Title of Invention	A NOVEL METHOD OF IN SITU NEAR FIELD ANTENNA PATTERN MEASUREMENT
Abstract	This invention relates to a system for converting Near Field Antenna data into Far Field antenna pattern. It consists of exciting means to execute an antenna by chirped/FMC W pulse, recording means for simultaneous recording of signals from the antenna and sample reference signals, compression means to separate and compress the signals to a hologram depicting the amplitude and phase distribution of antenna illumination function and transforming means to project and transforming said hologram to obtain far field antenna pattern. Fig. 2

Title of Invention

A NOVEL METHOD OF IN SITU NEAR FIELD ANTENNA PATTERN MEASUREMENT

Abstract

This invention relates to a system for converting Near Field Antenna data into Far Field antenna pattern. It consists of exciting means to execute an antenna by chirped/FMC W pulse, recording means for simultaneous recording of signals from the antenna and sample reference signals, compression means to separate and compress the signals to a hologram depicting the amplitude and phase distribution of antenna illumination function and transforming means to project and transforming said hologram to obtain far field antenna pattern. Fig. 2

Full Text	This invention relates to a system for converting Near-Field antenna data into Far-Field antenna pattern. Near Field antenna data is obtained by measuring the phase front of the Antenna Under Test herein after referenced as AUT and then mathematically transforming the phase front data into equivalent Far-Field Antenna pattern. The Near Field data is converted to Far-Field antenna pattern by the following steps. Conversion of measured Near-Field Data (complex data with both amplitude and phase) into antenna hologram i.e. Amplitude and Phase distribution over antenna aperture. Holographic back projection is done by 2D Match filtering and can be represented by the following equation. Formula (1) Where Holographic Amplitude and Phase distribution Measured Amplitude and Phase Distribution D Matched Filter (b) Projection of derived hologram into Far-Field antenna pattem by following equation. Where, Computed far-field response n - Samples in Elevation and m = samples in Azimuth X and y are distances in elevation and azimuth direction and 0 and are azimuth and elevation angles respectively. In conventional Near Field measurement antenna is excited with CW-wave with a defined carrier and a probe antenna scans full antenna aperture to collect raster data. Scanning of antenna aperture needs 3D/2D Scanner and Master Controller. Timing controller, signal generator and scanner controller are programmable devices for specific antenna near-field measurement. Continuous Wave (CW) based near-field antenna measurement systems are available globally. The present invention pertains to Near-Field Measurement by the use of pulsed FMCW or Chirped pulse, where match filter compression technique in time domain is used to detect signals from AUT. This concept has two advantages: (1) Most of the radar systems are equipped with chirped pulse and the radar system itself can be utilized to characterize the antenna in the integrated system itself. (2) Because of usage of chirp and range compression, all the caterers can be segregated in time gaiting, making possible in-situ measurement of antenna pattern of the typical radar systems. The proposed measurement scheme is not just restricted to antenna pattern measurement for radar systems, but can also be a generalized one with NF measurement systems upgraded with Chirp/FMCW source. PRIOR ART: General setup for Near-Field antenna measurement comprises of a probe antenna with a scanner system. Vector Network Analyzer (VNA) measurement system, Timing Controller, AUT and microwave anechoic chamber with absorbers. The signal used is a CW and the phase and amplitude distribution during measurement process can be detected by a VNA. Since conventional system uses CW as signal source, unwanted reflections are eliminated by using Microwave absorbers in anechoic chamber. Major disadvantages of VNA based CW mode antenna near-field measurement system are: AUT can be tested for single CW frequency only. Use of bulky and expensive setup elements like microwave absorbers and Network Analyzer. OBJECTS OF INVENTION: The invention aims to develop a new mode of NF measurement for typical antenna, used in radar systems, by the use of chirped pulse of the system itself. This method essentially allows in-situ measurement of the antenna, used in radars. This method also ensures antenna pattern measurement over full bandwidth of the system instead of single frequency measurement, available in conventional NF measurement set up. This scheme does not require elaborate anechoic chamber for measurement. Only those unwanted reflections and scatterings within one range resolution cell need to be attenuated by local absorbers. The measurement system do not need expensive VNA instrument for measurement. Simple High bandwidth oscilloscopes can be used for data recording. This method can be extended to conventional NF set up by using a chirped/FMCW source for measuring antenna pattern. DESCRIPTION OF INVENTION; 1. Antenna is excited by a chirped/FMCW signal. For radar systems, the system itself can be used for such measurement. 