Microwave Transponder Modulation Without Mixers or Harmonic Filters
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Solution Overview
Problem
Existing transponders for target localization, particularly those using microwave mixers for amplitude or phase modulation, are complex, costly, and require bulky filters to eliminate spurious radiation and harmonics, making them inefficient and expensive to implement.
Innovation Solution
A device for modulating a microwave signal using a circuit with a phase shift circuit, variable gain amplifiers, and a switch controlled by a rectified sinusoidal signal to route phase-shifted channels, eliminating the need for filters by producing a carrier-free modulated signal with no harmonic lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-linear systems (mixers) are used for amplitude or phase modulation, then modulation is achieved, but harmonic lines and spurious radiation are generated requiring bulky filters
Solution Approach 1:
The patent changes the modulation approach from non-linear amplitude/phase modulation to linear frequency modulation. By varying the frequency of the microwave signal linearly with the modulating signal, the system achieves modulation without generating harmonic lines, eliminating the need for bulky filters while maintaining manufacturing simplicity
Solution Approach 2:
The patent replaces the mechanical/non-linear mixer-based modulation system with a linear frequency modulation system. This substitution eliminates the harmful non-linear effects that generate harmonics, removing the requirement for complex filtering mechanisms while preserving the essential modulation function
2Ease of manufacture
If mixers and filters are used for modulation, then signal modulation is achieved, but the system becomes complex and expensive
Solution Approach 1:
The patent fundamentally changes the modulation parameter from amplitude or phase (requiring mixers) to frequency (achievable with simpler components). This parameter change enables modulation using only a voltage-controlled oscillator and frequency discriminator, eliminating mixers and filters, thereby reducing system complexity and cost while maintaining manufacturing ease
3Ease of manufacture
If non-linear modulation systems are used, then modulation is achieved, but calibration is required adding to implementation complexity
Solution Approach 1:
The patent replaces non-linear modulation mechanisms with linear frequency modulation. The linear relationship between the modulating signal and the output frequency eliminates the need for calibration, as the system responds predictably and proportionally to input signals without requiring adjustment or characterization of non-linear characteristics
4Ease of manufacture
If amplitude modulation with mixers is used, then modulation is achieved, but fundamental frequency and harmonics remain causing spurious radiation
Solution Approach 1:
The patent changes the modulation domain from amplitude to frequency. Frequency modulation inherently suppresses spurious radiation because the carrier frequency is continuously varied in a controlled manner rather than being chopped or modulated in amplitude, eliminating the generation of unwanted harmonic frequencies while keeping the system simple
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a low-cost, high-performance transponder that simplifies signal modulation, reduces unnecessary backscattered energy, and eliminates the need for complex filters, thereby enhancing efficiency and reducing size and cost.
Implementation Method 1
a circuit for generating a rectified sinusoidal signal
Implementation Method 2
a phase shift circuit capable of receiving said microwave signal as input comprising: o a first channel applying a given phase shift; o a second channel applying said given phase shift increased by π
Implementation Method 3
a variable gain amplifier whose gain is controlled by said rectified sinusoidal signal
Implementation Method 4
a switch controlled by said rectified sinusoidal signal, capable of routing alternately said first channel and said second channel at the input of said amplifier
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
The modulation consists - in amplifying (1) said microwave signal (21) phase shifted by a given angle according to a first sinusoidal signal (110), in order to obtain a first amplified signal and; - in amplifying (1) said microwave signal (22) phase shifted by said given angle increased by π according to a second sinusoidal signal (110, 115) phase shifted by π with respect to said first signal, in order to obtain a second amplified signal phase shifted by π with respect to said first amplified signal; the modulated microwave signal being the sum of said first amplified signal and said second amplified signal.