The phaseless antenna measurement technique is advantageous for high-frequency near-field measurements in which the uncertainty of the measured phase is a problem. In the phaseless measurement, which is expected to be used in the frequency band with a short wavelength, a slight positional deviation error of the probe greatly deteriorates the measurement result. This paper proposes a phase retrieval method that can compensate the measurement errors caused by misalignment of a probe and its jig. And this paper proposes a far-field estimation method by phase resurrection that incorporated the compensation techniques. We find that the positioning errors are due to the random errors occurring at each measurement point because of minute vibrations of the probe; in addition, we determine that the stationary depth errors occurring at each measurement surface as errors caused by improper setting of the probe jig. The random positioning error is eliminated by adding a low-pass filter in wavenumber space, and the depth positioning error is iteratively compensated on the basis of the relative residual obtained in each plane. The validity of the proposed method is demonstrated by estimating the far-field patterns using the results from numerical simulations, and is also demonstrated using measurement data with probe-positioning error. The proposed method can reduce the probe-positioning error and improve the far-field estimation accuracy by more over than 10 dB.

This paper shows experimental results of packet error rates (PERs) in wireless-LAN mounted printed circuit boards and gives a discussion on a mechanism of electromagnetic noise coupling that affects the PER. We utilized the amplitude probability distribution to investigate the noise coupling channel. We measured the magnetic near-field distribution to obtain information about noise sources. Based on measurement results, we also performed parallel plate resonance analysis to find out electromagnetic interference antennas. We confirmed that noise radiates from a power supply system of a digital circuit and its coupling to a receiving antenna causes an increase of the PER.

A new technique to estimate the Poynting vector distribution from near-magnetic-field measurement is proposed. To calculate the Poynting vector, both electric and magnetic field should be known. In the proposed method, only magnetic-field measurement of three orthogonal axes is required. Electric field is estimated from the measured magnetic field by using the Maxwell's equation. The modified Yee cell is employed to estimate electric field from the measured magnetic field. Finally, the Poynting vector is calculated from the measured magnetic field and the estimated electric field. Since the proposed method enables us to understand propagation direction of electro-magnetic energy, it can be utilized to locate an emission source and to investigate a mechanism of undesired emission. Experiments are carried out to discuss the accuracy and to validate practical usefulness.

This paper presents the near-field to far-field transformation for an outdoor radar cross section (RCS) range. Direct measurement of the large actual target requires quite a long measurement range. The near-field to far-field RCS transformation method achieves the reduction of measurement range. However the non-uniformity of the incident electric field distribution on the target causes some errors in RCS prediction. We propose a novel near-field to far-field RCS transformation method that can be applied to an outdoor RCS measurement. The non-uniformity of the incident electric field distribution is successfully resolved by introducing the correction term of the ground bounce. We investigate the validity of the proposed method by the simulation and measurement.

Spatial filtering is a useful method to suppress undesired reflection from unwanted scatters in Radar Cross Section (RCS) measurements. Actually, it is difficult to prepare an ideal field which satisfies the far-field criterion for RCS measurements of large targets. We applied the filtering method to a bistatic RCS measurement in a near field and investigated the validity of that method by varying the scanning angular span. Electromagnetic simulations show that predicted RCS profiles from near-field data with unwanted scatters closely matched far-field reference data of the test target. In conclusion, the results show that the method is effective for bistatic RCS measurements in practical field enviroments.

We have developed a near-field mapping system with a fiber-based electro-optic (EO) probe for microwave antenna characterization. In this probe, an EO crystal is mounted on the tip of an optical fiber through a collimating lens. Since the lens allows the crystal thickness to be lengthened by reducing the loss of an optical beam coupling back to the optical fiber, sensitivity is improved. Because the tip of the EO probe consists of a 1-mm-cubic EO crystal and contains no metallic components, there is very little disturbance of the mapped electric field. Fixing the optical fiber in a thin glass tube provides stable sensitivity during long-term mapping over a large area. The fabricated EO probe has a dynamic range larger than 45 dB, flat sensitivity from 1.95 to 20 GHz, and directivity with cross-axis sensitivity isolation greater than 30 dB. A comparison of the measured and calculated near fields of a dipole antenna showed negligible static or inductive coupling between the EO probe and the dipole antenna. Using a tissue-equivalent phantom to assess the specific absorption rate (SAR), we demonstrated the potential of the EO probe for mapping the electric field with information of amplitude and phase. The EO probe can detect an electric field of less than 0.6 V/m, which corresponds to a SAR of 0.5 mW/kg. This value satisfies the minimum detection limit defined in the regulations for determining SAR. This result shows the potential of the near-field mapping system with the fiber-based EO probe in practical applications.

