Publications

Transmit and receive Ku-band phased array designs are described for testing an airborne sense and avoid radar. The arrays are small with a size of 24 cm x 9 cm and operate from 13 to 17 GHz with electronic scanning from plus of minus 45 degrees in azimuth and plus of minus 30 degrees in elevation. A novel design architecture allows the use of multiple multilayered printed circuit boards and simple air cooling.

An active filter with a 50 omega buffer suitable as an anti-alias filter to drive a highly linear ADC is implemented in 0.13 um SiGe BiCMOS. This 6th-order Chebyshev filter has a 3 dB cutoff frequency of 28.3 MHz and achieves 36.5 dBm OIP3. Nonlinear digital equalization further improves OIP3 to 43.6 dBm. Measurements show 92 dB of rejection at the stopband and a gain of 49 dB. The measured in-band OIP3 of 43.6 dBm is 19 dB higher than previously published designs.

Electronically scanned arrays require a minimum number of controls, Nmin, given by the number of orthogonal beams that fill a prescribed scan sector. Most practical antenna arrays require considerably more than Nmin control elements, but overlapped subarray architectures can approach this theoretical limit. Figure 1 shows a block diagram of an overlapped subarray architecture. The overlapped subarray network produces a flattopped sector pattern with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. Each radiating element of the array is connected to multiple subarrays, creating an overlapping geometry. It is possible to scan one beam, or a fixed set of contiguous beams, over the main sector of the subarray with a set of Nmin phase shifters. Alternatively, digital receivers can be connected to the Nmin subarrays and multiple simultaneous beams can be formed digitally. Digital subarray architectures using a combination of element level phase shifters and subarray level receivers makes it possible to scan multiple beam clusters over all space. The conventional approach to the design and manufacturing of the overlapped subarray network shown in Figure 1 is challenging and costly due to the complexity of the microwave network. However, the design of the overlapped subarray beamformer using Radio Frequency Integrated Circuits (RFIC) represents a novel approach for implementing an efficient trade-off between the agility and capability of fully digital arrays and the cost effectiveness of analog arrays.