A wideband 90 • microstrip hybrid coupler with a bandwidth of 84.3% is proposed. The hybrid coupler consists of a two-section coupled-line power divider and a 90 • phase shifter. The two-section coupled-line is of natural broadband characteristics, and not only performs the role of impedance matching, but also makes the total circuit compact. The phase shifter employs a pair of open-and short-circuit stubs inserted into the reference transmission line to compensate the phase variation in proportion to the operating frequency for the conventional transmission line. Thus, the phase shifter possesses wideband performance on impedance matching as well as phase shifting. To prove the design methodology, a wideband 90 • hybrid coupler operating at 3 GHz is designed and fabricated. In the case of −15 dB reflection coefficient for all ports of the coupler, the output maximum amplitude unbalance is less than 1 dB, the phase variation is less than 5 degree, and the port isolation is better than 18 dB. INDEX TERMS Wideband hybrid coupler, broadband phase shifter, even-and odd-mode analysis.
Axial‐ratio (AR) bandwidth enhancement is achieved for a circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) using a wideband hybrid coupler (WHC) combined with dual probe feed. The presented WHC, comprised of a Wilkinson power divider and a wideband 90° shifter, delivers good characteristics in terms of 3 dB power splitting and consistent 90° (±5°) phase shifting over a wide bandwidth. In turn, the proposed CP DRA, for the employment of the WHC, in place of conventional designs, provides a significant enhancement on AR bandwidth and impedance matching. The antenna prototype with the WHC exhibits a 3 dB AR bandwidth of 48.66%, an impedance bandwidth of 52.5% for voltage standing wave ratio (VSWR) ≤ 2, and a bandwidth of 44.66% for a gain of no less than 3 dBi. Experiments demonstrate that the proposed WHC is suitable for broadband CP DRA design.
In this letter, a single‐layer broadband 90° phase shifter using H‐shaped network is proposed. To achieve broadband performance, we present an H‐shaped network by combining a section of stepped impedance transmission line with two pairs of λg/8 short‐ and open‐circuited stubs. Even‐odd mode analysis is carried out and the resulted equations is derived for the proposed device. The prototype is implemented on single‐layer printed circuit board for verification. The measured results agree well with the simulations, which demonstrates better than 15 dB return loss, less than 5° phase deviation and 0.76 dB insert loss across a fractional bandwidth of 101.7%.
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