2. The received signal and a sample of reference FMCW/Chirped pulse are recorded simultaneously in cheaper recording devices like High Bandwidth Digital Storage Oscilloscopes (DSO) 3. Compression of the received signal by reference Chirp/FMCW signal. Clearly the returns from antenna and unwanted signals can be segregated in time. 4. For each of the raster scan position, the antenna response is extracted in both amplitude and phase. By conventional near field processing, the raw data is compressed to hologram depicting the amplitude and phase distribution of antenna illumination function. Compression means are provided for separating unwanted signals from the received signals and compressing the same to a hologram and projection means are provided to project the derived hologram in far field for obtaining the final antenna pattern. Accordingly, this invention relates to a system for converting Near-Field Antenna data into Far-Field antenna pattern which comprises executing means for executing an antenna by chirped/FMCW pulse, recording means for simultaneous recording '^ of signals received from said antenna and a sample of FMCW chirped pulse signal reference, compression means for separating and compressing signals received from said antenna to produce hologram depicting the amplitude and phase distribution of antenna illumination function and transforming and projecting means to project said hologram in far field to obtain final antenna pattern. Recording means may be High Bandwidth Digital Storage Oscilloscope (DSO) This invention will now be described with reference to the figures in the accompanying drawings. Fig 1 shows far Field point to be resolved and its angular definition with the antenna under test. Fig 2 shows a block diagram of Near Field measurement set up using FMCW/ chirped match filter. Fig 3 shows compressed signal after the application of match filter indicating AUT returns embedded in front end reflections and back ground leakage. Fig 4(a) shows measured raw data of Near-Field magnitude response of an antenna under test, obtained by scanning probe across antenna aperture. Figure 4 (b) shows measured raw data of Near-Field Phase response of an antenna under test, obtained by probe scanning across antenna aperture. Figure 4(c) shows compressed Near-Field Hologram of Magnitude response of an antenna under test. Figure 4(d) shows compressed Near-Field Hologram of Phase response of an antenna under test. Figure 4(e) shows the 3-D View of computed Far-Field of an antenna after Holographic back projection. Figure 5 shows the flow-chart defining steps of operations in the using FMCW/Chirped match filter based antenna measurement system. Advantages of using the system are 1. It ensures measurement of antenna pattem over full bandwidth of operation also the said method provides more authentic measure of the antenna pattem. 2. The measurement can be integrated to typical radar systems which generally uses chirp/FMCW signals, which itself can be used as signal source and ensuring in-situ measurement of antenna patters. 3. The present invention is not restricted to antenna measurement of radar systems only but also the conventional NF measurement set-ups can be reconfigured for this time domain based measurements using a chirped/FMCW source. 4. As the unwanted reflections and scatterings can be eliminated by time gating, elaborate arrangement of anechoic chamber is not needed and also one can only ensure that all the reflection and scattering sources within only one resolution cell distance are questioned by using absorbers locally as also higher the pulse bandwidth of the system, lesser is the requirement of local absorbers. 5. The present invention will lead to a cheaper NF measurement system than the conventional ones. WE CLAIM: 1. A system for converting near-Field Antenna data into Far-Field antenna pattern which comprises executing means for executing an antenna by chirped/FMCW pulse, recording means for simultaneous recording of signals received from said antenna and a sample of FMCW / chirped pulse signal reference, compression means for separating and compressing signals received from said antenna to produce hologram depicting the amplitude and phase distribution of antenna illumination function and transforming and projecting means to project said hologram in far field to obtain final antenna pattern. 2. The system as claimed in claim 1 wherein said recording means is a High Bandwidth Digital Storage Oscilloscope. 3. A method of measuring the phase front by an antenna under text with a system as claimed in claims 1 and 2 and transforming mathematically the phase front data into equivalent antenna pattern using the equation: where, is the Holographic Amplitude and phase distribution, is the where, is the Measured Amplitude and Phase Distribution and is a 2-D Matched Filter; projecting the derived hologram into Far-Field antenna pattern by following equation: is the Computed far-field response, n is the samples in Elevation an m is samples in Azimuth, is the computed complex Holographic response, and where x and y are distances in elevation and azimuth direction and are elevation angles respectively.

Full Text

This invention relates to a system for converting Near-Field antenna data into Far-Field antenna pattern.

Near Field antenna data is obtained by measuring the phase front of the Antenna Under Test herein after referenced as AUT and then mathematically transforming the phase front data into equivalent Far-Field Antenna pattern. The Near Field data is converted to Far-Field antenna pattern by the following steps.

