Broadband Power Limiter Using Impedance Transformers
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Solution Overview
Problem
Current broadband limiter products for microwave communication systems are inadequate in handling high-power CW signals, with limitations in frequency range, insertion loss, recovery time, and leakage output power, failing to protect sensitive MMIC circuits effectively.
Innovation Solution
A broadband power limiter design incorporating shunt diodes and impedance transformers, specifically a step-down transformer at the input and a step-up transformer at the output, providing improved frequency characteristics and power capacity, suitable for integration with GaAs low-noise amplifier circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional broadband limiter products are used, then frequency coverage is achieved, but power handling capability is limited to 1-3 watts and insertion loss is high at 2 dB
Solution Approach 1:
The limiter is divided into multiple functional sections: input matching network, shunt diode limiter core, and output matching network. Each section is optimized independently to handle high power while maintaining low insertion loss, with the shunt diodes providing power limiting and the matching networks providing impedance transformation and broadband performance
Solution Approach 2:
Different parts of the circuit have different impedance values optimized for their specific functions. The input and output matching networks use specific impedance transformations to match the 50-ohm system while allowing the shunt diodes to operate at optimal impedance points for high power handling and low insertion loss
2Speed
If conventional limiter designs are used, then simple structure is maintained, but recovery time is long at 1000 ns
Solution Approach 1:
The biasing network and DC blocking capacitors are removed from the circuit. The shunt diodes operate in a passive manner without requiring external bias voltages, which eliminates the slow discharge paths through biasing resistors and allows the diodes to recover almost instantly after limiting action
Solution Approach 2:
The shunt diodes automatically switch between conducting and non-conducting states based on the instantaneous signal voltage alone, without requiring external control or biasing circuits. This self-regulating behavior enables extremely fast recovery time as the diodes respond directly to the signal envelope
3Object-affected harmful factors
If conventional limiter products are used, then basic protection function is provided, but leakage output power is high at 20 dBm
Solution Approach 1:
The shunt diodes are selected and biased to operate at specific impedance points that optimize the trade-off between leakage reduction and power handling. The impedance transformation networks are designed to present optimal load conditions to the diodes, maximizing their ability to clamp leakage while maintaining low insertion loss
4Power
If broadband performance is prioritized, then frequency coverage 2-20 GHz is achieved, but power capacity is limited
Solution Approach 1:
The power limiting function and broadband matching function are merged into a unified circuit architecture. The shunt diodes provide power limiting while the integrated matching networks simultaneously provide broadband impedance transformation, allowing both high power capacity and 2-20 GHz coverage without requiring separate functional blocks
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 the limiter to handle greater than 10 watts of CW power with reduced insertion loss and rapid recovery time, ensuring effective protection of MMIC circuits across a 2-20 GHz frequency band while maintaining low leakage output power.
Implementation Method 1
the broadband power limiter of the invention is based on one or more shunt diodes connected between a signal line to be protected and ground
Implementation Method 2
a first impedance transformer connected between the shunt diode circuit and the input terminal; and a second impedance transformer connected between the shunt diode circuit and the output terminal
Implementation Method 3
each conductor in the array is electromagnetically coupled to each other conductor in the array by at least one of side-coupling and broadside coupling
Data Source
AI summary
The invention provides a novel broadband power limiter having improved frequency characteristics and power capacity, suitable for use with GaAs low-noise amplifier circuits. The power limiter includes a shunt diode circuit and two impedance transformers. The first transformer is a step-down impedance transformer connected between the shunt diode circuit and the input to the limiter, and the second transformer is a step-up impedance transformer connected between the shunt diode circuit and the output of the limiter. The invention further provides a method for limiting the power of an input signal, comprising the steps of: transforming the input signal from the input impedance to an intermediate impedance; shunting a portion of the input signal to ground; and transforming a remaining portion of the input signal from the intermediate impedance to an output impedance. The invention further provides a novel impedance transformer suitable for use in the broadband power limiter and a method for providing such an impedance transformer.