Electromagnetic field probes inevitably disturb the original distribution of the field when they are positioned close to a device. This disturbance in turn affects measurement accuracy and device operation. We developed an optical magnetic field probe, comprising a loop antenna element and an electro-optic crystal, for highly accurate magnetic near-field measurement in the GHz frequency range. We analyzed the invasiveness of the optical magnetic field probe quantitatively both experimentally and using finite difference time domain simulation. We found that eliminating the metal cable reduced the disturbance of the surrounding field that was to be measured. In addition, we investigated the magnetic field detection characteristics of the probe and its influence on the operation of a microstrip line. The optical magnetic field probe was less invasive and provided more accurate measurement.

We have shown that a photonic sensor can be used as an electric-field probe for planar near-field measurements of X-band antennas. Because an antenna on the photonic sensor is small (about 0.1 λ) compared to the wavelength, the photonic sensor can directly measure the amplitude and the phase of the electric field close (about 0.3 λ) to the apertures of antennas without disturbing the electric field to be measured. Therefore we can obtain the antenna pattern by transforming the measured electric field without probe compensation. To verify the merits of the photonic sensor, we have evaluated the antenna patterns of a standard gain horn antenna and a microstrip array antenna at 9.41 GHz. Comparing the results obtained using the photonic sensor with those obtained using the conventional open-ended waveguide probe and other methods, we have shown that the antenna patterns agree with each other within 1 dB over wide ranges of directivity.

Harmonic distortions of a recently developed lightweight film-type ESPAR (Electronically Steerable Passive Array Radiator) antenna are investigated experimentally. These distortions arise from the nonlinearity of the varactor diodes that are directly integrated with the parasitic radiator elements to control the antenna's radiation pattern. A reactive-near-field measurement technique that employs low-interference probes in an ultra-small anechoic box is used to reduce experimental time and cost. An anti-series varactor pair is introduced and compared with the conventional single varactor. Consequently, an ESPAR antenna equipped with the anti-series varactor pair exhibits remarkable suppression of nonlinear distortion. In particular, the second- and the third-order harmonic is reduced by approximately 20 dB and 12 dB from the level of a single varactor type ESPAR antenna, respectively.

In this paper we propose a new far-field RCS prediction method using cylindrical or planar near-field RCS data. First we derive the relation between RCS and the scattering coefficient using physical optics technique. The far-field RCS prediction algorithm is obtained by approximating the relation using the condition of Fresnel region and the paraxial constraint of scanning angle in the case of cylindrical or planar scanning. Finally we predict the far-field RCS using measured or calculated near-field RCS data of the conducting rectangular prism or plate. The validity of the proposed algorithm is demonstrated.

The wave forms of electric and magnetic fields radiated by short gap discharges are measured to analyze electrostatic discharge (ESD) events in the near-field zone with the monopole antennas, the loop antenna and the 5.5GHz bandwidth waveform digitizer. The antenna outputs are corrected by the measured characteristics of the antennas. The relations between the measured electric field and the discharge currents are discussed.

The antenna factor measurement of the dipole antennas for electromagnetic interference (EMI) measurements is studied theoretically and experimentally. The 3-antenna method is applied to near-field. Near-field transmission characteristics between the transmitting and receiving dipole antennas is obtained by using the electromotive force (EMF) method, where sinusoidal current distributions are assumed. It is shown that the antenna factors can be measured from transmission values between two antennas and near-field correction factors at any height of each antenna.