Small Folded Shorted-Patch Antenna

In modern mobile and wireless communications systems, there is an increasing demand for small low-cost antennas. This is especially true for handheld wireless applications where a package-integrated antenna may be desirable such as in mobile phone handsets or Bluetooth chips. It is well known that planar structures, e. g. microstrip patch antennas, have a significant number of advantages over conventional antennas, such as low profile, light weight and low production cost. In some practical wireless communications systems such as GSM 1800, PCS 1900, IMT 2000, or Bluetooth ISM, however, their physical sizes may be too large for integration with RF devices. A number of techniques have been proposed to reduce the size of conventional halfwave (λ0/2, λ0 is the guide wavelength in the substrate) patch. The most straightforward approach is to use high dielectric constant substrate [1], however, it leads to poor efficiency and narrow bandwidth. Shorting posts also have been used in different arrangements to reduce the overall size of the patch antenna. A shorting wall [2] can reduce the patch size to λ0/4 while a shorting pin near the feed [3] can reduce the patch size even further. Introducing reactive loads can also reduce the resonant frequency [4]. It was found that the capacitive load reduces the resonant length of a patch from λ0/4 to less than λ0/8. In this paper we propose a simple technique for further reducing the size of a conventional shorted-patch antenna. By folding a wall-shorted patch antenna, the antenna length can be reduced to λ0/8. The resonant frequency of the folded shorted-patch antenna can be further reduced by more than a half through an adjustment of the width of shorting walls and the height of the folded patch. This means that the overall length (λ0/16) of the new folded shorted patch antenna can be eight times shorter than the length of a conventional patch (λ0/2).