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#41
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Testing superluminal transmission of near field light waves.
The RF antenna group at NTNU university has looked into your network analyzer/balanced dipole/balun experimental setup and has preformed tests on a similar setup. They concluded that the observed phase shift results are unreliable due to external room reflections and that the experiment needs to be performed in an anechoic chamber. In their tests they used an Agilent-E8364B S parameter Network Analyzer (10MHz-50GHz), a HP 85052D4 Calibration kit, a 30cm balanced dipole antenna with built in Balun (500MHz resonant frequency, 60cm wavelength), an E field probe (a 0.5m cable with about 1cm exposed wire), 1m HF Cables with SMA connectors, 10dB attenuators (placed at the input to the Balun/Antenna and at the output of the E field probe). A full calibration (using the cal kit - short, load, open, thru) was performed on the analyzer including the RF cables and attached attenuators. The Analyser was swept from 400MHz-600MHz while monitoring the S21 phase at 500MHz. Linear as well as nonlinear phase vs distance relations were observed as the probe was moved from next to the dipole to the dipole wavelength (60cm). A 2GHz -20GHz Anechoic chamber is available here, but preliminary tests with the antenna at 1.5GHz (3rd harmonic of antenna) showed that phase calibration of the analyzer is not possible due to losses in the the long cables (10m), needed to connect the antenna and probe to the analyzer outside the chamber. It has been recommended that a small Anechoic chamber be constructed specially designed for this experiment, enabling the analyzer and 1m cables to be calibrated. The chamber should include a nonreflective mechanism enabling the probe to be moved in small repeatable increments within the wavelength of the antenna. The new chamber will take some time to design, build and test, and the cost could be prohibitively expensive. During the next few weeks I will check into this possibility. doug wrote: William wrote: I agree that the experiment I did should be checked, but I think it is best to do the experiment in the lab using high frequency test equipment like you are trying to do. As you have said the experiment is very difficult to do right and there is a better chance of controlling all the phenomena involved in a standard RF lab environment using commercial test equipment. I also agree that it is essential that these near-field measurement tests show nonlinear phase shift behavior in the nearfield before progressing to a wide bandwidth signal transmission experiments. I am very surprised by your experimental results. The transverse field phase vs distance solution I presented in my paper is what is predicted by Maxwell's equations (p.12, near-field dipole paper). I have checked it both analytically and numerically (p.23-25). In addition the solution has also been checked by other researchers, analytically and numerically: http://ceta.mit.edu/pier/pier56/05.0505121.Sten.H.pdf http://xxx.lanl.gov/abs/physics/0311061 Intuitively one can also see the nonlinear phase shift by looking at the transverse field solution (Eq. 53). The exp[i(kr-wt)] term is a light speed propagating term, and the part in the brackets is a complex term that is a function of kr. This complex term can be expressed in polar coordinates as a phasor, where the phase will cause the over phase of the field to deviate from kr. In the nearfield, the kr term is small thereby making the making the term in the brackets approximately equal to 1, corresponding to 0 deg phase difference from kr. In the farfield the term in the brackets becomes approximately -(kr)^2 corresponding to -180 deg phase difference from kr. In between the nearfield and the farfield the -i(kr) term is dominant, causing the phase to be about -90 deg there. If you will refer to the transverse Electric field phase vs kr curve (ref. fig.12) you will see that the theoretically derived curve agrees with these observations. Relative to a light propagating field, the phase is 0 deg in the nearfield, approximately -90 deg in between the nearfied and farfield, and -180 deg in the farfield. Experimentally it is known that the E field generated by a slow moving charge is proportional to it's position. Oscillating charges cause other nearby charges to oscillate in unison with no observed phase difference. In the nearfield, the B field is experimentally known to be proportional to the current. Oscillating charges are known to generate magnetic fields which are -90 deg phase shifted from the charge motion. In the farfield it has been experimentally observed that the transverse electric and magnetic fields are in phase and propagate at the speed of light. I order for the transverse E field and B field to align in the farfield, given that they are not aligned in the nearfield, their phase vs distance curves must be nonlinear in the nearfield. Do you have any ideas what the problem is? It is hard to believe that Maxwell's equations could be wrong in the prediction of this nonlinear phase shift effect. The defining result is what reality thinks. After there are reproducible experimental results, it will be the time to go through the equations. The experiment is simple. The analysis is not and there have been comments from others who have disagreed with your assumptions. I am not making any assumptions about either your derivations or their disagreements. Until I know more exactly what you have done I can only speculate. First of all I am extremely wary of any test that uses more than one frequency which can generate phase shifts from band limited elements such as the balun and antenna, or from frequency dependent reflections. But if I understand you correctly, even though the Analyzer is sweeping frequencies, you are effectively using only one frequency by