Three descriptors of antenna performance appropriate for ultrawide-band (UWB) applications are proposed and described: energy pattern, correlated energy pattern, and correlation coefficient pattern. The parameters are indicative of how a particular antenna will behave with a receiver employing correlation detection of broadband pulses. Numerical simulations of canonical dipole antennas demonstrate the significance of these parameters. In particular, there are substantial differences between total energy quantities and correlated energy quantities, showing that consistency of radiated pulse shape is a critical issue in UWB antenna performance. A further numerical example using crossed linear dipoles shows that even an antenna system exhibiting an isotropic radiation pattern at all frequencies does not provide an isotropic correlated energy pattern and hence cannot provide truly omnidirectional performance when pulse fidelity is considered.

Pattern descriptors for UWB antennas

Near-field scanning can be used to determine the far-field emissions of electronic devices. In general, this requires phase-resolved electric and magnetic near-field data. To capture a broad frequency range relatively quickly, a multichannel oscilloscope can be used for data capture. The phase relationship of the fields between different space points and between the electric and the magnetic field needs to be known. Consequently, it is required to determine the complex-valued probe factor (PF) of the probe, cable, and amplifier chain. This paper presents a fast and efficient calibration method which uses the same setup and instruments during calibration and measurement, and it allows for easy and economical integration of the calibration hardware and software into the scanning system. Known fields are created by a microstrip trace driven with a comb generator. By referencing measured data to this known field, the PF is obtained over a broad frequency range by capturing one time-domain waveform.

An Effective Method of Probe Calibration in Phase-Resolved Near-Field Scanning for EMI Application

Ultra wideband impulse radio (UWB-IR) technology is an ideal candidate for wireless networks that can be utilized for short-range, high-speed, low power, and low cost indoor applications. The link budget of the free space propagation loss is usually estimated by using Friis' transmission formula. However, it is not directly applicable to ultra wideband impulse radio transmission systems, in particular the single band impulse radio, as the formula is expressed as a function of the frequency. Moreover, the waveform may be distorted due to the frequency characteristics of the antenna, and the comparison between Tx and Rx waveforms is not straightforward. The paper discusses the free space link budget evaluation of UWB-IR systems based on the extended Friis' transmission formula. The matched filter is considered at the receiver side to maximize the SNR for evaluation. An experimental evaluation of the antenna transfer function needs the three-antenna method for the calibration of the reference antenna. The technique gives very accurate results and is very useful for design and evaluation of UWB impulse radio transmission systems, especially for the evaluation of waveform distortion effects.

/pdf/free-space-link-budget-evaluation-of-uwb-ir-systems-2c996zbqir.pdf

Free space link budget evaluation of UWB-IR systems

The capability of the level set method is illustrated for shape and location reconstruction using real measurement data in the range of 3-8 GHz. An experimental setup is utilized to measure the S-parameters using two Vivaldi antennas revolving around metallic pipes of different cross-sections. A two-dimensional reconstruction of the pipe's cross section is retrieved using the level set algorithm combined with the method of moments and the frequency hopping technique. The results show good agreement between the reconstructed cross section and the true configuration. This indicates to the strength of the level set method and its ability to cope with the noise in real measurements.

Experimental Microwave Validation of Level Set Reconstruction Algorithm

We have proposed a method for evaluating the free-space antenna factor of a log-periodic dipole antenna (LPDA) with a time-domain technique. The proposed method is based on a time-domain analysis and a pulse-compression technique. The proposed method enables the direct wave to be isolated from reflected waves on the ground plane of an open-area test site (OATS) and evaluation of the free-space antenna factor. In a measurement, two LPDAs are held on masts at a height of 6 m above the ground and are separated by 10 m. The direct wave is separated using a Wiener filter obtained from frequency-domain data at 3 m antenna separation. The proposed method can completely separate the direct wave from other waves from the ground plane of an OATS. The expanded uncertainty (k = 2) of LPDAs was estimated to be from 0.38 to 0.45 dB over the frequency range from 300 to 1000 MHz.

Measurement and Uncertainty Analysis of Free-Space Antenna Factors of a Log-Periodic Antenna Using Time-Domain Techniques

The near-field 3-antenna method for measuring the complex antenna factor (CAF) is proposed in order to reduce the effect of the measurement site and background noise. The transmission coefficients in the far-field region are calculated from those measured in the near-field and theoretically obtained near-field correction factors (NCF). The CAF of monopole antennas are measured using the proposed method in a frequency range up to 6 GHz. From the measurement results, the dependency of CAF values on the antenna distance is small. These results indicate that our theory including the NCF is applicable for the measurements of the CAF of simple-structure antennas.

H. Iida

Papers

Measurements of complex antenna factor by the near-field 3-antenna method