Digital baseband processing method and device for very high frequency omnidirectional beacon signal, and receiver

Abstract

The invention discloses a digital baseband processing method and device for a very high frequency omnidirectional beacon signal and a receiver, and relates to the technical field of signal processing, and the technical scheme is characterized in that the method comprises the following steps: carrying out AM demodulation on a VOR baseband signal to obtain a VOR envelope signal; processing the VOR envelope signal through band-pass filters BPF1, BPF2 and BPF3 to obtain a variable phase signal, a first reference phase signal, Morse code audio and air-ground communication voice; performing FM demodulation on the first reference phase signal to obtain a second reference phase signal; and carrying out amplitude normalization on the variable phase signal and the second reference phase signal, then carrying out Ref-Var phase discrimination to obtain a phase difference between the two signals, and converting the phase difference into an azimuth angle of the aircraft. By adopting the digital design, the use of analog devices is reduced, the system integration level is increased, higher angle measurement precision can be obtained, and the navigation performance required by civil aviation area navigation can be better met.

Description

Technical Field

[0001] The present invention relates to the field of signal processing technology, and more specifically, to a digital baseband processing method, device and receiver for very high frequency omnidirectional beacon signals. Background Art

[0002] The Very High Frequency Omnidirectional Range (VOR) system is a very important short-range radio navigation system used in the aviation field. It consists of two parts: a ground station and an onboard VOR receiver on an aircraft. The onboard VOR receiver receives and processes the signal transmitted by the ground station, and can obtain the azimuth of the aircraft relative to the ground station. It is used in conjunction with the flight management system of modern civil airliners to realize the regional navigation (RNAV) function of the aircraft. The operating frequency range of the VOR signal is 108.00~117.95MHz, with a frequency interval of 50kHz, and a total of 200 channels.

[0003] like Figure 1 As shown in the figure, the VOR ground station transmits a radio frequency signal modulated by two low-frequency signals, one of which is a reference phase signal: a signal obtained by frequency modulating a 9960Hz subcarrier with a 30Hz modulating wave, and the phase of the modulated wave is the same in 360 degrees around the ground station; the other is a variable phase signal: an amplitude modulated signal of a 30Hz modulating wave, and its phase changes with the radial azimuth of the VOR station. Figure 2 As shown, the airborne VOR equipment performs frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling on the received VOR signal to obtain two digital baseband signals, namely the in-phase component (I) and the quadrature component (Q). Digital baseband processing is performed on them to calculate the phase difference between the reference phase signal and the variable phase signal, and then converted into the azimuth of the aircraft relative to the ground station.

[0004] However, most existing VOR receivers use analog signal processing methods to implement VOR signal demodulation, detection, filtering, frequency discrimination, phase discrimination, etc. through analog circuits; there are also digital processing methods based on zero-crossing detection, which estimate the phase by finding the sampling moment of the zero-crossing point of the sinusoidal signal, so the estimation error depends on the sampling rate. However, the processing accuracy of the above methods is limited and cannot meet the occasions with high navigation accuracy requirements, such as the accuracy requirements within the performance-based navigation specification RNP 1. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a digital baseband processing method, device and receiver for very high frequency omnidirectional beacon signals, which adopt a digital design, reduce the use of analog devices, increase system integration, make the equipment more compact, lightweight and low-power, and can obtain higher angular measurement accuracy, and better meet the navigation performance required for civil aviation regional navigation.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a digital baseband processing method for a very high frequency omnidirectional beacon signal is provided, comprising the following steps:

[0008] Perform AM demodulation on the VOR baseband signal to obtain the VOR envelope signal;

[0009] The VOR envelope signal is processed by the bandpass filter BPF1 to obtain a variable phase signal;

[0010] The VOR envelope signal is processed by a bandpass filter BPF2 to obtain a first reference phase signal;

[0011] The VOR envelope signal is processed by the bandpass filter BPF3 to obtain the Morse code audio and air-to-ground communication voice;

[0012] Performing FM demodulation on the first reference phase signal to obtain a second reference phase signal;

[0013] The variable phase signal and the second reference phase signal are amplitude normalized and then Ref-Var phase detection is performed to obtain the phase difference between the two signals and convert it into the azimuth of the aircraft.

