Present high power load-pull technology is based on either active fundamental re-injection or mechanical tuners1-4. Although in principle an active load-pull system can present an arbitrary load impedance, the architecture of these systems is not amenable to generating the extremely high power necessary to emulate a sub 1 W load at 1 kW PEP. The current state of the art in mechanical tuners is limited in resistance to approximately 1 W, although narrowband systems can go lower5. To overcome the limitation posed by mechanical tuners, many researchers have adopted quarter-wave prematching networks to transform the tuner impedance to lower impedance. With this approach, it is possible to present a sub 1 W resistance necessary for high power transistor characterization.
A SUB 1 W LOAD-PULL QUARTER-WAVE PREMATCHING NETWORK BASED ON A TWO-TIER TRL CALIBRATION
Traditional Noise Parameter Measurements
A traditional noise parameter measurement setup, it includes a vector network analyzer (VNA) and a separate noise figure analyzer. For s-parameter measurements, the tuner is set to 50 ohms, and the two RF switches connect the device under test (DUT) to the VNA. For noise measurements, the switches connect the noise source to the DUT input and the noise receiver to the DUT output. An optional load tuner (not shown) is sometimes used when the DUT is highly reflective, to reduce sensitivity to error.
The tuner is pre-characterized at every frequency independently. This means that there is a unique set of tuner positions for each frequency, ensuring a good spread of source impedance points at every frequency. The tuner can be characterized separately, or as part of an in-situ system calibration. The advantage of doing it separately is that the same tuner file can be used for a long time, and then a hybrid in-situ calibration can quickly get the remaining s-parameter blocks.
The in-situ system calibration normally uses two VNA calibrations: a 2-port calibration at the DUT reference planes, and a 1-port s22 calibration at the noise source reference plane. By subtracting error terms, the 2-port x-parameters from the noise source to the DUT can then be determined. If the optional load tuner is used, then a 1-port s11 calibration at the noise receiver reference plane is also used to determine the 2-port s-parameters from the DUT to the noise receiver.
A hybrid in-situ calibration uses tuner data that is already characterized. The same VNA calibrations are still used to determine the 2-port s-parameters from the noise source to the DUT plane, which are then de-embedded to remove the tuner s-parameters. The result will be s-parameter blocks that include everything except the tuner.
After the system TRL calibration, the traditional noise receiver calibration and DUT noise parameter measurement are both done one frequency at a time[3][4]. This is because the noise parameter extraction involves complex math that is sensitive to small errors, and the pattern of source impedance points is important to get well-conditioned data[2]. Measuring one frequency at a time solves this by allowing the impedance pattern to be selected in an optimal manner for each frequency.
Pulsed IV testing to precisely measure the RF Devices
There are various methods characterizing the devices working on the signal networks using RF and other frequencies. Pulsed IV is one of the methods used for testing the devices working on electronic signals like as microwave and RF frequencies. This can be applied to test and specify the characteristics of the DUT after carrying out the calibration process carefully.
The testing procedure that uses the Pulsed (IV) current has become more prevalent these days for evaluating performance of the semiconductor devices. This process of testing uses pulse sources that is supplying a current pulse to the device under test and do the measurements with pulse measurement device. The technique of Pulsed IV measurement is used mainly on the large signal analysis.
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.
THEORY OF LOAD AND SOURCE PULL MEASUREMENT
Load pull consists of varying or “pulling” the load impedance seen by a device-under-test (DUT) while measuring the performance of the DUT. Source pull is the same as load pull except that the source impedance is changed instead of the load impedance.
Load and source pull is used to measure a DUT in actual operating conditions. This method is important for largesignal, nonlinear devices where the operating point may change with power level or tuning. Load or source pull is not usually needed for linear devices, where performance with any load can be predicted from small signal x-parameters.
Calibrating to measure output power and gain consists of measuring the available input power at the power source reference plane and the coupling value of the directional coupler. If the coupler had perfect directivity, then coupling could be measured with only a short at the source power reference plane. However, finite directivity causes the apparent reflection to vary with reflection-phase, so a more accurate coupling value is found by taking the average of both short and open measurements. This minimizes directivity errors, although good coupler directivity is still important for the best accuracy.
Once the available input power and coupling are known, the output power, transducer gain, and power gain can all be measured with any combination of source or load impedance. Output power is the power delivered to the load. Transducer gain is the ratio of delivered output power to available input power. Power gain is the ratio of delivered output power to delivered input power.
