Synthesis of a dielectric rod array for a multiple beam reflector antenna
At the Delft University of Technology a new transportable atmospheric radar (TARA), having a sophisticated antenna system, is under construction. The antenna of TARA has multiple beams pointing in different directions. The beams are switched electronically by means of a parabolic dish fed by a dielectric rod array located in the focal plane. Moumen and Ligthart (1999) showed that an array consisting of two dielectric rods separated by 0.77/spl lambda/, where /spl lambda/ stands for the wavelength, is needed in order to achieve a well focused beam at 15/spl deg/ with low side-lobes. However, due to this small separation distance, degradation of the radiation pattern and mismatches, due to mutual coupling, become a serious problem. This paper presents a method to synthesise the dielectric rod array (amplitude and phase distribution) that takes into account mutual coupling effects.
Design of a focal plane dielectric rod array for feeding a multiple beams reflector antenna
The design and construction of an array of two dielectric rod antennas of compact size (i.e. 0.55/spl lambda//spl times/1.54/spl lambda/ cross dimensions) and very low inter-port coupling (S/sub 12/), even at a separation distance of 0.77/spl lambda/, is the subject of this paper. All computed secondary patterns were obtained with the commercial code GRASPS. To predict mutual coupling effects (i.e., mismatches and pattern degradations) between two dielectric rod antennas, an approximate technique was used Moumen et al. 1998). Related measurement results are provided.
Directivity optimization of a reflector antenna with cluster feeds: A closed-form solution
The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of a single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 \lambda parabolic reflector scanning 10 beamwidths, the optimum-directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 \lambda , it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d , the optimum design may exhibit the supergain phenomenon, namely, extremely high directivities achieved by an oscillatory cluster excitation.