What is an Impedance Stub Tuner?
A stub tuner is a type of impedance tuner that is used to set a particular load impedance value. Impedance tuners like the stub tuner are used to evaluate how various components and systems respond to non-50 impedance matches. Impedance tuners are usually used to identify the load impedance which supports maximum power transfer.
The basic operationality behind an impedance tuner is to offer some sort of variable impedance, or VSWR, across a bandwidth. Stub tuners are low cost easy to manufacturer impedance tuners that can be used for a certain set of frequencies. They are widely used for test and measurement purposes where the DUTs need to be evaluated across various impedance conditions.
A stub is a length of transmission line. In a stub tuner a short-circuited section of transmission line is placed along the main signal line. As the figure below shows, the stub is attached to the main transmission line at 90°. Therefore, such tuners tend to introduce a variable shunt susceptance into the transmission line. The value of the shunt susceptance is equivalent to the length of the stub/ short-circuited section. The ‘d’ can be moved to vary the value of shunt susceptance.
A stub tuner often uses more than one stub – Two, Three and sometimes even more stubs can be used. Each stub can have a different length and be placed at and different distance from the transmission line. The spacing between stubs of the tuners regulates the range of impedances that can be matched.
The impedance of the transmission line varies and is usually dependent on the frequency of operation. The minimum operating frequency of a stub tuner is determined by the frequency at which the maximum stub movement is equal to half a wavelength. On the other hand, the upper frequency level is typically dependent on the connectors or waveguide interface used.
Stub Tubers are available in both manual and automatic formats. In the case of a manual tuner, the length of each stub can be controlled manually. Automatic stub tuners used the same principle as the manual tuners to vary the impedance but do so automatically i.e once the impedance is specified, the tuner calculates and regulates the length of each stub to provide the required impedance.
When selecting a Stub Impedance Tuner it is very important to specify the following:
Tuning Type: Manual or Automatic
Number of Stubs: Usually available in 2 Stub, 3 Stub and 4 Stub options
Frequency of Operation: This is very important as most stub tuners are designed for a specific frequency range. The frequency range is regulated by the length of the stubs and interconnects used.
Interface Type: This can be coaxial connectors or Waveguides.
everything RF has created a search tool for impedance stub tuners. We have listed products from most companies and made them searchable by specification. Users can view product specifications, download datasheets and get quotes on stub tuners based on their requirements.
