Characterization of a Photonics E-Field Sensor as a Near-Field Probe

Authors: Brett T. Walkenhorst, Vince Rodriguez, James Toney
Publication: AMTA 2017
Copyright Owners: NSI-MI Technologies, SRICO

In this paper, we explore the possibility of using a photonics-based E-field sensor as a near-field probe. Relative to open-ended waveguide (OEWG) probes, a photonics probe could offer substantially larger bandwidths. In addition, since it outputs an optical signal, a photonics probe can offer signal transport through optical fiber with much lower loss than what can be achieved using RF cables.

We begin with a discussion of the theory of the device followed by a summary of results of a photonics sensor that was tested in a spherical near-field (SNF) range. In these tests, data were collected with the photonics probe in the test antenna position to characterize various probe parameters including polarization discrimination, probe gain, effective dynamic range, and probe patterns. Results are presented along with discussions of some of the advantages and disadvantages of using a photonics probe in a practical system based on the lessons learned in the SNF testing.

Comparing Predicted Performance of Anechoic Chambers to Free Space VSWR Measurements

Author: Vince Rodriguez
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

Indoor antenna ranges must have the walls, floor and ceiling treated with RF absorber. The normal incidence performance of the absorber is usually provided by the manufacturers of the materials; however, the bi-static or off angle performance must also be known. In reference [1], a polynomial approximation was introduced that gave a prediction of the reflected energy from pyramidal absorber. In this paper, the approximations are used to predict the quiet zone (QZ) performance of several anechoic chambers. These predictions are compared with full wave analysis performed in CST Suite®. A 12 m wide by 22 m long with a height of 12 m chamber was analyzed at 700 MHz. The QZ performance was compared to the polynomial predictions showing a difference of less than 2.2 dB. In addition, comparisons are made with measurements of the QZ performance of anechoic chambers. Measurements performed per the free space VSWR method of three different chambers are compared with the prediction that uses the polynomials presented in [1]. The chambers are: a 18 m long by 11.5 m wide and 11.5 m in height operating from 100M MHz to 12 GHz; a 13.41 m by6.1 m by 6.1 m operating from 800 MHz to 6 GHz; and a 14 m long by 4.12 m by 4.27 m operating in the X band. The results show that the polynomial approximations can be used to give a reasonably accurate and safe prediction of the QZ performance of anechoic chambers.

Effects due to Antenna Mount in Base Station Antenna Measurements

Authors: John McKenna, Vivek Sanandiya, Larry Cohen
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

Cellular Base Stations require efficient performance validation methods. One performance criterion is the radiation pattern. Our measurements show a radiation pattern change caused by the antenna mount structure, though industry guidance [1] does not yet control or mention this aspect of the test configuration. Consequently, the current guidance leads toward lack of repeatability. We recommend industry guidance be amended to include post-BSA distance as a test configuration parameter.

Measured Data is presented showing radiation pattern dependencies upon the mount in a CATR implementation. Explanations as to the Root Cause are stated.

Group Delay Measurement For Satellite Payload Testing

Authors: A.C. Newell, S.F. Gregson, P. Pelland, D. Janse van Rensburg
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

In this paper, we present a method for measuring antenna group delay (GD) in a planar near-field range. The technique is based on a set of three antenna pairs, measured sequentially, from which the insertion phase of the measurement system and the near-field probe can be resolved. Once these parameters are known, insertion phase for the device under test (that is to say a Tx or Rx antenna) can be measured and GD calculated as the negative frequency derivative of the insertion phase with respect to frequency. An added complexity in the case of a near-field measurement is the near-field probe is in close proximity to the device under test, does not satisfy the far-field condition. We also show that group delay can be extracted from a single near-field measurement point in the antenna’s aperture plane, leading to significant test time savings. Measured results are presented and discussed.

