Keerti S. Kona

Coded aperture subreflector array for high resolution radar imaging

HRL Laboratories has been developing a new approach for high resolution radar imaging on stationary platforms. High angular resolution is achieved by operating at 235 GHz and using a scalable tile phased array architecture that has the potential to realize thousands of elements at an affordable cost. HRL utilizes aperture coding techniques to minimize the size and complexity of the RF electronics needed for beamforming, and wafer level fabrication and integration allow tiles containing 1024 elements to be manufactured with reasonable costs. This paper describes the results of an initial feasibility study for HRL’s Coded Aperture Subreflector Array (CASA) approach for a 1024 element micromachined antenna array with integrated single-bit phase shifters. Two candidate electronic device technologies were evaluated over the 170 - 260 GHz range, GaN HEMT transistors and GaAs Schottky diodes. Array structures utilizing silicon micromachining and die bonding were evaluated for etch and alignment accuracy. Finally, the overall array efficiency was estimated to be about 37% (not including spillover losses) using full wave array simulations and measured device performance, which is a reasonable value at 235 GHz. Based on the measured data we selected GaN HEMT devices operated passively with 0V drain bias due to their extremely low DC power dissipation.

Scanning mircostrip arrays using controlled mutual reactance with parasitic elements

We investigate a linear array of microstrip patches consisting of excited elements spaced >λ with two parasitic patches in between. Varactor-controlled reactances are used to terminate the parasitic elements, to provide variable coupling between patches and to vary the reactive part of the input impedance of excited elements. A full wave analysis model is used to obtain the impedance matrix of the system. Subsequently a genetic algorithm optimization is used to obtain the reactance terminations to scan over an angular range of 0 to 45° in the H-plane. This low cost array can adaptively reconfigure for arbitrary shaped beams, and has the ability to steer a null.

Non-Foster circuits for wideband and wide-angle scan in phased arrays

Contiguous collinear dipoles connected with non-Foster circuits (NFCs) was proposed for improving the bandwidth of arrays. Prior literature focused on use of ideal negative inductance and for broadside scan only. This paper presents results of a feasibility study to evaluate and characterize performance of dipole arrays loaded with non-Foster circuits in terms of VSWR, gain, bandwidth (L Ku band). The results show that NFCs help improve the scan performance and bandwidth in dipole based phased arrays. Stability analysis with the generalized Nyquist method could not identify a stable configuration for the NFC circuit itself covering the entire L Ku band.