KEYWORDS: Directional couplers, Capacitors, Microwave radiation, Control systems design, Circuit switching, System integration, Systems modeling, Waveguides, Manufacturing, X-ray lasers
The paper describes the design method and simulations results of high directivity planar directional couplers with impedance transformation between the main and the coupled ports. Presented couplers are realized in microstrip line technology. The basic idea is to allow for coupling between two different impedance transmission lines. The coupling is realized by lumped capacitors soldered at two ends of coupled lines section. The proposed directional couplers are narrowband and high directivity. Wide range of coupling factors is easy to achieve. The example structures presented in the paper have a few levels of coupling factors and have been designed for operating frequencies 1.3 GHz and 3.0 GHz. The directivity of the couplers is better than 30 dB in the narrow bandwidth and the impedance matching is better than 25 dB at any port.
The presented high directivity narrowband multi-layer couplers consist of two transmission lines located on different layers of PCB board and coupled through spatially small coupling structures. The main lines are coupled only at two points. The coupling value can be set from 3 dB to 30 dB. The couplers can be realized in different multilayer stack-ups thus can be easily integrated into variety of PCB circuits. The directivity of the couplers is better than 30 dB in the narrow relative bandwidth of 2 %. The matching is better than 25 dB.
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