U.S.S. Curtiss Propagation Measurements
Propagation measurements have been made in the cargo hold of the U.S.S. Curtis, a naval cargo ship, while it was docked at Port Hueneme. The purpose of this testing was to determine the ultra-wideband channel response inside the cargo hold, which is basically a metal box. Because of all the metal surfaces, a lot of multipath (with long delay spread) was expected and observed. The tests performed consisted of three basic types: 1) Time domain propagation measurements with a 50 GHz digital sampling scope, 2) frequency response measurements with a network analyzer, and 3) interference measurements with a spectrum analyzer. The basic test setup is shown below in Figure 1.
Figure 1. Test setup for time domain tests
The time-domain tests used a PRF (pulse repetition frequency) of 500 kHz generated by the Clock Generator. The pulse generated by the Avtech Pulser is a narrow Gaussian-shaped pulse about 1 nanosecond in duration. The frequency response tests required the Avtech Pulser and the Sampling Scope to be disconnected and replaced with the network analyzer for S12 type two-port tests. The test setup for the interference test involved connecting the Rx antenna to a spectrum analyzer and measuring the spectrum from 0 Hz to 3 GHz. A series of tests were performed at various locations within the cargo hold and at each location time domain and network analyzer measurements were taken for comparison. One such set of measurements is shown below. Figure 2 shows the time waveform while Figure 3 shows the frequency response measurement from the network analyzer for the same Tx and Rx antenna locations. In Figure 4, the inverse Fourier Transform of the network analyzer data is compared with the time-domain waveform of Figure 2. Figure 5 shows the same data as Figure 4, but with both waveforms plotted on top of each other to show how closely the two waveforms agree. Note in Figure 2 many reflections can be observed and the multipath appears to be noticeable for about 2 microseconds after the first line-of-sight path.
Figure 2. Time domain measurement (same measurement in both pictures)
Figure 3. Frequency response measurement
Figure 4. Comparison of time-domain and frequency-domain measurements
Figure 5. Side-by-side comparison of the time and frequency domain measurements