reading only the phase at one particular frequency as the E field probe is moved incrementally away from the Dipole antenna. I assume you have calibrated the Analyzer and test cables using a calibrated short, open, and 50 ohm terminators at the end of the test cables, thus effectively flattening out the transfer function of these elements. I also assume the Analyzer is able to measure at least 1 deg phase changes, which is needed to differentiate linear from nonlinear phase behavior in the nearfield. Can the analyzer be operated at just 1 frequency just to be sure the sweeping is not causing any problems (eg. intermode mixing etc.). As someone who does this kind of measurement every day, I have a pretty good idea of the limits. First of all, the hp8753 is a stepped frequency analyzer which sets a frequency and then takes the data so you worries about sweeping effects do not exist. I have a stack of hp calibration kits with a large selection of loads, mismatches, opens and shorts. The transfer function of the system is not important at a single frequency. It is important if you are measuring frequency dependence but that is not being done. The data were looked at at different frequencies but the phase comparisons were done at fixed frequencies. You can look up the specs of the 8753 family to see what the resolutions are. By the way have you checked that the input impedance of the probe/Analyzer combined with the antenna to probe reactance (which changes as the probe is moved away)is not generating a phase shift which could be masking the true phase in the nearfield? There are 10db attenuators at the end of the antenna and the end of the voltage probe. This isolates the cables and test set from the changing impedances. Could reflections from the probe be reflecting from the Dipole antenna causing the phase shift in the nearfield to be masked? The probe is .5" long and this effect would show up with varying lengths of e field probes. The two probes I used showed no difference. I would like to make these measurements with a B field probe when I get a chance. In order to be able to really understand your experimental results, I will need to know more about your experimental test setup and test results. This will also enable the duplication of your experiment. I am really quite surprised by these comments on things that are second or third order effects when there are problems with your measurement that are zeroth or first order. You have no antenna, just a voltage probe trying to radiate. You have no impedance match anywhere. You have not isolated the transmitter. You have no ground plane (the table just makes life complicated) You have a dc circuit which does not match what you think your rf circuit is. The important part of the measurement is to create a geometry which is what you think it is. A dipole antenna in free space is far more predictable than any system with a ground plane. All parts of the system have to be isolated from each other so you are only varying what you think you are varyings. For instance, changing the load on most cheap rf equipment (and the hamtronics fits that category) will cause changes in amplitude,phase and harmonic content. Once all the parts are properly characterized and isolated, then you can vary whatever parameter you want with confidence that it is the only one you are changing. When the experiment is done properly, the results will speak for themselves. If you get different results than I do, then we need to look for the reason for those differences. I have listed a large number of problems with your setup. If you fix those things, we will be in a position to compare results. doug wrote: William wrote: Hi Bill, Thank you for the offer, but I think that duplicating the type of experiment I showed in paper would not yield much new information. What really needs to be done is to develop a wideband transmitter and antenna system that can handle modulations bandwidths 1/10 of the carrier. This will enable us to study the propagation speed of random information, which is what everyone wants to know. This is not a trivial design and I don't even know if it can be done. I will have to give it some thought. If I do get something to work, I will let you know. trimmed discussion I am not replying to I think you have this backwards. The first thing to do is to replicate the experiment you did. It seems you still believe it is correct. I have given a list of mistakes you have made. With your setup, no one with rf experience will take it seriously. I showed it to a colleague and he laughed. The basic experiment you are basing your work on must be done correctly and repeatably. You are not using proper antennas, you have not impedance matched anything so you do not know what the fields are, you do not have an infinite ground plane.... You probably are seeing an odd field distribution from the geometry you have created. My repeat of your experiment showed no anomalous effect on the phase. In order to have any effect to discuss, you are required to show a nonlinear phase with distance. I get a straight line for the phase versus distance curve which means that there is a constant value for c at all distances. It shows the same effect at different frequencies so I also have the time dependence which thus also shows no anomaly. There is no point in doing the time domain experiment when you can do the frequency domain experiment much more easily. They are equivalent and can be done on the same piece of equipment. One can build the modulator you suggest but there is no need. Again the frequency domain is the same thanks to our friend fourier. I have spent the last ten years designing and using frequency domain radars. If the phase versus frequency is linear at all frequencies, there is no effect to study. |
#42
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Testing superluminal transmission of near field light waves.
