A novel hardware configuration for an adaptive beamforming array using quadrature mirror filter banks
✍ Scribed by Sathish Chandran
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 167 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0895-2477
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✦ Synopsis
artificial reflections for the open microstrip of Figure 4, whose substrate thickness is h s 3⌬, but whose width w is 10⌬, 6⌬, and 2⌬. The calculated data show that errors increase with decreasing wrh values. The increase, once again, of the error is due to departure from the TEM wave model, behavior which was already reported in the literature w x 11 .
To demonstrate the performance of the proposed technique for obtaining and using the absorption coefficients in problems with discontinuities, a simulation of the bandpass filter was carried out. The filter geometry is shown in the Ž inset of Figure 6, which was discretized into a 20⌬ = 80⌬ = . 120⌬ lattice, where ⌬ is 0.212 mm, and the number of PML layers is equal to three. The ESN algorithm was allowed to Ž . run for 10,000 time steps ⌬ t s 0.176 ps , and the computed data for the S -parameter were plotted in Figure 6. For 21 w x comparison, data generated using the conventional SNM 11 are also plotted, as are the measured data. The lattice used w x for the SNM simulation in 11 was identical to the lattice size used in this work. However, the SNM simulation would have required at least 55.5 Mbytes of memory, compared to only 27.6 necessary for the ESN simulation, not to mention that it w x would have taken ten times as long 9 . As can be seen from the plot, the agreement among the measured, SNM, and ESN results is quite good. Finally, it should be added that all results presented in this paper were generated on a 200 MHz PentiumProᮋ computer with 32 Mbytes of RAM memory, taking 18.4 s per unit cell and time step.
IV. CONCLUSION
A numerical method of obtaining the absorption coefficients for use in PMLs in microstrip transmission-line-type problems was presented. The proposed approach was shown to yield small reflections from lattice boundaries, using as few as three PML layers. It was demonstrated that the absorption coefficients can be obtained from a 1-D problem and applied directly to similar 3-D geometries with the same material parameters. However, it is important to add that the use of 1-D ''loss'' coefficients is best suited for 3-D problems which support TEM or quasi-TEM fields distributions. For other 2-D and 3-D problems, a corresponding 2-D or 3-D optimization should be carried out to obtain the appropriate set of ''loss'' coefficients for the PMLs.