[Paper Review] Optimum Design of a 4x4 Planar Butler Matrix Array for WLAN Application

Wriddhi Bhowmik, Shweta Srivastava|arXiv (Cornell University)|Apr 26, 2010

Microwave Engineering and WaveguidesEngineering4 references16 citations

TL;DR

This paper presents an optimized 4x4 planar Butler matrix array designed for 5.2 GHz WLAN applications using FR4 substrate (εr=4.9, h=1.6mm), enabling switched beam smart antenna systems. The design integrates microstrip antennas, hybrid couplers, cross-couplers, and phase shifters, with MATLAB-based calculations and SONNET simulations validating performance, achieving effective beamforming with reduced multipath fading and interference.

ABSTRACT

In recent years, high-speed wireless communication is in vogue. In wireless communication systems, multipath fading, delay and interference occurres by reflection or diffraction. In a high-speed wireless communication, it becomes a necessary to separate desired signal from delay or interference signal. Thus to overcome these problems Smart antenna systems have been developed. Basically there are two types of smart antenna systems, one is Switched beam system and another Adaptive array system.This paper presents the optimum design of a 4x4 plannar Butler matrix array as a key component of a switched beam smart antenna system, operating at 5.2 GHz for WLAN with a dielectric substrate, FR4 of er =4.9 and h=1.6mm. Conception details, simulation results and measurements are also given for the components (microstrip antenna, hybrid couplers, cross-coupler, phase shifter) used to implement the matrix. In this dissertation, mathematical calculations for all the components using MATLAB is done and then every individual component is designed using the commercial software SONNET. Then these entire components have been combined on a single substrate and simulated using SONNET.

Motivation & Objective

• To address multipath fading, delay, and interference in high-speed wireless communication systems.
• To develop a cost-effective, planar Butler matrix array for switched beam smart antenna systems in WLAN environments.
• To optimize component design (antennas, couplers, phase shifters) for 5.2 GHz operation on FR4 substrate.
• To integrate all components on a single substrate and validate performance via simulation and measurement.
• To provide a practical, scalable solution for beamforming in 802.11a-based WLAN systems.

Proposed method

• Conducting mathematical analysis using MATLAB for all Butler matrix components: microstrip antennas, 3 dB hybrid couplers, cross-couplers, and phase shifters.
• Designing individual components using the commercial electromagnetic simulator SONNET for accurate electromagnetic modeling.
• Integrating all components onto a single FR4 substrate (εr=4.9, h=1.6mm) to form the complete 4x4 Butler matrix array.
• Simulating the full array system using SONNET to evaluate radiation patterns, phase responses, and beamforming performance.
• Validating design through simulation results and comparing with theoretical expectations for beam steering and directivity.
• Employing standard microstrip line theory and impedance matching techniques to ensure proper signal distribution and phase control.

Experimental results

Research questions

• RQ1 How can a 4x4 planar Butler matrix be optimally designed for 5.2 GHz WLAN applications using low-cost FR4 substrate?
• RQ2 What is the performance of individual Butler matrix components (hybrid couplers, phase shifters, cross-couplers) when simulated and integrated on a single substrate?
• RQ3 To what extent does the integrated Butler matrix achieve accurate beamforming with minimal side lobes and phase errors?
• RQ4 How do simulation results compare with theoretical expectations for beam steering and directivity in a switched beam system?
• RQ5 Can a fully planar, low-cost Butler matrix array be effectively realized for practical WLAN deployment?

Key findings

• The 4x4 Butler matrix array was successfully designed and simulated using SONNET, demonstrating stable beamforming at 5.2 GHz.
• The use of FR4 substrate (εr=4.9, h=1.6mm) enabled a cost-effective and manufacturable planar design suitable for WLAN applications.
• MATLAB-based calculations ensured accurate component sizing, particularly for phase shifters and couplers, minimizing phase errors.
• Simulation results confirmed consistent phase shifts across the array, enabling precise beam steering across multiple directions.
• The integrated design achieved acceptable gain and directivity with low side lobe levels, validating the feasibility of the approach.
• Measured and simulated results showed good agreement, confirming the reliability of the SONNET-based simulation framework for such arrays.