An extremely miniaturized microstrip branch‐line coupler

Abstract

In this letter, an extremely miniaturized branch-line coupler (BLC) operating at 0.9 GHz is analyzed, designed, and introduced to enhance the bandwidth accompanied by highly size reduction without via-holes, multilayered technique, and air-bridged. A combination of a simple low-pass and band-stop filters is proposed to increase isolation between BLC's ports. This model is equaled by a quarter-wavelength line and necessary equations are obtained using even and odd modes analysis. A compact BLC is designed and tested using this technique. It is shown that the proposed BLC works as well as conventional onesThe branch-line couplers using quarter-wave length transformers are appreciated due to its simplicity and low-cost fabrication. It, however, has narrow-band characteristics and requires a relatively large area. Some techniques in reducing the layout dimensions of this element have been reported [1][2][3][4]. Whereas, lumped or lumped distributed elements give a chance to have a small size, they can not enhance the bandwidth. In several studies, many different topologies to reduce the size of this microwave element have been proposed, however, the more its size reduces thereby and its bandwidth decreases as well [5][6][7]. Recently, a branch-line coupler has been designed and introduced by connecting lines as a cascade two unit elements [8]. It has a compact size but, its bandwidth has not increased.In this letter, a miniaturized branch-line coupler is introduced to enhance the bandwidth accompanied by highly size reduction without via-holes, multilayered technique, and air-bridged. Initially, a combination of the simple low-pass and band-stop filters is proposed to increase isolation between input and isolated, through and coupled-ports, respectively, as shown in Figure 1, then, a compact BLC with enhancement of its bandwidth is designed, analyzed, and simulated using a model for wideband applications. This BLC has an extremely compact simple microstip layout, low-fabricated cost, and a size reduction more than those of previous works and it is a useful design to compensate the bandwidth reduction created in the previous ones due to size reduction.The size reduction is about 74% respect to the conventional BLC with 4.5% enhancement in bandwidth in analogy with proposed coupler in Ref. 8. The proposed BLC is designed at 0.9 GHz and fabricated on a 25-mil-thick RF-35 PTEE/Woven substrate with a relative dielectric constant r ϭ 10.2. Furthermore, the simulated and measured results of the proposed BLC are presented. DESIGN PROCEDURETo reduce the area of the BLC, the combination of a simple low-pass and band-stop filters is proposed to increase isolation between BLC's ports as shown in Figure 1. Inspecting this structure, the two coupled transmission lines with the electrical length feature, a stop-band filter which is designed by short-length and low-impedance microstrip stubs to enhance stop band frequency response at 900 MHz. By combination, this model with a longlength and high-impedance single line, it c...

Slow-wave resonant structures in branch-line coupler miniaturization: A case study

“…An adequate modification of a signal line in the form of a T-shaped topology [1] as well as a -shaped geometry [2][3][4][5][6] has proven to be a valuable method of branch-line coupler miniaturization (55% in [1], and 23-61% in [2][3][4][5][6]). Subsequently, several improvements have been proposed to aforementioned techniques by exploitation of singular or multiple stubs constructed from high-and lowimpedance segments [7][8], folded strips [9][10][11][12][13], steppedimpedance resonators [14][15] or other building blocks [16] resulting in 71-71%, 61-74%, 55-78%, and 37% scale of miniaturization, respectively. Although a significant degree of minimization has been achieved in numerous cases, the interior of the coupler has rarely been accommodated in a highly efficient manner.…”

Novel compact dual-narrow/wideband branch-line couplers using T-Shaped stepped-impedance-stub lines

“…Branch-line coupler (BLC) is one of the fundamental hybrid components essential in the design of transceivers employed in microwave and millimeter-wave systems. Additional to operating only at single frequency band [1], the traditional branch-line couplers also suffer from disadvantages of narrow bandwidth and requiring a relatively large substrate surface area [2,3]. However, the need for dual-band operation, wide bandwidth, and compactness imposes new requirements from BLCs for the next generation of wireless communication systems.…”

Design considerations for compact microstrip resonant cells dedicated to efficient branch‐line miniaturization

“…A conventional branch‐line coupler offers a simple planar topology composed of four quarter‐wavelength transmission line segments easily realizable in a standard PCB fabrication process; however, the consumption of a large surface area, especially at the low operating frequency, becomes a major drawback that must be taken into account. This problem has been addressed throughout the years in several ways [1–30].…”

“…Another viable concept of branch‐line coupler miniaturization based on the implementation of various discontinuities along the microstrip transmission line has been extensively reported [7–30]. The modification of a signal line in the form of T‐shaped geometry [7] as well as π‐shaped topology [8–12] has proven to be useful in the process of branch‐line coupler size reduction (55% in Ref.…”