TO SATISFY THE NEEDS FOR BOTH low and high frequencies in ground-penetrating radar (GPR), an Ultra Wideband (UWB) GPR that transmits a short-time pulse signal is often used. To ensure that its performance is sufficient, Ahmet Serdar Turk and Hakkl Nazli from the Scientific and Technical Research Council of Turkey (TUBITAK) have developed a hyper-wideband horn-array design. It is essentially an array combination of partial-dielectric transverse electromagnetic (PD-TEM) horn antennas, which obtain hyperwideband antenna characteristics from 150 MHz to 10 GHz for multiband impulse GPR.

A modified version of the partially loaded transmission-line antenna method (PLTLM) was used to analyze the structure. Both reference antennas and a PD-loaded TEM horn array (PDTEMA) model were measured from 50 MHz to 10 GHz using an HP8719D vector network analyzer from Agilent Technologies (www.agilent.com). The results showed that two designsthe PDTEMA horn and gratingmodel Vivaldi-shaped version of the PDTEM horn (PDVA)can reach extended bandwidth ratios up to 25:1. The typical gain band of the ridged-horn (RH) antenna is 20:1 and similar to the loaded TEM horns.

The PDTEMA attains at least twice broadened UWB gain characteristics. Its -10 dB gain band is more than 50:1. In addition, the PDTEMA horn can obtain a voltage standing wave ratio (VSWR) of less than 2 with an average value of 1.5 over the 50:1 frequency band. Input impulse reflection level of roughly -0.15 can easily be achieved for 1-GHz sub-band and 10-GHz full-band transformations. See "Hyper-Wide Band TEM Horn Array Design for Multi Band Ground- Penetrating Impulse Radar," Microwave And Optical Technology Letters, Jan. 2008, p. 76.