[0014] Further, the bandpass filter BPF1 allows a frequency of 30 Hz to pass, filters out a DC component, and the starting frequency of the upper stop band is not higher than a frequency of 300 Hz;

[0015] The lower stopband cutoff frequency of the bandpass filter BPF2 is not less than 3400 Hz, the passband start frequency is not higher than 9480 Hz, and the passband cutoff frequency is not less than 10440 Hz;

[0016] Also, the passband start frequency of BPF3 is not higher than 300 Hz, the cutoff frequency is not lower than 3400 Hz, the lower stopband cutoff frequency is not lower than 30 Hz, and the upper stopband start frequency is not higher than 9480 Hz.

[0017] Furthermore, the process of performing FM demodulation on the first reference phase signal is specifically as follows:

[0018] The modulated signal is down-converted to zero frequency by orthogonal demodulation, and I and Q signals are output;

[0019] The I and Q signals are passed through the low-pass filter LPF1 respectively to filter out the frequency-doubled components during orthogonal mixing;

[0020] The I and Q baseband signals are subjected to frequency discrimination after filtering out the frequency multiplication components during orthogonal mixing to obtain a second reference phase signal.

[0021] Furthermore, the process of down-converting the modulated signal to zero frequency by using orthogonal demodulation is specifically as follows:

[0022] Output to the same phase branch through the digital controlled oscillator: i [n] = sin(w S n);

[0023] And, through the digitally controlled oscillator to the orthogonal branch output: s Q [n] = cos(w S n);

[0024] Among them, s I [n] is the I-channel signal; s Q [n] is the Q-path signal; w s is the angular frequency of 9960 Hz; n is the time interval relative to the peak moment of the reference phase.

[0025] Furthermore, the passband cutoff frequency of the low-pass filter LPF1 is not less than 480 Hz, and the stopband start frequency is not higher than 19440 Hz;

[0026] After LPF1:

[0027] I-channel baseband output:

[0028] Q-channel baseband output:

[0029] Among them, ref 2I (n) is the baseband signal of I; ref 3Q (n) is the Q-band signal; U2 is the amplitude of the reference phase signal; m is the frequency modulation index; w is the 30 Hz angular frequency; and n is the time interval relative to the reference phase peak moment.

[0030] Furthermore, the process of performing frequency discrimination on the I and Q baseband signals after filtering out the frequency multiplication components during orthogonal mixing is specifically as follows:

[0031] Divide the I and Q baseband signals to obtain a first signal;

[0032] Taking the arc tangent of the first signal, the second signal is obtained;

[0033] The second signal is derived, the difference between the two preceding and following sampling points is calculated by a digital processing method, and then the second reference phase signal is obtained after normalization.

[0034] Furthermore, the expression for normalizing the amplitude of the variable phase signal is specifically:

[0035]

[0036] in, is the normalized value of the variable phase signal amplitude; Var(n) is the variable phase signal; K is the accumulation time window;

[0037] The expression for normalizing the amplitude of the second reference phase signal is specifically:

[0038]

[0039] in, is the normalized value of the second reference phase signal amplitude; Ref3(n) is the second reference phase signal.

[0040] Furthermore, the Ref-Var phase discrimination process is specifically as follows:

[0041] Through the multiplier output The double frequency component is filtered out by the low-pass filter LPF2, and only the DC component is retained. The stop band starting frequency is not higher than 30Hz; w is the 30Hz angular frequency; n is the time interval relative to the reference phase peak moment;

[0042] The output of the low-pass filter LPF2 is multiplied by 2 and then an inverse cosine function is obtained to obtain a phase difference θ between the variable phase signal and the second reference phase signal.

[0043] In a second aspect, a digital baseband processing device for a very high frequency omnidirectional beacon signal is provided, comprising:

[0044] An AM demodulation unit is used to perform AM demodulation on the VOR baseband signal to obtain a VOR envelope signal;

[0045] A first filtering unit, used for processing the VOR envelope signal through a bandpass filter BPF1 to obtain a variable phase signal;

[0046] A second filtering unit, used for processing the VOR envelope signal through a bandpass filter BPF2 to obtain a first reference phase signal;

[0047] The third filtering unit is used to process the VOR envelope signal through the bandpass filter BPF3 to obtain the Morse code audio and air-to-ground communication voice;

[0048] An FM demodulation unit, configured to perform FM demodulation on the first reference phase signal to obtain a second reference phase signal;

[0049] The phase detection processing unit is used to perform Ref-Var phase detection on the variable phase signal and the second reference phase signal after normalizing their amplitudes, obtain the phase difference between the two signals, and convert it into the azimuth of the aircraft.

