high reflection coefficient and phase shift

[tsp]

Hi,

Can somebody explain, how a high reflection coefficient is related to
phase shift? Some of the book I have been reading on LNAs say that
as long as we have a high reflection coefficient we can phase shift
and transform a 50 ohm impedance to short circuit. How does this
happen? How would it work if I was to look at a Smith Chart?

Thanks,
tsp

 

[Gareth]

tsp wrote:

Hi,

Can somebody explain, how a high reflection coefficient is related to
phase shift? Some of the book I have been reading on LNAs say that
as long as we have a high reflection coefficient we can phase shift
and transform a 50 ohm impedance to short circuit. How does this
happen? How would it work if I was to look at a Smith Chart?

A high reflection coefficient means a point near the edge of the Smith
chart, a phase shift can move that point round the edge of the chart, so
you can get to a short circuit (or open circuit if you wanted) with the
appropriate phase shift.

Another way of looking at it is that you choose a phase shift such that
the reflected wave arrives 180 degrees out of phase with the original
wave, so the voltage cancels and you get zero volts as you would with a
genuine short circuit.

Gareth.

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