JEM’s SNF Chamber Capabilities

JEMs spherical near-field (SNF) antenna test chamber is the fastest facility available for full 4 pi steradian data collection. Using an array of electronically scanned probes to scan a full 360 degree measurement plane, our technicians can complete measurements in minutes rather than hours.

Our SNF chamber can perform tests over frequencies from 400 MHz to 6 GHz, enabling testing of antennas for AMP, PCS, GSM, Bluetooth™, IEEE 802.11, GPS and other new and evolving wireless systems. Mounting the antennas in free space or on human subjects allows us to measure radiation patterns, efficiency, average gain, and any human body interaction to the radiating device.

SNF Physical Setup

antenna testing snf

Fixturing

Our existing structures allow us to fixture multiple antennas during the allotted test time.  If the weight of the antenna under test is off-center by more than 36”, or if the antenna requires a specific configuration, a custom fixture may be necessary. Customers have the option to design, as well as provide their own fixtures. To download the pdf drawing of the mounting pattern, click here. Alternatively, you may send us a request for the dxf artwork file, and we will respond as promptly as possible.

Data Output

JEM’s Spherical Chamber can generate a wide range of data, i.e. 3D or 2D Radiation Patterns, Swept Gain and Efficiency Plots, and ASCII Data Files including amplitude, axial ratio, polarization, and phase.
See typical radiation pattern data plots below.

25MHz Dipole 2450MHz Steered Array1850MHz CP Spiral
 3D Data Plot  3D Data Plot  3D Data Plot 
2D Data Plot2D Data Plot2D Data Plot

   


 

Frequently Asked Questions

Measurements:

Calibration:

  • What are your calibration procedures?

    The Spherical Chamber uses an array of probes to measure the spherical performance of antennas. Once a year, a Probe Calibration is performed by the chamber manufacturer to normalize the amplitude and phase of each probe in the array. Once a month, a gain calibration is performed using a broadband horn and a series of dipoles. A reference circuit in the range provides a gain offset to correct for temperature variations between monthly calibrations. 
    The Spherical Chamber can be calibrated using either Gain or Efficiency standards.

  • What calibration reference standards do you use?

    From 1-6GHz, we use a broadband horn that was measured for gain at Georgia Tech using NIST traceable standards. From 400-999MHz, we use a series of dipoles that were measured for efficiency using the Wheeler Cap method.

  • I would rather use my own gain standard in a specific frequency band. Is that possible?

    Yes. Special calibrations can be performed. All that is required is a standard measurement in the range. The calibration procedure will be performed as part of your range time. The gain accuracy of any measurements will be referenced to your standard.

Mechanical Mounting:

  • How are antennas mounted in the range?

    The range has a Styrofoam column with a flat foam table in the center of the ring. Antennas are positioned on top of the column. We have a laser sight to help center the antenna in the ring. Foam blocks and pieces are available to help position oddly shaped samples. Other fixtures can be used to mount equipment that will not work with a foam column.

    What is the largest sample size allowed? 
    We have had an aircraft door as large as 5’ x 6’ in the range.

  • What is the heaviest sample allowed?

    If the sample can be safely lifted into position by two people, it can be measured in the range. We have numerousfixtures besides the foam column that allow for different sizes and shapes.

  • We have a really oddly shaped and heavy device that needs testing. Can we design and bring our own fixture?

    Customers can bring their own mounting fixtures. The hole pattern of the base pedestal is available. Mechanical drawings are available to assist customers in mounting and centering their devices. Download the pdf drawing and dxf artwork of the mounting pattern by clicking here.

  • What connector do you use?

    The cable in the range uses an SMA connector. We have various adapters, but it usually better for each customer bring their own adapters and loads.

  • What cable do you use? How is it positioned?

    A cable runs up the center of the foam column. There is a cutout near the top to allow for a cable loop. The cable running through the column has a lossy coating to minimize reflections. A 12 inch cable at the top has ferrite beads to minimize currents on the outside jacket.

  • I need to use other equipment in the range during the measurement.

    AC power is available inside the range. We have various absorber pieces that can be used to cover ancillary equipment during the test.

Mechanical Handling the Data:

  • Capabilities Physical Setup Fixturing Data Output Frequently Asked Questions high-speed spherical antenna rf test chamber with human subject JEM's SNF Chamber Capabilities JEM's spherical near-field (SNF) antenna test chamber is the fastest facil

    All of the data exported is in standard ASCII text format and can be read by Excel, MatLab, and other standard software packages.

  • Can I look at specific data cuts and frequencies during the measurement session?

    It is your time to spend as you want. We cannot process data while a measurement is taking place. But in between measurements, you can look at graphs and data. All it costs is the time taken to process the data.

  • What data output is available?

    We collect all of the spherical data using the software that runs the Spherical Chamber. We will export ASCII data files according to your needs. Typical data packages are:

    • Full spherical E-Phi and E-Theta values at each frequency. This data can be Linear and/or Circular.
    • Maximum Gain. This is the maximum gain measured regardless of peak beam position.
    • Efficiency in dB and/or %.
    • Axial Ratio

    Individual Phi or Theta cuts can be exported, but are extremely time consuming given multiple samples. Most customers process the E-Phi and E-theta data for specific pattern cuts later to save time for sample measurements.

  • How will I get my data?

    Data can be burned to a CD or DVD. We can copy your data to a memory stick. We also have an FTP site that you can download your data from. You will be emailed a link for the download site. You are the only customer who will be able to access your data from the FTP site.

  • How long will the data be on your system?

    We will keep your data for at least 1 month unless you tell us to delete it.

  • We have sight sensitive samples. Can these be accommodated?

    We have run sight sensitive samples in the range. We have a camera in the range that can be disabled. Once we have run you through the antenna mounting procedure, you can mount your own samples. We do not need to see your antennas to measure them and process the information.

  • Can JEM measure classified antennas?

    Whether or not we can measure and process the data from a classified antenna is defined by your particular program, and can only be determined by your Security Officer. The range is in a separate building and can be isolated. The measurement frequency band can be padded with extra frequencies to hide specific points. We have dealt with sight sensitive samples. 
    Our system computer has removable drive bays, and can be unplugged from the JEM computer network. If you send us a blank hard drive ahead of your measurement session, we can format the drive and clone the operating system and measurement software required. We will boot up the system with your drive. At the end of the session you can take it with you.

Scheduling/Invoicing: