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CW radar operation in the focused near-field

Published in:
2019 Intl. Applied Computational Electromagnetics Society Symp., ACES, 14-19 April 2019.

Summary

In this paper we will show by computer simulation and by measurements that the horn antennas of a bi-static radar operating in the near-field have a distinct maximum at a non-zero range. By focusing the antennas on this hot spot a low-powered, continuous-wave Ku-band radar could detect flying mosquitoes at very short range.
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Summary

In this paper we will show by computer simulation and by measurements that the horn antennas of a bi-static radar operating in the near-field have a distinct maximum at a non-zero range. By focusing the antennas on this hot spot a low-powered, continuous-wave Ku-band radar could detect flying mosquitoes at...

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Polarization ratio determination with two identical linearly polarized antennas

Published in:
2017 IEEE AP-S Symp. on Antennas and Propagation and USNC Radio Science Meeting, 9-14 July 2017.

Summary

This paper describes a method for determining the complex polarization ratio using two identical, linearly polarized antennas. By Fourier transform analysis of s21 measurements with one of the antennas rotating about its axis a circular polarization ratio is derived which can be transformed into an equivalent linear polarization ratio. A linearly polarized reference antenna is not required. The technique was verified by electromagnetic simulations and illustrated by measurements in an anechoic chamber with two 3.3 GHz square patch antennas.
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Summary

This paper describes a method for determining the complex polarization ratio using two identical, linearly polarized antennas. By Fourier transform analysis of s21 measurements with one of the antennas rotating about its axis a circular polarization ratio is derived which can be transformed into an equivalent linear polarization ratio. A...

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A rotating source polarization measurement technique using two circularly polarized antennas

Published in:
38th Mtg. and Symp. of the Antenna Measurement Techniques Assoc., AMTA 2016, 30 October - 4 November 2016.

Summary

This paper combines the standard two-antenna gain measurement technique with the rotating source method for measuring the polarization ratio and tilt angle of the polarization ellipse of a circularly polarized antenna. The technique is illustrated with two identical helical antennas, one for the source and one for the antenna-under-test (AUT), facing each other. Measurements of the voltage transfer ratio are made over one 360 degree on-axis rotation of the source while the AUT remains stationary. The rotation causes the phase of the electric field of the principal polarization to rotate in one direction and the phase of the cross polarization to rotate in the opposite direction. A Discrete Fourier Transform (DFT) of the data from a single rotation is insufficient to resolve the two polarization components. Leakage from the principal polarization will most likely cover up the low-level opposite polarization signal. However, the DFT resolution can be artificially increased by appending to the measured data, precisely M-1 copies of the data. Now the polarization components will be separated by 2M revolutions. Application of a heavy weighting function to the augmented data and a phase compensation to the DFT allows a clear determination of the amplitude and phase of the on-axis principal and cross polarization components. The technique was verified by electromagnetic simulations and by measurements in an anechoic chamber with two 6-turn 5.8 GHz helical antennas separated by 4 feet. There was very good agreement between the simulations and measurements of the polarization ellipse tilt angle and a -20 dB polarization ratio.
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Summary

This paper combines the standard two-antenna gain measurement technique with the rotating source method for measuring the polarization ratio and tilt angle of the polarization ellipse of a circularly polarized antenna. The technique is illustrated with two identical helical antennas, one for the source and one for the antenna-under-test (AUT)...

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3D printed conformal array antenna: simulations and measurements

Summary

A conformal array antenna has been investigated using a combination of 3D printer and copper plating techniques. Circular patch antenna elements were copper plated onto a 3D printed dielectric substrate made of ABS-M30 material. Measured and simulated element reflection coefficient, element gain patterns, and array scanned beam radiation patterns at L band are in good agreement.
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Summary

A conformal array antenna has been investigated using a combination of 3D printer and copper plating techniques. Circular patch antenna elements were copper plated onto a 3D printed dielectric substrate made of ABS-M30 material. Measured and simulated element reflection coefficient, element gain patterns, and array scanned beam radiation patterns at...

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A modification of the two-antenna method to determine the phase center location as well as the gain of a wideband antenna

Published in:
2015 IEEE Int. Symp. on Antennas and Propagation, 19-24 July 2015.

Summary

A technique is presented for determining the amplitude center or phase center location of a wideband Vivaldi antenna at measurement distances of a few wavelengths. It is based on the well known two-antenna gain measurement technique but makes the antenna separation a variable. The phase center separation is shown to be proportional to the derivative of a transmission matrix loss parameter which is constant and independent of the antenna separation. A linear least squares fit to transmission loss parameters measured at several antenna separations is shown to yield the antenna gain and phase center location.
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Summary

A technique is presented for determining the amplitude center or phase center location of a wideband Vivaldi antenna at measurement distances of a few wavelengths. It is based on the well known two-antenna gain measurement technique but makes the antenna separation a variable. The phase center separation is shown to...

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The directivity of a Yagi-Uda antenna from an effective propagation constant

Published in:
IEEE Int. Symp. Antennas and Propagation (APSURSI), 7-13 July 2013.

Summary

A technique is presented for determining the directivity of a long, uniform Yagi-Uda antenna. It is shown that the maximum directivity is limited by the propagation constant of the particular antenna structure. The propagation constant can be determined by means of a two-part antenna test fixture with M and M + 1 directors.
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Summary

A technique is presented for determining the directivity of a long, uniform Yagi-Uda antenna. It is shown that the maximum directivity is limited by the propagation constant of the particular antenna structure. The propagation constant can be determined by means of a two-part antenna test fixture with M and M...

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Maximum directivity of a series-fed microstrip array antenna for wireless application

Published in:
AP-S/URSI 2011, IEEE Antennas and Propagation Society Int. Symp. and USNC/URSI National Radio Science Mtg., 3-8 July 2011, pp. 1327-1330.

Summary

An omnidirectional colinear microstrip array antenna is modeled as a ladder network. A formula is derived for the maximum directivity of a series-fed colinear antenna with an infinite number of ladder sections. It is shown that the maximum directivity is asymptotically limited and depends upon the product of the seriece impedance and shunt admittance of the equivalent ladder network. The result is verified by simulation and experiment.
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Summary

An omnidirectional colinear microstrip array antenna is modeled as a ladder network. A formula is derived for the maximum directivity of a series-fed colinear antenna with an infinite number of ladder sections. It is shown that the maximum directivity is asymptotically limited and depends upon the product of the seriece...

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Phased array calibrations using measured element patterns

Published in:
1995 IEEE Int. Symp. Digest, Antennas and Propagation, Vol. 2, 18-23 June 1995, pp. 918-921.

Summary

A technique to compensate for differences in phased array element patterns is presented. Each measured element pattern is approximated by a virtual array whose excitation function is determined by the Woodward-Lawson synthesis technique. By extending the virtual array beyond the physical array dimensions, mutual coupling and edge diffraction effects can be separated. An example is given where calibration by coupling matrix inversion resulted in significantly reduced array pattern sidelobes.
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Summary

A technique to compensate for differences in phased array element patterns is presented. Each measured element pattern is approximated by a virtual array whose excitation function is determined by the Woodward-Lawson synthesis technique. By extending the virtual array beyond the physical array dimensions, mutual coupling and edge diffraction effects can...

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Phased-array calibration by adaptive nulling

Published in:
MIT Lincoln Laboratory Report TR-915

Summary

The limitations to ultra-low sidelobe performance are explored using a 32-element linear array, operating at L-band, contianing transmit/receive (T/R) modules with 12-bit phase shifters. With conventional far-field calibrations, the average sidelobe level of the array was about-40dB. In theory, considerably lower sidelobe performance is expected from such an array. Initially, sidelobe performance was thought to be limited by inadequate calibrations. An examination of individual array element patterns showed a mirror-symmetric ripple which could be attributed to edge effects in a small array. Simulations indicated that more precise calibrations would not compensate for these element-pattern differences. An adaptive calibration technique was developed which iteratively adjusted the attenuator and phaser commands to create nulls in the antenna pattern in the direction of the nulls of a theoretical antenna pattern. With adaptive calibrations, the average sidelobe level can be lower to 60dB. The technique can be used for interference suppression by implementing antenna patterns with deep nulls in specified directions.
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Summary

The limitations to ultra-low sidelobe performance are explored using a 32-element linear array, operating at L-band, contianing transmit/receive (T/R) modules with 12-bit phase shifters. With conventional far-field calibrations, the average sidelobe level of the array was about-40dB. In theory, considerably lower sidelobe performance is expected from such an array. Initially...

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Low-sidelobe phased array antenna characteristics using the planar near-field scanning technique: theory and experiment

Published in:
MIT Lincoln Laboratory Report TR-870

Summary

Characteristics of a low-sidelobe phased array antenna are investigated using the technique of planar near-field scanning. The theory associated with the planar near-field scanning technique, with and without probe compensation, is reviewed and an application of the theory is made. The design of an experimental low-sidelobe phased array antenna consisting of monopole elements which are corporate-fed using high precision transmit/receive modules is described. Accurate array radiation patterns are obtained both theoretically and experimentally using centerline scanning at less than one wavelength distance from the antenna. The effects of the antenna probe on the array near-field pattern, plane-wave spectrum, and far-field pattern are demonstrated theoretically using a method of moments numerical simulation. Comparisons of the array theoretical near-zone electric field and array received voltage due to a V-dipole near-field transmitting probe are made. It is shown that a V-dipole theoretical probe antenna can accurately model a practical near-field measurement probe consisting of an open-ended rectangular waveguide surrounded with anechoic material.
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Summary

Characteristics of a low-sidelobe phased array antenna are investigated using the technique of planar near-field scanning. The theory associated with the planar near-field scanning technique, with and without probe compensation, is reviewed and an application of the theory is made. The design of an experimental low-sidelobe phased array antenna consisting...

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