Measurement of Antenna System Noise Temperature Using Planar Near-Field Data

Authors: A.C. Newell, P. Pelland, S.F. Gregson, D. Janse Van Rensburg
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

This paper presents the results of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. The ratio of antenna gain to system noise temperature (G/T) is usually determined in a single measurement when the antenna is alternately pointed towards the “cold sky” and a hot radio source such as the sun or a star with a known flux density. The antenna gain is routinely determined from nearfield measurements and with the development of this new technique, the system noise temperature can also be determined using the same measurements. The ratio of G/T can therefore be determined from planar near-field data without moving the antenna to an outdoor range. The noise temperature is obtained by using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent or “imaginary space” portion of the spectrum. Near-field data is obtained using a data point spacing of λ/4 or smaller and the plane-wave spectrum is calculated without applying any probe correction or Cos(θ) factor. The spectrum is calculated over real space corresponding to propagating modes of the far-field pattern and also the evanescent or imaginary space region where kx2+ ky2 ≥ k2. Actual evanescent modes are highly attenuated in the latter region and therefore the spectrum in this region must be produced by “errors” in the measured data. Some error sources such as multiple reflections will produce distinct localized lobes in the evanescent region and these are recognized and correctly identified by using a data point spacing of less than λ/2 to avoid aliasing errors in the far-field pattern. It has been observed that the plane wave spectrum beyond these localized lobes becomes random with a uniform average power. This region of the spectrum must be produced by random noise in the near-field data that is produced by all sources of thermal noise in the electronics and radiated noise sources received by the antenna. By analysing and calibrating this portion of the spectrum in the evanescent region the near-field noise power can be deduced and the corresponding noise temperature determined. Simulated and measured data will be presented to illustrate and validate the measurement and analysis techniques.

On The Design of Door-Less Access Passages to Shielded Enclosures

Author: Vince Rodriguez
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

RF shielded enclosures have been common features in laboratories and manufacturing areas for over 70 years. They provide a quiet environment where RF measurements can be performed without interference from outdoor sources and are used to keep potentially classified frequencies and modulations from leaking out. In general, these shielded rooms have shielded doors to maintain the shielding integrity of the enclosure until they are opened. In some cases, to maintain the shielding integrity as personnel moves from the inside to the outside of the room and vice-versa, dual shielded doors with a small vestibule between them are used. However, the presence of multiple doors increases the time to access the enclosure. To solve this, some enclosures are designed featuring access passages to maintain the shielding integrity over a broad frequency without the use of doors. Although this type of access has been around for over 40 years, its design has never been discussed in the literature. In this paper, a door-less access is analyzed and some design rules are presented. The limitations of these accesses are also presented. While clearly they do not have the shielding performance of a shielded door, they are ideal for certain applications.

On the Disadvantages of Tilting the Receive End-Wall of a Compact Range for RCS Measurements

Author: Vince Rodriguez
Publication: AMTA 2017
Copyright Owner: NSI-MI Technologies

Tilting the receive end wall of a compact range anechoic chamber to improve Radar Cross-Section (RCS) measurements has been a tool of the trade used since the earliest days of anechoic chambers. A preliminary analysis using geometrical optics (GO) validates this technique. The GO approach however ignores the backscattering modes from the reflected waves from a field of absorber. In this paper, a series of numerical experiments are performed comparing a straight wall and a tilted wall to show the effects on both the quiet zone and the energy reflected back towards the source antenna. Two Absorber covered walls are simulated. Both walls are illuminated with a standard gain horn (SGH). The effects of a wall tilted back 20° are computed. The simulations are done for 72-inch long absorber for the frequency range covering from 500 MHz to 1 GHz. The ripple on a 10 ft (3.05 m) quiet zone (QZ) is measured for the vertical wall and the tilted wall. In addition to the QZ analysis a time-domain analysis is performed. The reflected pulse at the excitation antenna is compared for the two back wall configurations Results show that tilting the wall improves measurements at some frequencies but causes a higher return at other frequencies; indicating this method does not provide a broadband advantage.

Atlanta

1125 Satellite Blvd. NW,
Ste. 100
Suwanee, GA 30024 USA

+1 678 475 8300
+1 678 542 2601

Los Angeles

19730 Magellan Dr.
Torrance, CA 90502 USA

+1 310 525 7000
+1 310 525 7100

NSI-MI UK

C/O AMETEK LAND,
Stubley Lane,
Dronfield, S18 1DJ UK

+44 1246 581500
  www.nsi-mi.co.uk

AMTA 2022

Denver, CO Finding your local time... 59 Days 2022.amta.org
This site is using cookies for analytical purposes and to provide a better user experience. Read our Privacy Policy for more information.