Abstract
The branch-line coupler (BLC) is an important device in radio frequency (RF) and microwave (MW) circuits. The main drawbacks of the conventional BLC are as follows: first, the four long quarter-wavelength (λ/4) transmission line sections occupy a large size, especially at the low frequencies, and second, the presence of unwanted harmonics. This research paper presents a compact 750 MHz BLC with harmonics suppression using resonators. The typical BLC consists of four λ/4 branches, two series arms of 35 Ω and two shunt arms of 50 Ω impedances. In the proposed BLC, these long branches are replaced with two types of compact resonators. The proposed resonators have the same responses at the operating frequency of 750 MHz and suppress higher frequencies. The designed BLC is simulated, fabricated and measured. The results show that the proposed BLC has good performance at 750 MHz with a bandwidth of 200 MHz, which provides more than 26% fractional bandwidth (FBW). It has a very compact size, about 84% size reduction, as compared with the typical BLC. Moreover, the fabricated BLC suppresses the 2nd up to 7th unwanted harmonics with a high suppression level.
Highlights
Couplers are widely used in radio frequency (RF) and microwave (MW) circuits for combining/dividing input power [1]
The typical branch-line coupler (BLC) consists of four λ/4 branches. It consists of two series arms with 35 Ω and two shunt arms with 50 Ω impedances, which make this component undesirably large, especially at low frequencies, and susceptible to unwanted harmonics
The Conventional Coupler The typical BLC consists of four λ/4 branches, two series arms of 35 Ω and two shunt arms of 50 Ω impedances
Summary
Couplers are widely used in radio frequency (RF) and microwave (MW) circuits for combining/dividing input power [1]. The typical branch-line coupler (BLC) consists of four λ/4 branches It consists of two series arms with 35 Ω and two shunt arms with 50 Ω impedances, which make this component undesirably large, especially at low frequencies, and susceptible to unwanted harmonics. In many designs [2–5], low-pass filters (LPFs) are used as the coupler branches to miniaturize the structure and suppress the harmonics. This technique gives good results but increases the design complexity and the insertion loss. 2. The Conventional Coupler The typical BLC consists of four λ/4 branches, two series arms of 35 Ω and two shunt arms of 50 Ω impedances. Two vertical resonators are used instead of the two long vertical branches, and two horizontal resonators are used instead of the two long horizontal branches
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