[0050] According to a third aspect, an airborne VOR receiver is provided, comprising at least one digital baseband processing device for a very high frequency omni-directional range beacon signal as described in the second aspect.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. The digital baseband processing method of the VHF omnidirectional beacon signal provided by the present invention adopts a digital design, reduces the use of analog devices, increases system integration, makes the equipment more compact, lightweight and low-power, can obtain higher angle measurement accuracy, and can better meet the navigation performance required for civil aviation regional navigation;

[0053] 2. The present invention can meet the occasions with higher requirements for navigation accuracy, such as the accuracy requirement within RNP 1 based on the performance-based navigation specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0055] Figure 1 It is a schematic diagram of the relationship between the VOR signal envelope and the aircraft azimuth in the prior art;

[0056] Figure 2 It is a working principle diagram of airborne VOR equipment in the prior art;

[0057] Figure 3 is a processing flow chart of a VOR baseband signal in Embodiment 1 of the present invention;

[0058] Figure 4 It is a functional block diagram of the digital baseband processing device in embodiment 2 of the present invention. DETAILED DESCRIPTION

[0059] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0060] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When a component is referred to as being "connected to" another component, it can be directly or indirectly connected to the other component.

[0061] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0062] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0063] Embodiment 1: A digital baseband processing method for a very high frequency omnidirectional beacon signal, such as Figure 3 As shown, the digital baseband signal processing module uses a sampling rate of f B Receive the I and Q digital VOR baseband signals and then process them in the following steps.

[0064] Step 1: Perform AM demodulation on the VOR baseband signal, that is, perform symbol-by-symbol square summing and square root calculation on the I and Q paths respectively.

[0065] After AM demodulation, the VOR envelope signal is obtained. The mathematical expression is as follows:

[0066] u(n)=U0+U1cos(wn-θ)+U2cos(w S n+msin(wn))+U3a(n);

[0067] Among them, U0 is the carrier amplitude; U1 is the amplitude of the variable phase signal, and the spectrum is located at the 30Hz frequency point; U2 is the amplitude of the reference phase signal, and the spectrum is distributed in the range of 9460±480Hz; U3 is the amplitude of the Morse code signal and the voice signal, the spectrum of the voice signal is in the range of 300~3400Hz, and the spectrum of the Morse code tone is at the 1020Hz frequency point; n is the time interval relative to the peak moment of the reference phase; is 30Hz angular frequency; is the angular frequency of 9960Hz; θ is the azimuth of the aircraft; m=16 is the frequency modulation index; a(n) is the Morse code signal and the voice signal.

[0068] Step 2: The VOR envelope signal passes through the bandpass filter BPF1 to obtain a variable phase signal: Var(n)=U1cos(wn-θ. BPF1 should be able to pass the 30Hz frequency, filter out the DC component, and the upper stopband starting frequency should not be higher than 300Hz (the lowest frequency of the voice signal spectrum).

[0069] Step 3: The VOR envelope signal passes through the bandpass filter BPF2 to obtain the first reference phase signal: ref1(n)=U2cos(w S n+msin(wn)). The reference phase signal is an FM signal with a center frequency of 9960Hz. According to the VOR envelope signal expression, its carrier frequency ranges from 9480Hz to 10440Hz. Therefore, the lower stopband cutoff frequency of BPF2 is not less than 3400Hz (the highest frequency of the voice signal spectrum), the passband start frequency is not higher than 9480Hz, and the passband cutoff frequency is not less than 10440Hz.

[0070] Step 4: Perform FM demodulation on the first reference phase signal to obtain a second reference phase signal. The FM demodulation steps are as follows:

[0071] (1) The modulated signal is down-converted to zero frequency using quadrature demodulation. The numerically controlled oscillator (NCO) outputs the same phase branch. I [n] = sin(w S n), and output s to the orthogonal branch Q [n] = cos(w S n).

