A Novel Dual Band Branch Line Coupler and its Application to Design a Dual Band 4 × 4 Butler Matrix

Abstract

A novel dual band branch line coupler (BLC) has been proposed, designed, implemented, and analyzed in this paper. A dual band 4 $\times 4$ Butler matrix (BM) has also been developed by employing the proposed BLC. To realize the proposed BLC, PI and modified PI-shaped transmission lines (TLs) as dual band TLs, with the complete derivation of the design equations, have also been introduced. The proposed BLC is equivalent to a dual band ±90° BLC and a dual band ±45° phase shifter combination and capable of performing a dual band operation for 2.3 to 4.4 frequency ratios. In order to verify the proposed approach, a dual band BLC for 1GHz and 2.85GHz frequencies has been designed and implemented. For the proposed BLC, equal power division between the output ports has been achieved with maximum ±0.2dB amplitude imbalance and a phase difference of +45°/-135°±1° at frequency 1GHz and +135°/-45°±2° at frequency 2.85GHz between the output ports for port1/port4 excitation. By employing the proposed BLC, a dual band 4 $\times 4$ BM has also been developed. Compared to the existing dual band BMs, the 4 X 4 BM offers a simpler design, compact size, and design with fewer number of components.

Keywords

• Branch line coupler
• dual band
• Butler matrix
• PI shaped transmission line
• frequency ratio
• compact size