William wrote:
The RF antenna group at NTNU university has looked into your network analyzer/balanced dipole/balun experimental setup and has preformed tests on a similar setup. They concluded that the observed phase shift results are unreliable due to external room reflections and that the experiment needs to be performed in an anechoic chamber. In their tests they used an Agilent-E8364B S parameter Network Analyzer (10MHz-50GHz), a HP 85052D4 Calibration kit, a 30cm balanced dipole antenna with built in Balun (500MHz resonant frequency, 60cm wavelength), an E field probe (a 0.5m cable with about 1cm exposed wire), 1m HF Cables with SMA connectors, 10dB attenuators (placed at the input to the Balun/Antenna and at the output of the E field probe). A full calibration (using the cal kit - short, load, open, thru) was performed on the analyzer including the RF cables and attached attenuators. The Analyser was swept from 400MHz-600MHz while monitoring the S21 phase at 500MHz. Linear as well as nonlinear phase vs distance relations were observed as the probe was moved from next to the dipole to the dipole wavelength (60cm). A 2GHz -20GHz Anechoic chamber is available here, but preliminary tests with the antenna at 1.5GHz (3rd harmonic of antenna) showed that phase calibration of the analyzer is not possible due to losses in the the long cables (10m), needed to connect the antenna and probe to the analyzer outside the chamber. It has been recommended that a small Anechoic chamber be constructed specially designed for this experiment, enabling the analyzer and 1m cables to be calibrated. The chamber should include a nonreflective mechanism enabling the probe to be moved in small repeatable increments within the wavelength of the antenna. The new chamber will take some time to design, build and test, and the cost could be prohibitively expensive. During the next few weeks I will check into this possibility. doug wrote: William wrote: I agree that the experiment I did should be checked, but I think it is best to do the experiment in the lab using high frequency test equipment like you are trying to do. As you have said the experiment is very difficult to do right and there is a better chance of controlling all the phenomena involved in a standard RF lab environment using commercial test equipment. I also agree that it is essential that these near-field measurement tests show nonlinear phase shift behavior in the nearfield before progressing to a wide bandwidth signal transmission experiments. I am very surprised by your experimental results. The transverse field phase vs distance solution I presented in my paper is what is predicted by Maxwell's equations (p.12, near-field dipole paper). I have checked it both analytically and numerically (p.23-25). In addition the solution has also been checked by other researchers, analytically and numerically: http://ceta.mit.edu/pier/pier56/05.0505121.Sten.H.pdf http://xxx.lanl.gov/abs/physics/0311061 Intuitively one can also see the nonlinear phase shift by looking at the transverse field solution (Eq. 53). The exp[i(kr-wt)] term is a light speed propagating term, and the part in the brackets is a complex term that is a function of kr. This complex term can be expressed in polar coordinates as a phasor, where the phase will cause the over phase of the field to deviate from kr. In the nearfield, the kr term is small thereby making the making the term in the brackets approximately equal to 1, corresponding to 0 deg phase difference from kr. In the farfield the term in the brackets becomes approximately -(kr)^2 corresponding to -180 deg phase difference from kr. In between the nearfield and the farfield the -i(kr) term is dominant, causing the phase to be about -90 deg there. If you will refer to the transverse Electric field phase vs kr curve (ref. fig.12) you will see that the theoretically derived curve agrees with these observations. Relative to a light propagating field, the phase is 0 deg in the nearfield, approximately -90 deg in between the nearfied and farfield, and -180 deg in the farfield. Experimentally it is known that the E field generated by a slow moving charge is proportional to it's position. Oscillating charges cause other nearby charges to oscillate in unison with no observed phase difference. In the nearfield, the B field is experimentally known to be proportional to the current. Oscillating charges are known to generate magnetic fields which are -90 deg phase shifted from the charge motion. In the farfield it has been experimentally observed that the transverse electric and magnetic fields are in phase and propagate at the speed of light. I order for the transverse E field and B field to align in the farfield, given that they are not aligned in the nearfield, their phase vs distance curves must be nonlinear in the nearfield. Do you have any ideas what the problem is? It is hard to believe that Maxwell's equations could be wrong in the prediction of this nonlinear phase shift effect. The defining result is what reality thinks. After there are reproducible experimental results, it will be the time to go through the equations. The experiment is simple. The analysis is not and there have been comments from others who have disagreed with your assumptions. I am not making any assumptions about either your derivations or their disagreements. Until I know more exactly what you have done I can only speculate. First of all I am extremely wary of any test that uses more than one frequency which can generate phase shifts from band limited elements such as the balun and antenna, or from frequency dependent reflections. But if I understand you correctly, even though the Analyzer is sweeping frequencies, you are effectively using only one frequency by reading only the phase at one particular frequency as the E field probe is