Active arrays, Circular arrays, HF antennas, Reflector antennas


Conventional high-frequency (HF) circular phased arrays, such as the Wullenweber circular array, have a cost factor that increases at a greater-than-square law rate as its radius is increased to produce larger apertures. A new method of forming simultaneous beams in an HF circular array has been proposed in which beams are formed in the space within the array from pickup element energy that has been amplified and reradiated. Such a device is called a circular active reflector antenna (CARA), and its cost increases at a substantially linear rate as its radius is increased to form larger apertures. This paper describes calculations of the distribution of reradiated energy within such an array in order to study the effect of changes in array configuration. A cost analysis is presented to establish the dependence of array cost on array size for both the conventional and CARA types of arrays. In addition, the performance of an experimental CARA array is reported. An experimental CARA array consisting of a 120° partially filled sector of 1500 m radius, forming six beams over a 2° field of view was constructed at a site in Utah to demonstrate the feasibility of the concept. Measurements made on the experimental array showed that at 14-MHz, it formed beams 0.7° wide at the 3-dB points, which agrees closely to the calculated value. The sidelobe response also compared closely to the level and angular position calculated for the sidelobes of the partially filled sector array tested. No evidence of instabilities or intermodulation distortion was noted.

Document Type

Peer-Reviewed Article

Publication Date


Permanent URL



Original Publication Citation

Knight, L., and G. Barry. "A Circular Active Reflector Antenna (CARA), Energy Distribution Calculations, and an Experimental Test." Antennas and Propagation, IEEE Transactions on 23.2 (1975): 228-36




Ira A. Fulton College of Engineering and Technology


Electrical and Computer Engineering