Polar Antenna: The Spatial Dance of Electromagnetic Waves and the Dimensional Cipher of Information Transmission
In the storage rooms of the British Museum in London, quietly displayed is the original apparatus Hertz used in 1888 to confirm the existence of electromagnetic waves—those rudimentary metal oscillators that inadvertently revealed the directional characteristics of electromagnetic field oscillations in space. This property of electromagnetic waves, known as polarization, has become a key dimension for enhancing spectrum efficiency in modern wireless communication systems through the precise design of polar antennas. From the dual-polarized Massive MIMO arrays of 5G base stations to the circularly polarized communication links between Mars rovers and Earth, polarized antennas, with their precise control over the vector direction of electromagnetic waves, weave an invisible network of information across spatial dimensions.
I. The Physical Picture of Antenna Polarization Dimension
The essence of electromagnetic wave polarization is the trajectory of the electric field vector within the plane perpendicular to the direction of propagation. When a pair of metallic oscillators are aligned vertically, the radiated electric field vector oscillates within the vertical plane, forming a vertically polarized wave; if the oscillators are placed horizontally, they generate a horizontal polarization. This linear polarization state is the most fundamental form of polar pattern, widely applied in FM broadcasting and terrestrial television signal transmission. Measurements by the U.S. Federal Communications Commission (FCC) indicate that in urban environments, vertically polarized signals experience 3-5dB less penetration loss through buildings compared to horizontally polarized signals, explaining why 4G/5G base station antennas generally adopt vertical polarization configurations.
When the endpoint of an electric field vector traces an elliptical path over time, elliptical polarization is formed. This state can be seen as a generalized form of both linear and circular polarizations, with its axial ratio (AR) determining the purity of the polarization. The BeiDou satellite navigation system employs right-handed elliptical polarization with an axial ratio of 3dB, maintaining an 87% polarization matching efficiency even in complex terrains. The creation of perfectly circularly polarized waves requires strict phase control; a certain inter-satellite laser communication terminal uses quartz wave plates to convert linear polarization into circular polarization, enhancing the interstellar link's resistance to Faraday rotation interference by twenty times.
II. The Engineering Interpretation of Polarized Antennas
The core performance of polarized antennas lies in their ability to redistribute radiated power in space. An isotropic antenna serves as a theoretical reference antenna with uniform radiation characteristics and a antenna gain benchmark of 0dBi. In practical applications, dipole antennas often serve as reference antennas, with a gain of 2.15dBi resulting from focusing energy in the vertical plane. The true power of polarization technology, however, is demonstrated by reconfigurable antennas capable of dynamically switching or synthesizing various polarization states—a particular millimeter-wave phased array at the 28GHz band, through polarization multiplexing, enhances spectral efficiency to 40bps/Hz, which is four times that of traditional single-polarization systems.
Omnidirectional antennas face unique challenges in polarization design. A typical whip antenna achieves 360° coverage in the horizontal plane while its vertically polarized beam forms a "doughnut" shape in the elevation angle. To enhance vertical plane radiation efficiency, base station antennas use collinear array structures: stacking eight λ/2 oscillators vertically, aided by parasitic elements, compresses the vertical beam width to 7°, increasing the gain to 14dBi. This design is crucial for 5G micro-base stations requiring broad horizontal coverage coupled with precise vertical energy projection.
III. The Information Revolution of Polarization Dimension
In dense urban environments, polarization diversity becomes a powerful tool against multipath fading bottlenecks. Dual-polarized antennas establish spatial diversity through orthogonal polarization channels, reducing signal correlation to below 0.3. Tests show that LTE base stations using ±45° dual polarization improve edge user throughput by 35%, particularly in high-rise building areas where polarization diversity gains can reach 6dB. Pioneering tri-polarization antenna systems at the 28GHz millimeter-wave band add a circular polarization dimension, breaking through air interface capacities to exceed 100Gbps, laying the physical foundation for 6G holographic communications.
In satellite communications, polarization multiplexing pushes spectral efficiency to new heights. The Flex system by the International Telecommunication Satellite Organization utilizes orthogonal circular polarization frequency reuse to achieve quad reuse on the C-band with the same frequency. Its key technology lies in polarization isolation—through precisely engineered feed networks, isolation between co-frequency orthogonal polarization channels is improved to 35dB, effectively suppressing interference signal quality by more than 1/3000. This polarization purity enables geosynchronous satellites to increase their equivalent isotropic radiated power (EIRP) to 53dBW, supporting transoceanic 4K ultra-high-definition broadcasting.
IV. The Material Revolution of Polarization Control
Metamaterial technology provides new degrees of freedom for polarization control. Smart polarizers based on liquid crystal tunable units can complete line-to-circular polarization conversion within 1ms by applying 0-5V voltage to alter liquid crystal molecular alignment, thus modulating electromagnetic wave phase. An electronic warfare system employing this technology achieves polarization deception of enemy radar signal strength, reducing radar cross-section (RCS) by 15dB. Graphene metasurfaces exhibit even greater potential: by electrically controlling graphene's Fermi level, dynamic adjustment of polarization conversion ratios across the 0.1-10THz range supports core components for 6G terahertz communications.
In quantum communications, polarization-encoded photons serve as information carriers. China's Mozi quantum satellite employs the BB84 protocol, utilizing four polarization states (horizontal, vertical, +45°, -45°) for quantum key distribution. Its polarization compensation system uses piezoelectric ceramic rotating wave plates to maintain star-ground link polarization alignment error within 0.5° at an adjustment frequency of 200 times per second, ensuring quantum bit error rates remain below 2%. Such extreme precision in polarization control enables the possibility of 1200 km quantum key transmission.
V. The Future Frontier of Polarization Technology
Studies in bioelectromagnetics have found that certain insect compound eyes can perceive light polarization, inspiring new generations of polarization imaging sensors. A military reconnaissance system analyzes ground reflection wave polarization characteristics to identify 95% of camouflaged targets in vegetated areas. In civilian fields, polarization radar is advancing rapidly in autonomous driving systems: a 77GHz polarized millimeter-wave radar improves pedestrian recognition accuracy to 99.7%, maintaining a 93% detection rate even in heavy rain.
In deep space exploration, polarization technology is unlocking cosmic mysteries. The Square Kilometer Array radio telescope's polarization observation mode maps large-scale cosmic magnetic fields by analyzing neutral hydrogen's 21cm line polarized radiation, achieving polarization measurement precision of 0.001°, sufficient to detect minute perturbations in intergalactic magnetic fields billions of light-years away. Precision measurements of pulsar polarization profiles are opening new avenues for gravitational wave detection—the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) successfully captured low-frequency ripples of cosmic background gravitational waves by analyzing the time-varying polarization characteristics of 43 millisecond pulsars.
From the linear polarized waves excited by Hertz's resonator to the single-photon polarization states manipulated by quantum satellites, polarization technology remains a core dimension of the interaction between electromagnetic waves and matter. As 6G systems achieve dynamic polarization agility through intelligent metasurfaces and brain-computer interfaces leverage polarization encoding to overcome neural signal transmission bottlenecks, this seemingly classical electromagnetic attribute is shining anew in the digital era. Perhaps, in the near future, quantum repeaters based on polarization entanglement will realize intercontinental quantum communication, all beginning with those ancient metal rods' directional antenna oscillations in electromagnetic fields—a starting point for humanity's decoding of spatial dimension secrets and a gateway to infinite possibilities.
