Electromagnetic Anechoic Chamber Research Articles

The Development of Copper Clad Laminate Horn Antennas for Drone Interferometric Synthetic Aperture Radar

Interferometric synthetic aperture radar (InSAR) is an active remote sensing technique that typically utilises satellite data to quantify Earth surface and structural deformation. Drone InSAR should provide improved spatial-temporal data resolutions and operational flexibility. This necessitates the development of custom radar hardware for drone deployment, including antennas for the transmission and reception of microwave electromagnetic signals. We present the design, simulation, fabrication, and testing of two lightweight and inexpensive copper clad laminate (CCL)/printed circuit board (PCB) horn antennas for C-band radar deployed on the DJI Matrice 600 Pro drone. This is the first demonstration of horn antennas fabricated from CCL, and the first complete overview of antenna development for drone radar applications. The dimensions are optimised for the desired gain and centre frequency of 19 dBi and 5.4 GHz, respectively. The S11, directivity/gain, and half power beam widths (HPBW) are simulated in MATLAB, with the antennas tested in a radio frequency (RF) electromagnetic anechoic chamber using a calibrated vector network analyser (VNA) for comparison. The antennas are highly directive with gains of 15.80 and 16.25 dBi, respectively. The reduction in gain compared to the simulated value is attributed to a resonant frequency shift caused by the brass input feed increasing the electrical dimensions. The measured S11 and azimuth HPBW either meet or exceed the simulated results. A slight performance disparity between the two antennas is attributed to minor artefacts of the manufacturing and testing processes. The incorporation of the antennas into the drone payload is presented. Overall, both antennas satisfy our performance criteria and highlight the potential for CCL/PCB/FR-4 as a lightweight and inexpensive material for custom antenna production in drone radar and other antenna applications.

A Novel Chrysanthemum-Like Fractal Structure Multi-Band Antenna for Mobile Terminals

This paper incorporates the structural characteristics of chrysanthemums in nature and fractal geometry theory into the antenna structure design and a novel-structured fractal multiband fractal microstrip antenna with a chrysanthemum petal structure is proposed. The antenna can cover commercial frequency bands from the second to fourth generation (4G), satellite navigation, wireless local area networks, and Bluetooth. The antenna radiator imitates the structure of chrysanthemum’s petals in nature, and a basic arc shape is iterated many times according to a certain proportional coefficient. After simulation and comparison, the second iteration can achieve the best antenna performance, and the antenna adopted the coplanar waveguide feeding method to broaden the antenna bandwidth. The antenna covers three effective frequency bands of 1.58–2.68 GHz (64.7%), 2.76–4.01 GHz (33.9%), and 4.68–5.35 GHz (13.4%). The antenna dielectric board is made of FR-4 material, the dielectric constant is 4.4, and the actual size is 41 × 29 × 1.6 mm3. The antenna performs fractal iteration at a small size, and the approximate calculation of the frequency band is completed by comparing the ratio of each ring to the current vector diagram. The design of the antenna is to use HFSS for antenna modeling and parameter optimization, and the model under different conditions were compared and analyzed. By comparing the test results of the antenna prototype with the simulation structure in the electromagnetic anechoic chamber, the rationality of the antenna is verified.

Applications of AMC-based impedance surfaces

The recent and major enhancements of artificial magnetic conductor (AMC) and their applications namely RCS reduction, low-profile antennas and holographic leaky wave antennas are reviewed. Full-wave simulations are compared to measurements of fabricated models, and a good agreement is attained. All of the measurement were conducted in the Arizona State University electromagnetic anechoic chamber (EMAC).

Frequency Spectrum Analysis of Electromagnetic Waves Radiated by Electric Discharges

In this paper, we analyzed the frequency spectrum of the electromagnetic waves radiated by an electric discharge as a basic study to develop an on-line diagnostic technique for power equipment installed inside closed-switchboards. In order to simulate local and series arc discharges caused by an electric field concentration and poor connections, three types of electrode systems were fabricated, consisting of needle and plane electrodes and an arc generator meeting the specifications of UL 1699. The experiment was carried out in an electromagnetic anechoic chamber, and the measurement system consisted of a PD free transformer, a loop antenna with a frequency bandwidth of 150 kHz-30 MHz, an ultra log periodic antenna with a frequency bandwidth of 30 MHz-2 GHz, and an EMI test receiver with a frequency bandwidth of 3 Hz-3 GHz. According to the experimental results, the frequency spectra of the electrical discharges were widely distributed across a range of 150 kHz-400 MHz, depending on the defects, while commonly found between 150 kHz and 10 MHz. Therefore, considering the ambient noise and antenna characteristics, the best frequency bandwidth for a measurement system to monitor abnormal conditions by detecting electromagnetic waves in closedswitchboards is 150 kHz-10 MHz.

Reflection characteristics of a composite planar AMC surface

This study investigates the reflection characteristics of a composite Artificial Magnetic Conductor (AMC) surface consisting of multiple orthogonal gradient AMC surfaces arranged in a two-dimensional periodic pattern. The gradient AMC surface in this study consists of square metal patches of variable size printed on a grounded dielectric substrate. Due to the orthogonal placement of the gradient AMC surface, the incident energy of a plane wave normally incident on the composite AMC surface will be reflected into four major lobes away from the impinging direction. To achieve a systematical design, a simple formula based on array antenna theory was developed to determine the reflection pattern of the gradient AMC surface illuminated by a normal incident plane wave. A time-domain full-wave simulation was also carried out to calculate the electromagnetic fields in the structure and the far-field patterns. The scattering patterns of the structure were measured in an electromagnetic anechoic chamber. Results confirm the design principle and procedures in this research. Since such a composite AMC surface can be easily fabricated using the standard printed circuit board technique without via-hole process, it may have potential applications in beam-steering and radar cross section reduction.

