Microstrip ring resonators are now used in bandpass filter applications to overcome the influence that parasitic components generated at short circuited points in resonators have on circuit losses and resonance frequencies. Referring to FIG. 1, a conventional split-ring resonator BPF 10 is shown. The BPF 10, having a single-ended input port and a double-ended output port, comprises a first split-ring resonator 12, and a second split-ring resonator 14. The first and second split-ring resonators 12 and 14 each have a gap 20 and 26, respectively, therein. A capacitor (C.sub.t) 18 is connected across gap 20, and a capacitor (C.sub.t) 24 is connected accross gap 26 to decrease the size of the resonators. A signal may be applied to the BPF through a capacitor (C.sub.c) 16. The signal is filtered by the BPF 10 and the resulting filtered signal is provided at the output of the BPF 10 through a capacitor (C.sub.c) 28. There are applications for such BPFs that require that the output or input of the BPF 10 be coupled to a component requiring a balanced input or output. For example, if the BPF 10 were to be coupled to a balanced mixer (i.e., a balanced input is required by the mixer) a transformer would generally be used to provide a balanced output. Thus, it would be advantageous to have a split-ring resonator filter having a balanced output port or a balanced input port, or to have a balanced input port and a balanced output port.
USPTO Backgrounds
USPTO Backgrounds