Conversion of measured Near-Field Data (complex data with both amplitude and phase) into antenna hologram i.e. Amplitude and Phase distribution over antenna aperture. Holographic back projection is done by 2D Match filtering and can be represented by the following equation.
Formula (1)
Where

Holographic Amplitude and Phase distribution

Measured Amplitude and Phase Distribution

D Matched Filter

(b) Projection of derived hologram into Far-Field antenna pattem by following equation.

Where,

Computed far-field response

n - Samples in Elevation and m = samples in Azimuth X and y are distances in elevation and azimuth direction and 0 and are azimuth and elevation angles respectively.

In conventional Near Field measurement antenna is excited with CW-wave with a defined carrier and a probe antenna scans full antenna aperture to collect raster data. Scanning of antenna aperture needs 3D/2D Scanner and Master Controller. Timing controller, signal generator and scanner controller are programmable devices for specific antenna near-field measurement. Continuous Wave (CW) based near-field antenna measurement systems are available globally.

The present invention pertains to Near-Field Measurement by the use of pulsed FMCW or Chirped pulse, where match filter compression technique in time domain is used to detect signals from AUT. This concept has two advantages: (1) Most of the radar systems are equipped with chirped pulse and the radar system itself can be utilized to characterize the antenna in the integrated system itself. (2) Because of usage of chirp and range compression, all the caterers can be segregated in time gaiting, making possible in-situ measurement of antenna pattern of the typical radar systems. The proposed measurement scheme is not just restricted to antenna pattern measurement for radar systems, but can also be a generalized one with NF measurement systems upgraded with Chirp/FMCW source.

PRIOR ART:

General setup for Near-Field antenna measurement comprises of a probe antenna with a scanner system. Vector Network Analyzer (VNA) measurement system, Timing Controller, AUT and microwave anechoic chamber with absorbers. The signal used is a CW and the phase and amplitude distribution during measurement process can be detected by a VNA.

Since conventional system uses CW as signal source, unwanted reflections are eliminated by using Microwave absorbers in anechoic chamber. Major disadvantages of VNA based CW mode antenna near-field measurement system are:

AUT can be tested for single CW frequency only.

Use of bulky and expensive setup elements like microwave absorbers and Network Analyzer.

OBJECTS OF INVENTION:

The invention aims to develop a new mode of NF measurement for typical antenna, used in radar systems, by the use of chirped pulse of the system itself. This method essentially allows in-situ measurement of the antenna, used in radars. This method also ensures antenna pattern measurement over full bandwidth of the system instead of single frequency measurement, available in conventional NF measurement set up. This scheme does not require elaborate anechoic chamber for measurement. Only those unwanted reflections and scatterings within one range resolution cell need to be attenuated by local absorbers. The measurement system do not need expensive VNA instrument for measurement. Simple High bandwidth oscilloscopes can be used for data recording. This method can be extended to conventional NF set up by using a chirped/FMCW source for measuring antenna pattern.

DESCRIPTION OF INVENTION;

1. Antenna is excited by a chirped/FMCW signal. For radar systems, the system itself can be used for such measurement.

2. The received signal and a sample of reference FMCW/Chirped pulse are recorded simultaneously in cheaper recording devices like High Bandwidth Digital Storage Oscilloscopes (DSO)

3. Compression of the received signal by reference Chirp/FMCW signal. Clearly the returns from antenna and unwanted signals can be segregated in time.

4. For each of the raster scan position, the antenna response is extracted in both amplitude and phase. By conventional near field processing, the raw data is compressed to hologram depicting the amplitude and phase distribution of antenna illumination function. Compression means are provided for separating unwanted signals from the received signals and compressing the same to a hologram and projection means are provided to project the derived hologram in far field for obtaining the final antenna pattern.

Accordingly, this invention relates to a system for converting Near-Field Antenna data into Far-Field antenna pattern which comprises executing means for executing an antenna by chirped/FMCW pulse, recording means for simultaneous recording '^ of signals received from said antenna and a sample of FMCW chirped pulse signal reference, compression means for separating and compressing signals received from said antenna to produce hologram depicting the amplitude and phase distribution of antenna illumination function and transforming and projecting means to project said hologram in far field to obtain final antenna pattern.

Recording means may be High Bandwidth Digital Storage Oscilloscope (DSO)

This invention will now be described with reference to the figures in the accompanying drawings.

