Ultra-wideband (UWB) and impulse radiating antennas (IRAs)

Ultra-Wideband (UWB) Impulse Radiating Antennas (IRAs) are widely used in impulse radar applications, underground mine detection, communication, and jamming systems. This dissertation presents a basic understanding of IRAs, properties of an ideal IRA, and modifications of IRAs based on detailed frequency domain simulations and measurement results.; As a paradigm of an IRA, we built an Inverted Trapezoidal Pulse Antenna at UCLA. The antenna encompassed ultra-wideband properties in the reflection coefficient and a stable far-field pattern from 1.2 GHz to 4.5 GHz. Subsequently, the antenna's trapezoidal radiator was replaced with a triangular radiator of nearly equal size, which broadened the reflection coefficient bandwidth from 1.2 GHz to 25 GHz range. A Tilted Inverted Triangular Pulse Antenna was also introduced to stabilize the far-field pattern from 1.2 GHz to 10 GHz.; Our preliminary efforts allowed us to concentrate mainly on reflector IRAs. An IRA's radiation characteristics were measured, in both the spherical near-field and the far-field anechoic chambers, at UCLA. A Method of Moments (MoM) based software was employed to calculate the current distributions and far-field patterns. The results were used to increase the radiation efficiency and to improve the far-field characteristics of the antenna. The calculated far-field patterns concurred with the measured results.; As an initial modification of the reflector IRA, the feeding arm angle was adjusted to 70° for maximum radiation efficiency. The end parts of the feeding arms were also tapered to avoid the stored energy at the arm-reflector junctions. The result was a more symmetric aperture field. Eventually, we combined the Vivaldi antenna and the TEM coplanar transmission line as one feeding structure to improve the radiation efficiency and the input impedance of the reflector IRA. An efficiency of up to 40% was gained in the frequency band of 2 GHz to 5 GHz. This result far exceeded the 20.9% achieved with the 45° arm angle traditional design and the 28.4% produced by the 70° arm angle tapered design. Ultimately, all the above mentioned antennas were excited to radiate a 0.5 ns impulse. Noticeably, the radiated impulses from the Vivaldi fed reflector IRA were 2.94 dB, 1.87 dB, and 1.63 dB higher than the 45° traditional, the 70° traditional, and the 70° tapered feeding arms reflector IRAs, respectively.; We also studied the Cavity Backed Annular Patch Antennas (CABAPAs). Total Active Reflection Coefficient (TARC) was formulated for determining the frequency response and the radiation performance of a multi-port antenna. The TARC formula is the square root of the following: sum of all incident powers at the ports minus the radiation power, divided by the sum of all the incident powers at the ports. The TARC presented a superior function for evaluating the frequency bandwidth and radiation performance of multi-port antennas.