Solutions


Simulated Coalescence of Linearizer and TWTA Components		[ back ]
The Challenge A well-established telecommunications company designs and manufactures linearizers for traveling wave tube amplifiers (TWTA). Combined with the TWTA, the linearizer enhances the gain characteristics of the amplifier. Because of physical limitations, technicians cannot directly measure the performance of the TWTA joined with its corresponding linearizer. This constraint presents a challenge especially in evaluating the intermodulation distortion inherent from multitone or gaussian noise excitation. This desired analysis must be derived from separate measurements of the two devices. The Solution Larson Automation has developed software to anticipate the behavior of the union of the TWTA with the appropriate linearizer given the continuous wave (CW) characteristics of these individual components. The simulation provides the engineer with a valuable assessment of the end-to-end distortion of gain, phase, and intermodulation. Introduction With the deployment of TWT amplifiers (TWTA) in satellite communication systems, engineers seek to reduce power consumption while minimizing costs. The coupling of the TWTA with a properly fitted linearizer counteracts the compression of amplifier gain and exploits the energy of the nonlinear gain region. Due to geographical and financial impediments, direct measurement of the performance of such a linearizer-TWTA (LTWTA) combination is impractical and requires an alternative test method. Therefore, the engineers required a computer-aided simulation to test the validity of their products. As a specialist in test software development, Larson Automation offered its support for the LTWTA test system.
System Description In order to characterize the linearizer, we employ an Anritsu 37525 network analyzer to measure the changes in gain and phase with respect to varying levels of input power. The network analyzer provides the linearizer with a CW signal and measures the corresponding output power and phase. These quantities are then composed with predetermined TWTA characteristics to derive the output power and phase of the expected LTWTA. Furthermore, these CW characteristics are sufficient to determine the intermodulation output power of the TWTA and the LTWTA. Derivation of the expected noise power ratio (NPR) is also important in assessing the amplifier's efficiency in transmitting several signals within adjacent bands.

A comparison between LTWTA characteristics and that of the unaided TWTA	Software Description Larson Automation provides engineers with a powerful mathematical tool that simplifies the complexities of data processing. Implemented in the C programming language, the simulation incorporates basic mathematics for the computation of combined gain and phase. The software also utilizes more advanced theory to compute the third-order intermodulation product output power and the NPR.
Aside from the valuable numerical analysis, the graphical user interface (GUI) is equally important in simplifying the tasks of the engineers. The simulator sports an intuitive interface that controls the measurement instrumentation as well as the manipulation of the transfer characteristics of the device-under-test (DUT). Finally, the software presents all relevant information graphically for quick interpretation of the data.		The graphical user interface (GUI) provides easy configuration of the test system
Larson Automation, Inc. Address: 960 Rincon Circle, San Jose, CA 95131 Tel: (408) 432-4800 Fax: (408) 432-4848 Email: info@larsonautomation.com