moved incrementally away from the Dipole antenna. I assume you have calibrated the Analyzer and test cables using a calibrated short, open, and 50 ohm terminators at the end of the test cables, thus effectively flattening out the transfer function of these elements. I also assume the Analyzer is able to measure at least 1 deg phase changes, which is needed to differentiate linear from nonlinear phase behavior in the nearfield. Can the analyzer be operated at just 1 frequency just to be sure the sweeping is not causing any problems (eg. intermode mixing etc.). As someone who does this kind of measurement every day, I have a pretty good idea of the limits. First of all, the hp8753 is a stepped frequency analyzer which sets a frequency and then takes the data so you worries about sweeping effects do not exist. I have a stack of hp calibration kits with a large selection of loads, mismatches, opens and shorts. The transfer function of the system is not important at a single frequency. It is important if you are measuring frequency dependence but that is not being done. The data were looked at at different frequencies but the phase comparisons were done at fixed frequencies. You can look up the specs of the 8753 family to see what the resolutions are. By the way have you checked that the input impedance of the probe/Analyzer combined with the antenna to probe reactance (which changes as the probe is moved away)is not generating a phase shift which could be masking the true phase in the nearfield? There are 10db attenuators at the end of the antenna and the end of the voltage probe. This isolates the cables and test set from the changing impedances. Could reflections from the probe be reflecting from the Dipole antenna causing the phase shift in the nearfield to be masked? The probe is .5" long and this effect would show up with varying lengths of e field probes. The two probes I used showed no difference. I would like to make these measurements with a B field probe when I get a chance. In order to be able to really understand your experimental results, I will need to know more about your experimental test setup and test results. This will also enable the duplication of your experiment. I am really quite surprised by these comments on things that are second or third order effects when there are problems with your measurement that are zeroth or first order. You have no antenna, just a voltage probe trying to radiate. You have no impedance match anywhere. You have not isolated the transmitter. You have no ground plane (the table just makes life complicated) You have a dc circuit which does not match what you think your rf circuit is. The important part of the measurement is to create a geometry which is what you think it is. A dipole antenna in free space is far more predictable than any system with a ground plane. All parts of the system have to be isolated from each other so you are only varying what you think you are varyings. For instance, changing the load on most cheap rf equipment (and the hamtronics fits that category) will cause changes in amplitude,phase and harmonic content. Once all the parts are properly characterized and isolated, then you can vary whatever parameter you want with confidence that it is the only one you are changing. When the experiment is done properly, the results will speak for themselves. If you get different results than I do, then we need to look for the reason for those differences. I have listed a large number of problems with your setup. If you fix those things, we will be in a position to compare results. doug wrote: William wrote: Hi Bill, Thank you for the offer, but I think that duplicating the type of experiment I showed in paper would not yield much new information. What really needs to be done is to develop a wideband transmitter and antenna system that can handle modulations bandwidths 1/10 of the carrier. This will enable us to study the propagation speed of random information, which is what everyone wants to know. This is not a trivial design and I don't even know if it can be done. I will have to give it some thought. If I do get something to work, I will let you know. trimmed discussion I am not replying to I think you have this backwards. The first thing to do is to replicate the experiment you did. It seems you still believe it is correct. I have given a list of mistakes you have made. With your setup, no one with rf experience will take it seriously. I showed it to a colleague and he laughed. The basic experiment you are basing your work on must be done correctly and repeatably. You are not using proper antennas, you have not impedance matched anything so you do not know what the fields are, you do not have an infinite ground plane.... You probably are seeing an odd field distribution from the geometry you have created. My repeat of your experiment showed no anomalous effect on the phase. In order to have any effect to discuss, you are required to show a nonlinear phase with distance. I get a straight line for the phase versus distance curve which means that there is a constant value for c at all distances. It shows the same effect at different frequencies so I also have the time dependence which thus also shows no anomaly. There is no point in doing the time domain experiment when you can do the frequency domain experiment much more easily. They are equivalent and can be done on the same piece of equipment. One can build the modulator you suggest but there is no need. Again the frequency domain is the same thanks to our friend fourier. I have spent the last ten years designing and using frequency domain radars. If the phase versus frequency is linear at all frequencies, there is no effect to study. |
#43
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Testing superluminal transmission of near field light waves.
