Spherical Near-field Measurements Research Articles

Real-time spherical near-field handset antenna measurements

A new spherical near-field measurement system, dedicated to personal-communications applications, has been installed at e-tenna Corporation. The system, sold by Satimo, uses an electronically scanned probe array, and offers a dramatic reduction of the measurement time (by a factor ranging from 60 to 1,000) with respect to conventional mechanical scanners. This test range has undergone extensive acceptance testing, which has verified the specified measurement accuracy. The speed of the system, combined with the availability of full-sphere measurement data, enables rapid measurement of antenna efficiency. The system also enables the measurement of other parameters, such as the percentage of radiated power dissipated into the body of a human test subject operating a cellular telephone.

General Analytic Correction for Probe-Position Errors in Spherical Near-Field Measurements.

A general theoretical procedure is presented to remove known probe-position errors in spherical near-field data to obtain highly accurate far fields. We represent the measured data as a Taylor series in terms of the displacement errors and the ideal spectrum of the antenna. This representation is then assumed to be an actual near field on a regularly spaced error-free spherical grid. The ideal spectrum is given by an infinite series of an error operator acting on data containing errors of measurement. This error operator is the Taylor series without the zeroth-order term. The n th-order approximation to the ideal near field of the antenna can be explicitly constructed by inspection of the error operator. Computer simulations using periodic error functions show that we are dealing with a convergent series, and the error-correction technique is highly successful. This is demonstrated for a triply periodic function for errors in each of the spherical coordinates. Appropriate graphical representations of the error-contaminated, error-corrected and error-free near fields are presented to enhance understanding of the results. Corresponding error-contaminated and error-free far fields are also obtained.

Spherical near-field scanning at the Technical University of Denmark

The early work (1969-79) on spherical near-field antenna measurements at the Technical University of Denmark (TUD) is outlined. A spherical near-field transmission formula is described and the first probe-corrected spherical near-field measurements are discussed. The TUD-ESA (European Space Agency) joint effort on spherical near-field testing is also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of spherical near-field measurements to microwave holographic diagnosis of antennas

Microwave diagnosis of antennas is considered as a viable tool for the determination of reflector surface distortions and location of defective radiating elements of array antennas. A hybrid technique based on the combination of the spherical near-field measurements and holographic metrology reconstruction is presented. The measured spherical near-field data are first used to construct the far-field amplitude and phase patterns of the antenna on specified regularized u-v coordinates. These data are then utilized in the surface profile reconstruction of the holographic technique using a fast-Fourier-transform (FFT)/iterative approach. Results of an experiment using a 156-cm reflector antenna measured at 11.3 GHz are presented for both the original antenna and the antenna with four attached bumps. Several contour and gray-scaled plots are presented for the reconstructed surface profiles of the measured antennas. The recovery effectiveness of the attached bumps has been demonstrated. The hybrid procedure presented is used to assess the achieved accuracy of the holographic reconstruction technique because of its ability to determine very accurate far-field amplitude and phase data from the spherical near-field measurements. >

The receiving antenna as a linear differential operator: Application to spherical near-field scanning

The general receiving antenna is represented as a linear differential operator converting the incident field and its spatial derivatives at a single point in space to an output voltage. The differential operator is specified explicitly in terms of the multipole coefficients of the antenna's complex receiving pattern. When the linear operator representation is applied to the special probes used in spherical near-field measurements, a probe-corrected spherical transmission formula is revealed that retains the form, applicability, and simplicity of the nonprobe-corrected equations. The new spherical transmission formula is shown to be consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.

Suppression of reflections by directive probes in spherical near-field measurements

The influence of probe correction in spherical near-field measurements on signals from outside the test volume is investigated theoretically and experimentally. It is found that the suppression of reflections obtained by a directive probe is not disturbed by the probe correction. A geometric relation between the antenna "minimum sphere" and the probe pattern beamwidth is established, whose satisfaction guarantees the absence of numerical instabilities in the far-field computation. The condition is sufficient, but not necessary if the "minimum sphere" of the antenna is in the near field of the probe.

Improved algorithm for probe-corrected spherical near-field/far-field transformation

The technique for computation of antenna far fields from spherical near-field measurements has been improved, allowing large antennas to be treated. The efficiency and accuracy is demonstrated for an antenna without rotational symmetry and about 50 wavelengths in diameter.

Probe correction of spherical near-field measurements

Probe correction has been implemented in a computer program which calculates antenna far fields from spherical nearfield measurements. The computer program has been applied to near-field measurements on a satellite model, and the accuracy of the computed far field is significantly improved, compared with the results obtained without probe correction.