A time‐domain measuring technique for ultra‐wide band antennas

Abstract

The measured IL of the miniature DBRs are 0.55 dB (parallel capacitors) and 0.44 dB (series capacitors), respectively. This leads to unloaded quality factors equal to 98 and 110, respectively. Hence, when the capacitors are connected in series a 12% improvement of unloaded quality factor of the miniature DBR can be obtained. The obtained %M are 76% (parallel) and 70% (series). The 6% difference is simply due to the meander realization used in the first case 0. CONCLUSIONSA new miniaturized DBR topology has been proposed. A capacitor connected in series with the stub allows reducing the miniature DBR size by 70%. Compared with the miniature DBR published in 0, the new topology leads to the same miniaturization ratio with improved performance, and more robust design. The obtained results are: an improvement of 12% for the unloaded quality factor and a better agreement between measurement and simulation results using the same CAD tool (ADS Momentum TM ). Based on the knowledge of the radiated far-field waveform for a given excitation, time-domain characteristic functions can be derived, allowing the evaluation of the antenna response for any other excitation waveform. Time-domain impulse response (or effective height) and time-domain reflection coefficient are such characteristic functions that provide a complete knowledge of the radiated field waveform and of the reflected voltage waveform at the antenna input, respectively; however, these functions of time are not essentially figures of merit. For this reason, energy-based descriptors have been derived from the above characteristic functions. Energy gain, energy pulse matching ratio, and normalized correlation coefficient are such descriptors.In a previous work [1], we proposed an energy reflection coefficient that can be calculated from the time-domain reflection coefficient. The latter was measured by using the time-domain reflectometry (TDR) technique. In this article, we propose a time-domain technique for measuring the impulse response of an ultra-wide band antenna. As opposed to traditional single-antenna techniques, our method can provide a simpler separation of the three signals at the antenna input (i.e., excitation signal, antenna input reflected signal, and received signal), even though they might be superposed. Measurements are performed in a low-noise environment, such as a Faraday cage; in that case, the antenna under test is placed close to one cage wall.Experimental results using our method are presented for a UWB folded dipole antenna operating in the lower band for military UWB applications.The time-domain differential single-antenna method provides accurate results as long as far-field conditions are granted. However, such a constraint prevents one from using the method to measure electrically large antennas. That is, the antenna under test cannot be placed too far away from the Faraday cage wall considered as a reflector, given that the shorter the distance, the longer the time-span available for extracting the response. It is obviously more d...

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