Abstract
Multi-function wireless systems demand multi-channel transmit/receive (TR) modules, particularly as multiple functions are required to operate simultaneously. In each channel, passive components, including bandpass filters, must be compact, or at least transversely compact; thus, the entire circuitry of the channel will be slender, and consequently multiple channels can be parallel-arranged conveniently. In this work, single-ended and balanced bandpass filters for multi-channel applications are presented. As a unique resonator, the U-shaped stepped impedance resonator (USIR) can achieve size miniaturization compared with its corresponding uniform impedance resonator (UIR) counterpart. Hence, with the utilization of USIRs, the proposed bandpass filters are able to acquire compact transverse sizes. Moreover, by using the source–load coupling scheme, two transmission zeros (TZs) are respectively generated at the lower and upper sides of the passbands, which is useful for improvement of the selectivity performance. In addition, spurlines are introduced at the input and output ports to produce another TZ to further enhance the stopband performance, which cannot be acquired by the UIR or stepped impedance resonator (SIR). To verify the aforementioned idea, one single-ended and one balanced bandpass filter are implemented, with experimental results in good agreement with the corresponding simulations. Meanwhile, as compared with some similar works, the proposed balanced filter achieves compact transverse size, sharp selectivity skirt, and wide stopbands up to the fourth-order harmonic with suppression over 20 dB, which illustrates its suitability for differential signal transmission application in microwave circuits and systems.
Highlights
Different kinds of radio frequency (RF) and microwave systems for various wireless applications like commutation, radars, and sensors have been widely investigated
The U-shaped stepped impedance resonator (USIR) is utilized as basic resonator for size reduction while the source–load coupling topology is able to produce two transmission zeros (TZs) for selectivity performance, and spurlines included at the source and load node can generate an extra TZ to enhance the stopband performance
L = ZH, θ half is equal to π, which is the very electrical length of the conventional half-wavelength uniform impedance resonator (UIR) under the dominant resonant mode; as ZL > ZH, θ half is able to larger than π; as ZL < ZH, θ half can be smaller than π
Summary
Different kinds of radio frequency (RF) and microwave systems for various wireless applications like commutation, radars, and sensors have been widely investigated. With compact transverse size are quite useful for multi-channel systems The dumbbell-shaped resonator is etched on the ground plane of the differential filter to improve its CMRR to 57 dB [14] Both the SIRs and interdigital capacitors are utilized together to produce two TZs for the balanced filter in [15]. A single-ended and a balanced filter are investigated, taking account of size, selectivity, and stopband simultaneously. The USIR is utilized as basic resonator for size reduction while the source–load coupling topology is able to produce two TZs for selectivity performance, and spurlines included at the source and load node can generate an extra TZ to enhance the stopband performance.
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