A novel defected ground structure for an active device mounting and its application to a microwave oscillator

This letter is to present a new defected ground structure (DGS), which is useful for mounting an active device, and its application to a microwave oscillator. The newly proposed DGS circuit is useful for mounting a transistor such as a BJT or field effect transistor (FET) on ground plane. In order to bias dc to a transistor, it is necessary to implement the dc isolated circuit in a practically applied active device with a DGS. For dc isolation, each branch of DGS should be isolated from ground. However, the proposed DGS structure with dc isolations introduces a degradation of gain performance for a transistor and changes the matching point. In order to overcome these limits, we have investigated a coupling method by using the simple coupling capacitor without degradations in RF performances. This letter displays the comparison of several measurements for the fabricated DGS circuits including the case that compensates the degradations due to the dc isolation. Furthermore, a design example of a microwave oscillator with the proposed DGS is demonstrated to show the validity of this letter.