A Wideband BPF Using SIR With Wide Spurious Suppression

The bandpass filters are most widely used in radio frequency (RF) front end equipment of the microwave wireless communication systems. The parallel-coupled line structures are popular for the bandpass filters such as the parallel-coupled lines cascaded together [1]. The parallelcoupled lines combined with open-stub lines for harmonic suppression improvement was also proposed [2]. Furthermore, size reduction and high selectivity are essential and required for fabricating bandpass filters. The filter used the pseudo-interdigital step impedance resonators for improving the skirt characteristics and compact size has been reported [3]. Moreover, asymmetrical stepped impedance resonator (ASIR) structure can also reduce the size and provide the transmission zero by tuning λ/4 stubs and asymmetrical capacitive loads of the open loop resonator [4-6]. Recently, the method of determining feed positions in the coupled half-wavelength SIR bandpass filters is proposed by using the concept of impedance matching [7]. In [8] and [9], SIRs with different dimensions of parallel-coupled lines and transmission zeros tuning to improve the rejection of the filters have been investigated. This paper proposes a compact wideband bandpass filter using techniques of embedded feed and slot for improved spurious suppression. In the content, the designed resonator and parameter study are described in Sec.2. The prototype filter and measurement result are shown in Sec.3. The last section is a conclusion.