I pushed the wrong button on the last post. Reply is below
William wrote: The RF antenna group at NTNU university has looked into your network analyzer/balanced dipole/balun experimental setup and has preformed tests on a similar setup. They concluded that the observed phase shift results are unreliable due to external room reflections and that the experiment needs to be performed in an anechoic chamber. In their tests they used an Agilent-E8364B S parameter Network Analyzer (10MHz-50GHz), a HP 85052D4 Calibration kit, a 30cm balanced dipole antenna with built in Balun (500MHz resonant frequency, 60cm wavelength), an E field probe (a 0.5m cable with about 1cm exposed wire), 1m HF Cables with SMA connectors, 10dB attenuators (placed at the input to the Balun/Antenna and at the output of the E field probe). A full calibration (using the cal kit - short, load, open, thru) was performed on the analyzer including the RF cables and attached attenuators. The Analyser was swept from 400MHz-600MHz while monitoring the S21 phase at 500MHz. Linear as well as nonlinear phase vs distance relations were observed as the probe was moved from next to the dipole to the dipole wavelength (60cm). Reflections show up quite visibly when you sweep frequencies. A 2GHz -20GHz Anechoic chamber is available here, but preliminary tests with the antenna at 1.5GHz (3rd harmonic of antenna) showed that phase calibration of the analyzer is not possible due to losses in the the long cables (10m), needed to connect the antenna and probe to the analyzer outside the chamber. You should use an antenna at its proper frequency. It has been recommended that a small Anechoic chamber be constructed specially designed for this experiment, enabling the analyzer and 1m cables to be calibrated. The chamber should include a nonreflective mechanism enabling the probe to be moved in small repeatable increments within the wavelength of the antenna. The new chamber will take some time to design, build and test, and the cost could be prohibitively expensive. During the next few weeks I will check into this possibility. I think they are trying to make this too hard. First of all, higher frequencies are your friend. If possible, do the experiment at 2GHz and put it in the anechoic chamber. I have no idea what the comment about the long lines is about. The long lines do introduce loss and phase shift but that is constant and, since all you want is the slope of phase versus distance, any offset is meaningless and can be ignored. Doing a full phase calibration is a nuisance anyway. You can build an antenna for any frequency you want in an afternoon in the machine shop. Small brass pipe makes a good basis. Ream it to a convenient size to give 50 ohms with a .125" center conductor of brazing rod, cut a slot to the length of your elements and then make the elements out of brazing rod as well. Very careful attention should be paid to the details of the connector end and the mating to the connector. these antennas work very well over a +-20% bandwidth. A much easier and cheaper way of doing this is to go outside. Mount the antenna above the ground with its axis vertical. This puts the minimum radiation point aimed at the ground. Put some absorber directly below the antenna if you want. At 500MHz, the absorber is mostly for show but if you go to 1000 or 1500MHz it actually will absorb something. This geometry has several advantages. The reflections are small. At higher frequencies, if you sweep enough, you can fft the data, window out the relections and then fft back to the frequency domain. Even without this, the reflections will be small. doug wrote: William wrote: I agree that the experiment I did should be checked, but I think it is best to do the experiment in the lab using high frequency test equipment like you are trying to do. As you have said the experiment is very difficult to do right and there is a better chance of controlling all the phenomena involved in a standard RF lab environment using commercial test equipment. I also agree that it is essential that these near-field measurement tests show nonlinear phase shift behavior in the nearfield before progressing to a wide bandwidth signal transmission experiments. I am very surprised by your experimental results. The transverse field phase vs distance solution I presented in my paper is what is predicted by Maxwell's equations (p.12, near-field dipole paper). I have checked it both analytically and numerically (p.23-25). In addition the solution has also been checked by other researchers, analytically and numerically: http://ceta.mit.edu/pier/pier56/05.0505121.Sten.H.pdf http://xxx.lanl.gov/abs/physics/0311061 Intuitively one can also see the nonlinear phase shift by looking at the transverse field solution (Eq. 53). The exp[i(kr-wt)] term is a light speed propagating term, and the part in the brackets is a complex term that is a function of kr. This complex term can be expressed in polar coordinates as a phasor, where the phase will cause the over phase of the field to deviate from kr. In the nearfield, the kr term is small thereby making the making the term in the brackets approximately equal to 1, corresponding to 0 deg phase difference from kr. In the farfield the term in the brackets becomes approximately -(kr)^2 corresponding to -180 deg phase difference from kr. In between the nearfield and the farfield the -i(kr) term is dominant, causing the phase to be about -90 deg there. If you will refer to the transverse Electric field phase vs kr curve (ref. fig.12) you will see that the theoretically derived curve agrees with these observations. Relative to a light propagating field, the phase is 0 deg in the nearfield, approximately -90 deg in between the nearfied and farfield, and -180 deg in the farfield. Experimentally it is known that the E field generated by a slow moving charge is proportional to it's position. Oscillating charges cause other nearby charges to oscillate in unison with no observed phase difference. In the nearfield, the B field is experimentally known to be proportional to the current. Oscillating charges are known to generate magnetic fields which are -90 deg phase shifted from the charge motion. In the farfield it has been experimentally observed that the transverse electric and magnetic fields are in phase and propagate at the speed of light. I order for the transverse E field and B field to align in the farfield, given that they are not aligned in the nearfield, their phase vs distance curves must be nonlinear in the nearfield. Do you have any ideas what the problem is? It is hard to believe that Maxwell's equations could be wrong in the prediction of this nonlinear phase shift