Browse Prior Art Database

Weather Radar System

IP.com Disclosure Number: IPCOM000073595D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Raabe, HP: AUTHOR

Abstract

This meteorological surveillance system collects data from a constant altitude layer rather than from cones of constant elevation angle as in conventional systems.

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Weather Radar System

This meteorological surveillance system collects data from a constant altitude layer rather than from cones of constant elevation angle as in conventional systems.

The transmitted energy is distributed over the entire elevation range rather than confined to a pencil beam as in the conventional radar. Hence, the entire elevation cross section is illuminated. he receiving beam is a pencil beam as in the conventional radar; however, it is electronically steered in elevation at such a high rate that it tracks the instantaneous pulse echo as it returns from a selected altitude layer. Thus a complete constant-altitude sweep can be performed in every interpulse period. Because the mechanical scan is limited to azimuth rotation, the total scanning time is substantially less than in conventional weather systems.

The rapid elevation scan may be obtained with antenna arrays. The antenna array is designed as a frequency scanner. For example, when fed a lower radio frequency, the beam points at a higher elevation angle. The transmitted signal consists of as many pulses as there are beam positions. The radio frequencies and peak powers of these pulses are chosen according to the associated beam positions. These pulses may be transmitted simultaneously or sequentially. In the latter case, a continuous up-sweep of frequency and power may be employed.

The echo radiation will contain pulses of all transmitted frequencies, assuming that scatterers are present at all ranges and elevation angles. A narrow-band receiver, operating with a local oscillator, whose frequency is swept down at the programmed rate for a selected altitude, and with an IF amplifier tuned to a fixed frequency band, rejects returns from undesired elevation angles. Hence, elevation discrimination does not lie with the antenna array. It is necessary that the frequency spectrum equal the product of the elevation position and the IF bandwidth. For example, if the number of elevation positions is 20 and the IF bandwidth is 2 MHz, the RF spectrum must be spread over a minimum of 40 MHz. At a radio frequency of 3000 MHz, this is only a 1.3 percent variation. From the array designer's point of view, a wider variation might be preferred.

Multiple beam radars, sweeping through several altitude layers simultaneously, can be implemented by parallel receivers with separate, individually programmed, local oscillators.

In the operation of a dual-beam radar as seen in Figur...