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Abstract-This article reports on a study of the dielectric constants of ceramic dispersions in the polyethylene matrix at microwave frequency. The exponential and logarithmic mixture rules are studied in three ceramic powders of fillers with dielectric constants 10, 20, and 36, respectively. The experimental values of the dielectric constants of the mixtures are compared to those obtained by using different mixing laws. The mixing rules are also adopted to calculate the dielectric constants of pure ceramics from the measured dielectric constants of composites with various concentrations. The theories on errors of calculations are studied. The most adequate mixture equation for measuring the dielectric constants of pure ceramics is suggested.

insets of the figure. It is seen from the figure that the leakage constant ␣ of the double-grating antenna is larger than that of the single-grating antenna with and without a dielectric shell, because of the strong perturbation effect on the guided wave caused by the two grating layers. It can also be seen that the leakage constant of the double-grating antenna reaches the maximum of the leakage constant for the single-grating structure, when t g1 is very small, about 0.01, which is achieved where t g1 Ͼ 0.15 for the single-grating structure without a shell and where t g1 Ͼ 0.1 for the single grating antenna with a shell. In addition, the leakage constant ␣ of the double grating antenna remains larger in the entire region of t g1 (as calculated) than that of the single structure for the region of t g1 Ͼ 0.05. This means that under the condition of the same radiation strength, the length of the double grating antenna can be considerably reduced. It is found from Figure 3 that the leakage constant of the single grating antenna with shell increases rapidly as the thickness of t g1 increases. The reason for this is that the shell layer makes the fields of the surface wave concentrate within the grating layer, so that the perturbation effect on guided wave is strengthened prominently. CONCLUSIONA new millimeter-wave omnidirectional circular rod antenna with double dielectric gratings is investigated theoretically. As a boundary value problem, the antenna is analyzed with the rigorous mode-matching method to obtain the complex eigenvalue, from which the radiation characteristics of the antenna are completely determined. Numerical results show that under the condition of the same radiation intensity, the double-grating antenna has smaller dimensions than that of the single one. This characteristic is of essential and practical significance in the case where limitation of the system's in size and weight is strictly required. By beveling the vertical portion of an inverted-L patch into a triangular shape and incorporating a probe feed with a short probe pin, a broadband probe-fed patch antenna has been demonstrated [1]. In such a broadband design, the patch's vertical portion provides a smooth transition region between the signal source and the patch's horizontal portion, the antenna's main radiating portion. This design method is similar to the beveling technique studied in [2]. In addition, although a thick air-layer substrate is used (about 10% of the wavelength of the center operating frequency), the short probe pin (only about 3 mm) of the probe feed introduces negligible inductance to the antenna's input impedance, thus good impedance matching is easily obtained over a wide bandwidth for this kind of probe-fed inverted-L patch antenna. In this paper, we demonstrate that, by applying a corner-truncating technique [3] to such an inverted-L patch antenna, broadband CP operation can also be obtained. To demonstrate the proposed broadband CP antenna with a corner-truncated inverted-L patch, a prototype suitable for WLA...

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A novel broadband circularly polarized printed‐spiral‐strip antenna is presented. The antenna consists of a printed spiral strip of about 1.4 wavelengths in length wound into about one turn and mounted above a ground plane with a thick air layer. By using a 50Ω probe feed along with a long feeding strip and a coupled long‐shorting strip for exciting the printed spiral strip, good circular polarization (CP) radiation over a wide bandwidth (larger than 20%) is achieved, which makes the proposed antenna well suited for applications in the 5‐GHz WLAN band. Details of the proposed antenna design and the experimental results obtained for a constructed prototype are presented. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 163–165, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20080