Seunghyeon Hwang - Academia.edu (original) (raw)

Papers by Seunghyeon Hwang

In this paper we present a methodology for the direction of arrival (DOA) estimation using the in... more In this paper we present a methodology for the direction of arrival (DOA) estimation using the induced voltages that are measured at the feed points of electrically small resonant dipole antenna arrays illuminated by the signal of interest. The matrix pencil method is applied directly to the induced voltages to estimate the DOA of the various signals. Using electrically small resonant antennas can be advantageous if they are spaced half a wavelength apart as it will significantly reduce the mutual coupling between the various antenna elements. However, the electrically small antennas can also be placed in close proximity of each other saving the real estate and thus making it possible to deploy phased arrays on small footprints. For the latter case it may be necessary to use the transformation matrix to compensate for the strong mutual coupling that may exist between the antenna elements. The transformation matrix converts the voltages that are induced at the loads corresponding to the feed point of the array operating in the presence of mutual coupling and other near field scatterers to an equivalent set (ULVA) consisting of omni-directional isotropic point radiators equally spaced and operating in free space. Three different scenarios are presented to illustrate the methodology. First we consider resonant dipole elements spaced half wavelength apart, electrically small resonant antenna elements spaced half wavelength apart and electrically small resonant antenna elements placed in close proximity of each other to reduce the footprint without affecting the performance of the phase array. Numerical examples are presented to illustrate the principle of this methodology.

In this paper polarization adaptivity on transmit has been used to enhance the received signals d... more In this paper polarization adaptivity on transmit has been used to enhance the received signals directed to a pre-selected receiver in a near-field multi-input multi-output (MIMO) environment. The objective here is to select a set of weights on the transmitting antennas adapted to individual receivers based on the principles of reciprocity. Using the polarization properties, when the number of receiving antennas is greater than the number of transmitting antennas, the transmitted signal may be directed more to a particular receiver location while simultaneously minimizing the reception signal strength at other receivers. Numerical simulations have been made to illustrate the novelty of the proposed approach.

ABSTRACT In this paper we present how we choose the proper number of virtual array elements from ... more ABSTRACT In this paper we present how we choose the proper number of virtual array elements from the real array for direction of arrival (DOA) estimation using a conformal hemispherical real array and a single snapshot of the data. The number of virtual array is achieved by using singular value decomposition (SVD) of a real array manifold and the concept of the interpolation techniques. Then, the transformation matrix is generated from both the virtual array manifold and the real array manifold. A numerical simulation has been made to illustrate of the proposed approach. We estimate direction of arrival (DOA) of signals using the matrix pencil method.

In this paper a technique is presented on how to enhance the received signals in a near field mul... more In this paper a technique is presented on how to enhance the received signals in a near field multi-input multi-output (MIMO) environment where beam forming is not possible. This is done through the use of adaptivity on transmit. This technique is based on the principle of reciprocity, is independent of the material medium in which it is transmitting, and incorporates near-field environments and multipath. The objective here is to select a set of weights adapted to each receiver to be applied to each transmitting antenna, which is a function of the user location, so that the transmitted signal at the carrier frequency may be directed to a particular receiver location while simultaneously minimizing the received signal strengths at other receiver locations. Numerical simulations have been made to illustrate the novelty of the proposed approach.

Microwave and Optical Technology Letters, 2005

The equivalent isotropically radiated power (EIRP) degradation due to random position errors for ... more The equivalent isotropically radiated power (EIRP) degradation due to random position errors for space-time adaptive processing (STAP) is presented, based on the relationship between the EIRP degradation and the standard deviation or the uniform bound of the probability distribution of location of the antenna elements. We simulate a direct data domain least-squares (D 3 LS) approach for STAP. In this simulation, two situations are considered. In the first case, the antenna elements at every time instance are assumed to have different spatial positions from the previous time instance. For the other case, the antennas are assumed to be randomly located, but are assumed to be fixed in a coherent processing interval (CPI). It is demonstrated that whether the locations of the antenna are fixed or vary within a CPI with identical random errors, the output signalto-interference and noise ratio (SINR) are almost the same. When the antenna elements are moved randomly, the output SINR is less than the unperturbed case. We can develop a bound on the EIRP degradation due to the D 3 LS approach to STAP based on the random position errors.

IEEE Transactions on Antennas and Propagation, Dec 1, 2006

There has been a plethora of papers dealing with wireless communication that use techniques, whic... more There has been a plethora of papers dealing with wireless communication that use techniques, which when viewed from the perspective of a Maxwellian framework raise more questions than they answer. By Maxwellian framework we imply not only the relevance of electromagnetics in studying communication systems but also the proper interpretation of an ensemble processing in mathematical physics which was first introduced by Maxwell to study the behavior of an aggregate of molecules rather than the property of individuals. Initially, most of the modern signal processing techniques was developed for scalar acoustic problems. However, with the advent of wireless, these same techniques are being applied to the vector electromagnetics problem, which is fundamentally different in concept with respect to the scalar acoustic problem. The objective is to discuss some of these concerns associated with some of the current modeling methodologies particularly related to propagation modeling and antenna diversity. A goal is to initiate a dialog about the scientific merits of these new applications. One of the points to be made is that an incorrect use of probability theory can often lead to erroneous conclusions that directly contradict the principles of physics. A few examples are presented to initiate this dialog, mainly the applicability of scalar techniques to the vector wireless problem, including a proper interpretation of the Shannon channel capacity theorem. A methodology is also presented to illustrate how a simple multiple-input-multiple-output system can be based on the principles of reciprocity. Integration of the electromagnetic principles in some of the current methodologies of signal processing and communications theory may lead to a better system.

