A Circular Array with Improved Focusing Properties

Abstract

A concentric circular array consisting of two rings is proposed to focus the radiated field at a point in the near-field zone. In the proposed two-ring array, the radius of the outer ring was chosen so that the radiated fields from all elements on the two rings add constructively at the focal point, thus no phase shifter is needed in this design. The N elements of the inner ring are uniformly excited in unity amplitude and zero phase, while the M elements on the outer ring are excited uniformly in phase, and given uniform magnitude excitations of N/M . Therefore, two deep nulls are achieved on both sides of the focus to enhance the focal width. The focusing properties are investigated by exploring the array parameters, such as variation of the focused field along the normal to the array, field distribution on the focal plane, and depth of field (size of the focal spot). Computer simulations using the MATLAB environment are performed by point source radiators. For verification, the array was simulated using the CST microwave studio, and the obtained results showed good agreement. The array is useful for hyperthermia and imaging applications.

A Focused Circular Array with Variable Focal Length

“…In a recent paper [20], we proposed a focused circular array comprising elements arranged on two concentric rings. The radius of the outer ring was determined such that the distances between the elements on this ring and the focal point differed by one wavelength from those for the elements on the inner ring.…”

“…Therefore, only M ×N /4 phase shifters are needed in comparison with the case of the conventional M × N rectangular focused array. Moreover, the outer and inner rings are supplied with equal power, and the elements on each ring have uniform excitations in amplitude and phase thus simplifying the feed network [20]. In the search to reduce the feed network's complexity and to mitigate the need for phase shifters, a Ka-band, multilayer, nearfield-focused substrate integrated array antenna was presented in [21].…”

“…In this contribution, the design presented in [20] is developed to offer a variable focal length by adding a single variable phase shifter, while at the same time placing no condition on the radii of the rings. The variation of the focal length is achieved by feeding the elements of the inner ring through a single variable phase shifter that compensates the path difference of the two rings and yields focusing at a certain distance from the array.…”