The propagation of ultra wide band (UWB) signals through walls is analyzed. For this propagation studies, it is necessary to consider not only propagation at a single frequency but in the whole band. The UWB radar output signal is formed by both transmitter and antenna. The effects of antenna receiving and transmitting responses for various antenna types (such as small and aperture antennas) are studied in the frequency as well as time domain. Moreover, UWB radar output signals can be sub- stantially affected due to electromagnetic wave propaga- tion through walls and multipath effects.

UWB Propagation through Walls

A procedure for evaluating the directivity of an antenna under test from near-field measurements on a spherical scanning surface is proposed. It uses a formula in closed form for computing the total radiated power from the knowledge of the radiation intensity samples on the far-field sphere. These last are determined via an efficient probe compensated near-field–far-field transformation technique based on a nonredundant sampling representation of the probe voltage. The samples are collected on a spiral wrapping the near-field spherical surface from pole to pole. With respect to the classical spherical scanning, this innovative way of collecting the data allows the reduction of the time required for the samples acquisition by means of a continuous movement of the positioning systems. The effectiveness of the proposed procedure is assessed by numerical simulations.

Directivity Computation by Spherical Spiral Scanning in Near Field Region

A simple formula for estimation of gain is verified for the shaped-beam antenna. As an example, experimental results of five Hogg-horn antennas, along with their mean values, are published and compared with the simple approximation of gain. The simple gain approximation could be very valuable for system engineers to accurately estimate antenna gain and perform EMC calculations (estimations of interference and susceptibility).

Estimation of Antenna Gain

Gain Estimation of Doubly Curved Reflector Antenna

An effective technique is proposed in this paper for evaluating the directivity of an antenna under test from near-field measurements on a cylinder. It employs a closed-form formula for computing the total radiated power from the knowledge of the radiation intensity samples on the far-field sphere. These samples are determined via a probe-compensated near-field–far-field transformation and result to be even in number on each parallel. The effectiveness of such a procedure is assessed through numerical tests. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 686–691, 2006; Pubished online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21443

Computation of antenna directivity from cylindrical near–field measurements

Starting with a common formula for directivity, given beamwidths, the author gives the modifications needed to improve the accuracy when the distribution is known. Also included is a nomograph that shows the parameters of the Taylor single-parameter distribution, and allows trade studies versus the sidelobe level.

J.D. Mahoney

Papers

Directivity of planar antennas