[Paper Review] On the Feasibility of Multi-Mode Antennas in UWB and IoT Applications below 10 GHz

Nils L. Johannsen, Nikolai Peitzmeier+2 more|arXiv (Cornell University)|Dec 15, 2019

Antenna Design and Analysis14 references33 citations

TL;DR

This paper proposes multi-mode antennas with up to eight orthogonal ports per radiator to enable high data rates (100+ Gb/s) and robust IoT connectivity below 10 GHz. By leveraging characteristic mode theory and symmetry, the antennas support both multi-stream beamforming for UWB and single-element beamforming for IoT, achieving up to 6 dBi gain via mode selection and up to 2 dB additional gain through mode combination, significantly improving link margin and sum-rate performance with minimal hardware overhead.

ABSTRACT

While on the one hand 5G and B5G networks are challenged by ultra-high data rates in wideband applications like 100+ Gbps wireless Internet access, on the other hand they are expected to support reliable low-latency Internet of Things (IoT) applications with ultra-high connectivity. These conflicting challenges are addressed in a system proposal dealing with both extremes. In contrast to most recent publications, focus is on the frequency domain below 10~GHz. Towards this goal, multi-mode antenna technology is used and different realizations, offering up to eight uncorrelated ports per radiator element, are studied. Possible baseband architectures tailored to multi-mode antennas are discussed, enabling different options regarding precoding and beamforming.

Motivation & Objective

• Address the conflicting demands of ultra-high data rates and massive low-data-rate IoT connectivity in sub-10 GHz bands.
• Develop a systematic design approach for multi-mode antennas using symmetry and characteristic mode theory to achieve high port orthogonality.
• Enable flexible beamforming strategies—both multi-stream and single-element beamforming—using multi-mode antennas at base station and mobile terminals.
• Evaluate the performance gains of single-element beamforming and multi-mode array beamforming in realistic UWB and IoT scenarios.
• Assess sum-rate performance as a function of distance and number of ports, with practical hardware cost considerations.

Proposed method

• Design multi-mode antennas using characteristic mode analysis on symmetric planar radiators (e.g., hexagonal shapes) to identify orthogonal radiation modes.
• Implement excitation via inductive or capacitive coupling at current maxima/minima to excite specific characteristic modes independently.
• Model the multi-mode antenna as an overlay of uniform planar arrays, each corresponding to one excitable mode.
• Apply hybrid beamforming and digital beamforming architectures at the base station, with single-element beamforming at the mobile terminal using mode selection or combination.
• Use the WINNER II A1 NLOS channel model with ZF precoding and DVB-S2 coding to simulate sum-rate performance over distance.
• Evaluate port orthogonality via a Kronecker channel model, tolerating correlation down to -9 dB after accounting for transmit and receive side effects.

Experimental results

Research questions

• RQ1 Can multi-mode antennas with up to eight orthogonal ports be designed efficiently using symmetry and characteristic mode theory in sub-10 GHz bands?
• RQ2 To what extent can single-element beamforming using multi-mode antennas improve link margin and reliability in IoT applications?
• RQ3 How does the number of ports per element (4, 6, 8) affect the achievable sum-rate and communication range in UWB and IoT scenarios?
• RQ4 What is the performance gain of mode combination over mode selection in single-element beamforming?
• RQ5 How robust is the system to imperfect port orthogonality, and what level of correlation is tolerable for practical implementation?

Key findings

• Single-element beamforming via mode selection achieves a peak gain of approximately 6 dBi across a wide angular range, significantly enhancing link margin for IoT devices.
• Combining multiple modes through constructive interference provides an additional 2 dB gain over single-mode selection, improving performance with digital beamforming.
• The sum-rate performance increases with the number of ports per element, with 8-port configurations enabling higher data rates and extended communication range compared to 4- and 6-port designs.
• The system remains robust to port correlation, tolerating a correlation power of up to -9 dB (after accounting for both transmit and receive sides), supporting practical implementations.
• A codebook-based mode selection approach achieves near-optimal performance with minimal hardware complexity, using only switches to select the best mode.
• The proposed design workflow based on symmetry and characteristic mode analysis enables systematic, scalable design of multi-mode antennas with high port orthogonality and minimal structural modification.