The objective of the measurement is to get the power and gain values at the DUT reference planes. Although the tuners are very low loss, bias tees and other components may be included as part of the “ stub tuner” characterization, so the loss must be considered. To get the output power at the DUT reference plane, the dissipative loss of the load tuner is added to the raw measured output power. To get the available input power at the DUT reference plane, the dissipative loss of the source tuner is subtracted from the calibrated available input power. To get the delivered input power at the DUT input reference plane, the reflected power at the source is subtracted from the calibrated available power at the source. The dissipative loss of the source tuner is then subtracted from the result to shift from the source power reference plane to the DUT input reference plane.
Waveguide Adaptors and their Uses
The wave guide adaptors are used for connecting the various coaxial transmission equipments and resources with each other and develops the signal harmonics in large signal operated networks. The waveguide adaptors are made in accordance with standard requirements of different signal network operating systems. These adaptors are providing the waveguide transmission port from the coaxial sources.
These adaptors are working on different bandwidths and systems. These adaptors are made up of different materials and provide supports to different application in various situations. The waveguide adaptors are having several components that include a rectangular platform that is used as housing made up of rectangular waveguide tubing.
This provides the platform for the waveguide adaptor. It is made up of the different materials as per the requirements. The other parts of a waveguide adaptor are standard waveguide flange; this is needed to support the transmission of signals. These two components are fixed on the metallic end plate the holds both these parts in connection to each other. All these components are fixed with the waveguide adaptor coaxial probe and assembly.
The coaxial probe assembly used in the waveguide adaptor is similar with the assembly used in the SMA connectors. This assembly can also be used in waveguide band pass filters with coaxial interfaces. If you are using the waveguide adaptor with the SSMA connectors then you have to make new probes according to the requirements.
The housing part of the waveguide is used to connect with the modified female to female connectors using coaxial adapter. Asides this bottom broad wall part of the waveguide have four holes for metallic tuning screws. While designing and assembling a small waveguide adaptor some fabrication is also needed that can be carried out by using the metallic alloys like as copper alloys and stainless steel. It can be taken as per the requirement and durability aspect. There are various methods of making waveguide platforms that uses the waveguide adopters and coaxial assemblies.
The technique of electro forming waveguide generation is used for the purpose of signal transmissions for the complex structures. This is quite expensive and used for large signal operating networks. It is made by electroplating the same kind of materials in different layers of the structure to be used for waveguide purpose.
Apart from this the waveguide constructions are carried out through different methods like as Dipbrazing and machining. But all these waveguide structures need to be connected to the coaxial assemblies using different types of waveguide adaptors that are considered on the basis of the typical mechanical attributes like as size and dimensions. Asides these the factors like as return loss, bandwidth support and others environmental attributes are to be considered before selecting the waveguide adapter.
SOLT Calibration with non Insertable thru Connection
This is a method of network calibration that is used in electronics field. It is often termed as on wafer calibration. The standards used in this calibration are termed as short open load and thru which constitutes the SOLT calibration kit. These standards are used to calculate the calibration algorithm which is important to make error free measurements. This method is carried out by connecting a short circuit, and open circuit and a load in successive manner to one port of the and the measurements are taken to complete the reflection calibration within a vector network analyzer plane.
This is typical calibration method that implies three impedance and one transmission standards to specify the reference plane. The three impedances are matched typically with the three standards a Short, Open, Load, and Thru which constitutes the SOLT calibration setup. While as in the other calibration methods like asTRL calibration and others the thru reflection and line standards are used to measure the calibration.
Both of the calibration methods are used and any of the calibration setup can be used to measure the performance of the network as per the availability of calibration standards and functionality of the network analyzer.
The SOLT calibration method is quite useful in deciding the measurement for network performance that is specified as per the mechanical dimensions. While performing SOLT Calibration process you must find the standard values. Then you should attach the calibration setup with the above standards to the Network Analyzer calibration port, the end of a cable, or inside a test fixture where the measurement is to be made. This is considered as the reference plane or measurement plane.
The network connections like as the insert-able connection like as male to female cable connection and others. These connections don’t require other external connections. The external adapters or devices are used to complete the through connection during SOLT calibration. While performing network calibration you must use all the components that are to be used in calibration or else it may result in measurement error.
Calibration can be done without insertable thru this is useful in handling the non-insertable devices. The simplest method of doing this is by using a set of phase-equal adapters with shorts, opens, and loads of male and female adaptors. Now by connecting one adapter to complete the through connection during calibration and then replacing it to swap by another adapter connected with the Device Under Test gives the calibration measurements.
This method of calibration is quite useful in designing the devices operating on the cascading networks and uses high frequencies but can be tested with insertable thru connection. It is quite useful in RF devices. Apart from this there are various other methods of calibration.