Fig 1 shows far Field point to be resolved and its angular definition with the antenna under test.

Fig 2 shows a block diagram of Near Field measurement set up using FMCW/ chirped match filter.

Fig 3 shows compressed signal after the application of match filter indicating AUT returns embedded in front end reflections and back ground leakage.

Fig 4(a) shows measured raw data of Near-Field magnitude response of an antenna under test, obtained by scanning probe across antenna aperture. Figure 4 (b) shows measured raw data of Near-Field Phase response of an antenna under test, obtained by probe scanning across antenna aperture. Figure 4(c) shows compressed Near-Field Hologram of Magnitude response of an antenna under test. Figure 4(d) shows compressed Near-Field Hologram of Phase response of an antenna under test. Figure 4(e) shows the 3-D View of computed Far-Field of an antenna after Holographic back projection.

Figure 5 shows the flow-chart defining steps of operations in the using FMCW/Chirped match filter based antenna measurement system.

Advantages of using the system are

1. It ensures measurement of antenna pattem over full bandwidth of operation also the said method provides more authentic measure of the antenna pattem.

2. The measurement can be integrated to typical radar systems which generally uses chirp/FMCW signals, which itself can be used as signal source and ensuring in-situ measurement of antenna patters.

3. The present invention is not restricted to antenna measurement of radar systems only but also the conventional NF measurement set-ups can be reconfigured for this time domain based measurements using a chirped/FMCW source.

4. As the unwanted reflections and scatterings can be eliminated by time gating, elaborate arrangement of anechoic chamber is not needed and also one can only ensure that all the reflection and scattering sources within only one resolution cell distance are questioned by using absorbers locally as also higher the pulse bandwidth of the system, lesser is the requirement of local absorbers.

5. The present invention will lead to a cheaper NF measurement system than the conventional ones.

WE CLAIM:

1. A system for converting near-Field Antenna data into Far-Field antenna pattern which comprises executing means for executing an antenna by chirped/FMCW pulse, recording means for simultaneous recording of signals received from said antenna and a sample of FMCW / chirped pulse signal reference, compression means for separating and compressing signals received from said antenna to produce hologram depicting the amplitude and phase distribution of antenna illumination function and transforming and projecting means to project said hologram in far field to obtain final antenna pattern.

2. The system as claimed in claim 1 wherein said recording means is a High Bandwidth Digital Storage Oscilloscope.

3. A method of measuring the phase front by an antenna under text with a system as claimed in claims 1 and 2 and transforming mathematically the phase front data into equivalent antenna pattern using the equation: where, is the Holographic Amplitude and phase distribution, is the where, is the Measured Amplitude and Phase Distribution and is a 2-D Matched Filter; projecting the derived hologram into Far-Field antenna pattern by following equation: is the Computed far-field response, n is the samples in Elevation an m is samples in Azimuth, is the computed complex Holographic response, and where x and y are distances in elevation and azimuth direction and are elevation angles respectively.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=j5dc/NdZXNbYe39zSFv2xg==&loc=egcICQiyoj82NGgGrC5ChA==

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Patent Number

272096

Indian Patent Application Number

244/CHE/2008

PG Journal Number

12/2016

Publication Date

18-Mar-2016

Grant Date

17-Mar-2016

Date of Filing

30-Jan-2008

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

INDIAN SPACE RESEARCH ORGANISATION (ISRO) HEADQUARTERS, AN INDIAN GOVERNMENT ORGANIZATION ANTARIKSH BHAVAN NEW B.E.L ROAD BANGALORE 560 094

Inventors:

#	Inventor's Name	Inventor's Address
1	TAPAN MISRA	SPACE APPLICATIONS CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) AMBAVADI VISTAR PO JODHPUR TEKRA AHMEDABAD 380 015
2	RAKESH BHAN	SPACE APPLICATIONS CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) AMBAVADI VISTAR PO JODHPUR TEKRA AHMEDABAD 380 015
3	DEEPAK PUTREVU	SPACE APPLICATIONS CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) AMBAVADI VISTAR PO JODHPUR TEKRA AHMEDABAD 380 015
4	NIDHI CHAWLA	SPACE APPLICATIONS CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) AMBAVADI VISTAR PO JODHPUR TEKRA AHMEDABAD 380 015
5	DILIP B DAVE	SPACE APPLICATIONS CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) AMBAVADI VISTAR PO JODHPUR TEKRA AHMEDABAD 380 015

PCT International Classification Number

H01Q7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA