Broadbanding of concentric planar ring arrays by space tapering

The paper discusses the application of concentric ring arrays as a new approach to space tapering for planar arrays. It describes the design of an array of non-uniformly spaced concentric rings of non-uniform density containing discrete elements. The array can be operated over a large frequency range and wide scan-angles. The ring array was designed to simulate the performance of a Taylor-weighted circular aperture. An array having a diameter of 34 wavelengths was designed with ten concentric rings containing a total of 759 elements and a thinning factor of 0.21. This array has a side-lobe level of −20 dB or better over a range of sin θ up to 2.5 at mid-band. Taking a dielectric filled square-guide as the radiating element, the mutual coupling was calculated. The element spacing is 0.498 λmid for the innermost and 1028 λmid for the outermost ring. The mutual coupling does not produce any appreciable deleterious effect on the array-factor. For the scan angle of θ0 = 60° and ϕ0 = 0°, the array has a side-lobe level better than −20 dB for a frequency range of 0.75 λmid to 1.25 λmid.