Antenna Array Reactance Cancellation Using Non-Foster Circuits
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Solution Overview
Problem
Superdirective antenna arrays face limitations due to high Q values, leading to efficiency and bandwidth constraints, with existing solutions either failing to reduce antenna Q or resulting in narrowband or low-efficiency outcomes.
Innovation Solution
The use of non-Foster circuits (NFCs) to cancel self and mutual reactance in antenna arrays, employing active devices that are not bound by Foster's reactance theorem, thereby reducing the antenna quality factor and improving RF efficiency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If superdirective antenna arrays are designed to achieve high directivity, then beam directionality is improved, but antenna Q increases leading to reduced efficiency and bandwidth
Solution Approach 1:
The patent applies parameter changes by transforming the reactive parameters of the antenna array through non-Foster circuits. Specifically, negative capacitance and negative inductance values are introduced to cancel the positive reactance components, thereby changing the impedance parameters to achieve both high directivity and reduced Q factor simultaneously
Solution Approach 2:
Non-Foster circuits serve as intermediary components between the antenna elements and the feed network. These circuits mediate the impedance transformation by introducing negative reactance that cancels the mutual coupling effects, enabling the array to achieve superdirective patterns without the usual Q factor penalty
2Volume of moving object
If antenna elements are placed in close proximity to achieve electrically small array, then array size is reduced, but mutual coupling increases causing difficulty in feed network design
Solution Approach 1:
Non-Foster circuits are introduced as intermediary components between closely spaced antenna elements. These circuits actively compensate for mutual coupling effects by providing negative reactance that cancels the coupling-induced impedance changes, thereby simplifying feed network design despite the tight element spacing
Solution Approach 2:
The patent changes the impedance parameters of the antenna elements by applying negative capacitance and inductance through non-Foster circuits. This parameter transformation counteracts the mutual coupling effects that arise from close element spacing, enabling electrically small array design without excessive feed network complexity
3Adaptability or versatility
If passive circuits are used to cancel reactance, then bandwidth is limited by Foster's reactance theorem, but active non-Foster circuits overcome this limitation
Solution Approach 1:
The patent inverts the conventional approach by using active non-Foster circuits that provide negative reactance instead of passive circuits with positive reactance. This inversion allows the system to overcome Foster's reactance theorem limitations and achieve broadband operation, as the negative reactance can be made frequency-independent over a wide range
Solution Approach 2:
The patent replaces passive mechanical/circuit elements with active electronic components (transistors, operational amplifiers) that can generate negative impedance. This substitution enables dynamic control of reactance cancellation and achieves broadband performance that is impossible with passive components alone
Data Source
AI summary
An antenna array containing two or more radiating elements, with nearest neighbor radiating elements connected together with a non-Foster circuit at terminals of the radiating elements such that mutual reactance of the elements is reduced over a wider bandwidth than which would be obtained if the non-Foster circuits were omitted.