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Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completness. Good correlation between the computed results and mesurements is observed.

In personal wireless communications systems, multipath propagation has a significant effect on system design and performance. Signal strength fading caused by destructive interference between multiple replicas of the signal of interest arriving at the receiver over different paths often is the limiting factor in system range/fidelity. Antenna diversity is one technique that can be used to help overcome multipath fading. This paper presents a description of experiments, data processing, and results used to evaluate the diversity performance of three candidate dual-antenna handset configurations: two side-mounted planarinverted F antennas (PIFA's), a back-mounted PIFA with a top-mounted helix, a top-mounted PIFA, and a "flip" monopole. In particular, the indoor industrial, scientific, and medical (ISM) band (902-928 MHz) propagation channel was of interest. These experiments did not include operator proximity effects, and in these tests, the dual-antenna handset remained stationary while the transmitter was moved along predetermined indoor paths. The issue of data normalization for extraction of fast fading behavior from measured data will be addressed, with results showing its effect on observed correlation presented. Also, measured indoor fading distributions are presented and seen to fit the Rician and Rayleigh models well. From the diversity results presented, it is seen that the three proposed dual-antenna handsets yield sufficient decorrelation to warrant consideration for use in diversity systems. Index Terms-Antenna diversity, correlation coefficient, handset antennas, multipath fading. Michael A. Jensen (S'93-M'95) received the B.S. (summa cum laude) and M.S. degrees in electrical engineering from Brigham Young University

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