Compact Broadband High-Directivity Microstrip Directional Coupler

Abstract

The difference between phase velocities of the odd and even modes in inhomogeneous microstrip coupled lines makes the microstrip directional coupler a poor device regarding directivity. In this work, this issue is successfully compensated by the addition of a matching network at the ports of coupled lines. Furthermore, the proposed matching network, composed of a single segment of microstrip line, was extensively studied providing significant insights for the design of a compact and broadband device. As result, simple design equations based on coupled lines S-parameters are obtained, as well as the achievable operation limits of the proposed matching network. Finally, in order to validate the proposed design methodology, a compact microstrip directional coupler is constructed to operate with directivity higher than 30 dB and coupling of 17 dB over a 600-MHz bandwidth.

Closed‐loop controlled microwave beamformer

“…The directional coupler with high directivity presented in Figure 6A is a key element for the proper calibration of the proposed beamformer. The method for designing this component, in that a matching circuit is employed to compensate for the undesired effects caused by the difference between phase velocities of even and odd modes in microstrip couplers, is discussed in Reference 55 Figure 6B shows the measured frequency response of the prototype. As seen in this figure, it exhibits a return loss better than 30 dB, an average coupling of 17.5 dB, and a directivity greater than 35 dB from 2.0 to 2.4 GHz.…”

2.3 GHz Microstrip Rectangular Structured Hybrid Coupler for WiMax applications

“…In terms of the geometry any slot shape would provide similar results ranging from the rectangular ones to the dumbbell shape, therefore providing a reliable and easy to manufacture device with suitable S parameters [6].Furthermore, high variation in the geometry ,in terms of the slots between "U" or rectangularly shaped coupler is shown to decrease substantially return loss and isolation parameters, if the DGS is utilized [5][6].To overcome the mentioned deterioration one may perform extensive parametric study with tunning until the required results for the given geometry are obtained [6]. In terms of improved directivity one may utilize matching network design and therefore a compact directional coupler with less computationally demanding design is achieved [7].…”

“…In addition an improved directivity is observed if the microstrip coupler is subdivided into a symmetrical sections and by tunning and optimizing the overall width and height of the coupler and making it a quarter wavelength [7][8]. This in turn makes the stepped impedance coupler and due to the symmetrical structure it is simple to design and tune, which makes the coupler with the improved directivity inexpensive [8].…”