Radar distance measuring device

• US 5,659,321 A
• Filed: 05/10/1995
• Issued: 08/19/1997
• Est. Priority Date: 09/15/1993
• Status: Expired due to Fees

• Current Assignee: Endress+Hauser GmbH+Co (ENDRESS)
• Original Assignee: Endress+Hauser GmbH+Co (ENDRESS)
• Inventors: Burger, Stefan, Otto, Johanngeorg
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/433,440
• Time in Patent Office: 832 Days
• Field of Search: 342/118, 342/122, 342/124, 342/128, 367/908, 73/290 R
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 7/03 Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
• CPC Class Codes: H03D 9/00 Demodulation or transference of modulation of modulated electromagnetic waves demodulating light, transferring modulation in light waves G02F2/00
• CPC Class Codes: H03D 9/06 Transference of modulation using distributed inductance and capacitance

Abstract

A conventional radar module (1) for level measurements is designed for operation within a specific, narrowly restricted frequency range. To enable level measurements to be implemented at a substantially higher frequency without involving any change in the existing radar module (1) whatsoever, a frequency converter circuit (2) is inserted between the duplexer antenna (7) designed for said higher frequency and the antenna port (A) of the radar module (1). This frequency converter circuit (2) which can be realized at small expense converts the lower frequency into the higher frequency in the direction from the radar module (1) to the antenna (7) and the higher frequency into the lower frequency in the opposite direction.

Claims

1. A radar level measuring device comprising:

(a) an antenna for emitting microwaves toward the surface of a material in a container and for receiving the echo waves reflected from the surface;

(b) a radar module having an input/output port for delivering a microwave signal having a first frequency f₁, the radar module comprising an evaluation circuit for determining, from the received echo signals, the transit time of the microwaves to the material surface and back; and

(c) a frequency converter circuit having a first converter circuit port connected to the input/output port of the radar module and a second converter circuit port connected to the antenna, the frequency converter circuit comprising;

(1) a local oscillator for generating an output signal having a second frequency f₂, the local oscillator including an output port;

(2) a mixer having

(i) a first mixer port connected to the output port of the local oscillator;

(ii) a second mixer port through which signals can be transmitted to and received from the radar module; and

(iii) a third mixer port through which signals can be transmitted to and received from the antenna;

(3) a low pass filter having a cut-off frequency that is higher than the first frequency f₁, the low pass filter having a first low pass filter port connected to the first converter circuit port and a second low pass filter port connected to the second mixer port; and

(4) a high pass filter having a cut-off frequency that is less than a third frequency f₃ corresponding to the sum of the first frequency f₁ and the second frequency f₂, the high pass filter having a first high pass filter port connected to the second converter circuit port and a second high pass filter port connected to the third mixer port;

wherein the mixer is adapted for

3. The level measuring device as set forth in claim 1, wherein the third frequency f₃ is at least twice the first frequency f₁.

2. mixing the output signal from the local oscillator having the second frequency f₂ with the signal from the radar module having the first frequency f₁, to generate signals delivered at the third mixer port having the third frequency f₃ and a frequency corresponding to the difference of the first frequency f₁ and the second frequency f₂ ;

and

2. mixing the output signal from the local oscillator having the second frequency f₂ with a signal from the antenna having the third frequency f₃, to generate signals delivered to the second mixer port having a frequency corresponding to the sum of the second frequency f₂ and the third frequency f₃ and the first frequency f₁ corresponding to the difference of the second frequency f₂ and the third frequency f₃

wherein a bi-directional signal path is established between the radar module and the antenna via the two converter circuit ports of the frequency converter circuit, the low pass filter the mixer, and the high pass filter to permit use of the radar module delivering the first frequency f₁ for level measurement at the third frequency f₃ which is higher than the first frequency f₁.

4. The level measuring device as set forth in claim 2, wherein the first frequency f₁ is about 5.8 GHz and the third frequency f₃ is about 24 GHz.