To obtain adequately narrow beams, high frequency radars (HF) commonly employ long receiving arrays since they must be large in comparison with the transmission wavelengths. In such radars the overall system beamwidth can be reduced for a given size of the receiving array, by transmitting signals sequentially from a small number of sector coverage antennas, suitably positioned relative to the array. A comprehensive study of this technique applied to the frequency modulated continuous wave radars (FMCW) is presented, and the bearing- Doppler ambiguities arising from the use of sequential transmission have been investigated. The practical usefulness of the technique has been verified experimentally by measuring the overall system beam patterns both before and after the application of a dual transmission scheme. The experimental procedure required an active transponder capable of simulating a target of large echoing area, a special beam forming network capable of slewing the receiving beam in small steps, and a dual transmission switching unit. The design and development of these items of test equipment are discussed. Radar signal processing using the double Fourier transformation with subsequent phase correction has been proposed, and the recorded experimental data was processed according to these techniques. The measured beam patterns have been presented for single and dual transmission schemes. In addition to the beam narrowing studies a family of slow rise of sensitivity sequences (SRS) have been developed which could improve FMCW radar operation in a monostatic mode, also a new and compact shaping and switching signal generator has been designed and developed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509931 |
| Date | January 1984 |
| Creators | Ghannad, M. S. |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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