Four-Arm Sinuous Antenna With Low Input Impedance for Wide Gain Bandwidth

Since cognition has become an important topic in Electronic Warfare (EW) systems, Electronic Support Measures (ESM) are used to monitor, intercept and analyse radar signals. Low Probability of Intercept (LPI) radars is preferred to be able to detect targets without being detected by ES systems. Because of their properties as low power, variable frequency, wide bandwidth, LPI Radar waveforms are difficult to intercept with ESM systems. In addition to intercepting, the determination of the waveform types used by the LPI Radars is also very important for applying counter-measures against these radars. In this study, a solution for the LPI Radar waveform recognition is proposed. The solution is based on the training of Support Vector Machine (SVM) after applying Principal Component Analysis (PCA) to the data obtained by Time-Frequency Images (TFI). TFIs are generated using Choi-Williams Distribution. High energy regions on these images are cropped automatically and then resized to obtain uniform data set. To obtain the best result in SVM, the SVM Hyper-Parameters are also optimized. Results are obtained by using one-against-all and one-against-one methods. Better classification performance than those given in the literature have been obtained especially for lower Signal to Noise Ratio (SNR) values. The cross-validated results obtained are compared with the best results in the literature.

Electronic support measures (ESM) systems use different methods for direction finding (DF). Performance of a DF antenna array is an essential measure of the overall ESM system. A common DF method of phase interferometry using a circular interferometer is discussed. Typically a circular interferometer employs a polarizer to match the desired incident polarizations to the polarization of the antenna array. This paper describes a simulation method for evaluation of polarizer impact on direction finding performance of a circular interferometer. Simulation of DF antenna performance of a circular interferometer with and without a polarizer, using method-of-moments antenna simulation and spreadsheet based post-processing. The benefits of simulation include being a cost effective way of performance prediction for a new design or for the influence of installation structures on an existing system. Sample DF accuracy results are discussed and compared to previously published specifications. This work is based on analysis conducted on the ESM system for the surface combatant force guided missile frigates (FFG ) upgrade project.

This paper covers development trends in communication and radar electronic warfare (EW). Threat scenario and role of EW sensors in developing Electronic Order of Battle (EOB) are described. EW is subdivided into Electronic Support Measure (ESM), Electronic Counter Measure (ECM) and Electronic Counter-counter Measure (ECCM) systems. Developments in communication ESM and ECM systems and their constituents are described. Under COM ECM, jammer system configuration and realisation of the constituent subsystems, jamming strategies used for effectively countering various types of communications are described. Developments in critical subsystems and configurations of typical radar EW systems are discussed. Finally the status of the indigenous developments in ESM, ECM and integrated systems are described.

This paper investigates integrated waveform design for radar systems to simultaneously achieve a low probability of intercept (LPI) by an adversary electronic support measure (ESM) system while maintaining communications with other radar nodes. A reconfigurable intelligent surface (RIS) is exploited and jointly designed to enhance the achievable performance of the whole system. LPI detection based on the ESM’s feature analysis on the radar waveform is achieved under the constraints of a desired signal-to-interference-and-noise ratio for the radar detection and a desired signal-to-noise ratio-based quality of service for the communication channels. To deal with the resulting non-convex optimization problem, a suboptimal composite algorithm with polynomial complexity is proposed. The initial feasible solution of the algorithm is efficiently obtained through an asymptotic optimization problem. Finally, the complexity of the proposed algorithm is analyzed. Simulation results including comparisons with baselines highlight the effectiveness of the proposed scheme.

A 1.3 GHz dual stage i.c. for logarithmic successive detection (s.d.) amplifiers is described. A complete amplifier using three i.c.' s achieves a signal compression accuracy of ± 1dB over an input dynamic range of 65dB at a frequency of 450MHz. This device is aimed at electronic support measures (e.s.m.) systems and is also applicable to high performance signal regenerators such as those used in fibre optic data links.

The field of circular (or cylindrical) arrays has received far less attention than that devoted to linear and planar arrays. At first sight this seems surprising since one of their principal advantages is the ability to deflect beams electronically through 360° with little change of either beamwidth or sidelobe level. Circular arrays have been applied, to a limited extent, in both communication systems and navigational aids since the late 1930s. There has, however, been surprisingly little change in their scale of application since that date, though there are now signs of a significant increase of interest in such arrays for applications to DF (Direction Finding) and ESM (Electronic Support Measures) systems. The analysis and general understanding of the properties of circular arrays has progressed steadily for many years and the most significant developments were probably made by several groups of workers in the 1960s when the concept of phase mode excitation was developed. The lack of applications in the past is prob ably due to the fact that the basic problems of exciting circular arrays with the correct values of amplitude and phase are, in general, more complex than for linear arrays. Furthermore, electronic scanning of directional patterns for circular arrays may be difficult to implement and can require both the amplitude and phase of each element of the array to be changed.

Detection of the changes in Multi-Functional Radar (MFR) work modes is a critical situation assessment task for Electronic Support Measure (ESM) systems. There are two major challenges that must be addressed: (i) The received radar pulse stream may contain multiple work mode segments of unknown number and duration, which makes the Change Point Detection (CPD) difficult. (ii) Modern MFRs can produce a variety of parameter-level (fine-grained) work modes with complex and flexible patterns, which are challenging to detect through traditional statistical methods and basic learning models. To address the challenges, a deep learning framework is proposed for fine-grained work mode CPD in this paper. First, the fine-grained MFR work mode model is established. Then, a multi-head attention-based bi-directional long short-term memory network is introduced to abstract high-order relationships between successive pulses. Finally, temporal features are adopted to predict the probability of each pulse being a change point. The framework further improves the label configuration and the loss function of training to mitigate the label sparsity problem effectively. The simulation results showed that compared with existing methods, the proposed framework effectively improves the CPD performance at parameter-level. Moreover, the F1-score was increased by 4.15% under hybrid non-ideal conditions.

