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Inversion of the material parameters for a sample usually requires that the sample fill the waveguide cross-section. Alternative methods require that a non-filling sample be aligned along the center-line of the waveguide. However, it is not known how errors in placement impact the accuracy of the inversion. Hence, a numerical simulation to assess these errors is beneficial to the community. The extraction of the S-parameters from a rectangulardielectric-filled waveguide is conducted numerically by means of the Finite Element Method (FEM) and the Thru-Reflect-Line (TRL) calibration technique. Three different ratios of dielectric sample width (d) to waveguide width (a) are primarily studied. The results are then validated with experimental data on the X-band. An assessment of error with respect to position will be presented at the meeting.
In previously reported work, the groundwave correction approach was presented for measurement of the gain of vertically polarized antennas in the presence of a seawater groundplane. This approach was limited to application in the commercial HF (2-30 MHz) band due to a variety of factors, including the geometry of the test range, and so can not always be applied at higher frequencies. This paper will discuss a method for measuring the gain and azimuthal pattern performance of antennas operating in the commercial VHF band (50-175 MHz) that has been developed at the NUWC Fishers Island Antenna Range, and will discuss its application and implementation.
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
This paper describes the first experience gained with a new carbon composite compact range reflector (C3R2). The reflector’s backup structure is made entirely of carbon fiber reinforced composite material. An outstanding advantage of this design is its superior mechanical and thermal-environmental stability. This yields improvement in the overall performance. We have revised the process by which compact range reflectors are designed and modeled, making use of professionally authored software. We describe the results of electromagnetic field probe measurements made at the factory. Special attention is given to new results at W-band – in the 75 to 100 GHz regime.
A generally practiced way to improve the sidelobe accuracy in antenna measurements is by repeating and averaging the measurements in different positions in the quiet zone (also referred to as APC or AAPC, depending on the application). An alternative new way for improving the accuracy of compact range measurements is by moving the compact range feed in different locations. This can easily be achieved for both horizontal and vertical directions. Although feed scanning causes a boresight shift, this can be easily compensated if the feed positions are selected intelligently. A significant measurement speed improvement can be realized by using multiple feeds in the relevant locations, instead of moving a single feed sequentially into these locations. Feed scanning APC has been successfully tested in the Ericsson Microwave Systems Compact Range, where it is now practiced in high accuracy radar antenna measurements.
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.
In this paper, we study the possibility to use an amplitude hologram as a reflection-type collimating element to produce a plane wave in the compact antenna test range (CATR). So far, we have used holograms as transmission-type elements only. The hologram studied here has a diameter of 600 mm and it operates at the frequency of 310 GHz. It is a computer-generated slot pattern etched on a thin metal-plated dielectric film. We have simulated and measured the plane wave field reflected from the hologram. The maximum measured ripples are only 1.6 dB and 20°, peak-to-peak. The reflection-type hologram has some advantages over the transmission-type one. For example, the power loss is about 4 dB lower for the reflection-type hologram. In addition, a CATR based on the reflection-type hologram can be situated in a much smaller space. To demonstrate the capability of the reflection-type hologram in actual antenna testing, the radiation pattern of a small reflector antenna was measured at 310 GHz.
Direction Finding (DF) systems have long been an area of intense research within the Air Force Research Laboratory. There are presently two types of existing DF systems: wideband multi-mode antennas and interferometers. Wideband multi-mode DF systems allow for a large bandwidth but present a low resolution and high variance. Interferometers provide high accuracy and low variance but are narrow band and require a large number of single aperture antenna elements. An effort has commenced to incorporate a broadband DF system with high resolution using two multi-mode spiral antennas. Using an interferometer of multi-mode elements, we can provide high resolution and wideband operation without using numerous antennas. This paper presents the results of extensive wideband measurements carried out on a four-arm spiral antenna and the associated modeformer. These measurements are used to assess and validate the angle estimation capability of the multi-arm spiral antenna.
