Antenna Test Equipment And Antenna Testing In Relation To Emi And Cell Phones

By Author: convurgency
Total Articles: 16
Comment this article

There are a number of testing methods and equipment types used to establish types and function ranges for various antennas. Of these types all are used in determining the effective range and output for Cellular phone systems in addition to varied uses that other types of antenna possess. The first step in determining what an antenna should be used for is applying measurement techniques to it. These are tests that ensure the antenna meets desires specifications for the task it is needed for. Some things checked for are gain, pattern, radiation, polarization, beamwidth and impedance.

Antenna pattern is a measurement of response by the antenna to the plane wave incident from a given direction and the relative density of power seen by the wave transmission properties of the antenna in a given direction. We find that reciprocal antenna have identical patterns for both. The various types of measurement techniques that have been developed for antenna patterns include far-field with the AUT place in the far-field of a range antenna, near-field for measurement of the field close to the antenna, and the compact range which uses ...
... a reflector to create a far-field reading at a closer distance. This can be achieved through a ground-bounce technique.

Another option is the Electromagnetic near-field scanner. This is used to determine the spatial distribution of the field through single or multiple field probes of the near-field region around the antenna being tested which is then post processed with associated numerical methods that converts the test data into an approximation of the field. Some of the additional data required include voltage as a function of the time or frequency. Any object that radiates or stores an electromagnetic field intentionally or not should be considered th DUT. Voltage patterns are mapped in either planar, cylindrical, or spherical services as a specified number of spatial samples.

While scanners were developed originally to test signals from microwave antennas, these days they find application in EMI testing. A scanner can be used to localize real EMI sources from within a DUT. Because of this the scanner should be located in the reactive region of DUT so it can detect spatial localization of the charges and surface densities of currents directly from the probe signal pattern. The distance range is usually rather small, from 1mm to 30 μm depending on what is being scanned. When attempting to localize field emissions within frequency domain use of a digital storage oscilloscope as a signal receiver can function as both time domain detection and Fourier transform signal processing. These scans can be one of three types, rectangular planar scanning, polar planar scanning, and cylindrical planar scanning. Each of these is transformed into far-field by applying a Fourier or Laplace transform to them.

A number of parameters are tested for with antenna. Some, like polarization and SWR are easily measured. Others, like impedance, requires specialized equipment. Measuring radiation patterns is another thing that needs a complex setup with enough clear space to place a sensor in the far field of the antenna or a anechoic chamber for such measurements coupled with a study of the geometry and the ability to rotate the antenna while the test in in progress.

Radiation patterns are the cartesian or polar graphic image that shows the field strength that is transmitted or received by the antenna. Such graphics who sidelobes and backlobes in addition to the main direction. Often several curves are required to depict the entire field. When radiation is symmetrical about an axis then one graph is typically enough. These are defined as the locus of all points where emitted power per unit surface is equal. Directive gain, usually in decibels may be depicted also.

The ratio of power radiated to the power received from a transmitter is called efficiency. This is not SWR, which actually is the amount of power absorbed and directed into heat instead of RF. Components of SWR include radiation and loss resistance factors which reduce efficiency.

The range of frequencies that an antenna can work under with a specified level of performance is the antenna's bandwidth. Often this is determined by looking at the frequencies in which the SWR is less than 2:1.

The ratio of maximum intensity divided by that of a hypothetical isotropic antenna of the same power is the antenna directivity. This is a dimensionless ratio and is expressed numerically or in decibels. This is also the peak value of directive gain. This is not the power gain, and is not related to efficiency.

To understand the basic concept of cellular system and learn how these EMI devices works, one must have a sound understanding of antenna test equipment. Here you can find out the very basics of Antenna testing and can get the comprehensive knowledge abot the working of your cell phone.