Reflector Impulse Radiating Antennas Research Articles

Partition lens system for focusing field from PSIRA with TSVS feed on biological target

The Impulse Radiating Antenna (IRA) is suited for radiating picosecond electromagnetic impulse for the treatment of skin cancer. The feed of the reflector IRA is an ultra-wideband antenna. In this proposed work, a Tapered Slot Vivaldi Shaped (TSVS) feed arm is designed for Prolate Spheroidal Reflector (PSR). The feed antenna is placed at the first focal point of the PSR. The picosecond electric pulse is launched from the first focal point and is focused at the second focal point where the target is placed. Next Partition dielectric lens system is designed to enhance the electric field and reduce the spot size of the focused pulse. The TSVS feed arm is matched from 500 MHz to 10 GHz. The 3 dB angular beam width of the proposed IRA with 50 cm aperture diameter is 4.3°, and the radiation efficiency is 63% at 10 GHz. Simulation results show that the full width half maximum of electric field intensity is reduced by 57% in the axial direction and 20% in the lateral direction when compared to the conical feed IRA without lens. The three layer partition lens system greatly reduces the spot size from 1.187 to 0.75 cm, when compared to five layer spherical dielectric lens and increases the electric field by 65%.

A High-Power Reflector Impulse Antenna with Dual-Tem Source

There are different demands on radiation efficiency and direction pattern according to various ultra-wideband (UWB) antennas and high power applications. To obtain more radiating gain on bore-sight of paraboloidal reflector and centralized radiating direction, a novel feeding structure called dual-TEM source has been designed and applied in half-paraboloidal reflector impulse radiating antenna (IRA) applications. Simulation results proved that this proposed half-paraboloidal reflector IRA with dual-TEM source provided greater radiation performance on bore-sight as a result of the synthesized power in the aperture space of paraboloid. Moreover, lots of simulation work and comparison have been done in different feeding models to summarize a relative optimal feeding structure.

On the Characterization of a Reflector Impulse Radiating Antenna (IRA): Full-Wave Analysis and Measured Results

There is a growing demand for impulse radiating antennas (IRAs) to receive and transmit short pulses. The basic concepts of IRA are reviewed and the far-field pattern versus frequency of an ideal IRA is characterized based on the fundamental properties of IRA. It is shown that the transmitted pulse is ideally in the form of a time derivative of the input pulse. The physical optics simulation results show that the far-field characteristics of a parabolic reflector are very close to an ideal IRA if it is fed properly. The reflector IRA was constructed, analyzed and measured at UCLA. The near-field and far-field characteristics of the reflector IRA are studied using both the method of moments (MoM) full-wave simulations and the frequency domain measurements. In this paper, the radiation mechanism of the reflector IRA is studied using a detailed current distribution on the parabolic reflector and the feeding structure at different frequencies. Applying either the calculated current distribution on the reflector IRA or the measured near-field results, it is seen that the aperture field intensity of the parabolic reflector is not the same in the two principle planes and as a result the beam-widths in the two principle planes are different. The far-field patterns of the antenna are measured and the calculated far-field patterns support the measured results. The calculated current distribution results provide a guideline on how to properly change the feeding structure to achieve a more uniform aperture field and increase the antenna radiation efficiency

Improved Feeding Structures to Enhance the Performance of the Reflector Impulse Radiating Antenna (IRA)

This paper considers the improvement of the feeding structure of the reflector impulse radiating antenna (IRA). Full-wave analysis and measured results of the orthogonal cross-coplanar plate reflector IRA shows that the aperture fields are not uniform. The arm angle is varied as an optimization factor and it is shown that the arm angle of 70deg has the maximum radiation efficiency. The termination load and the arm tapering effects are studied using simulation and measurement results. Furthermore, the effect of radius of circle of symmetry is studied and it is shown that a greater circle provides higher gain. A combination of transverse electromagnetic (TEM) horn antenna and the conical coplanar TEM transmission line is investigated to avoid tiny structure at the focal point and make the connection between the coaxial cable and the feeding arms more convenient. It is shown that a small triangle does not degrade the antenna performance but helps to excite the antenna by a coaxial cable. Finally a combination of the Vivaldi antenna and the coplanar transmission line is introduced to improve the antenna performance. The simulation results for the new antenna show that the antenna efficiency is improved to 45% at the frequency band between 2 GHz to 6 GHz in comparison to the 20.9% for the traditional design and 29.7% for the tapered design. The calculated far-field results of all these antennas are used to radiate a 0.5 ns impulse. The radiated impulse from the Vivaldi fed reflector IRA is 3.55, 2.41, and 2.12 dB higher than the same radiated impulses from the reflector IRA fed by a 45deg traditional feeding arms, 70deg traditional feeding arms, and 70deg tapered feeding arms, respectively

