Microstrip Directional Coupler With Compensation Circuits For Wideband Operation
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Solution Overview
Problem
Existing couplers face limitations in achieving a flat coupling factor and high directivity over a wide frequency range, particularly in low-frequency bands, where they become bulky and inefficient, and are typically restricted to low operating frequency ranges.
Innovation Solution
A microstrip directional coupler combined with compensation circuits made of passive components, including a low-pass filter and attenuation regulator circuits, is used to maintain a small size and achieve a stable coupling factor and improved directivity across an ultra-wide frequency range from HF to UHF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional microstrip or stripline directional coupler structures are used at low operating bands, then the coupling factor and directivity can be achieved, but the size of the coupler becomes very large
Solution Approach 1:
The coupler is divided into multiple sections along the main transmission line, with each section having different characteristic impedances and lengths. This segmentation allows the coupler to achieve wideband operation with reduced overall size by optimizing each section's contribution to the coupling and directivity characteristics across different frequency ranges.
Solution Approach 2:
The invention employs variable characteristic impedances and lengths for different sections of the coupler, along with adjustable coupling coefficients. By changing these parameters across different frequency bands, the coupler maintains compact dimensions while achieving consistent performance from HF to UHF ranges.
2Adaptability or versatility
If waveguide directional coupler structures are used, then the coupling factor can be achieved, but the bandwidth is narrower and the structure is bulky in size
Solution Approach 1:
The invention replaces traditional waveguide mechanical structures with microstrip transmission lines that incorporate lumped electronic components (capacitors and inductors). This substitution enables planar integration, significantly reducing the coupler size while achieving ultra-wideband operation through the synergistic combination of distributed and lumped elements.
Solution Approach 2:
The coupler combines microstrip transmission line structures with lumped passive components (capacitors and inductors) to create a composite system. This hybrid approach leverages the advantages of both distributed and lumped elements to achieve wide bandwidth with compact dimensions, overcoming the limitations of pure waveguide or microstrip designs.
3Adaptability or versatility
If passive components are used in the coupler, then the coupling factor can be calculated and achieved, but the coupler is only applicable for low operating frequency range
Solution Approach 1:
The invention incorporates feedback mechanisms through the careful design of the compensation circuit topology, where the interaction between series and shunt passive components creates frequency-dependent impedance transformations. This feedback effect compensates for frequency variations, maintaining stable coupling factor across the ultra-wideband range from HF to UHF.
Solution Approach 2:
The invention uses frequency-dependent parameter variations in the passive components, where the reactance of capacitors and inductors changes with frequency to compensate for the natural frequency response variations of the transmission lines. This parameter modulation maintains consistent coupling performance across different operating frequencies.
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 enables a coupler with a coupling factor of 56 dB, insertion loss of 70 dB, and directivity greater than 15 dB, maintaining performance across 20-500 MHz with reduced size, and ensures well-matched impedance and reduced effective electrical length, suitable for high power transmitters in various frequency bands.
Implementation Method 1
Two secondary transmission lines with a characteristic impedance of 50Ω and a length L1 are electrically coupled with the main transmission line 5 at the opposite terminals
Implementation Method 2
compensation circuit 7 is composed of a low pass filter 10 and two attenuation regulator circuits 14 that are installed in parallel
Implementation Method 3
attenuation regulator circuits 14 including resistor 15, inductor 16, capacitor 17 and ground terminal 18 compensates the coupling factor between the input port 1 and the coupled port 3
Data Source
AI summary
The invention proposes a four-port coupler using micro-strip line in combination with ultra-wide-band compensation circuits. It can be applied for communication systems or information machine systems. The main feature of the invention is the structure and the distribution of the components in the compensation circuit to reduce the size of the coupler. The proposed coupler includes: microstrip directional coupler and compensation circuits, in which the microstrip directional coupler consists of one main line and two secondary transmission lines; the main transmission line has two ports: input and output ports; each secondary is connected to a load and a compensation circuit. The compensation circuit is composed of a low-pass filter and two parallel attenuation regulator circuits.