The uses and Importance of Stub Tuners

There are various devices used to modify the impedance factor in various subsystems and devices used for calibration. One of such devices is Tuner that are used in various signal operating networks and related systems. These tuners are very useful in calibrating techniques where the impedance of the sources are to be adjusted to set with precise tuning of the frequencies. There are various types of tuners like as the Stub tuner and Slide screw tuner. These are different in the design but perform on the same basics of working. These tuners are used to measure the impedance settings and modify them as per the requirements.

The most important use of the stub tuner is to set the impedance matching which is critical for RF operation systems. These are widely used in carrying out the operations like as Load pull and noise measurements for both production and laboratory usages. The stub tuner is best suitable in the cases where continuous use of the tuner is not required. This is quite effective and provides the best alternative for other tuning devices. There are two types of stub tuners; dual stub tuner and multiple stub tuners. These tuners are basically impedance transformers. The stub tuners provide the various impedances in the given systems that are to be optimized. It is used to provide a variable shunt in the coaxial transmission susceptances situated at fixed distance. A stub tuner consists of the two or more short-circuited, variable length lines (stubs) connected at right angles to the primary transmission line. These tunable shorts are operated on the half wavelength at the minimum operating frequency.

These tuners provide the system to correct the phase and amplitude standards at the same time.  It is very useful to adjust the reflection coefficient of the phase and amplitude simultaneously. The distance between the stubs is the factor to specify the range on the impedance that the stub tuner can match and tune. These tuners re useful but can be misleading because of the unpredictable reflection behaviors in case of the multiple stub tuners. The multiple stub tuners cannot be used to match the amplitude and phase simultaneously. The multiple stub tuners are not easier to operate as they can create problems in effective reflection management.

There are various uses of the stub tuners that make them useful over other devices in Load Pull. While carrying a load pull the measure is recommended to be set at the maximum or approximately close to it. This is almost impossible in practical cases because of the power loss in the tuners itself therefore it becomes difficult to get the optimum net result at DUT reference plane.  However, if the mismatch range is not very high (5transistors or higher) the chances for a reasonable accuracy are high and falling below it becomes difficult to search around the optimum.

This method is useful and effective over the other methods as it is cost effective and don’t give negative effects like as self heating and transient trapped charges. The factors like as self heating and trapped charges can be producing misleading results of the tests. The pulsed IV testing process delivers the accurate data on the devices needed to improvise the devices. This is best suitable to measure the test results in RF devices like as the transistors, switched and amplifiers relating to nonlinear responses.

There are two types of test methods used for testing in the pulsed environment; i.e. pulsed IV sweeps and transient (single pulse) testing method. If the DUT is associated with the double channels including pulse source and a pulse measurement system the results can be recoreded easily. This makes it very cost effective.

The results produced under different biased conditions for the Pulsed IV measurement sweeps carried out in pulsed system can be easily compared with the results produced in DC tests. The graphs of the curves produced by showing drain voltage VD and drain current ID behavior under different bias conditions are similar to that of the pulsed testing.

The basics of the pulsed IV testing are set to provide the pulses with non-zero value for both gate and drain voltage, often referred to as the operating point or quiescent (q) point. This technique is very useful for condition and based on the applicability of the low-duty-cycle pulse to the DUT. This helps in avoiding the self-heating and carrier-trapping effects that can deviate the exact results. The method of  load pull testing is used to support the test results of overall measurements carried for a device.

The pulse width that is used in this technique ranges from milliseconds to nanoseconds.  The selection of the pulse widths depends upon the DUT, materials and test parameters. The standard source-measure units (SMUs) are usually used to measure the results on millisecond pulse widths. The shorter pulses (microseconds to nanoseconds) are generally more effective for avoiding self heating and charge-trapping effects. Therefore, short-pulse pulsed I-V testing of RF transistors generally allows the creation of more useful models.