An analysis of the input impedance of. a Rectangular Dielectric Resonator Antenna (RDRA) operated at the dominant mode TE/sub 111/ is presented. The effects of the probe length and its position with respect to the resonator on the resonance frequency and the input impedance of the antenna are investigated. The antenna structure is numerically simulated using the High Frequency Structure Simulator (HFSS) software package based on the Finite Element Method (FEM). A few experimental set-ups were examined and resonance frequency and input impedance were measured. The results show good agreement between theory and experiments and also the significance of the distance between the resonator and feed probe in simulation.

This paper presents a non-destructive, non-invasive method for measuring the input impedance of a Radio Frequency Identification (RFID) transponder (tag) antenna at the operating frequency The derivation of the theoretical basis for determining the antenna impedance is presented along with the experimental measurement method using a Vector Network Analyzer (VNA) in conjunction with a Giga-Hertz Transverse Electromagnetic (GTEM) cell where the tag is located. By providing three different terminations to the antenna, the frequency dependent parameters can be measured in order to define a two-port network and determine the input impedance of the antenna. All measurements were performed using the actual RFID tag that operates in UHF (915 MHz) band. The resulting input impedance of the antenna was validated with the electromagnetic simulation software by constructing a model of the testing system and applying the proposed measurement method. The simulated results were found to be in agreement with the experimental measurements accounting for any discrepancies.

A fast and accurate CAD model based on cavity model analysis has been proposed to predict the input impedance and bandwidth of a tunable right angle isosceles triangular patch antenna (RAITPA). The effect of suspended substrate on the input impedance and bandwidth has been thoroughly investigated. The accuracy of the present model is computed against the HFSS simulated results. The present model shows very good agreement with the simulated results. For designing the MIC on semiconductor materials with e r ≥ 10, this model will be widely applicable.

This paper first examines and corrects Storer’s theory of circular loop antennas, and then investigates theoretically the proposed Ω-shaped loop-dipole antenna. Special emphasis is given to the analysis of the effect of the higher-order terms of the Fourier series as a remainder on the current distribution, input impedance, and radiation patterns of the thin-wire circular loop antenna. It is found that the remainder must be included in the calculation of the current distribution and input impedance but can be neglected to simplify the calculation of far-field radiation. Then, a theoretical model is proposed to analyze the radiation fields, directivity, and input impedance of the proposed Ω-shaped loop-dipole antenna based on the loop and dipole antennas’ theories. Analytical expressions for the radiation fields, directivity, and input impedance of the Ω-shaped loop-dipole antenna are derived. The theoretical and numerical results are compared for the Ω-shaped loop-dipole antennas of practical interests. They are in good agreement.

Moment-method calculations are presented for the input impedance of wire antennas attached on-axis to a conducting body of revolution (BOR) of arbitrary geometry. The study of the wire antenna is carried out using integral equations of both reduced and exact kernel. The analysis of the BOR takes advantage of the symmetry of revolution that allows the expansion of the current in Fourier series, which takes advantage of the mode orthogonality and reduces the computer time required. Results for current distribution and input impedance are obtained for several structures such as vertical and nonvertical monopoles over circular ground planes and conical bodies. Measurements of impedance are presented to check numerical results. These are also compared with results of other methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A practical way to adjust the input impedance of a rectangular patch antenna is to vary the feed position. The inset-fed patch provides a method of impedance control with a planar feed configuration. The goal of this paper is to further study the inset-fed patch in order to examine the dependence of the input impedance on the inset notch geometry, as well as to realize design tables that show the notch depth to obtain the best input match (minimum |S/sub 11/|) for the inset patch when using a 50 /spl Omega/ feed.

Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the reciprocity theorem. Compared to the Hertzian dipole, which is the only type of source that has been considered in the literature, the resonant dipole substantially improves the performance of periodic LWA in terms of radiated power, efficiency and bandwidth. Numerical results are given for a resonant dipole over the frequency range of 60-70 GHz and compared with those obtained from commercial softwares, FEKO ® and Ansys HFSS ® , showing an excellent agreement with considerable improvement in terms of memory usage and computational speed.

There is an industry need for wideband baluns to operate across several decades of bandwidth covering the HF, VHF, and UHF spectrum. For readers unfamiliar with the term "balun," it is a compound word that combines the terms balanced and unbalanced. This is in reference to the conversion between a balanced source and an unbalanced load, often requiring an impedance transformation of some type. It's common in literature to see the terms "balanced" and "unbalanced" used interchangeably with the terms "differential" and "single-ended," and this article will also share this naming convention. These devices are particularly useful in network matching applications and can be constructed at low cost and a relatively small bill of materials. Wideband baluns first found widespread use converting the balanced load of a dipole antenna to the unbalanced output of a single-ended amplifier. These devices can also be found in solid-state differential circuits such as amplifiers and mixers where network matching is required to achieve the maximum power transfer to the load. In the design of RF power amplifiers, wideband baluns play a critical role in an amplifier's performance, including its input and output impedances, gain flatness, linearity, power efficiency, and many other performance characteristics.This article describes the theory of operation, design procedure, and measured results of the winning wideband balun presented at the 2013 IEEE Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium (IMS2013), sponsored by the MTT-17 Technical Coordinating Committee on HF-VHF-UHF technology. The wideband balun was designed to deliver a 4:1 impedance transformation, converting a balanced 100 Ω source to an unbalanced 25 Ω load. It was constructed using a multiaperture ferrite core and a pair of bifilar wires with four parallel turns.