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Monthly Archives: February 2012

THEORY OF LOAD AND SOURCE PULL MEASUREMENT

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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

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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.