Band S receiver to integrate Doppler meteorological radar system

• Grant number: 02/07911-4
• Support Opportunities: Research Grants - Innovative Research in Small Business - PIPE
• Start date: February 01, 2003
• End date: March 31, 2005
• Field of knowledge: Engineering - Electrical Engineering - Electrical, Magnetic and Electronic Circuits
• Principal Investigator: Jorge Hidemi Ohashi
• Grantee: Jorge Hidemi Ohashi
• Company: Omnisys Engenharia Ltda
• City: São Bernardo do Campo

Abstract

The basic objectives of this project are: to develop a band S receiver to integrate in the Doppler meteorological radar system, under development in Omnisys, and to set up a team that is specialized and trained in the development of new products which involve similar knowledge to that acquired during the implementation of the project. The classic radar receiver is of the superheterodyne type with phase coherence and the use of linear amplifiers for the extraction of video signals. The transmitted signals which return to the receiver present very low amplitudes and are amplified by a low noise amplifier which is characterized by a high gain and low noise figure. This signal is then amplified and converted into an FI frequency of 30 megahertz (MHz) by means of a mixer which emits a pulse between the transmitted frequency and that of a high stability local oscillator (STALO). The frequency of the local oscillator can be syntonized 30 (MHz) above the transmitted frequency (supradyne) or be syntonized 30 (MHz) below the transmitted frequency (infradyne). The mode of operation to be used in the present project is supradyne. Phase coherence is also very important during the process of extracting the video signals. The synchronous transmission signal which marks the start of the transmission and the cadence of the radar’s interrogations is present in the receiver so as to synchronize the video extraction. This synchronous signal is used as a reference of the oscillation circuit in 30 MHz known as COHO (oscillator coherence), in order to maintain the same phase of the transmitted signal. In the logarithmic amplifying circuit the FI signal is amplified and the logarithmic video signal extracted which is used to generate the AGC (Automatic Gain Control) used to centralize the linear amplifier’s dynamic so as to control the gain. In the linear amplifying circuit the FI signal is amplified and, by means of a mixer which emits a pulse between the FI and the COHO signal, the signal for linear videos I and Q is extracted which are in phase quadrature to resolve problems of ambiguity. Due to the fact that the Magnetron valves alter their oscillation frequency with the passage of time, an AFC (Automatic Frequency Control) circuit is required which, by means of a comparison between the frequency transmitted and that of the local oscillator, ensures that the FI frequency is maintained at 30 MHz; if there is any alteration, an error signal is generated. There are two possible ways to maintain the FI frequency. The first is to use the error signal generated by the AFC, adjust the Magnetron, and correct its transmission frequency; and the second is to use the error signal generated by the AFC and adjust the local oscillator correcting its frequency. The receiver to be developed will use the option of correcting the frequency of the local oscillator. (AU)