In this paper, we address the multistatic localization problem when the transmitter position is not known and the synchronizations among the receivers and with the transmitter are not available. Aided by a calibration object, the problem is solvable where the unknown object position, the transmitter position and the synchronization errors can be estimated using the time delay measurements from the direct paths between the transmitter and receivers, and the indirect paths reflected by the calibration and unknown objects. To solve this challenging problem, we propose a three-step estimation method that obtains a different unknown in each step. Specifically, the transmitter position is estimated by formulating a constrained weighted least squares (CWLS) problem in the first step, and a linear weighted least squares estimator follows to determine the synchronization errors in the second step. Finally, the object position is estimated by formulating a different CWLS problem in the third step. The solutions are closed-form in all three steps, and thus, the proposed method is computationally efficient. Furthermore, the proposed method is extended to the more practical scenario in which the calibration object position error is present. The mean square error analysis validates that the object position estimate is able to achieve the Cramer-Rao lower bound performance under small Gaussian noise, which is further confirmed by numerical simulations.

Owing to the unprecedented development in terahertz (THz) sources and detectors in the last decade, technologists and researchers have intensified their efforts to develop advanced THz sensing and imaging systems with superior performance and unique functionalities. One of the key elements to realize such systems is the ability to monolithically integrate high-performance semiconductor devices with THz antennas and other passive structures. In recent years, devices based on interband tunneling in III-V heterostructures have emerged as promising candidates for THz detection that offer extremely high nonlinearity, high sensitivity, low noise, fast response, and room temperature operation. In this paper, we first review the development of heterostructure backward tunnel diodes (HBDs) in the InAs/AlSb/AlGaSb material system that have been demonstrated with detection sensitivity that outperforms the current state of the art (e.g., the fundamental limit of Schottky diodes) and with noise-equivalent power (NEP) below 0.2 pW/Hz½. We then present the monolithic integration of HBDs with planar folded dipole antennas (FDAs) using submicrometer-scale airbridges to achieve optimized impedance matching for high-performance and compact THz detectors and focal-plane array (FPA) imaging systems. In addition, the potential of using HBDs for realizing THz systems with advanced functionalities such as spectroscopic FPAs (using frequency-tunable THz antennas) and polariametric detection/imaging systems will be discussed. Finally, the integration of HBDs into waveguides for more advanced THz sensing and imaging (e.g., a six-port reflectometer for near-field imaging) will be discussed.