Chao-Hsiang Liao

Energy Patterns of UWB Antenna Arrays With Scan Capability

A beam scanning technique is developed with a time delay for ultrawideband (UWB) arrays. In addition, we give a formulation for the time domain array factor for UWB antenna arrays. An UWB comb taper slot antenna array with large element spacing and impulse excitation is studied and four-element UWB linear array systems with element spacings of 2.5, 8.5, and 18 cm in the broadside direction and 20 degree scanning are implemented. The voltage response, spectrum response, energy pattern and energy gain for from simulation and measurement are in good agreement. The periodic grating lobes of the UWB antenna array do not occur in the energy pattern, even if the element spacing and scan angle are large. Simulation and measurement results for the energy pattern and voltage response in various directions are studied to validate the theory of an UWB antenna array with scan capability. The measured peak energy gain of arrays in the broadside direction and 20 degree beam scanning with element spacings of 8.5 and 18 cm are 10.79/10.78 dBi and 9.53/9.06 dBi, respectively.

New Development of Parallel Conformal FDTD Method in Computational Electromagnetics Engineering

In this paper, we summarize the new development of hardware-acceleration techniques and a parallel conformal Finite-Difference Time-Domain (FDTD) method in computational electromagnetics engineering. We investigate the performance of a parallel conformal FDTD method on different hardware platforms, such as Intel and AMD processors, with vector-arithmetic logic unit (VALU) acceleration, a regular PC cluster, a high-performance server cluster, the use of a graphics-processing unit (GPU), and an IBM CELL processor. The FDTD method, which is parallel in nature, is one of the best candidate numerical methods for using multiple-core processors and computer clusters to efficiently simulate various electromagnetic problems. Several representative examples, such as a UWB (ultra-wideband) antenna array and reflector antennas, are employed to demonstrate the engineering applications of the parallel conformal FDTD method.

Compact antenna test range without reflector edge treatment and RF anechoic chamber

There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflectors edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zones performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.

Side lobe control of UWB antenna array for real beam radar imaging

The ultra wideband (UWB) array waveform is essential to the improving of resolution for microwave imaging. Large antenna arrays provide high angular resolution microwave images. These images are plagued with artifacts caused by high side lobes. Specifically, these artifacts are false targets and target break-up or speckle. In this paper, an UWB comb taper slot antenna array with large element spacing and impulse excitation is studied. The four-element UWB array system with uniform and non-uniform element spacings in the broadside direction is analyzed by energy pattern for side lobe control. A technique for beam scanning with a time delay technique is developed for UWB arrays. Different excitation pulse width is studied for peak side lobe that is far away from the designed beam direction of UWB array with uniform element spacings of 8.5 and 18 cm. Energy patterns for simulation and measurement are in good agreement. The periodic grating lobes of the UWB antenna array do not occur in the energy pattern, even if the element spacing and scan angle are large. In general, the optimum design of array element spacing is required for special applications.

UWB antenna array

This paper compares the performances of ultra wideband (UWB) arrays that use sinusoidal waveform for power pattern and ultra-short pulse waveform for energy pattern. In general, antenna arrays cannot have element spacing larger than one wavelength in any plane because the resulting grating lobes absorb much power, which will limit the bandwidth of antenna arrays. In particular, there are substantial differences between power pattern and energy pattern for UWB arrays. The grating lobes of UWB antenna array will not occur at the energy pattern even if the element spacing of array is larger than one wavelength. The limited antenna power patterns in frequency domain are used to describe the antenna performance. The energy pattern of antenna is the total response of power patterns in frequency domain. Energy pattern are quite similar to that of power pattern for narrow band antennas. It is enough to describe the antenna performance in narrow band communication systems. However, the limited antenna power patterns in frequency domain are not enough for UWB arrays in communication systems. Energy pattern will be easier to describe the energy pattern instead of power pattern for UWB arrays. In order to verify the theory of antenna pattern in energy, numerical simulations of UWB arrays with different element spacing are demonstrated the significance of these parameters and measured by the impulse time domain radar system. These results are of particular importance to the emerging technology of base band or time domain communications and remote sensing.

Could the antenna pattern be in energy instead of in power

In general, the limited antenna power patterns in frequency domain are used to describe the antenna performance. It is enough to describe the antenna performance in narrow band communication systems. However, the limited antenna power patterns in frequency domain are not enough for ultra wideband (UWB) antennas or arrays in communication systems. The energy pattern of antenna is the total response of power patterns in frequency domain. It will be easier to describe the energy pattern instead of power pattern for UWB antennas. In this paper, electromagnetic energy, electromagnetic power, energy pattern, energy gain, energy directivity and energy efficiency will be discussed. In order to verify the theory of antenna pattern in energy, Yagi Uda antenna, marrow band multibeam smart antenna, UWB bow-tie slot antenna, UWB comb taper slot antenna, and UWB antenna arrays with different element spacing are studied and measured by the impulse time domain system. The energy pattern is quite similar to that of power pattern for narrow band antennas. The grating lobes of UWB antenna array will not occur at the energy pattern even if the element spacing of array is larger than one wavelength.

A UWB microwave imaging radar system for a small target detection

An ultra-wide band (UWB) radar system to detect a small target is proposed. A three-dimensional target model is used in the investigations. A circular array with UWB coplanar waveguide (CPW)-fed bow-tie slot antennas is used in the radar system. The transmitting antenna is excited by the impulse waveform while the other antennas are used as the receivers, i.e., a single transmitter and multi- receivers. This system provides wide angular coverage in both elevation and azimuth plane at receiver side. By using a simple delay-and-sum (DAS) beamforming method, a synthetic focal point is created and a high resolution image can be reconstructed from the backscatter signals. From the simulation results, the position of image agrees with that of the target.

Energy patterns for UWB antennas and array

In this paper, the energy pattern of various UWB antennas will be studied by the impulse time domain radar system. The UWB antennas will include omni directional antenna, directional antenna, and high directivity antenna array. They are discussed in the following sections. Energy patterns of UWB antenna and its measurement system with impulse time domain radar is described in this paper. Three radiation energy patterns have been presented for the two kinds of UWB antennas and UWB antenna array. The time response waveform for antennas depends on geometry of antenna and EM incident directions. Detail of discussion will be presented.

UWB antenna array for real beam radar imaging

The four element ultra-wideband (UWB) comb taper slot antenna array with 18 cm element spacing is used for receiving the wideband scattering signal. A double ridge wideband antenna is used as the transmitting antenna and the above developed large aperture UWB array is used as the receiving antenna. The transmitting antenna and the receiving antenna are placed close to each other for quasi monostatic radar imaging. The total linear scan length of target is 200 cm. The receiving impulse signal is achieved not only by the measurement but also by the simulation tool of GEMS. The receiving impulse signals at various positions are processed by the delay and sum algorithm. The results of real beam radar imaging from both simulation and experiment are well agreed.

Radiation of Dipole Antenna inside the Water with Time Gating Technique

Most of the biomedical images are studied with EM (electromagnetic) wave propagating to the tissues which is buried inside the higher dielectric material. In this paper, the dipole antenna is designed for studying the biomedical imaging of tissues which is buried inside the water. Due to the material of the dipole antenna was made from coaxial cable; therefore it has waterproof capability. The scattering parameters (S11, S12) and radiation patterns are measured by the frequency domain VNA (Vector Network Analyzer) and three dimensional microwave biomedical measurement system. The power attenuates largely when the EM wave radiation inside the water. Antenna impedance mismatches in different depths of water, however, by using time gating technique method obtains accurate measured results. The detail discussion of scattering parameters and radiation patterns inside the water will be described in the following section.