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NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been used to improve performance in anechoic chambers and has been demonstrated over a wide range of frequencies on numerous antenna types. MARS is a post-processing technique that involves analysis of the measured data and a special filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical or far-field range or Compact Antenna Test Range (CATR). It has also been applied to extend the useful frequency range of microwave absorber to both lower and higher frequencies than its normal operating band. This paper will demonstrate the use of the MARS capability in evaluating the performance of anechoic chambers used for spherical near-field measurements, as well as in improving chamber performance.
This paper presented a theoretical and numerical investigation of the performance comparison of Compact Antenna Test Range (CATR) equipped with Hybrid and Super Hybrid modulated serrations. The performance of the quiet zone will be degraded for a traditional CATR without both an edge treatment of the reflector antenna and a high quality anechoic chamber. Usually, the ripples in both the phase and magnitude of the field intensity inside the quiet zone are caused by stray signals, which come from edge diffraction. In order to solve the edge diffraction problems, edge treatments such as a different shaped serrated edge are often applied along the edge of the reflector antenna. The quiet zone field analysis of such reflectors has traditionally taken the form of ray tracing using numerical integration of the reflector surface currents called physical optics (PO). PO technique is used to obtain Fresnel Zone field of a plane square aperture embedded with a hybrid and super hybrid serrated CATRs. It is observed that super hybrid serrated CATR gives lesser ripples and enhanced quiet zone width than hybrid serrated CATR.
A new method is here proposed to accurately evaluate the Specific Absorption Rate (SAR), e.g. of a mobile phone, through free-space measurements. The method takes advantage of the simple yet powerful plane-wave spectrum (PWS) representation of the electromagnetic (EM) field. The emitting device is tested in an anechoic chamber, where the two tangential components of the electric field are measured (amplitude and phase) and expanded into their PWS. These experimental data are subsequently fed to an equivalent transmission-line representation of the planar stratified structure composed by stacking the half-space made of free-space and the stratified flat phantom. Numerical simulations have shown that this method allows to accurately reconstruct the E field distribution inside a homogeneous phantom, with a worst-case error of 26 % in the estimation of the peak E field [1,2]. Furthermore, the proposed method is the first practical procedure for assessing the SAR in a stratified phantom, where the standard approach of moving a probe inside a liquid-filled phantom is no more feasible.
Till recently, the testing of installed aircraft radars antennas and radomes required the dismantle of the units from the aircraft in order to measure theirs electromagnetic properties inside a classical anechoic chamber. Such operations were difficult, particularly time consuming and did not fully characterize the antenna within its operational environment. For these reasons, ELTA issued a request for an “in situ” spherical near-field test system that could be used for “on board testing of radars” located inside the nose of an aircraft. SATIMO responded with a solution based on its own proprietary rapid probe array technology already employed extensively worldwide for antenna testing. The facility was recently delivered to ELTA and “in-situ” measurement of a radar antenna and radome were performed (fig.1&2). This new generation of test system performs multi-beam, multi port and multi-frequency dual polarized complex measurements at a step of 3-degree in azimuth and elevation over a full hemisphere in a few minutes. It is fully autonomous and mobile so it can be used indifferently indoor or outdoor. Continuous wave or pulsed electromagnetic measurements are obtained thanks to an advanced software which allows the user to control the main radar parameters. Diagnostic of faulty elements in the radar is also possible through a special automated measurement mode. The antenna test system has been completed and validated through a detailed acceptance test plan including inter comparison with a traditional planar near field test range. This paper presents the general design consideration and a summary of the results of the extensive verification tests.
A full time domain characterization bench is realized in the CEA-LETI-Minatec anechoic chamber, to automatically derivate UWB antennas transfer function from waveform acquired by a fast sampling oscilloscope. Time domain measurement technique brings several advantages: faster and simpler measurements, out of band antenna behavior, intrinsic time windowing… Several time domain performance criteria are processed. A comparative method takes into account distortion due to the pulse generator and the test bench. Two different bands 0.3-2 GHz and 2-12 GHz are available. The comparison between frequency and time domain measurements shows excellent results (less than 0.3 dB on gain and 1° on phase) on the 2-12 GHz frequency band. Limitations of the proposed method are also addressed. The dynamic range is better than 35 dB thanks to averaging. Minimum bandwidth limit is evaluated to measure wideband and narrow band antennas.
