Planar Dual-Band MIMO Antenna With Independent Varactor Tuning
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Solution Overview
Problem
Existing 5G sub-6 GHz antenna designs face challenges in achieving compact size, wide-band tuning capabilities, and independent/concurrent frequency reconfigurability while supporting multiple bands, often resulting in limited tuning and larger board dimensions.
Innovation Solution
A dual-band MIMO antenna apparatus with concentric annular slot elements and varactor diodes, allowing independent and concurrent tuning across two frequency bands, utilizing a microstrip feed-line and biasing circuitry with RF chokes and current-limiting resistors, enabling compact size and efficient frequency adjustment between 1.7 GHz and 3.8 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If slot-based antenna designs are used to achieve compact size and wide-band tuning capabilities, then tuning capabilities and compactness are improved, but board dimensions and device complexity increase
Solution Approach 1:
The antenna element is segmented into two concentric annular slots (inner and outer slots) that can be independently tuned. Each slot has its own varactor diode, allowing separate frequency control. This segmentation enables dual-band operation and wide frequency coverage while maintaining a compact planar structure on the substrate.
Solution Approach 2:
The antenna incorporates varactor diodes that can dynamically change their capacitance values based on applied voltage, enabling real-time frequency tuning. The reactance of each annular slot can be independently adjusted by controlling the bias voltage to its varactor diode, allowing the antenna to adapt to different frequency bands (e.g., 1.7-2.4 GHz and 2.4-3.8 GHz) without physical reconfiguration.
2Adaptability or versatility
If multiple antenna elements are integrated for MIMO operation within given space, then MIMO capability is improved, but space utilization and antenna separation become constrained
Solution Approach 1:
The antenna employs a nested concentric annular slot configuration where an inner annular slot is positioned within a larger outer annular slot. Both slots share the same center point and are separated by a ground plane. This nested arrangement allows two antenna elements to be integrated in a compact area, enabling MIMO operation while minimizing the overall board footprint.
Solution Approach 2:
The antenna elements are arranged in a coplanar configuration on the substrate, utilizing the two-dimensional plane efficiently. The concentric annular slots are positioned at different radial distances from the center, creating spatial separation in the radial dimension while maintaining the same angular coverage. This dimensional arrangement enables MIMO operation with adequate element separation within a compact circular footprint.
3Adaptability or versatility
If frequency reconfigurability is implemented with independent tuning for each element, then frequency agility is improved, but circuit complexity and manufacturing difficulty increase
Solution Approach 1:
The antenna design uses identical concentric annular slot structures for both antenna elements, with each element having the same varactor diode-based tuning mechanism. This universal design approach simplifies manufacturing by using repeated patterns and standard components. The same substrate, slot geometry, and biasing circuitry are used for both elements, enabling independent frequency tuning while maintaining manufacturing simplicity and consistency.
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 provides a compact, efficient dual-band antenna with improved radiation patterns and impedance matching, achieving peak gains of 4.3 dBi at 3.6 GHz and 2.98 dBi at 2.52 GHz, with an envelope correlation coefficient of less than 0.5, suitable for 4G and 5G networks.
Implementation Method 1
the varactor diodes change in capacitance due to a reverse bias voltage
Implementation Method 2
The locations of the varactor diodes can be selected to provide an impedance match of the antenna to an electrical load of the microstrip feed-lines
Implementation Method 3
The antenna elements can be excited using microstrip feed-lines placed on the substrate
Implementation Method 4
radiation patterns of the antenna elements are configured to support an envelope correlation coefficient of less than 0.5
Data Source
AI summary
A reconfigurable, dual-band, MIMO antenna apparatus, a planar MIMO antenna system utilizing the antenna apparatus, and a method of transmitting and receiving a signal by the antenna apparatus are provided. The apparatus includes a dielectric planar substrate, a first element, a second element, two varactor diodes per element, and a microstrip feed-line. The first element and the second element each have slotted concentric annular rings. The second element is separated on the dielectric planar substrate from the first element, but is coplanar on the dielectric planar substrate with the first element. The two varactor diodes are placed in series with biasing circuitry, the biasing circuitry including RF chokes and current-limiting resistors. The microstrip feed-line feeds both antenna elements. The dual-band antenna elements can each be independently and concurrently tunable to two signal frequencies bands.