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Yongjiu Zhao
Yongjiu Zhao
Professor in the College of Electronic and Information Engineering at Nanjing University of Aeronautics and Astronautics

Nanjing University of Aeronautics and Astronautics Selects AWR Software

 
May 1st, 2013 by Yongjiu Zhao

UNIVERSITY BACKGROUND

Nanjing University of Aeronautics and Astronautics (NUAA) is one of China’s premier learning and research institutions and has developed into a comprehensive university especially focused on aerospace engineering. Established in 1952, NUAA strives to provide a world-level research and education system for its 24,600 students, 600 of who are international students from over 30 countries.

THE DESIGN CHALLENGE

NUAA was searching for a more user-friendly, integrated alternative to the current set of high-frequency design tools used in the classroom. To objectively evaluate AWR’s Microwave Office® RF and microwave design software, the university chose to redesign an existing compact and high selectivity dual-band, dual-mode bandpass filter for GPS and WLAN applications. The filter was designed using a short, stub-loaded folded resonator with source load coupling. The 3dB fractional bandwidths of the two passbands were about 3.4 percent at 1.57GHz and 9.9 percent at 5.2GHz. Because there was interference between the main signal path and the folded arms of the resonator, it was necessary to generate five transmission zeros near the passband edges and in the upper stopband in order to improve the frequency selectivity and stopband performance.

THE AWR SOLUTION

AWR’s Microwave Office software’s advantages as they pertain to this design include both its integrated design environment and its ease-of-use. The filter design was implemented using AWR’s unique electromagnetic (EM) based X-model transmission line models (Figure 1). In contrast to conventional models, these highly accurate circuit models provide both electrical model and physical layout representation and yield fast simulation results that are as accurate as full EM simulation. Therefore, as soon as the filter schematic was drawn, the layout was readily available for EM verification and to send off for PCB fabrication.

Figure 1: Schematic and layout of the filter, composed of Microwave Office elements readily found within its components library.

Because the circuit model was simulated instantaneously, parameter tuning and preliminary optimization of the filter were straightforward. At the back end of the design flow, the layout was sent to AWR’s AXIEM® 3D EM simulator directly from the schematic – no geometry redraw was needed for the EM simulation (Figure 2).

Figure 2: AXIEM layout of the filter.

A parameterized full EM model was used in interpolation mode to enable fast offline execution of statistical analysis with full EM accuracy.

Following this methodology, NUAA was then able to do extensive yield sensitivity studies of PCB substrate dielectric constant (Er), board thickness (H), and geometric properties related to manufacturing tolerances. The design team discovered that the design was critically sensitive to variations in Er, which must be controlled within 0.1 percent and H within 20 μm for perfect yield. In contrast, the design was not very sensitive to geometry variations within regular processing tolerances (Figures 3 and 4).

NUAA appreciated the flexible methodology that the AWR Design Environment™ enabled. The ability to seamlessly switch between circuit and full EM simulation models at various stages of the design resulted in an efficient, robust, and user-error resilient design process. The evaluation proved that the measured results agreed extremely well with the AWR results, in particular the AXIEM EM simulated results (Figure 5).

Figure 5: Comparison between measurements (black) and AXIEM simulations (magenta).

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