effect. The defining result is what reality thinks. After there are reproducible experimental results, it will be the time to go through the equations. The experiment is simple. The analysis is not and there have been comments from others who have disagreed with your assumptions. I am not making any assumptions about either your derivations or their disagreements. Until I know more exactly what you have done I can only speculate. First of all I am extremely wary of any test that uses more than one frequency which can generate phase shifts from band limited elements such as the balun and antenna, or from frequency dependent reflections. But if I understand you correctly, even though the Analyzer is sweeping frequencies, you are effectively using only one frequency by reading only the phase at one particular frequency as the E field probe is moved incrementally away from the Dipole antenna. I assume you have calibrated the Analyzer and test cables using a calibrated short, open, and 50 ohm terminators at the end of the test cables, thus effectively flattening out the transfer function of these elements. I also assume the Analyzer is able to measure at least 1 deg phase changes, which is needed to differentiate linear from nonlinear phase behavior in the nearfield. Can the analyzer be operated at just 1 frequency just to be sure the sweeping is not causing any problems (eg. intermode mixing etc.). As someone who does this kind of measurement every day, I have a pretty good idea of the limits. First of all, the hp8753 is a stepped frequency analyzer which sets a frequency and then takes the data so you worries about sweeping effects do not exist. I have a stack of hp calibration kits with a large selection of loads, mismatches, opens and shorts. The transfer function of the system is not important at a single frequency. It is important if you are measuring frequency dependence but that is not being done. The data were looked at at different frequencies but the phase comparisons were done at fixed frequencies. You can look up the specs of the 8753 family to see what the resolutions are. By the way have you checked that the input impedance of the probe/Analyzer combined with the antenna to probe reactance (which changes as the probe is moved away)is not generating a phase shift which could be masking the true phase in the nearfield? There are 10db attenuators at the end of the antenna and the end of the voltage probe. This isolates the cables and test set from the changing impedances. Could reflections from the probe be reflecting from the Dipole antenna causing the phase shift in the nearfield to be masked? The probe is .5" long and this effect would show up with varying lengths of e field probes. The two probes I used showed no difference. I would like to make these measurements with a B field probe when I get a chance. In order to be able to really understand your experimental results, I will need to know more about your experimental test setup and test results. This will also enable the duplication of your experiment. I am really quite surprised by these comments on things that are second or third order effects when there are problems with your measurement that are zeroth or first order. You have no antenna, just a voltage probe trying to radiate. You have no impedance match anywhere. You have not isolated the transmitter. You have no ground plane (the table just makes life complicated) You have a dc circuit which does not match what you think your rf circuit is. The important part of the measurement is to create a geometry which is what you think it is. A dipole antenna in free space is far more predictable than any system with a ground plane. All parts of the system have to be isolated from each other so you are only varying what you think you are varyings. For instance, changing the load on most cheap rf equipment (and the hamtronics fits that category) will cause changes in amplitude,phase and harmonic content. Once all the parts are properly characterized and isolated, then you can vary whatever parameter you want with confidence that it is the only one you are changing. When the experiment is done properly, the results will speak for themselves. If you get different results than I do, then we need to look for the reason for those differences. I have listed a large number of problems with your setup. If you fix those things, we will be in a position to compare results. doug wrote: William wrote: Hi Bill, Thank you for the offer, but I think that duplicating the type of experiment I showed in paper would not yield much new information. What really needs to be done is to develop a wideband transmitter and antenna system that can handle modulations bandwidths 1/10 of the carrier. This will enable us to study the propagation speed of random information, which is what everyone wants to know. This is not a trivial design and I don't even know if it can be done. I will have to give it some thought. If I do get something to work, I will let you know. trimmed discussion I am not replying to I think you have this backwards. The first thing to do is to replicate the experiment you did. It seems you still believe it is correct. I have given a list of mistakes you have made. With your setup, no one with rf experience will take it seriously. I showed it to a colleague and he laughed. The basic experiment you are basing your work on must be done correctly and repeatably. You are not using proper antennas, you have not impedance matched anything so you do not know what the fields are, you do not have an infinite ground plane.... You probably are seeing an odd field distribution from the geometry you have created. My repeat of your experiment showed no anomalous effect on the phase. In order to have any effect to discuss, you are required to show a nonlinear phase with distance. I get a straight line for the phase versus distance curve which means that there is a constant value for c at all distances. It shows the same effect at different frequencies so I also have the time dependence which thus also shows no anomaly. There is no point in doing the time domain experiment when you can do the frequency domain experiment much more easily. They are equivalent and can be done on the same piece of equipment. One can build the modulator you suggest but there is no need. Again the frequency domain is the same thanks to our friend fourier. I have spent the last ten years designing and using frequency domain radars. If the phase versus frequency is linear at all frequencies, there is no effect to study. |
#44
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Testing superluminal transmission of near field light waves.
Doug ...