This paper describes an automated ellipticity measurement system for ultra-wideband (UWB) circular-polarization antennas. The system comprises a double-ridged horn (DRH) antenna, a high-precision polarization rotator, an antenna-under-test (AUT) positioner, a vector network analyzer (VNA), and a controlling computer. The liner-polarized DRH antenna typically rotates 360° in 5°-intervals controlled by the rotator. At each angle, the VNA sweeps an ultra-wide bandwidth to measure the path gain. The least squares method was employed to find the axial ratio (r >= 1) and inclination angle at each frequency by fitting the plots to an anticipated peanut shell curve. Since the conventional cross polarization discrimination (XPD) has been defined for narrowband antennas, we proposed the wideband XPD as a frequency integration of the square of the circular polarization ratio (x), where x = (r + 1) / (r - 1), embracing a certain bandwidth. The wideband XPD represents the total power ratio between co- and cross-polarizations in the bandwidth. We measured the ellipticity and the wideband XPD of an axial-mode helical antenna using this system.
A strong interest exists in the commercial and military sectors for small and broadband antennas. For instance, in the automotive industry there is a need for a single antenna operating in the frequency range of 825-2500 MHz (AMPS, DAB, GPS, PCS, SDARS). For military applications, there is also a need to have a single aperture which permits operation in different communication bands and can be also used for imaging and guidance applications. These needs require wide band antennas, such as the miniaturized spiral antenna. In this paper we present the implementation of a spiral antenna situated on a ground plane that is fully functional at the size of 0.16 wavelength onward. Low profile (0.05 wavelength) and broadband operation design goals bring unique challenges, which must be confronted with multiple-front techniques. A combination of antenna geometry design and material loading results in the desired miniaturization effect. Further techniques, including the use of distributed resistors ensure good axial ratio and VSWR. Pattern uniformity and phase linearity of the antenna was also improved. In addition, we also examine the effectiveness of broadband spiral antenna miniaturization as a function of loading material’s dielectric constant.
Standard Gain Horns (SGH) are normally used as reference antennas in antenna measurements. Gain charts for SGH are provided by the supplier. These charts give the gain of the SGH in dBi versus frequency but do not provide any information on the phase variations versus frequency. For complete antenna calibration, one needs the phase as well as gain data for SGH over the frequency band of interest. To obtain the gain and phase data, one can use the three-antenna method which requires three independent measurements and, therefore, is more susceptible to measurement errors. Note that if one has access to two identical antennas, the three-antenna method reduces to a single measurement which is more desirable. In practice, however, one does not have access to two identical antennas. In this paper, a novel method which mimics measurements with two identical antennas is described. In the method, one performs S11 type measurements on the antenna of interest by placing the antenna in front of a large conductive flat plate. The late term in the S11 measurements is then used to obtain the boresight gain and phase of the antenna under test. The measured gain and phase data of several antennas obtained using the proposed method is presented and compared with the results obtained using the three-antenna method as well as with analytical results.
ABSTRACT We are in the era of wireless communications and devices. The antennas that enable these technologies are electrically small and can be challenging to test and analyze. Yet, the industry is becoming more standardized, and so too are the tests and certifications being adopted to validate these antennas. These antennas must undergo “antenna measurements” to characterize such information as far-field patterns and gain. Additionally, hand-held devices, such as cell phones, must satisfy requirements of the Over-the-Air (OTA) performance tests as specified by the Cellular Telecommunication and Internet Association (CTIA). These tests require a measurement system that can accurately collect data on a spherical surface enclosing the AUT. This system also has to provide the appropriate data analysis capabilities and has to be constructed from dielectric materials to minimize reflections.
• 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.
Radiation efficiency is an inherent property of an antenna that relates the net power accepted by an antenna to the total radiated power. It is especially useful for handset antennas where the radiation patterns are often of less use for comparing competing antennas. Radiation patterns though not as useful for direct comparisons, still provide one method by which efficiency can be calculated. To accurately calculate the efficiency from patterns, it becomes necessary to obtain multiple pattern measurements (cuts). A larger number of cuts whilst yielding more accurate efficiency results, significantly increase measurement time. Thus an antenna designer is often forced to trade off accuracy against measurement time since both quick and accurate measurements are desired. The focus of this paper is to quantify this trade off, in order to provide guidelines on the number of pattern measurements required for accurate efficiency results. Simulated and measured far-field radiation patterns are used and various numbers of cuts are utilized to quantify the loss in accuracy with a reduced number of cuts. The techniques outlined are geared primarily towards cellular handset antennas.
