection methods using field data. The results show that the proposed method has an encouraging detection ability and high computational efficiency.

We develop a method for calculating transverse static polarizability (per unit length) of a bulk nanowire by taking in to account the temporal and spatial dispersion. To describe these phenomena, we developed analytical theory based on local random-phase approximation and plasmon pole approximation. Our theory is very general in the sense that it can be applied to any material which can be characterized by a bulk dielectric function of the form ε(w,k). The theory is applied to calculate the transverse static polarizability of dielectric nanowire.

Multi-path time delay spread is a very important factor in the bit error rate of high-frequency ionospheric communication channels and in the target detection performance of over-the-horizon radars. In this study, the probability density distribution of multi-path time delay and Doppler shift of ionospheric radio signal are derived using Rayleigh fading. Moreover, the probability density distribution of time delay, average power of the received signal, and received signal variance are discussed in detail. Using a designed experimental circuit, the measured value of the multi-path time delay spread is obtained from three given radio paths by the sweep-frequency pulse sounding technique. The average value of the multi-path time delay spread that changes with the ratio K, which is the operating frequency of the basic maximum usable frequency, is also analyzed and fitted using the least-squares fitting method. Theoretical and statistical research shows that for a given radio path and specific frequency, the multi-path time delay spread approximately follows a normal distribution. The average time delay spread decreases with the increase in the ratio K; however, it eventually approaches a steady value. The results of this research provide an empirical reference for further prediction and estimation of the time delay spread of a radar wave propagating through the ionosphere.

Design of (2 x 2) E-shaped microstrip patch antenna array integrated with spiral ring resonators (SRRs) is introduced for the reduction of cross-polar (XP) radiation. The addition of SRRs in the array structure does not affect other characteristics of the array antenna. The array is designed to function in the 5.25 GHz which corresponds to IEEE 802.11a wireless LAN application. The characteristic analysis such as return loss (RL), bandwidth (BW), and radiation patterns of the antenna with and without SRRs have been investigated. The array offers a bandwidth of 405 MHz (For RL < -10 dB) covering frequencies ranges from 5.175 to 5.580 GHz and gain of 12.60 dBi has been achieved. The array has been studied both numerically and experimentally by introducing SRRs. The XP radiation has been reduced by 10.5 dB with two sets of SSRs of similar geometry placed in between the patch elements of the array structure. Prototype antennas with and without SRRs have been fabricated tested and a remarkable agreement is obtained between the measured and the simulated results.

In High-Frequency (HF) Over The Horizon (OTH) radar, the space-time variations of the ionospheric channel, the external noise level (environment and man-made) as well as the transmission channel bandwidth limitations, are among the most critical and challenging aspects for the design and the operational management. Specifically, the knowledge of the ionosphere behaviour in a real time configuration is of primary importance because of the way it influences the frequency selection. This implies that a HF radar must have a high level of adaptability in order to deal with external constraints. For this purpose, a suitable frequency management system is needed. In this paper, a representation of the ionosphere propagation channel from a radar point of view is provided. Specifically, radio-electric parameters of the radar link are revisited by extending the concept of Maximum Usable Frequency (MUF), which is typically used in the communication field. The Ionospheric Propagation Chart (IPC) and Maximum Transmitted Frequency (MTF) are also introduced as new concepts. The present work is supported by simulation results.

This paper presents a simple microstrip filtering-antenna with compact size for WLAN application. The T-shape resonator through an inset coupling structure can be treated as the admittance inverter and the equivalent circuit of the filtering-antenna is exactly the same as the bandpass filter prototype. With a little extra circuit area, the proposed filtering-antenna has almost twice wider bandwidth, good skirt selectivity and high suppression in the stopband compared to the conventional microstrip antenna.