Engineering topics

Chan, C. H.

Publications and source records attributed to Chan, C. H..

4 records

NASA NTRS1991

Application of the extended boundary condition method to Monte Carlo simulations of scattering of waves by two-dimensional random rough surfaces

The extended boundary condition method is applied to Monte Carlo simulations of two-dimensional random rough surface scattering. The numerical results are compared with one-dimensional random rough surfaces obtained from the finite-element method. It is found that the mean scattered intensity from two-dimensional rough surfaces differs from that of one dimension for rough surfaces with large slopes.

Tsang, L.↗

NASA NTRS1982

A new SPS antenna design to reduce grating lobes

In the Solar Power Satellite system, the antenna's misalignment will produce well defined grating lobes. These gratings lobe peaks occur every 440 km and are potentially hazardous to the environment. One way to suppress these peaks is to phase control every power module. The cost due to the increase in receiving electronics and processors, however, could prove to be prohibitive. A new design of the antenna involving the addition of two broad gaps, one along the x axis and another along the y axis is proposed. The gap distance is exactly one half of the distance between the center of two neighboring subarrays. Calculation of far field radiation patterns shows that the design reduces grating lobe peaks without sacrificing power in the main lobe.

Chan, C. H.↗

NASA NTRS1980

Pilot signals for large active retrodirective arrays

It was suggested that for large active retrodirective arrays, as in the solar power system, a two tone uplink pilot signal with frequencies symmetrically situated around the downlink frequency be used in order to reduce ionospheric biases and to lower the cost. Unfortunately such a system faces the following difficulties: (1) the pi-ambiguity, and (2) a large phase difference between the downlink and uplink signals. It is shown how the pi-ambiguity can be easily removed by using a two tone uplink signal with both frequencies situated at one side of the downlink frequency, and the phase difference can be greatly reduced with a three tone or a four tone uplink pilot signal.

Chan, C. H.↗

NASA NTRS1980

Pilot signals for large active retro-directive arrays

It has been suggested that for large active retrodirective arrays, as in the solar power system, a two tone uplink pilot signal with frequencies symmetrically situated around the downlink frequency be used in order to reduce ionospheric biases and to lower the cost since a two tone receiver is economically much cheaper than a single tone phase locked receiver. Such a system now faces two difficulties: the Pi-ambiguity; and a large phase difference between the downlink and uplink signals. The Pi-ambiguity is shown to be easily removed by using a two tone uplink signal with both frequencies situated at one side of the downlink frequency, and the phase difference can be greatly reduced with a three tone or a four tone uplink pilot signal.

Chan, C. H.↗