A hemi-spherical near-field test system with to be considered. This type of test system offers a added far-field capability is described. The facility has practical solution to the test problem in that combined been constructed for the characterization of automotive motion of a probe antenna and the object under test, antennas. The test system consists of an 11m tall allows for spherical data acquisition covering one half of dielectric gantry, a 6.5m diameter in-ground turntable and the spherical surface. The configuration also allowsa 28m-diameter radome enclosure. Special software integration of a conducting ground plane as well as a required to compensate for the reflectivity in the facility radome enclosure for weather protection andand the hemi-spherical truncation was developed and confidentiality. forms an integral part of this test system. The characteristics of this facility are described in this paper The characteristics of this newly developed and measured data is presented. facility are described in the following section of this paper.
This paper presents the methodology we use to measure radiation patterns of small terminal antennas. The in-house developed measuring system is capable to record radiation patterns on the entire sphere and recorded values are not corrupted due to proximity of a large dual-axis positioner. As a feed cable had been identified as a primary factor modifying electrical properties of small antennas, we eliminated the feed cable at all by use of a built-in generator. Such generator is mounted back-toback to the measured antenna. Most preferable the generator should be supplied with a battery, but use of a wired dc supply with a typical supplier is also acceptable in many instances. Such a concept of setup brings about many problems with providing a reference signal to an antenna receiver. Perhaps, firm operation of a reference channel is hard to accomplish without using advanced engineering means. Among them may be a switch with permanent power monitoring in its channels or an optoelectronic leg in the antenna microwave feed.
Abstract Historically, most commercially available Local Oscillator (LO) distribution systems have used a closed loop control system to set LO power levels. As frequency switching times decrease, the time constant of the control loop can introduce errors to precision antenna measurements. This paper will discuss the basics of the remote mixing test system, and then discuss the limitations of various current approaches. Finally, it will introduce an open loop LO distribution system, and discuss the design considerations for the various components of the system.
A uniquely inexpensive solution to Frequency-Modulated Continuous-Wave (FMCW) radar was developed, using low cost Gunn oscillator based microwave transceiver modules. However these transceiver modules have stability problems causing them to be unsuitable for use in precise FMCW radar applications, when just one module is used. In order to overcome this problem, a unique radar solution was developed which uses a combination of 2 transceiver modules to create a precise FMCW radar system. This FMCW radar system was then used in a small Synthetic Aperture Radar (SAR) imaging system. The SAR imaging system was composed of a 12 foot long linear track to which the FMCW radar system was mounted. The FMCW radar system would traverse the linear track, acquiring data to be used for producing SAR imagery. The combination of the small aperture length, narrow bandwidth transmit chirp, and overall frequency instability of the FMCW radar system created a number of SAR imaging problems which were unique in this application. However, it was found that when these issues were properly addressed it was possible to create SAR imagery on a low budget.
The development of Radio Frequency Identification (RFID) system for tracking and controlling goods and products, and obtaining information from people and objects are growing very rapidly in modern telecommunication area. The read range is one of the most important key factors of the RFID system. The possible read range is decided by the system specifications, such as transmitted power, antenna gain, receiver sensitivity, etc. In this paper, the read ranges of a commercial RFID system with various antennas and measurement configurations in an anechoic room are measured. The read range of 900 MHz-band RFID is calculated and compared with the measured read range. Also, actual read range is strongly influenced by real operating circumstances. The measurement results are compared with the read ranges measured in indoor office environments.
Operating frequencies in the gigahertz range is creating an increased need for electromagnetic compatibility (EMC) testing. In the United States, FCC regulations require conformance to radiated and conducted emissions specifications. An EMC laboratory was established at Cal Poly San Luis Obispo (screen room, test instrumentation, and software) and an experiment was developed to explore conducted emissions effects. This paper will describe the test configuration, explain the calibration procedure needed to acquire accurate measurements, and illustrate measurement techniques applied to two example systems. In addition, the data collection process is illustrated through software donated by CKC Laboratories (EMC specialists). To verify the functionality of the laboratory and to assess measurement accuracy, two 12V/15W switching power supplies are characterized for conducted emissions performance; one as supplied by the vendor (KGCOMP) and a second unit with the EMC filters removed. The noise spectrum for both units are plotted against frequency and compared to FCC specifications. The unaltered unit is shown to be in compliance, thus verifying the accuracy of the test procedure and instrumentation.