Development of a Near-Field Bistatic Synthetic Aperture Radar for Complex Target Reconstruction

This paper begins with a description of the design, construction, and characterization of a small electromagnetic anechoic chamber, developed specifically to house a bistatic ISAR system for the analysis of rock samples. Particular emphasis is given to the practicalities of construction, with the intention of assisting those in a similar position, wishing to build an anechoic chamber on a tight budget. The second part of the paper outlines efficient algorithms that may be applied to the tomographic and topographic reconstruction of complex targets within the viewing geometry of this ISAR system.

Electromagnetic Anechoic Chambers used from Microwaves to Millimeter-Waves and Ultra Broadband Wave Absorbers

The electromagnetic anechoic chambers have been widely used for many purposes with the advance of communications from microwaves to millimeter-waves. In this paper, the electromagnetic anechoic chamber used from microwaves to millimeter-waves is explained, and the ultra broadband wave absorbers for these electromagnetic anechoic chambers are stated. The some recent results of measurement are shown to ascertain the performance of these absorbers at the sub-millimeter-waves.

Design and construction of a multipurpose wideband anechoic chamber

An electromagnetic anechoic chamber has been constructed at the Multimedia University. It is designed to operate over a very wide frequency range from 30 MHz through 18 GHz. It can be used for electromagnetic compatibility (EMC) tests, antenna measurements, radar cross section (RCS) measurements, testing RF transceivers, calibration of scatterometers, and other electromagnetic research experiments. The geometry of the chamber is asymmetrical, consisting of a combination of rectangular and tapered volumes. The size of the chamber is about 64 ft /spl times/ 32 ft /spl times/ 24 ft high. Ease of construction and ease of lining of the absorbers were preserved so that the actual quietness is comparable to the theoretical simulation result. The transmitting source is placed at one end of the chamber, and the receiving antenna or object under test is placed in a designated quiet zone at the other end. The walls and ceilings are configured such that no first-order and or second-order reflections (except those reflected from the floor) propagate into the quiet zone. Hence, less-expensive absorbers can be used to achieve the required wideband performance. Reflection from the floor is required by the international EMC standards for radiated electromagnetic interference (EMI) emission tests; therefore, the chamber is designed for this capability. However, absorbing material can be placed on the floor to convert a semi-anechoic chamber into a fully anechoic chamber for radar and antenna measurements.

Characterisation of electromagnetic anechoic chamber by finite element method

A finite element solver for the complex electric field vector has been used to characterise an anechoic chamber. The chamber walls are lined with ferrite tiles and the absorbing boundary condition has been modified to model the tile as a surface impedance. The chamber has also been characterised experimentally so that a full comparison of results has been possible in the range 30 to 200 MHz.

RCS measurements, transformations, and comparisons under cylindrical and plane wave illumination

Monostatic RCS measurements of a long bar (at X-band) and of a scale model aircraft (at C-band) were performed under the quasi-plane wave illumination produced by a dual parabolic-cylinder CATR. At Arizona State University's ElectroMagnetic Anechoic Chamber (EMAC) facility, these measurements were repeated under the cylindrical wave illumination produced by a March Microwave Single-Plane Collimating Range (SPCR). The SPCR measurements were corrected using the reference target method. the corrected SPCR measurements are in good agreement with the CATR measurements. >

Electromagnetics at Arizona State University

Several research areas being investigated in the Department of Electrical Engineering at Arizona State University's College of Engineering and Applied Sciences are discussed. The topics of research include antennas, propagation, scattering, microwave circuits and devices, microwave measurements, and optical communications. The University's electromagnetic anechoic chamber, which is designed to perform precision antenna-pattern and radar-cross-section (RCS) measurements in the microwave region, is described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental study on direction dependency of reflection coefficients of microwave electromagnetic anechoic chamber

For measurements of reflection coefficients in an anechoic chamber by the free-space voltage standing wave ratio (VSWR) method, the composite antenna technique, using a combination of two antennas, is proposed. Reliable data on reflection coefficients can be obtained by this technique, with respect to reflected waves from arbitrary directions. Using the measurement results, the direction dependency of reflection coefficients is studied in relation to specular reflection and to the directivity of a transmitting antenna.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An experimental study on the intensity of scattering wave by automobile body as multipath source in mobile communications

The measurement of the electromagnetic wave scattering pattern of a reduced automobile model by means of a microwave simulation experiment in an electromagnetic anechoic chamber is discussed. The results show that the maximum level of the automobile's scattering pattern reaches -10 to -22 dB compared with the incident wave intensity. This indicates that when a mobile station is in a heavy-traffic city zone, the scattering from vehicles in the vicinity of the station must be taken into account as a source of multipath. >

A study on the electric field distribution in an automobile body for an antenna system mounted inside the body

The electric field distribution in an automobile body must be known when developing an antenna system mounted inside the car body for mobile communication. A microwave simulation experiment was carried out in an electromagnetic anechoic chamber using 4 GHz band signals and a miniaturized automobile. The automobile model used in this simulation experiment was about 1/15 of the size of the actual automobile under consideration. A simpler box-type model with large apertures was also studied. The internal electric field distribution measured in the box model was estimated to be a combination of the resonant TE/sub Pmn/ modes excited in the box. which acted as a resonant cavity. The spatial and frequency dependence of the internal automobile's electromagnetic field for each model is plotted for the frequency range 3-5 GHz. >