Just one comment. I've been to Trondheim. I'm not sure if the snow has melted enough yet for outdoor experiments! But a big gymnasium might work! Otherwise, your suggestions are spot on. Bill Miller "doug" doug@doug wrote in message ... I pushed the wrong button on the last post. Reply is below William wrote: The RF antenna group at NTNU university has looked into your network analyzer/balanced dipole/balun experimental setup and has preformed tests on a similar setup. They concluded that the observed phase shift results are unreliable due to external room reflections and that the experiment needs to be performed in an anechoic chamber. In their tests they used an Agilent-E8364B S parameter Network Analyzer (10MHz-50GHz), a HP 85052D4 Calibration kit, a 30cm balanced dipole antenna with built in Balun (500MHz resonant frequency, 60cm wavelength), an E field probe (a 0.5m cable with about 1cm exposed wire), 1m HF Cables with SMA connectors, 10dB attenuators (placed at the input to the Balun/Antenna and at the output of the E field probe). A full calibration (using the cal kit - short, load, open, thru) was performed on the analyzer including the RF cables and attached attenuators. The Analyser was swept from 400MHz-600MHz while monitoring the S21 phase at 500MHz. Linear as well as nonlinear phase vs distance relations were observed as the probe was moved from next to the dipole to the dipole wavelength (60cm). Reflections show up quite visibly when you sweep frequencies. A 2GHz -20GHz Anechoic chamber is available here, but preliminary tests with the antenna at 1.5GHz (3rd harmonic of antenna) showed that phase calibration of the analyzer is not possible due to losses in the the long cables (10m), needed to connect the antenna and probe to the analyzer outside the chamber. You should use an antenna at its proper frequency. It has been recommended that a small Anechoic chamber be constructed specially designed for this experiment, enabling the analyzer and 1m cables to be calibrated. The chamber should include a nonreflective mechanism enabling the probe to be moved in small repeatable increments within the wavelength of the antenna. The new chamber will take some time to design, build and test, and the cost could be prohibitively expensive. During the next few weeks I will check into this possibility. I think they are trying to make this too hard. First of all, higher frequencies are your friend. If possible, do the experiment at 2GHz and put it in the anechoic chamber. I have no idea what the comment about the long lines is about. The long lines do introduce loss and phase shift but that is constant and, since all you want is the slope of phase versus distance, any offset is meaningless and can be ignored. Doing a full phase calibration is a nuisance anyway. You can build an antenna for any frequency you want in an afternoon in the machine shop. Small brass pipe makes a good basis. Ream it to a convenient size to give 50 ohms with a .125" center conductor of brazing rod, cut a slot to the length of your elements and then make the elements out of brazing rod as well. Very careful attention should be paid to the details of the connector end and the mating to the connector. these antennas work very well over a +-20% bandwidth. A much easier and cheaper way of doing this is to go outside. Mount the antenna above the ground with its axis vertical. This puts the minimum radiation point aimed at the ground. Put some absorber directly below the antenna if you want. At 500MHz, the absorber is mostly for show but if you go to 1000 or 1500MHz it actually will absorb something. This geometry has several advantages. The reflections are small. At higher frequencies, if you sweep enough, you can fft the data, window out the relections and then fft back to the frequency domain. Even without this, the reflections will be small. doug wrote: William wrote: I agree that the experiment I did should be checked, but I think it is best to do the experiment in the lab using high frequency test equipment like you are trying to do. As you have said the experiment is very difficult to do right and there is a better chance of controlling all the phenomena involved in a standard RF lab environment using commercial test equipment. I also agree that it is essential that these near-field measurement tests show nonlinear phase shift behavior in the nearfield before progressing to a wide bandwidth signal transmission experiments. I am very surprised by your experimental results. The transverse field phase vs distance solution I presented in my paper is what is predicted by Maxwell's equations (p.12, near-field dipole paper). I have checked it both analytically and numerically (p.23-25). In addition the solution has also been checked by other researchers, analytically and numerically: http://ceta.mit.edu/pier/pier56/05.0505121.Sten.H.pdf http://xxx.lanl.gov/abs/physics/0311061 Intuitively one can also see the nonlinear phase shift by looking at the transverse field solution (Eq. 53). The exp[i(kr-wt)] term is a light speed propagating term, and the part in the brackets is a complex term that is a function of kr. This complex term can be expressed in polar coordinates as a phasor, where the phase will cause the over phase of the field to deviate from kr. In the nearfield, the kr term is small thereby making the making the term in the brackets approximately equal to 1, corresponding to 0 deg phase difference from kr. In the farfield the term in the brackets becomes approximately -(kr)^2 corresponding to -180 deg phase difference from kr. In between the nearfield and the farfield the -i(kr) term is dominant, causing the phase to be about -90 deg there. If you will refer to the transverse Electric field phase vs kr curve (ref. fig.12) you will see that the theoretically derived curve agrees with these observations. Relative to a light propagating field, the phase is 0 deg in the nearfield, approximately -90 deg in between the nearfied and farfield, and -180 deg in the farfield. Experimentally it is known that the E field generated by a slow moving charge is proportional to it's position. Oscillating charges cause other nearby charges to oscillate in unison with no observed phase difference. In the nearfield, the B field is experimentally known to be proportional to the current. Oscillating charges are known to generate magnetic fields which are -90 deg phase shifted from the charge motion. In the farfield it has been experimentally observed that the transverse electric and magnetic fields are in phase and propagate at the speed of light. I order for the transverse E field and B field to align in the farfield, given that they are not aligned in the nearfield, their phase vs distance curves must be nonlinear in the nearfield. Do