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.
Highlights
The branch line coupler (BLC) plays a vital role in wireless communication systems
A simpler and compact design of the dual band 4 × 4 Butler matrix (BM) can be obtained if dual band BLC plays the role of a dual band 45◦ phase shifter as well
The dual band operation of the PI shaped transmission lines (TLs) is explained by taking transmission parameters of both the structures equal
Summary
The branch line coupler (BLC) plays a vital role in wireless communication systems. It is used to design crossovers, Butler matrices (BMs), and antenna arrays [1]–[4]. BLCs and dual band 45◦ phase shifters are required to design a dual band 4 × 4 BM [20]–[25]. A simpler and compact design of the dual band 4 × 4 BM can be obtained if dual band BLC plays the role of a dual band 45◦ phase shifter as well. BLC [15] performs a dual band operation for a limited range of frequency ratios (1.4 - 1.9). Dual band 4 × 4 BM can be designed for a limited range of frequency ratios by employing the BLC [15]. Zaidi et al.: Novel Dual Band BLC and Its Application to Design a Dual Band 4 × 4 BM and dual band ±45◦ phase shifter combination and capable of performing dual band operations for 2.3 to 4.4 frequency ratio, is proposed. It has been found in a comparative analysis that the developed BM has a simpler design, compact size, and fewer number components
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