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ABSTRACT:

This paper has presented formulations for the modeling of magnetic loss in the FETD simulations of electromagnetic fields. Unlike a frequency-domain finite-element formulation, or a traditional finite-difference time-domain formulation, incorporating magnetic loss into FETD formulations based on the wave equation requires certain care in the implementation. Specifically, additional integrals that involve the local magnetic field are required. However, these integrals can be treated as additional forcing-function vectors in a straightforward manner. In this paper, the planar element is replaced by a corrugated element. The effect of corrugation parameters are examined in relation to lower edge frequency, impedance bandwidth, and radiation properties. ACKNOWLEDGMENT ANTENNA GEOMETRY AND CONSTRUCTIONThe corrugated plate monopole was constructed using a planar sheet of 0.2-mm-thick brass and fed through a groundplane using an SMA feedprobe, as shown in Figure 1. The groundplane dimensions were 150 ϫ 150 mm. The height l and width w remained constant at l ϭ w ϭ 40 mm and a constant feedgap of g ϭ 2 mm was used. Thus, the antenna height above the ground plane was always 42 mm. The corrugations were realised by bending the brass plate periodically along its horizontal dimension, as shown in Figure 2. The element is folded using the parameters ␣ for the corrugation angle, d cp for the corrugation period, and d cd for corrugation depth. The number of corrugations (N) employed was varied from 1 to 2.5 and the values used for corrugation angle ␣ were 15°, 30°, 45°, and 60°. Full data for the various parameters is given in Table 1. IMPEDANCE BANDWIDTHThe return loss for the simple planar monopole of same dimension (40 ϫ 40 planar with 2-mm feedgap) was measured and found to be greater than 10 dB in the range 1.54 -2.96 GHz. The return loss was then measured for the various corrugation arrangements given in Table 1 on an RS vector network analyser. The antennas were simulated using the finite-integration time-domain method (CST microwave studio). A plot of the measured and simulated S 11 for ␣ ϭ 30°and N ϭ 1.5 is shown in Figure 3, which show good agreement. It was observed that the lower edge of the impedance bandwidth decreased with decreasing corrugation angle. This can prove useful when antenna height is restricted. It also was noted that the height reduction was at the expense of bandwidth, which also decreased with decreasing corrugation angle. It can be seen from the plot in Figure 3 that for N ϭ 1, the lower-edge frequency is reduced by 13% (210 MHz) for ␣ ϭ 30°and by 36% (560 MHz) for ␣ ϭ 15°. RADIATION CHARACTERISTICSThe radiation patterns were simulated at 2.0 GHz for ␣ ϭ 30°with N ϭ 1 and N ϭ 2.5 for the three principle planes. The H-plane patterns E (, ϭ 90) are illustrated in Figure 4(a). It is seen that the gain in the plane of the groundplane is about 0 dBi and omnidirectional for N ϭ 2.5, but the omnidirectional property is lost for N ϭ 1, due to a lift in the pattern and increased gain (5.2 dBi) toward ϭ ...

It is shown that a significant improvement in the radiation pattern stability with frequency can be achieved for the wideband planar monopole antenna. This is realised by the addition of a second orthogonal element, while maintaining the same overall surface area. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 294–296, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11357