Hi! I'm doing time domain gating in this way:first the s-parameter data that i get from network analyzer are transformed to time domain via IFFT, then i select the desired response using windows equation like Hamming e.t.c and finally i transform the gated response back to frequency domain but i don't get the expected result.Is there any normalization equation or some correction factor that i must apply after the gating procsses.Thanks.

(From: http://cp.literature.agilent.com/litweb ... 5723EN.pdf)

Also, if a simple gating function was used, a curious effect would occur at the endpoints of the time-gated frequency domain response in that the endpoints would be lower by 6 dB. Gating is performed solely in the frequency domain. The start and stop gate times define gate width from which the equivalent frequency domain gating function can be directly determined. Over the frequency range of interest, the gated value at

any point is determined by multiplying the original frequency response by the reverse of the gating frequency function centered at that frequency and then summing the result (convolving). At the last data point, the gate response center is at the endpoint of the band of interest. Any frequencies beyond the endpoint of the band will return zero so half of the gate function will be multiplied by zero and does not add to the sum.

This creates the result that any gating will distort the endpoints of the gated frequency response by lowering them by 6 dB.

The VNA time domain algorithm compensates for this roll-off through post-gate renormalization. This compensation function works perfectly for a unit time response at the center of the gate. However, if the gate is not symmetrical around the time function, then the result will show some errors in approximately the last 10 percent of the gated response when compared to the original frequency response.

In the bandpass mode, these errors will show up in the first and last 10 percent (approximately) of the gated frequency response.