A compact and sharp ultra-wide bandpass filter by using short-stub-loaded rectangular ring and split ring resonators

ABSTRACT

A compact and sharp-rejection ultra-wideband (UWB) microstrip bandpass filter (BPF) is presented. The proposed filter is constructed with multiple-mode resonator (MMR) and split ring resonator (SRR). Moreover, proposed structure consists of two doublets parallel coupling gaps at each side of a microstrip ring. In comparison with some other filters, this structure shows a significantly wider passband due to the introduction of a cross-coupling between the feed lines (input and output) which generate four pairs of attenuation zeros in the passband.

In order to control the transmission zeros in the passband and adjust the transmission zeros near the lower edge of the filter, a short stub loaded on microstrip rectangular ring is used. Also, In order to sharpen the upper edge of the filter, the SRRs have been used in both side of the doublets parallel coupling gaps which leads to the addition of one extra transmission poles at the upper edge of the filter. Consequently, a compact five-zero and one-pole UWB BPF is designed which exhibits extremely sharp-rejection skirts around the target passband.

The proposed filter has a passband covering 2.83–10.06 GHz and its measured 3 dB fractional bandwidth is about 112.5%. Furthermore, rejection level better than 20 dB in upper stop-band is extended to around 18 GHz. To our knowledge, the size of proposed UWB filter is more compact in comparison with known similar filters.

KEYWORDS:

• Bandpass filter (BPF)
• doublets parallel coupling gaps
• microstrip ring
• multiple-mode resonator (MMR)
• split ring resonator (SRR)
• ultra-wideband (UWB)