The purpose of this paper is to report on the application of Chebyshev absorbers in the design of a multi use anechoic chamber. The requirement was for a chamber which allowed for evaluation of various wireless devices to be evaluated in a multi use chamber. The purpose of the chamber is to support multiple programs and allow for the evaluation of both complete handsets as well as individual components of the wireless devices. Due to the dual purpose applications that were to be evaluated in this chamber neither a standard” antenna range” nor a “classic wireless” chamber fit the bill. In order to optimize the use of this chamber a unique design was developed which incorporates the best of both classical chamber designs. To improve the low frequency response of the chamber a Chebyshev pattern was designed for chamber termination wall. Due to the short length of the chamber in comparison to the target length a Chebyshev pattern was designed for the specular patches on the sidewalls, floor and ceiling to improve the “off angle” performance of the chamber.
Reflections in anechoic chambers can limit the performance and can often dominate all other error sources. NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been demonstrated to be a useful tool in the fight against unwanted reflections. MARS is a post-processing technique that involves analysis of the measured data and a special mode filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near field or far-field range. It has also been applied to extend the useful frequency range of microwave absorber down to lower frequencies. This paper will show typical improvements in pattern performance, and will show results of the MARS technique using data measured on numerous antennas.
OTA performance testing of active wireless devices has become an important part of evaluation and certification criteria. Existing test methodologies are extensions of traditional antenna pattern measurement techniques. A critical assumption of these methods is that the device under test utilizes a single active antenna. Advances in wireless technology continue to incorporate more complex antenna systems, starting with simple switching diversity and progressing to more advanced concepts such as adaptive arrays (smart antennas) and multiple-input multiple-output (MIMO) technologies. These technologies combine multiple antennas with various software algorithms that can dynamically change the behavior of the antennas during the test, negating the assumption that each position and polarization of an antenna pattern measurement represents a single component of the same complex field vector. In addition, MIMO technologies rely on the multipath interaction and spatial relationship between multiple sets of antennas. An anechoic chamber with a single measurement antenna cannot simulate the environment necessary to evaluate the performance of a MIMO system. New measurement methods and system technologies are needed to properly evaluate these technologies. This presentation will discuss the issues and evaluate possible solutions.
This paper will present techniques used to simulate semi-hemispherical spiral antennas with measured VSWR and antenna pattern data for performance verification. Previous work on semi-hemispherical spiral antennas has been done by Lobkova, Protsenko, and Molchanov [1]. GTRI researchers have built on this work by developing a MATLAB computer model to create a general semi-hemispherical spiral antenna pattern model. Parameters that can be adjusted include the radius of the sphere, the number of turns of the spiral, the creation of a 1-arm or 2-arm spiral, and the inclusion of dielectric material between the spiral and ground plane. In creating the MATLAB computer model, GTRI researchers found errors in the notation of the elliptical integral in [1] and added additional details for the calculation of the antenna pattern. The paper will then present the characterization of a specific example of a semi-hemispherical spiral antenna. First, the VSWR of a single antenna was measured using a standard HP8510 Network Analyzer setup. Next, antenna pattern data was measured for a single spiral antenna and a pair of spiral antennas on both the GTRI planar near-field range and the GTRI anechoic chamber. The paper will conclude with the presentation of the modeled and measured antenna pattern data for the single antenna case.
An infrared (IR) measurement technique, based on thermal principles, is presented to independently validate and verify (V&V) numerical codes used for computational electromagnetic (CEM) field predictions. This technique is applied to scattering and to complex systems such as antennas on aircraft. The IR technique produces a thermal image of the EM field over any two-dimensional area, usually a plane, proportional to the intensity of the incident EM field being measured. This IR image can be compared to the predicted image of the field calculated with a numerical CEM code over the same plane that was used in the measurements to confirm the field levels. Precise thermal measurements on metallic scale models of canonical aircraft shapes are made in a controlled anechoic chamber environment to make scattered field measurements around the model. The temperature distribution is converted to field intensity and plotted as a false color image of the field and compared to similar plots from a selected CEM code. The field can also be visualized with this IR method. This is the first step in a progressive approach to compare results of more sophisticated geometries using a suite of CEM codes to confirm the results of the IR measurements to develop confidence in the complementary measurement and simulation methods.
