J.R. James

Low SAR Ferrite Handset Antenna Design

The benefits resulting from the inclusion of ferrite in material loaded antennas are investigated, initially through the use of a spherical analytic model and then through a transmission line matrix simulation tool applied to a rectangular slab geometry. It is observed that a material with equality of relative permittivity and permeability in combination with specific positioning of the antenna in relation to the head, can result in the definitive small-size, high efficiency and bandwidth, low specific absorption rate (SAR) antenna. The accuracy of the simulations is validated both through efficiency and SAR measurements of three material coated monopole samples. Further research into optimizing the above attributes and translating them into a handset antenna leads to a multiband antenna design covering the GSM 1800, 1900, UMTS and Bluetooth bands, with a SAR value reduced by 88% compared to conventional phones and an efficiency of 38% at 1.8 GHz. A tri-band antenna design is also presented, utilizing currently available lossy ferrite material and it is considered as the first step towards the feasibility of the ultimate low SAR multiband ferrite handset antenna, until further material development specifically for antenna applications takes place

Measurement and modeling of a microwave active-patch phased array for wide-angle scanning

An active antenna consisting of an integrated oscillator with a passive radiator has been arrayed and beam-scanned using a new principle for phase shifting. The radiating elements consist of a transistor oscillator whose frequency is controlled by a rectangular microstrip patch antenna. Each oscillator is injection locked to an external source. The phase control of the radiated wave is achieved by varying the bias on the transistor. Individual element performance has been characterized for potential use as an array element and is comprehensively reported. Methods used to achieve configurations with full 360/spl deg/ phase control have been investigated utilizing novel configurations and cascaded oscillator pairs. Close to 360/spl deg/ of radiated phase control from each element has been achieved. Measured results on an experimental four-element S-band array indicate that beam scanning in excess of /spl plusmn/60/spl deg/ can be achieved. Mutual coupling effects on this new form of array are studied both experimentally and theoretically. A van der Pol (1934) model for the weak coupling that is occurring on the array is developed and used to qualitatively predict the phase offsetting on array elements. Reasonable agreement between theory and experiment is obtained and it is observed that good control of the coupling mechanism is essential to array performance within this new form of active integrated phase shifterless array.