The time domain measurement section is divided into two parts (Part I). In this part, we will continue to introduce the Gate Form .
Similar to window wave filter, the gate also has corresponding wave filter form and Measure can be optimized by selecting reasonable wave filter form:
(1) Minimum gate: the wave filter has highest sidelobe level, with sharpest edge falling and maximum band-pass ripples.
(2) Maximum gate: the wave filter has lowest sidelobe level, with slowest edge falling and minimum pass band ripples.
1. Passband Ripples of the Gate
The gate is a pass band (or band-stop) wave filter on time domain and each form of wave filter has different filter property. Figure below indicates band-pass ripples of four filters in different forms and the scale in the figure is 0.5dB/grid. It can be seen from the figure that the minimum gate has the largest band-pass ripples.
2. Sidelobe Level of the Gate
Four wave filters of different forms have different sidelobe levels, in actual Measure, there must be a balance between lower sidelobe level and faster cut-off ratio.
(1) The minimum gate is with highest sidelobe level and fasted cut-off speed, which is very applicable to filtering undesired interference near the response.
(2) The maximum gate is with lowest sidelobe level, slowest cut-off speed, widest gate band-pass and maximum attenuation outside the gate band.
3. Property Index of the Gate
Different forms of gate have different properties and the properties are defined by index below:
(1) Pass band ripples and sidelobe level: to descript the gate form.
(2) Cut-off time: it is the time between end time of the gate (at -6dB of the filter edge) and the first sidelobe peak point.
(3) Minimum gate span: it equals to end time minus start time and it is twice of the cut-off time.
Table 1 Property Index of Different Gates
|Gate Form||Pass Band Ripple||Sidelobe Level||Cut-off Time||Min. Gate Span|
|Min.||±0.10dB||-48dB||1.4/frequency span||2.8/frequency span|
|Standard||±0.10dB||-68dB||2.8/frequency span||5.6/frequency span|
|Width||±0.10dB||-57dB||4.4/frequency span||8.8/frequency span|
|Max.||±0.10dB||-70dB||12.7/frequency span||25.4/frequency span|
Each form of gate has a recommended minimum gate span to operate correctly, which is determined by limited cut-off ratio of the gate. If the gate span set is smaller than this minimum value, the Analyzer will produce effects below:
(1) The gate form is distorted, without pass band.
(2) Indication of start and end time is incorrect.
(3) Sidelobe level would be increased.
S3601 Series Vector Network Analyzer (100kHz – 3GHz / 8.5GHz)
S3602 Series Vector Network Analyzer (10MHz – Max.67GHz)
S3603D Vector Network Analyzer (300kHz – 20GHz)
SAV364X Series VNA Extension Module (Max. 325GHz)