ABSTRACT Conventional radar cross-section measurement ranges have limitations. Indoor anechoic chamber ranges have limitations with respect to the size of the objects that can be measured. Outdoor RCS ranges cannot be used in bad weather conditions and also pose a security problem when the designs are classified or proprietary. Limitations in availability are also common for both outdoor and indoor ranges. An alternative is to use a conventional lab area. The key to successful measurements of LO-targets in such high clutter environments is efficient coherent background subtraction. Coherent background subtraction was performed for ISAR and SAR and compared to the zero-Doppler subtraction method for ISAR in this study. The results from the measurements are compared with calculated results. We find that the ISAR and SAR techniques are comparable in performance but that it is advantageous to use ISAR for small objects due to practical reasons. We conclude that both SAR and ISAR can be utilized for LO targets.
This paper presents a method for measuring signal backscattering from an RFID tag and calculating tag radar cross-section (RCS), which depends on the chip input impedance. We present a derivation of a theoretical formula for RFID tag radar cross-section and an experimental RCS measurement method using a network analyzer connected to an antenna in an anechoic chamber where the tag is also located. The return loss of the antenna measured with and without the tag present in the chamber allows one to calculate the power backscattered from the tag and find tag RCS. Measurements were performed in anechoic chamber using RFID tag operating the base station (called “RFID reader”). RFID tag antenna is loaded with the chip whose impedance switches between two impedance states, usually high and low. At each impedance state, RFID tag presents a certain radar cross section (RCS). The tag sends the information back by varying its input impedance and thus modulating the back-scattered signal.
DSO National Laboratories (DSO) has commissioned a state-of-the-art combined near-field and far-field antenna test facility in 2004. This facility supports highly accurate measurement of a wide range of antenna types over 1–18 GHz. The overall system accuracy allows for future extensions to 40GHz and higher. The 11.0m x 5.5m x 4.0m (L x W x H) shielded facility houses the anechoic chamber and the control room. As the proffered location for this indoor facility is on top of an existing complex instead of the ground floor, antenna pickup is facilitated by a specialized loading platform accompanied by a heavy-duty state of the art fully automated 2.0m x 3.0m (W x H) sliding door, as well as an overhead crane that spans the entire chamber width. Absorber layout comprises 8-inch, 12-inch, 18-inch and 24-inch pyramidal absorbers. The positioning system is a heavy-duty high precision 3.6m x 2.9m (W x H) T-type planar scanner and AUT positioner. The AUT positioner system is configured as roll over upper slide over azimuth over lower slide system. This positioning system configuration allows for planar, cylindrical and spherical near-field measurements. A rapidly rotating roll positioner is mounted on a specialized alignment fixture behind the scanner to facilitate far-field measurements. Instrumentation is based on an Agilent PNA E8362B. Software is based on the MiDAS 4.0 package. A Real-Time Controller (RTC), accompanied by an 8-port RF switch, facilitates multi-port antenna measurements, with the possibility of interfacing to an active antenna.
A system for measuring large linear arrays of antennas has been developed, fabricated and tested. The system consists on a 12 meters structure where the antenna under test (a L band array of dipoles in this case) is positioned. The measurement probe (another dipole) moves on a linear slide and stops in front of each element of the array to acquire the electric field. All the system is installed on an semi-anechoic chamber, that can be lifted (with two synchronized stepped motors). This semi-anechoic chamber covers the top and side parts of the structure. The bottom part consists on a metallic reflector, that controls the reflections from each antenna element. Once the data is acquired, the data are processed to obtain the far field patterns and parameters of the antenna array (element amplitude and phase, beam width, side level, beam pointing …) All the results are presented in a windows environment, and all the system is integrated in a friendly user interface.
An antenna measurement system was developed to complement a new rectangular anechoic chamber (20’L x 10’W x 9’7”H) that has been established at California Polytechnic State University (Cal Poly) through donations and financial support from industry and Cal Poly departments and programs. Software algorithms were written to provide four data acquisition methods: continual sweep and step mode for both single and multiple frequencies. Log magnitude and phase information for an antenna under test is captured over a user-specified angular position range and the antenna's radiation pattern is obtained after post processing. Pattern comparisons against theoretical predictions are performed. Finally an RF link budget is calculated to evaluate the performance of the antenna measurement system.
