Low-Frequency Signal Generation in Space Based on High-Frequency Electric-Antenna Array and Doppler Effect | BIAI Journals & Magazine | IEEE Xplore

 Block diagram of 64-element long-array experiment based on 8-channel DAC and photographs of equipment and waveform of RE signals

Chinese Scientists Break Ground in Low-Frequency Signal Generation Using High-Frequency Antenna Arrays

Chinese researchers have successfully demonstrated a novel technique to generate low-frequency electromagnetic signals using high-frequency electric antenna arrays, potentially solving a long-standing challenge in communications and sensing technologies.

The research team, led by LI Daojing from the National Key Laboratory of Microwave Imaging at the Aerospace Information Research Institute of the Chinese Academy of Sciences, published their findings in the February 2025 issue of the Journal of Systems Engineering and Electronics.

Low-frequency electromagnetic waves are valuable for target detection and geological exploration due to their ability to penetrate materials. However, traditional methods of generating these signals require impractically large antennas, as conventional electric antennas must be approximately one-quarter wavelength of the signal they emit.

The new method leverages the Doppler effect and specialized antenna arrays to generate low-frequency signals using smaller, high-frequency antennas. By arranging multiple antenna elements in staggered arrays and precisely controlling the timing and phase of signals, the researchers were able to generate signals at frequencies far below what the individual antenna elements would typically produce.

In their experiments, the team successfully generated signals at 121 MHz, 40 MHz, and even as low as 10 kHz using 156 MHz radiating element signals—effectively demonstrating frequency conversion across a wide range.

"This holds significant implications for research on generating low-frequency signals with small-sized antennas," the researchers noted in their paper.

SIDEBAR: Why Lower Frequencies Matter - Beyond The Limits of Conventional Communications

Superior Penetration Capabilities

Lower frequency electromagnetic waves offer exceptional penetration capabilities that higher frequencies simply cannot match. This makes them invaluable for numerous specialized applications:

Foliage Penetration: Low-frequency signals can penetrate dense vegetation where higher frequencies are blocked. This capability is critical for military communications, search and rescue operations in forested areas, and remote sensing applications that need to "see through" tree canopies.

Underground and Underwater Communication: VLF (Very Low Frequency) and ELF (Extremely Low Frequency) waves can penetrate seawater to depths of 10-40 meters, enabling submarine communications without requiring vessels to surface. Similarly, these frequencies can penetrate soil and rock, making them useful for underground mining communications and geological surveys.

Building Penetration: Lower frequencies more easily pass through concrete, steel, and other building materials, improving indoor reception for emergency services and communication systems.

Extended Range and Reliability

Ground Wave Propagation: Low-frequency signals can follow the curvature of the Earth through ground wave propagation, enabling over-the-horizon communications without relying on satellites or repeaters.

Ionospheric Waveguide: VLF signals can travel in a zig-zag path between the Earth's surface and the ionosphere, allowing for remarkably stable global communications with signal attenuation as low as 2-3 dB per 1,000 km.

Resistance to Atmospheric Effects: Lower frequencies are less affected by rain, fog, and other atmospheric conditions that can severely degrade higher frequency signals.

Specialized Applications

Geological Exploration: Low-frequency electromagnetic methods are vital for detecting mineral deposits, groundwater, and geological structures that cannot be identified through surface observations alone.

Navigation Systems: Navigation aids like LORAN (Long Range Navigation) have historically used low frequencies because of their reliability and long range.

Natural Disaster Resilience: When infrastructure fails during natural disasters, low-frequency communication systems often remain operational due to their extended range and reduced dependence on dense networks of towers.

The emerging antenna miniaturization technologies featured in the main article could revolutionize these applications by making low-frequency communications more portable and accessible than ever before.

Related Research Fields

The Chinese team's work adds to a growing body of research on miniaturized low-frequency signal generation. Several parallel approaches have emerged in recent years:

Magnetoelectric (ME) Antennas have become a hot topic in VLF antenna miniaturization. These devices combine magnetostrictive and piezoelectric materials to convert mechanical resonance into electromagnetic signals. Recent research shows ME antennas can be reduced to "one-ten-thousandth of the size of conventional electric antennas," though they still face challenges with bandwidth and radiation intensity.

Phased Array Technologies have also advanced significantly, with researchers developing sophisticated electronically scanned arrays that can generate and direct signals with exceptional precision. These systems are increasingly important for 5G communications and radar applications.

Metamaterial Antennas utilize engineered materials with novel microscopic structures that enhance performance of miniaturized antenna systems. These materials can make antennas behave as if they were much larger than their actual size.

MEMS-Based Approaches use microelectromechanical systems to create tiny resonant structures that can generate electromagnetic signals, offering another path to extreme miniaturization.

The innovation described in the paper could enable more portable and mobile platforms for applications previously limited by antenna size requirements, potentially advancing fields such as underground exploration, long-range communications, undersea communications, and target detection.

Here's related research on low-frequency signal generation using antenna arrays that isn't cited in the paper.

Electromagnetic/Antenna Technologies

1. Neural Methods for Antenna Array Signal Processing

   • Reference: "Neural methods for antenna array signal processing: a review," ScienceDirect
   • Link: https://www.sciencedirect.com/science/article/abs/pii/S0165168401001852
   • Explores AI-based approaches for antenna array signal processing that could potentially enhance the efficiency of array-based signal generation systems.