Increasing the Focused Response of Impulse Radiating Antennas Through Polarization Control of Aperture Fields

Wide-band, focused aperture antennas like impulse radiating antennas (IRAs) can see improved aperture efficiency through control of the aperture shape and aperture field distribution. The shape of the aperture fields is largely dictated by the transverse electromagnetic mode distribution on the nondispersive feed of the IRA. In this paper we consider reshaping the aperture field by controlling the polarization of the fields reflected or transmitted by the focusing optic. In reflector IRAs, this polarization control is obtained by making the reflector out of uniaxially conducting filaments or wires. In lens IRAs, the polarization control is obtained by using a spatially varying wire grid polarizer. Optimum configurations are derived, and the expression for the far-zone radiated fields are given and compared with experimental measurements. For common antenna configurations and impedances, the aperture height can be increased by amounts ranging from 7% to 67%. An experimental prototype of a 200 /spl Omega/ reflector IRA demonstrated a 23% improvement in aperture height, and agreed almost exactly with the numerical predictions.

Effect of defocus on the prompt response of a reflector IRA

Impulse radiating antennas (IRAs) are an emerging class of antenna that are designed to radiate extremely short electromagnetic pulses with multiple decades of instantaneous bandwidth. The most common IRAs are made with a transverse electromagnetic (TEM) transmission line feeding a paraboloidal reflector. The IRA is usually constructed so that the electrical feed point of the TEM transmission line coincides with the focal point of the paraboloid. The paraboloidal reflector converts the spherical wave emanating from the feed point into a plane wave (i.e., a spherical wave centered at -/spl infin/). In many practical cases, the feed point and focal points are not exactly aligned, producing some defocus of the reflector. In this paper, we model the case of hyperbolic defocus because of its analytic form and compare this model with experimental measurements. A hyperboloidal reflector fed from one focus converts the expanding spherical wave into a second expanding wave which appears to emanate from the second focal point of the hyperboloid (which is behind the reflector). Hyperboloidal defocus is roughly equivalent to moving the electrical feed closer to the reflector than the optical focal point. Previous theoretical results from in-focus IRAs predicted that the E- and H-plane temporal responses should be symmetric with respect to the temporal center of the response. The results shown here demonstrate that the defocusing causes these responses to become asymmetric. The new results are in better agreement with experimental measurements of IRAs and provide a physical explanation for experimental results that differ from the original theory.

Effect of Aperture Feed and Reflector Configuration on the Time- and Frequency Domain Radiation Patterns of Reflector Impulse Radiating Antennas

The prompt off-boresight radiation from an arbitrary reflector impulse radiating antenna (IRA) is considered in both the time and frequency domains using a time-domain physical optics formalism. The theory is used to compare the performance between reflector IRAs with common transverse electromagnetic feed configurations that have been designed to maximize the boresight fields. It is found that moving the feed arms of reflector IRAs toward the vertical helps to reduce sidelobe levels, as reflector IRAs with their feed arms oriented at 60/spl deg/ from the horizontal have sidelobes that are 4-5 dB lower in the H plane and 1-2 dB lower in the E plane than more traditional reflector IRAs with feed arms oriented at 45/spl deg/. The lower sidelobes are accompanied by a higher peak gain, albeit with a wider beamwidth. There are corresponding significant differences in the time domain waveforms that result. The theory is verified by comparison with experimental data from a half IRA with feed arms at 45/spl deg/. The peak fields, pulse widths, and overall waveform shapes agree well between theory and experiment, though there are temporal asymmetries in the measured data that are not predicted by the theory.

Prompt aperture efficiencies of impulse radiating antennas with arrays as an application

A concept of prompt aperture efficiency is introduced for the purpose of comparing and optimizing the performance of impulse radiating antennas (IRAs). The aperture efficiencies of popular lens and reflector IRAs are computed as the ratios of peak radiated power densities on boresight compared with that produced by an ideal IRA with an aperture of equal area and equal total input power. Loss of aperture efficiency occurs through two distinct mechanisms: from power that falls outside the aperture and is lost and from nonuniform power and polarization distributions within the aperture. Both loss mechanisms are addressed, and means for increasing efficiencies are identified. The optimum aperture for a given feed structure is derived. Prompt aperture efficiencies approaching 100% are feasible in TEM-horn arrays and similar structures.