Reflections in antenna test ranges can often be the largest source of measurement errors, dominating all other error sources. This paper will show the results of a new technique developed by NSI to suppress reflections from the radome and gantry of a large hemi-spherical automotive test range developed for Nippon Antenna in Itzehoe, Germany. The technique, named Mathematical Absorber Reflection Suppression (MARS), is a post-processing technique that involves analysis of the measured data and a special filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near-field test range. It has also been applied to extend the useful frequency range of microwave absorber in a spherical near-field system in an anechoic chamber. The paper will show typical improvements in pattern performance and directivity measurements, and will show validation of the MARS technique using data measured on antennas in a conventional anechoic chamber.
At the Institut Fresnel in Marseille (France), we created an original experimental setup in order to test antennas and carry out scattering measurements in both monostatic and bistatic configurations. The main advantage of this setup is, of course, the multipurpose feature. Two main mechanical systems are installed in a large anechoic chamber. The first system is a spherical positioning setup which allows measurements of antennas and scattered fields for both bi-dimensional (2D) and three-dimensional (3D) targets. This setup consists of two carriages moving on a circular vertical arch and a third carriage which follows a circular path on a horizontal plane. A transmitter and a receiver can be fixed on any of these three carriages. A fourth rotating stage in the center of the spherical setup fixes the angular position of the antenna under test or of the scattering target. The second system is a far-field positioner which allows the measurement antenna patterns and RCS. To illustrate our activities with this original setup, we first show measurements of a metamaterial antenna prototype and then some results of scattered fields obtained on 2D and 3D targets used in studies of electromagnetic direct and inverse problems.
The electromagnetic field as projected by a 12 ft. prime focus offset fed compact range reflector with r-card edge terminations located in an existing chamber 20 ft. high, 30 ft. wide and 66 ft. long was probed using a broadband antenna to sample the field at 12 inch increments from the center line to the anechoic chamber wall. The purpose of the test was to evaluate the field roll off in dB to see if a narrower room would significantly impact the performance of the existing reflector system. The new chamber is 20 ft. high, 20 ft. wide and 40 ft. long. The probe data at six frequencies from 2.1 to 17.8 GHz indicated that 10 ft. off the center line the measured field level was -20 dB or greater below the level of the test region, which was our maximum acceptable field level goal. It is expected that the sidewall absorber will provide over 20 dB of bistatic attenuation for a total reflected field level of -40 dB, and is sufficient for conducting antenna pattern measurements in an anechoic chamber. Key Words: Compact Range, R-Card Terminations, Absorber Performance
The present paper introduces a new antenna design to be used in anechoic chambers. When measuring 3D patterns the receiving antenna in the anechoic chamber must be able to sense the two orthogonal components of the field that exist in the far field. This can be accomplished by mechanically rotating the source horn in the chamber. A better and faster approach is to use a dual polarized antenna and electronically switch between polarizations. This new design is a broadband (2-18GHz) antenna with dual polarization. The antenna is a ridged guide horn. The novel part is that the sides have been omitted. Numerical analysis and measurements show that this open-sided or open-boundary horn provides a better and more stable pattern behavior for the entire band of operation as well as good directivity for its compact design. The radiation and input parameters of the antenna are analyzed in this paper for the novel design as well as for some of the early prototypes to show some of the ill effects of bounded quadridge horn designs for broadband applications. Mechanically the antenna is built so that it can be mounted onto the shield of an anechoic room without compromising the shield integrity of the chamber.
• Total Isotropic Sensitivity Power (TIS), which is an acceptable Bit Error rate at a certain incident cell power. • Total Radiated Power (TRP), which is the total transmission power of the Mobile station. These measurements may be performed using the Agilent 8960 or the Rhode and Schwarz CMU 200 Base Station (BS) simulators. All measurements are done in an anechoic chamber and OTA (Over the air). This paper will describe the measurements that are required in order to comply with the CTIA Certification program - Test requirements for performing Radiated RF Power and Receiver Performance measurements on mobile handsets. The paper will summarize the system configuration and the features of this integrated test system.