This dissertation deals with three problems in the area of adaptive array processing for smart an... more This dissertation deals with three problems in the area of adaptive array processing for smart antenna and radar systems. First, the equivalent isotropically radiated power (EIRP) degradation due to random position errors in the location of the antenna elements in an array is derived through the expected value and standard deviation of the EIRP. The minimum tolerance of the array elements is presented by means of the relationship between the EIRP degradation and a standard deviation or the uniform bound of the probability distribution. Using this tolerance, the output signal to interference and noise ratio (SINR) is examined in the framework of adaptive processing using the direct data domain least squares (D 3 LS) approach. Also, it is applied to Space-Time Adaptive Processing (STAP). Then, a technique is presented on how to enhance the received signals in a near field multi-input multi-output (MIMO) environment where beam forming is not possible. This is done through the use of adaptivity on transmit. The methodology is to select a set of weights adapted to each receiver to be applied to each transmitting antenna so that the transmitted signal at the carrier frequency may be directed to a particular receiver location while simultaneously minimizing the received signal strengths at other receiver locations. Numerical simulations have been made to illustrate the novelty of the proposed approach. As a final topic, to choose the proper number of virtual array elements consisting of isotropic omni-directional point radiators operating in free space starting from a real array for direction of arrival (DOA) estimation and adaptive processing is derived from an arbitrary shaped nonuniformly spaced conformal array operating with mutual coupling effects using a single snapshot of the data. The number of elements in the virtual array is determined by using the singular value decomposition (SVD) of a real array manifold and the concept of interpolation. The transformation matrix is computed using the virtual array manifold and the real array manifold. Numerical simulations have been made to illustrate the accuracy of the proposed approach. The direction of arrival (DOA) of the signals using the Matrix Pencil method and the direct data domain least squares (D 3 LS) adaptive processing is estimated in evaluating the complex amplitude of the signal incident on a hemispherical array

2005 IEEE Antennas and Propagation Society International Symposium

The number of virtual array is achieved by using singular value decomposition (SVD) of a real arr... more The number of virtual array is achieved by using singular value decomposition (SVD) of a real array manifold and the concept of the interpolation techniques. Then, the transformation matrix is generated from both the virtual array manifold and the real array manifold. Through this interpolation technique, we perform direction of arrival (DOA) estimation using a conformal hemispherical real array and a single snapshot of the data. A numerical simulation has been made to illustrate of the proposed approach. We can estimate direction of arrival (DOA) of signals using the matrix pencil method.

Ieee Transactions on Antennas and Propagation, Dec 1, 2006

Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 54, NO. 12, DECEMBER 2006 3727 A Disc... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 54, NO. 12, DECEMBER 2006 3727 A Discussion About Some of the Principles/Practices of Wireless Communication Under a Maxwellian Framework ...

2005 IEEE Antennas and Propagation Society International Symposium, 2005

Microwave and Optical Technology Letters, 2005

Microwave and Optical Technology Letters, 2004

The stability of the laser was very good, as shown in Figure 3. In the following experiments, we ... more The stability of the laser was very good, as shown in Figure 3. In the following experiments, we used a 90:10 coupler as the laser output. Figure 4 shows the output power of the laser as a function of the absorbed pump power under the two different conditions above. Comparing these two curves, we can see that, when we used a 90:10 coupler as the laser output, the output power would decrease from 518.4 to 147.84 mW, and the slope efficiency would also decrease from 19% to 6.8%; however, the stability of the laser was increased. Therefore, we can understand that when we used a 90:10 couple as the laser output, most of the output laser was limited in the cavity. In this case, the laser could become stable, but only a small power could be output. Thus, both the output power and the slope efficiency would decrease. 4. CONCLUSION We have presented a cladding-pumped Erbium-ytterbium co-doped double-clad fiber-ring laser operating in the L-band. By using cladding-pumped EYDF, the maximum output power of the laser can achieve 518.4 mW with high output stability, and a slope efficiency of 19%; by utilizing ASE as a secondary pump source, it can operate in L-band. If tuning techniques were added to this mechanism, we would obtain a wavelength-tunable fiber-ring laser.

IEEE Transactions on Antennas and Propagation, 2000

We present a methodology for the direction of arrival (DOA) estimation using the induced voltages... more We present a methodology for the direction of arrival (DOA) estimation using the induced voltages that are measured at the loads connected to electrically small tuned dipole antenna arrays illuminated by the signal of interest (SOI). The matrix pencil method is applied directly to the induced voltages to estimate the DOA of the various signals. Using electrically small tuned antennas

IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics, 2005., 2005

2005 IEEE Antennas and Propagation Society International Symposium, 2005

Microwave and Optical Technology Letters, 2005

IEEE Transactions on Antennas and Propagation, Dec 1, 2006

2005 IEEE Antennas and Propagation Society International Symposium

Ieee Transactions on Antennas and Propagation, Dec 1, 2006

2005 IEEE Antennas and Propagation Society International Symposium, 2005

Microwave and Optical Technology Letters, 2005

Microwave and Optical Technology Letters, 2004

IEEE Transactions on Antennas and Propagation, 2000

IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics, 2005., 2005

2005 IEEE Antennas and Propagation Society International Symposium, 2005