# Window Shapefactor and Equivalent Noise Bandwidth

The following table shows a performance summary of the different types of windows supported by the 89600 VSA. Following the table is a section that describes the terms shapefactor and equivalent noise bandwidth.

## Window Shapefactor & Equivalent Noise Bandwidth

Window shapefactor is a frequency ratio. It is the ratio of the frequency at -3dB to the frequency at -60dB. Window shapefactor is sometimes called window selectivity.

Equivalent noise bandwidth (ENBW) compares a window to an ideal, rectangular time-window. It is the bandwidth of the rectangular window's frequency-domain shape that passes the same amount of white noise energy as the frequency-domain shape defined by the other window.

In the table below, the ENBW has been normalized by the time-record length. To compute the ENBW for a given time-record length, divide the ENBW by the time-record length. For example, a Hanning window on a 0.5 second time record would have an ENBW of 3 Hz (1.5 Hz-sec/0.5 sec). Notice that the ENBW is slightly larger than the 3 dB bandwidth.

The VSA's definition of resolution bandwidth (ResBW) is based on the normalized Equivalent Noise Bandwidth of the selected window type.

Window summary

Parameter

Uniform

Hanning

Gaussian Top

Flat Top

Leakage Performance

Poor

Relatively Good

Best

Good

Frequency Resolution: main length fixed

Poor**

Relatively Good

Good

Poor

Frequency Resolution: RBW fixed

Poor**

Good

Good

Best

Normalized Equivalent Noise BW

1.00 Hz-sec

1.50 Hz-sec

2.215 Hz-sec

3.8194 Hz-sec

3 dB BW

0.8844 Hz-sec

1.438 Hz-sec

2.091 Hz-sec

3.767 Hz-sec

Window ShapeFactor

716:1

9.1:1

4.0:1

2.45:1

Maximum Amplitude Error*

3.92 (dB)

1.42 (dB)

0.68 (dB)

< 0.01 (dB)

Highest Sidelobe

-13 (dB)

-31 (dB)

-125 (dB)

-95 (dB)

Sidelobe Fall Off

Parameter

Blackman-Harris

Kaiser-Bessel

Gaussian

Leakage Performance

Good

Good

Good

Frequency Resolution

Good

Good

Good

Normalized Equivalent Noise BW

2.0044 Hz-sec

2.0013 Hz-sec

2.0212 Hz-sec

Window ShapeFactor

3.79

3.78

4.45

Maximum Amplitude Error*

0.83 (dB)

0.83 (dB)

0.83 (dB)

Highest Sidelobe

-92 (dB)

-89 (dB)

-73 (dB)

Sidelobe Fall Off