2. Small, Low-Frequency Antenna Design Survey

   • Reference: "A Survey of Small, Low-Frequency Antennas: Recent designs, practical challenges, and research directions," IEEE Xplore
   • Link: https://ieeexplore.ieee.org/document/9655442/
   • Comprehensive review of techniques for miniaturizing antennas for low-frequency applications.

3. Metamaterial Antennas

   • Reference: "Metamaterial antenna," Wikipedia
   • Link: https://en.wikipedia.org/wiki/Metamaterial_antenna
   • Describes engineered materials with novel structures to enhance antenna performance and overcome size limitations.

4. Advanced Phased Array Technologies

   • Reference: "Phased array - Wikipedia" and "Phased Array Antennas: Principles, Advantages, and Types"
   • Links: https://en.wikipedia.org/wiki/Phased_array and https://resources.system-analysis.cadence.com/blog/msa2021phased-array-antennas-principles-advantages-and-types
   • Details on electronically scanned arrays that could complement the Doppler-based approach.

5. Thin-film, High-frequency Antenna Array

   • Reference: "Thin-film, high-frequency antenna array offers new flexibility for wireless communications," ScienceDaily
   • Link: https://www.sciencedaily.com/releases/2021/11/211103105022.htm
   • Novel materials-based approach to creating flexible antenna arrays.

Magnetoelectric and Mechanical Antenna Technologies

6. Magnetoelectric Antenna Arrays

   • Reference: "Array strategy enhances low-frequency radiation intensity and low-frequency magnetic field sensing SNR of magnetoelectric antenna," AIP Advances
   • Link: https://pubs.aip.org/aip/adv/article/14/7/075109/3302498/Array-strategy-enhances-low-frequency-radiation
   • Directly relevant research on how array strategies can improve magnetoelectric antenna performance.

7. Very Low Frequency Magnetoelectric Antennas

   • Reference: "A very low frequency (VLF) antenna based on clamped bending-mode structure magnetoelectric laminates," PubMed
   • Link: https://pubmed.ncbi.nlm.nih.gov/35878598/
   • Novel antenna design using magnetostrictive-piezoelectric combinations to achieve VLF generation.

8. MEMS Magnetoelectric Antenna

   • Reference: "A Low-Frequency MEMS Magnetoelectric Antenna Based on Mechanical Resonance," PubMed
   • Link: https://pubmed.ncbi.nlm.nih.gov/35744478/
   • Microelectromechanical systems approach to creating miniaturized low-frequency antennas.

9. Mechanical Transmitters Based on Magnetoelectric Heterostructures

   • Reference: "A Low Frequency Mechanical Transmitter Based on Magnetoelectric Heterostructures Operated at Their Resonance Frequency," PMC
   • Link: https://pmc.ncbi.nlm.nih.gov/articles/PMC6412229/
   • Uses mechanical resonance of composite materials to generate electromagnetic signals.

10. Miniaturized VLF Antenna Arrays

    • Reference: "Research on a miniaturized VLF antenna array based on a magnetoelectric heterojunction," Journal of Materials Science: Materials in Electronics
    • Link: https://link.springer.com/article/10.1007/s10854-021-07616-5
    • Research on achieving extremely small form factors for VLF generation using heterojunctions.

11. Enhanced Piezoelectric-Based Antenna Systems

    • Reference: "Crafting very low frequency magnetoelectric antenna via piezoelectric and electromechanical synergic optimization strategy," ScienceDirect
    • Link: https://www.sciencedirect.com/science/article/pii/S2352847824001266
    • Advanced materials design for magnetoelectric antennas with high performance parameters.

This research collectively represents significant advances in low-frequency signal generation technologies that complement the Doppler-effect based approach described in the original paper.

Paper Citation:

A. Cui et al., "Low-Frequency Signal Generation in Space Based on High-Frequency Electric-Antenna Array and Doppler Effect," in Journal of Systems Engineering and Electronics, vol. 36, no. 1, pp. 24-36, February 2025, doi: 10.23919/JSEE.2024.000079.

Abstract: Low-frequency signals have been proven valuable in the fields of target detection and geological exploration. Nevertheless, the practical implementation of these signals is hindered by large antenna diameters, limiting their potential applications. Therefore, it is imperative to study the creation of low-frequency signals using antennas with suitable dimensions. In contrast to conventional mechanical antenna techniques, our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect. We also defines the antenna array architecture, the timing sequency, and the radiating element signal waveform, and provides experimental prototypes including 8/64 antennas based on earlier research. In the conducted experiments, 121 MHz, 40 MHz, and 10kHz composite signals are generated by 156 MHz radiating element signals. The composite signal spectrum matches the simulations, proving our low-frequency signal generating method works. This holds significant implications for research on generating low-frequency signals with small-sized antennas.

keywords: {Antenna arrays;Time-frequency analysis;Radar antennas;Doppler effect;Array signal processing;Servers;Radar;frequency conversion;array signal processing;experimental verification;Doppler effect},

URL: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10684501&isnumber=10937286

Low-Frequency Signal Generation in Space Based on High-Frequency Electric-Antenna Array and Doppler Effect | BIAI Journals & Magazine | IEEE Xplore