Abstract: A wide band, single aperture antenna system (70) that provides simultaneous detection of both RHCP and LHCP signals. The antenna system (70) includes a multiple arm spiral antenna (10) that has spiral arm elements (12, 14, 16, 18) with no sharp transitions. To simultaneously both RHCP and LHCP sensitivity, an antenna feed is connected to both the center end and the outer end of each of the antenna arm elements (12, 14, 16, 18). A separate N-port transformer (74, 78) is connected to both the end feed and the center feed for all of the arms (12, 14, 16, 18) to provide impedance matching and cross-polarization compensation. An NXN port modeformer (76, 80) is connected to the N-port transformers (74, 78) to separate the various modes. The modeformers (76,80) separate the LHCP and RHCP modes to provide an accurate AoA estimation.

Abstract: The present invention provides a modeforming circuit (100). The modeforming circuit (100) includes a first matrix circuit (102) comprising an interconnected network of transmission lines (208-212) and phase shifters (216-218) that implement at least one N/2.times.N/2 identity matrix and at least one N/2.times.N/2 phase shift matrix. The first matrix circuit (102) is connected in series to a second matrix circuit (104). The second matrix circuit (104) includes an interconnected network of phase shifters that implements at least one N/2.times.N/2 phase shift matrix. The modeforming circuit (100) may further include a third matrix circuit (106) connected in series with the second matrix circuit (104). The third matrix circuit (106) includes a network of transmission lines (220-230) that reorder N inputs to N mode outputs. The first matrix circuit (102) may be implemented as a first matrix sub-circuit (108) connected in series with a second matrix sub-circuit (110) to provide even further reduced complexity.

Abstract: An implementation of a Butler matrix transformation used to process antenna signals and, in particular, to transform signals obtained from an N-port antenna into mode signals used for direction finding and other purposes. A reverse transformation is used when the antenna is operating in a transmit mode. Instead of using a single Nth order transformation matrix, the circuit of the invention employs a decomposed form of the transformation matrix, thereby reducing the complexity of the transformation by using lower-order matrices. In an example of the invention for an 8.times.8 transformation, the circuit complexity is further reduced by using an additional level of decomposition, in which phase shifting is effected by a circuit implementation of a single 8.times.8 diagonal phase shift matrix requiring only three phase shift circuits. Reduction in circuit complexity, particularly in the number of phase shift circuits, reduces bias errors in the overall transformation and reduces fabrication cost.