In this letter, a novel dual-band microstrip balun bandpass filter (BPF) is designed by using interdigital capacitor-loaded codirectional split ring resonators (CDSRRs). The utilized resonator is analyzed by coupled line theory and exhibits independently controllable dual resonance behavior. The proposed balun BPF is constructed by coupling two identical CDSRRs to rotationally symmetrical balanced output ports. Two transmission zeros (TZs) between the passbands can be observed by means of the CDSRRs. The designed balun BPF centered at 1.59 and 1.92 GHz was also fabricated and measured. The measured results show a good agreement with the predicted results. Phase and magnitude imbalances between the balanced output ports have been measured as better than 180 ± 5° and 0.4 dB, respectively. The proposed dual-band balun BPF exhibits high filtering performances in terms of closely spaced passbands, selectivity, and clean upper stopband.

中文翻译：

---

使用同向开口环谐振器的双频带巴伦 BPF


在这封信中，采用叉指电容负载同向开口环谐振器（CDSRR）设计了一种新型双频带微带巴伦带通滤波器（BPF）。所使用的谐振器通过耦合线理论进行分析，并表现出独立可控的双谐振行为。所提出的巴伦 BPF 是通过将两个相同的 CDSRR 连接到旋转对称平衡输出端口来构造的。通带之间的两个传输零点 (TZ) 可以通过 CDSRR 观察到。设计的以 1.59 和 1.92 GHz 为中心的巴伦 BPF 也被制造和测量。测量结果与预测结果非常吻合。经测量，平衡输出端口之间的相位和幅度不平衡分别优于 180 ± 5° 和 0.4 dB。所提出的双频带巴伦 BPF 在紧密间隔的通带、选择性和干净的上阻带方面表现出高滤波性能。