David Auckland

Reconfigurable antennas for wireless devices

New technologies in communications electronics, such as software-defined radio (SDR) and RF switches implemented using micro-electromechanical systems (MEMS), present new challenges and opportunities for antenna design. In sharp contrast to digital technology where Moores law reigns, a fundamental law of physics constrains the ability to realize electrically small antennas that are both efficient and broadband. As a result, covering several frequency bands concurrently with a single antenna having enough efficiency and bandwidth is a major challenge. One possible solution to this problem is to use reconfigurable antennas that tune to different frequency bands. Such an antenna would not cover all bands simultaneously, but provides narrower instantaneous bandwidths that are dynamically selectable at higher efficiency than conventional antennas. Such tunable-antenna technology is an enabler for software-definable radios, the RF front ends of which must be reprogrammable on the fly. This paper discusses the practical implementation issues, limitations, and measured results of small, narrowband, tunable antennas within portable handsets. Many of the concepts discussed in this paper will likely become practical and cost effective in the near future because of recent advances in RF MEMS switches.

Two-port model of an antenna for use in characterizing wireless communications systems, obtained using efficiency measurements

The agreement in these efficiency measurements validates the accuracy of the Satimo range, while highlighting the simplicity of the Wheeler cap. When one needs pattern data or the efficiency of an antenna in the presence of a surrogate hand and head, then a spherical near-field range, such as the Satimo system, is necessary. However, it is seen that a network analyzer and a Wheeler cap are sufficient for accurately measuring total antenna efficiency versus frequency for a small, solitary antenna. This total efficiency is the transfer function of the antenna, and may be used by system designers to evaluate the antennas bandpass and band-reject properties.

A Wideband Multimode Permeable Conformal Antenna thinner than λ/75 using advanced ferromagnetic laminate composite materials

A conformal permeable toroidal antenna operating in both a vertically polarized monopole mode and circularly polarized (CP) dipole mode in the UHF frequency range is designed based on theory of magneto-dielectric radiators. This antenna has been fabricated using a new advanced ferromagnetic laminate composite material whose high impedance and anisotropic properties enable an antenna that radiates via magnetic currents. The antenna, less than 0.5 m in diameter and less than 2 cm thick, was fabricated and tested. Including the imperfections of the feed network and a simple matching scheme, the antenna operates from 200 to 500 MHz with an input match of better than -10 dB, CP dipole realized gain as high as +2 dBi, and monopole mode vertically polarized gain as high as -1 dBi.

A non-modal formulation for electromagnetic transmission through a filled slit of arbitrary cross section in a conducting plane of finite thickness

Abstract : Three computer programs are presented for the analysis of electromagnetic transmission through a filled slit of arbitrary cross section in a conducting plane of finite thickness. The first and second programs utilize a non-modal and model formulation, respectively, which are derived in detail in an earlier report. Some approximate solutions are available when the slit cross section is a rectangular shape and these are investigated in the third program. The programs are all written in Fortran IV language. Quantities computed are equivalent electric and magnetic currents on the contour defining the slit cross section, transmission coefficients, gain patterns, and normalized field patterns. Sample input and output data are presented for each program. Detailed instructions concerning the use of each program and its capabilities are given. (Author)