Uplink beam steering using the intelligent quadrifilar helix antenna

The paper investigates the uplink beam steering potential of the intelligent quadrifilar helix antenna (IQHA) (see Agius, A.A. and Saunders, S.R., UK Patent No. 9803273.3, 1998). The approach relies on producing a variable radiation pattern by adjusting the phase relationships between its elements. The paper presents results obtained from an investigation of the effects of applying different weights to the individual elements of a meander line printed QHA (MPQHA) structure (see Chew, K.C.D. and Saunders, S.R., UK Patent Application No. 0204014.5, 2002) using a real time demonstrator. Appropriate sets of weights were identified with the aid of a numerical far-field simulation to maximise radiation in the direction of the base station and reduce losses in the head. The real time demonstrator uses a micro-controller to feed the identified weights through the digital phase shifters on the individual elements of the MPQHA structure. The measured radiation patterns are compared to the radiation pattern measured from a MPQHA with conventional phase quadrature feed. Measurements were made both in free space and in the presence of a phantom head so as to demonstrate the impact of near-field coupling. The specific absorption rate (SAR) was also monitored.