Traditional antenna design has long relied on a trial-and-error approach, where multiple physical prototypes are built and tested repeatedly to achieve an optimized solution. However, with the rise of simulation tools, designers now create software-based prototypes, significantly reducing the time required for analysis compared to traditional methods. Despite this shift, most processes still follow an iterative cycle: model the design, simulate its performance, modify the model, and repeat. Recently, some companies have introduced more advanced techniques that allow for a comprehensive evaluation of all design parameters in a single analysis, covering the entire design space and selecting the best option without the need for repeated iterations. This new method has been successfully applied in designing feed networks for WiMAX arrays, enabling full frequency coverage within the target band.
Over the past decade, numerous wireless technologies have emerged, such as Bluetooth, WLAN, 2.5G/3G cellular systems, RFID, and UWB. Each of these requires innovative antenna designs to unlock their full potential. As devices increasingly integrate multiple wireless technologies, antenna coupling becomes a major challenge, adding complexity to the design process. Modern PCs may include Wi-Fi, Bluetooth, and cellular antennas, leading to new issues related to interference and signal degradation.
A modern approach to antenna design involves modeling the initial concept and replacing key parameters with variables. The user defines the range for each variable, and the simulation engine generates models and performance predictions for all possible combinations. This reduces the time needed to find the optimal design, as it eliminates the need to build and test each version individually.
The goal of this project was to develop a WiMAX antenna array operating between 3.4 GHz and 3.65 GHz. With a wavelength of approximately 8.8 mm, the design used a central feeding technique to ensure all elements radiate in phase. A 50Ω coaxial probe fed the center of a 100Ω feeder, which was terminated with quarter-wave impedance transformers. These transformers converted the 100Ω impedance into two 50Ω lines, each feeding a chip antenna element.
One of the first steps was to calculate the edge impedance of the patch antenna and match it to the 50Ω feed using an impedance converter. This could be done through formulas or microwave theory. Another key constraint was ensuring sufficient isolation between the four radiating patches to prevent mutual interference.
The substrate thickness was set at 1.6 mm, with a relative dielectric constant (εr) of 3.58. Using an approximation formula, the corrected side length of the half-wavelength patch was determined. Assuming a chip antenna width of 25 mm, the edge impedance was calculated based on the length and width. A simple RF calculator helped determine the width of the 100Ω feeder on the given substrate.
Each connecting line segment had to match 50Ω, resulting in a microstrip bandwidth of 3.497 mm. Quarter-wave converters were used to connect the 50Ω segments to the 100Ω feeder, with specific dimensions calculated for optimal performance.
To evaluate the original design, Flomerics’ MicroStripes software was used for simulation. This tool employs the Transmission Line Matrix (TLM) method to solve Maxwell's equations in the time domain, allowing for a full broadband response in a single calculation. Compared to traditional E/H field approaches, TLM is more efficient in terms of memory and CPU usage, making it ideal for complex antenna simulations.
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