Abstract
An ultra-broadband multisection directional coupler designed in Monolithic Microwave Integrated Circuit (MMIC) technology has been presented. It has been shown for the first time that it is possible to achieve bandwidths exceeding one frequency decade, simultaneously taking under account technological constrains. The proposed directional coupler is composed of three coupled-line sections having different values of electrical lengths and coupling coefficients. The strongest coupled section has been designed as an asymmetric three-strip coupled-line section, whereas the rest of the sections have been implemented as symmetric two-strip coupled-line structures. To improve electrical performance of the coupler, a compensation method has been implemented together with loss analysis which has to be considered in lossy inhomogeneous medium. The proposed 3-dB directional coupler has been designed in PH25 process based on gallium arsenide (GaAs) from United Monolithic Semiconductors (UMS), and fabricated. The measurement confirms applicability of the design method in monolithic technology for such networks operating in bandwidth exceeding one frequency decade.
Highlights
Directional couplers are commonly utilized components in modern microwave engineering, where are well-implemented in measurement and radiolocation systems [1]–[4], as well as in wireless devices [5], [6]
Couplers can be divided into different topologies such as branch-line [7], [8], rat-race [9], [10] and couplers based on coupled-line sections [11], [12]
Monolithic directional couplers consisting of quarter-wave coupled-line sections are devoid of such a disadvantage and features one octave frequency response [22]–[24]
Summary
Directional couplers are commonly utilized components in modern microwave engineering, where are well-implemented in measurement and radiolocation systems [1]–[4], as well as in wireless devices [5], [6]. Couplers can be divided into different topologies such as branch-line [7], [8], rat-race [9], [10] and couplers based on coupled-line sections [11], [12]. The first two types are well-applicable solutions in monolithic technologies [13]–[18]. Classic approaches feature narrow frequency response, they are not suitable for broadband applications. To achieve wider bandwidth, hybrid couplers are designed as multisection structures [19], or additional elements such as impedance transformers have to be applied [20], [21]. Monolithic directional couplers consisting of quarter-wave coupled-line sections are devoid of such a disadvantage and features one octave frequency response [22]–[24]. To achieve wider bandwidth, such a coupler can
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