How Does the Current Appear to Look like on the Antenna Surface?

Sometime, the antenna parameters such as gain, standing wave ratio (SWR), and radiation pattern symmetry are not ideal, but we may not know how to adjust them. In fact, these issues are influenced by an invisible factor which is surface current. Surface current controls the direction of the antenna’s electromagnetic waves and also affects the overall antenna performance.

So, how can we assess the surface current of an antenna? While it’s not visible, but it is tangible. You can try it by placing your hand on the surface of the antenna, and you will notice that the antenna’s performance metrics will change rapidly. The area where the surface current flows is usually where this effect occurs. What we need to do is direct the surface current to the correct location, and by doing so, we can improve the antenna’s performance. Let’s explore how adjusting the surface current can enhance antenna parameters.

Analyzing Antenna Current Distribution

Current distribution is a description of the distribution of the electric current on the antenna surface. A thorough analysis of factors influencing current distribution is essential for optimizing antenna performance. By studying the way to visualize current flow, engineers can identify inefficiencies or areas of potential improvement, ultimately leading to better design and signal strength.

Factors Influencing Current Distribution

Several factors can also impact the current at the antenna surface:

• Antenna Geometry and Form: Current distribution is heavily influenced by the physical shape and dimensions.
• Operating Frequency: It decides the resonance of the antenna and the current distribution
• Impedance Matching: Impedance mismatches generate skewed current delivery due to reflection
• Antenna Material: High current conduction is supported by highly conductive material.
• Antenna Size to Wavelength Ratio: The ratio of the antenna dimension to the operating frequency determines current patterns.
• Feed Point Location: The location of the feed point determines the symmetry of current distribution.
• Grounding and Nearby Environment: Nearby structures can deflect current path with ground planes
• Polarization and Excitation: The excitation method determines the symmetry of the current distribution and the current direction.
• Temperature and Environmental Conditions: Extreme environmental conditions can change the material’s properties of electricity.
• Antenna Type: Different antenna structures naturally have varying current distributions.

Visualization Techniques of Current Flow

Visualizing current movement on the antenna surface is also of very significant worth to its performance. Current movement on the antenna can be represented by various techniques.

• Surface Current Density Plots: Theyare represented by color intensity to present the strength of the current at a measurement location. Areas of strong current are normally depicted by warm (red/orange), while areas of weaker current are depicted by cool (blue/green).
• Vector Field Diagrams: Both of them provide the magnitude and direction of the current with the aid of arrows.
• Current Distribution Simulation Tools: Computer software like CST Studio, FEKO, and Ansys HFSS provide 3D models with graphically illustrated current streams with animation to signal frequency or time varying behavior
• Surface Plots of the Electric Field: Plots of the electric field can exhibit current information. Stronger strength of the electric field is commonly with greater current movement.
• Near-Field Plotting: Plots of the near-field components of the electric and the magnetic fields are shown to monitor current movement within the antenna surroundings at hand.
• Animated Current Over Time Plotting: Time-domain simulations plot the current with respect to time to display the propagation with time
• E-Field and H-Field Plotting: Plotting the electric (E) and the magnetic (H) fields helps to graph the transfer of energy and the current path.
• Current Flow Over Animated Surface Current Arrows: Arrows superpose a 3D representation to show the magnitude and direction of the current.
• Color-Coded Heat Maps: Present magnitude is represented by color gradations with warm colours representing areas of highest present current with least current flow areas represented by cool colours.

Implications of Surface Current on Performance

The distribution of the surface current heavily influences antenna performance by affecting its radiation patterns, impedance matching, bandwidth, and efficiency.

Radiation Patterns

Radiation patterns are the directions of the radiation of the antenna of the energy. Current distributions on the antenna surface guide the way the electromagnetic waves are radiated and formed. Symmetrical current distributions generate symmetry radiation patterns while the asymmetrical ones generate distorted patterns.

Impedance Matching

Impedance matching will equal the transmission line to the antenna impedance to deliver the best transfer of the power. Improved current distribution will generate optimal impedance matching with less reflection and increased transmission of the power. Impedance mismatches will arise if the current is distributed less ideally with inefficient performance.

Bandwidth and Efficiency

Bandwidth and performance are the performance measures that are both influenced by current at the surface. Improved current distribution is commonly associated with stable resonance with a resultant increased performance of the bandwidth while inefficient current distribution will likely generate narrowband or unwanted frequency response. Improved radiation is produced by efficient current distribution with minimal loss of the power.

Case Studies

To illustrate the impact of surface current, let’s examine two common antenna types: dipole and monopole antennas.

Dipole Antennas

Dipole antennas consist of two conductors of a half-wave length with a feed at the centre of them. At resonance frequency, the current at the surface is of a sinusoid profile with the highest current at the centre and the minimum at the tips of the antenna. The resultant broadside radiation is due to this centrosymmetrical current profile with the antenna radiating the most at a direction perpendicular to the antenna axis.

Monopole Antennas

Monopole antennas are a half of a dipole antenna mounted on a ground plane. The current on the surface is at the highest at the feed point (base) and tapers upward on the antenna. Energy is reflected back by the ground to generate the omnidirectional pattern.

RFecho: A Reliability Source of Antennas

For those interested in performance antennae, RFecho offers a range of solutions that have the meticulous attention to current distribution to them.

Innovative Solutions Offered by RFecho

RFecho specializes in the designing and manufacture of high-performance antennas with a range of products that include:

• Wideband Antennas: Suitable for applications requiring coverage across multiple frequency bands.
• Dual Polarized Horn Antennas: Having a symmetric beam with high gain, best suited to antenna arrays of the radar cross-section
• Cavity Backed Spiral Antennas: Used in satellite communications, GPS tracking systems, and aerospace applications due to their circular polarization properties
• Log-Periodic Antennas: Famous for their broad-banded behavior and their periodic radiation shape, frequently applied to broadcasting, wireless communications, and systems of radars
• GPS Antennas: GPS antennae are satellite navigation antennae of high gain to directly receive information from the satellite.

Conclusion

The surface current significantly shapes antenna performance, influencing radiation patterns, impedance matching, bandwidth, and efficiency. Optimizing current distribution is critical for maximizing antenna performance in various real-world applications. Whether you’re designing antennas or selecting one for a specific application, understanding these factors is key to achieving the desired results.

References:

• The MathWorks, Inc. Current Visualization on Antenna Surface. https://www.mathworks.com/help/antenna/ug/current-visualization-on-the-antenna-surface.html