scholarly journals Methods for Noise Reduction in Far-Field Patterns Obtained From Cylindrical Near-Field Antenna Measurements

2012 ◽  
Vol 60 (12) ◽  
pp. 5635-5644 ◽  
Author(s):  
F. J. Cano-Facila ◽  
M. Sierra-Castaner
Keyword(s):  
Noise Reduction ◽  
Near Field ◽  
Far Field ◽  
Field Patterns ◽  
Antenna Measurements

Comparison of ultralow-sidelobe-antenna far-field patterns using the planar-near-field method and the far-field method

1995 ◽  
Vol 37 (6) ◽  
pp. 7-15 ◽  
Author(s):  
M.H. Francis ◽  
A.C. Newell ◽  
K.R. Grimm ◽  
J. Hoffman ◽  
H.E. Schrank
Keyword(s):  
Near Field ◽  
Field Method ◽  
Far Field ◽  
Field Patterns

Simultaneous Noise and Performance Measurements for High-Speed Jet Noise Reduction Technologies

2009 ◽  
Author(s):  
Dean Long ◽  
Steven Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Test Facility ◽  
Wave Radiation ◽  
Far Field ◽  
Shock Cell ◽  
Field Noise

Model scale tests are conducted to assess the Noise/Performance trade for high speed jet noise reduction technologies. It is demonstrated that measuring the near field acoustic signature with a microphone array can be used to assess the far field noise using a procedure known as acoustic holography. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Tests are conducted on convergent/divergent nozzles with three different area ratios, and several different chevron geometries. Noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. These results show good agreement with actual far field measurements from tests in the GE Cell 41 Acoustic Test Facility. Simultaneous performance measurement shows the change in thrust coefficient for different test conditions and configurations. Chevrons attached to the nozzle exit can reduce the noise by several dB at the expense of a minimal thrust loss.

scholarly journals Improved Handset Antenna Performance via an Electrically Extended Ground Plane

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Shirook M. Ali ◽  
Huanhuan Gu ◽  
Kelce Wilson ◽  
James Warden
Keyword(s):  
Absorption Rate ◽  
Specific Absorption Rate ◽  
Near Field ◽  
Ground Plane ◽  
Practical Approach ◽  
Far Field ◽  
Specific Absorption ◽  
Antenna Performance ◽  
Field Patterns ◽  
Surface Metal

A novel and practical approach is presented providing improved antenna performance without enlarging the antenna or the ground plane. The approach electrically extends the ground plane using wire(s) that behave as surface metal extensions of the ground plane. The wire extensions can be accommodated within typical handset housing or as part of the stylish metal used on the handset’s exterior perimeter; hence don’t require enlargement of the device. Consequently, this approach avoids the costs and limitations traditionally associated with physically lengthening of a ground plane. Eight variations are presented and compared with baseline antenna performance. Both far-field patterns and near-field electromagnetic scans demonstrate that the proposed approach controls the electrical length of the ground plane and hence its chassis wavemodes, without negatively impacting the characteristics of the antenna. Improvements in performance of up to 56% in bandwidth at 900 MHz and up to 12% in efficiency with a reduction of up to 12% in the specific absorption rate (SAR) are achieved. An 8% increase in efficiency with a 1.3% improvement in bandwidth and a 20% reduction in SAR is achieved at 1880 MHz. Thus, improvements in bandwidth are achieved without compromising efficiency. Further, improvements at lower frequencies do not compromise performance at higher frequencies.

The analysis of near and far field pattern through mode analysis and FFT in a finite periodic dielectric gratings

2015 ◽  
Vol 17 (1) ◽  
pp. 82-90 ◽  
Author(s):  
Tae-Bong Lee ◽  
Min-Nyeon Kim
Keyword(s):  
Near Field ◽  
Bloch Wave ◽  
Wave Number ◽  
Mode Analysis ◽  
Field Pattern ◽  
Far Field ◽  
Content Type ◽  
Coupled Method ◽  
Field Patterns ◽  
Dielectric Gratings

Purpose – The purpose of this paper is to analyze far and near field emitted field patterns through more exact calculation of the modes formed in finite periodic dielectric gratings. Design/methodology/approach – For the mode calculation, equations are newly defined by applying vertical boundary condition on the assumption that transverse electric modes are generated in the structure. After finding modes, near field patterns are calculated using the wave number and coefficient of the mode. Findings – Additionally, the results from these calculations are compared with that of the rigorous-coupled method. Finally, far field patterns are derived by applying fast Fourier transform to near field patterns and also compared with the results of rigorous-coupled method. Research limitations/implications – For convenience of coordinate, we use rectangular coordinate, though the shape of radome is a hemisphere. Practical implications – In this paper, the authors derive more exact near field patterns without the assumption of infiniteness so that these results can be used practically for a making real frequency-selective structure. Originality/value – Conventional periodic finite dielectric gratings analysis has been done using Floquet–Bloch wave theory, coupled-mode, rigorous-coupled method which is based on the assumption of infiniteness of the structure.

Near‐field and far‐field patterns of phase‐locked semiconductor laser arrays

1983 ◽  
Vol 42 (6) ◽  
pp. 495-497 ◽  
Author(s):  
D. R. Scifres ◽  
W. Streifer ◽  
R. D. Burnham ◽  
T. L. Paoli ◽  
C. Lindström
Keyword(s):  
Semiconductor Laser ◽  
Near Field ◽  
Far Field ◽  
Laser Arrays ◽  
Field Patterns ◽  
Semiconductor Laser Arrays

Automated near-field measurements to obtain far-field patterns of aperture antennas and phased arrays

2005 ◽  
Author(s):  
H. Ecker ◽  
C. Burns ◽  
N. Hightower ◽  
E. Burdette ◽  
J. Evans ◽  
...  
Keyword(s):  
Phased Arrays ◽  
Near Field ◽  
Field Measurements ◽  
Far Field ◽  
Field Patterns ◽  
Aperture Antennas
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