[0072] (2) The I and Q channels are respectively filtered through the low-pass filter LPF1 to remove the frequency-doubled components during orthogonal mixing. The passband cutoff frequency of LPF1 is not less than 480Hz, and the stopband start frequency is not higher than 19440Hz. After LPF1, the I channel baseband output Q-channel baseband output

[0073] (3) Frequency discrimination of I and Q baseband signals:

[0074] A. Divide the two signals and get

[0075] B. Take the inverse tangent of x1(n) and we get x2(n)=arctan(x1(n))=msin(wn);

[0076] C. To take the derivative of x2(n), the digital processing method can directly calculate the difference between the two sampling points before and after, that is, ref3(n) = x2(n) - x2(n-1), and then normalize it:

[0077] if Then Ref3(n) <Ref3(n)+π;

[0078] if Then ref3(n) <ref3(n)-π。

[0079] At this point, the phase detection is completed, and ref3(n) can also be expressed as ref3(n)=mcos(wn).

[0080] Step 5: The VOR envelope signal passes through the bandpass filter BPF3 to obtain the Morse code audio and air-to-ground communication voice. The passband start frequency of BPF3 is not higher than 300Hz, the cutoff frequency is not lower than 3400Hz, the lower stopband cutoff frequency is not lower than 30Hz, and the upper stopband start frequency is not higher than 9480Hz.

[0081] Step 6: Normalize the amplitude of the variable phase signal and the second reference phase signal respectively, and then perform Ref-Var phase discrimination to obtain the phase difference between the two signals, which can be converted into the azimuth of the aircraft.

[0082] (1) The peak value of the sinusoidal signal is the effective value times, so the amplitude normalization is performed according to the following formula:

[0083]

[0084]

[0085] is the normalized value of the variable phase signal amplitude, is the normalized value of the second reference phase signal amplitude. The cumulative time window is an integer multiple of the 30Hz modulation wave period. K = k × f B / 30Hz, k is a positive integer.

[0086] (2) Multiplier output The low-pass filter LPF2 needs to filter out the double-frequency components and retain only the DC components, so the starting frequency of its stop band is not higher than 30 Hz.

[0087] (3) Multiply the output of LPF2 by 2 and calculate its arc cosine function to obtain the phase difference θ between the variable phase signal and the reference phase signal.

[0088] Embodiment 2: A digital baseband processing device for a VHF omni-directional beacon signal, the device is used to implement the digital baseband processing method for a VHF omni-directional beacon signal as described in Embodiment 1, Figure 4 As shown, it includes an AM demodulation unit, a first filtering unit, a second filtering unit, a third filtering unit, an FM demodulation unit and a phase detection processing unit.

[0089] Among them, the AM demodulation unit is used to perform AM demodulation on the VOR baseband signal to obtain the VOR envelope signal; the first filtering unit is used to process the VOR envelope signal through the bandpass filter BPF1 to obtain the variable phase signal; the second filtering unit is used to process the VOR envelope signal through the bandpass filter BPF2 to obtain the first reference phase signal; the third filtering unit is used to process the VOR envelope signal through the bandpass filter BPF3 to obtain Morse code audio and air-to-ground communication voice; the FM demodulation unit is used to perform FM demodulation on the first reference phase signal to obtain the second reference phase signal; the phase detection processing unit is used to perform Ref-Var phase detection on the variable phase signal and the second reference phase signal after amplitude normalization, obtain the phase difference between the two signals, and convert it into the azimuth of the aircraft.

[0090] The present invention also describes an airborne VOR receiver, comprising at least one digital baseband processing device for the VOR signal described above.

[0091] Working principle: The present invention adopts digital design, reduces the use of analog devices, increases system integration, makes the equipment more compact, lightweight and low-power, can obtain higher angle measurement accuracy, and better meet the navigation performance required for civil aviation regional navigation.

[0092] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0093] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0094] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0095] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0096] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A digital baseband processing method for a very high frequency omnidirectional beacon signal, characterized in that: The following steps are involved: Perform AM demodulation on the VOR baseband signal to obtain the VOR envelope signal; The VOR envelope signal is processed by the bandpass filter BPF1 to obtain a variable phase signal; The VOR envelope signal is processed by a bandpass filter BPF2 to obtain a first reference phase signal; The VOR envelope signal is processed by the bandpass filter BPF3 to obtain the Morse code audio and air-to-ground communication voice; Performing FM demodulation on the first reference phase signal to obtain a second reference phase signal; The variable phase signal and the second reference phase signal are amplitude normalized and then Ref-Var phase detection is performed to obtain the phase difference between the two signals and convert it into the azimuth of the aircraft.

2. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 1, characterized in that: The bandpass filter BPF1 allows the 30 Hz frequency to pass, filters out the DC component, and the upper stopband starting frequency is not higher than 300 Hz; The lower stopband cutoff frequency of the bandpass filter BPF2 is not less than 3400 Hz, the passband start frequency is not higher than 9480 Hz, and the passband cutoff frequency is not less than 10440 Hz; Also, the passband start frequency of BPF3 is not higher than 300 Hz, the cutoff frequency is not lower than 3400 Hz, the lower stopband cutoff frequency is not lower than 30 Hz, and the upper stopband start frequency is not higher than 9480 Hz.

3. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 1, characterized in that: The process of performing FM demodulation on the first reference phase signal is specifically as follows: The modulated signal is down-converted to zero frequency by orthogonal demodulation, and I and Q signals are output; The I and Q signals are passed through the low-pass filter LPF1 respectively to filter out the frequency-doubled components during orthogonal mixing; The I and Q baseband signals are subjected to frequency discrimination after filtering out the frequency multiplication components during orthogonal mixing to obtain a second reference phase signal.

4. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 3, characterized in that: The process of down-converting the modulated signal to zero frequency by using orthogonal demodulation is specifically as follows: Output to the same phase branch through the digital controlled oscillator: I [n] = sin(w S n); And, through the digitally controlled oscillator to the orthogonal branch output: s Q [n] = cos(w S n); Among them, s I [n] is the I-channel signal; s Q [n] is the Q-path signal; w S is the angular frequency of 9960 Hz; n is the time interval relative to the peak moment of the reference phase.

5. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 3, characterized in that: The passband cutoff frequency of the low-pass filter LPF1 is not less than 480 Hz, and the stopband starting frequency is not higher than 19440 Hz; After LPF1: I-channel baseband output: Q-channel baseband output: Among them, Ref 2I (n) is the baseband signal of I; Ref 2Q (n) is the Q-band signal; U2 is the amplitude of the reference phase signal; m is the frequency modulation index; w is the 30 Hz angular frequency; and n is the time interval relative to the reference phase peak moment.

6. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 3, characterized in that: The process of performing frequency discrimination on the I and Q baseband signals after filtering out the frequency multiplication components during orthogonal mixing is specifically as follows: Divide the I and Q baseband signals to obtain a first signal; Taking the arc tangent of the first signal, the second signal is obtained; The second signal is derived, the difference between the two preceding and following sampling points is calculated by a digital processing method, and then the second reference phase signal is obtained after normalization.

7. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 1, characterized in that: The expression for normalizing the amplitude of the variable phase signal is specifically: in, is the normalized value of the variable phase signal amplitude; Var(n) is the variable phase signal; K is the accumulation time window; The expression for normalizing the amplitude of the second reference phase signal is specifically: in, is the normalized value of the second reference phase signal amplitude; Ref3(n) is the second reference phase signal.

8. The digital baseband processing method of a VHF omnidirectional beacon signal according to claim 1, characterized in that: The Ref-Var phase discrimination process is specifically as follows: Through the multiplier output The double frequency component is filtered out by the low-pass filter LPF2, and only the DC component is retained. The stop band starting frequency is not higher than 30Hz; w is the 30Hz angular frequency; n is the time interval relative to the reference phase peak moment; The output of the low-pass filter LPF2 is multiplied by 2 and then an inverse cosine function is obtained to obtain a phase difference θ between the variable phase signal and the second reference phase signal.

9. A digital baseband processing device for very high frequency omnidirectional beacon signals, characterized in that: include: An AM demodulation unit is used to perform AM demodulation on the VOR baseband signal to obtain a VOR envelope signal; A first filtering unit, used for processing the VOR envelope signal through a bandpass filter BPF1 to obtain a variable phase signal; A second filtering unit, used for processing the VOR envelope signal through a bandpass filter BPF2 to obtain a first reference phase signal; The third filtering unit is used to process the VOR envelope signal through the bandpass filter BPF3 to obtain the Morse code audio and air-to-ground communication voice; An FM demodulation unit, configured to perform FM demodulation on the first reference phase signal to obtain a second reference phase signal; The phase detection processing unit is used to perform Ref-Var phase detection on the variable phase signal and the second reference phase signal after normalizing their amplitudes, obtain the phase difference between the two signals, and convert it into the azimuth of the aircraft.

10. An airborne VOR receiver, characterized in that: The device comprises at least one digital baseband processing device for a VHF omni-directional beacon signal as claimed in claim 9.

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