Ultrasound beamforming

dbd  <d.dalrymple@sbcglobal.net> wrote:

>On Tuesday, March 5, 2019 at 7:51:47 AM UTC-8, mako...@yahoo.com wrote:
>
>> I agree with your statement, but
>> 
>>  I think the beam created by this "time domain method" will still vary
>as a function of frequency?
>> 
>> Because delay lines  create a phase shift that varies with frequency.
>> 
>> Because it is phase shift (not time delay)  that controls the beam
>> 
>> Am I wrong?
>
>Yes.
>
>> 
>> m
>
>In the broadband time delay beamformer, the delays set the beam pointing
>angles, which are constant in frequency. The beam widths will vary with
>frequency as the effective size of the array, in wavelengths, changes
>with frequency.

I am thinking that a yagi antenna is a narrowband beamformer whereas
a log periodic antenna is broadband, and their must be equivalents
in DSP.

Steve

On Tuesday, March 5, 2019 at 9:51:48 PM UTC-5, Steve Pope wrote:
> dbd  <d.dalrymple@sbcglobal.net> wrote:
> 
> >On Tuesday, March 5, 2019 at 7:51:47 AM UTC-8, mako...@yahoo.com wrote:
> >
> >> I agree with your statement, but
> >> 
> >>  I think the beam created by this "time domain method" will still vary
> >as a function of frequency?
> >> 
> >> Because delay lines  create a phase shift that varies with frequency.
> >> 
> >> Because it is phase shift (not time delay)  that controls the beam
> >> 
> >> Am I wrong?
> >
> >Yes.
> >
> >> 
> >> m
> >
> >In the broadband time delay beamformer, the delays set the beam pointing
> >angles, which are constant in frequency. The beam widths will vary with
> >frequency as the effective size of the array, in wavelengths, changes
> >with frequency.
> 
> I am thinking that a yagi antenna is a narrowband beamformer whereas
> a log periodic antenna is broadband, and their must be equivalents
> in DSP.
> 
> Steve

OK I get it now.
The geometry of the array creates signals that are offset in TIME, not offset in PHASE as I was thinking.  Therefore to get the signals to add constructively over a wide range of frequencies,  "all you need to do"  is use time delays to  time align the multiple signals and they will remain time aligned over a range of frequencies.  I was so accustomed to thinking in terms of phase that  I was incorrectly thinking that the array created signals that are shifted by a given amount of phase.  This is false.  They are shifted by a given amount of time, so all it takes is time delays to get the signals back  in alignment.       

Thank you all for the discussion.

Mark