you have any ideas what the problem is? It is hard to believe that Maxwell's equations could be wrong in the prediction of this nonlinear phase shift effect. The defining result is what reality thinks. After there are reproducible experimental results, it will be the time to go through the equations. The experiment is simple. The analysis is not and there have been comments from others who have disagreed with your assumptions. I am not making any assumptions about either your derivations or their disagreements. Until I know more exactly what you have done I can only speculate. First of all I am extremely wary of any test that uses more than one frequency which can generate phase shifts from band limited elements such as the balun and antenna, or from frequency dependent reflections. But if I understand you correctly, even though the Analyzer is sweeping frequencies, you are effectively using only one frequency by reading only the phase at one particular frequency as the E field probe is moved incrementally away from the Dipole antenna. I assume you have calibrated the Analyzer and test cables using a calibrated short, open, and 50 ohm terminators at the end of the test cables, thus effectively flattening out the transfer function of these elements. I also assume the Analyzer is able to measure at least 1 deg phase changes, which is needed to differentiate linear from nonlinear phase behavior in the nearfield. Can the analyzer be operated at just 1 frequency just to be sure the sweeping is not causing any problems (eg. intermode mixing etc.). As someone who does this kind of measurement every day, I have a pretty good idea of the limits. First of all, the hp8753 is a stepped frequency analyzer which sets a frequency and then takes the data so you worries about sweeping effects do not exist. I have a stack of hp calibration kits with a large selection of loads, mismatches, opens and shorts. The transfer function of the system is not important at a single frequency. It is important if you are measuring frequency dependence but that is not being done. The data were looked at at different frequencies but the phase comparisons were done at fixed frequencies. You can look up the specs of the 8753 family to see what the resolutions are. By the way have you checked that the input impedance of the probe/Analyzer combined with the antenna to probe reactance (which changes as the probe is moved away)is not generating a phase shift which could be masking the true phase in the nearfield? There are 10db attenuators at the end of the antenna and the end of the voltage probe. This isolates the cables and test set from the changing impedances. Could reflections from the probe be reflecting from the Dipole antenna causing the phase shift in the nearfield to be masked? The probe is .5" long and this effect would show up with varying lengths of e field probes. The two probes I used showed no difference. I would like to make these measurements with a B field probe when I get a chance. In order to be able to really understand your experimental results, I will need to know more about your experimental test setup and test results. This will also enable the duplication of your experiment. I am really quite surprised by these comments on things that are second or third order effects when there are problems with your measurement that are zeroth or first order. You have no antenna, just a voltage probe trying to radiate. You have no impedance match anywhere. You have not isolated the transmitter. You have no ground plane (the table just makes life complicated) You have a dc circuit which does not match what you think your rf circuit is. The important part of the measurement is to create a geometry which is what you think it is. A dipole antenna in free space is far more predictable than any system with a ground plane. All parts of the system have to be isolated from each other so you are only varying what you think you are varyings. For instance, changing the load on most cheap rf equipment (and the hamtronics fits that category) will cause changes in amplitude,phase and harmonic content. Once all the parts are properly characterized and isolated, then you can vary whatever parameter you want with confidence that it is the only one you are changing. When the experiment is done properly, the results will speak for themselves. If you get different results than I do, then we need to look for the reason for those differences. I have listed a large number of problems with your setup. If you fix those things, we will be in a position to compare results. doug wrote: William wrote: Hi Bill, Thank you for the offer, but I think that duplicating the type of experiment I showed in paper would not yield much new information. What really needs to be done is to develop a wideband transmitter and antenna system that can handle modulations bandwidths 1/10 of the carrier. This will enable us to study the propagation speed of random information, which is what everyone wants to know. This is not a trivial design and I don't even know if it can be done. I will have to give it some thought. If I do get something to work, I will let you know. trimmed discussion I am not replying to I think you have this backwards. The first thing to do is to replicate the experiment you did. It seems you still believe it is correct. I have given a list of mistakes you have made. With your setup, no one with rf experience will take it seriously. I showed it to a colleague and he laughed. The basic experiment you are basing your work on must be done correctly and repeatably. You are not using proper antennas, you have not impedance matched anything so you do not know what the fields are, you do not have an infinite ground plane.... You probably are seeing an odd field distribution from the geometry you have created. My repeat of your experiment showed no anomalous effect on the phase. In order to have any effect to discuss, you are required to show a nonlinear phase with distance. I get a straight line for the phase versus distance curve which means that there is a constant value for c at all distances. It shows the same effect at different frequencies so I also have the time dependence which thus also shows no anomaly. There is no point in doing the time domain experiment when you can do the frequency domain experiment much more easily. They are equivalent and can be done on the same piece of equipment. One can build the modulator you suggest but there is no need. Again the frequency domain is the same thanks to our friend fourier. I have spent the last ten years designing and using frequency domain radars. If the phase versus frequency is linear at all frequencies, there is no effect to study. |
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