Design of compact dual-band switchable bandpass filter

Abstract

A compact dual-band switchable bandpass filter is designed using two centrally-loaded open-loop resonators and six pin blocks. The pin diodes are loaded at the zero-voltage points of odd and even modes along the microstrip resonators, such that the two passbands operating at odd and even modes can be individually switched on or off. The isolations for the two passbands are greater than 20 dB.Introduction: Microstrip filters are important components in wireless communication systems. The bandpass filter (BPF), the most important kind, has been a research focus in recent years [1][2][3]. The microwave switch is another key building block in an RF system. Most existing switches are wideband and devoid of frequency selectivity. In a traditional microwave system, bandpass filters are cascaded with switches to implement the switch and frequency preference separately. The circuit area is large and the loss is high. To overcome this problem, switchable bandpass filters that integrate filters and switches are desired. Recently, piezoelectric and pin diode controlled switchable bandpass filters have been investigated, which have sharp cutoff, good selectivity and small circuit sizes [4][5]. These proposed switchable bandpass filters operated at single-band. In this Letter, a compact dual-band switchable bandpass filter is constructed using two centrally-loaded open-loop resonators and six pin blocks. By observation that the zero-voltage points along the microstrip resonators are separate for odd and even modes, pin diodes may be loaded at these zero-voltage points. Loading lumped elements at the zero-voltage points of odd modes has no effect on odd-mode operating, but has great effect on even-mode operating, and vice versa. This principle permits us to design a compact dual-band switchable filter. The two passbands can be controlled independently.

Multi-band reconfigurable microwave filter using dual concentric resonators

“…This discrete switching between the bands at the RF front end is well suited for dynamic spectrum allocation. The primary concern in designing these filters is to bring in multiband operation in a single filter structure with reduced size and minimal device complexity . These discretely switchable filter finds their major application in the area of dynamic spectrum allocation by embedding it on the feedline of the antenna …”

Switchable Dual-Band Filter With Common Quarter-Wavelength Resonators

“…This concept has been extended to the designing of switchable quad-band filters [8]. Another approach to designing switchable dual-band filters involve using dual-frequency resonators [9], [10] whose two resonance frequencies can be arbitrarily adjusted. The concurrent dual-band filter consists of dual-frequency resonators uses fewer resonators than the first type needs.…”

Novel LTCC switchable bandpass filter using vertically short-ended sir

“…Reconfigurable and switchable devices are in great demand in modern wireless communication and radar systems due to their advantages in improving the capability of wireless systems. To meet these requirements, there are many reconfigurable bandpass filters (BPFs), with passband switching ability , have been widely developed. To integrate the BPF and its switch into a single circuit, the most effective design method is to use PIN diodes to turn on or off the passband .…”

“…To meet these requirements, there are many reconfigurable bandpass filters (BPFs), with passband switching ability , have been widely developed. To integrate the BPF and its switch into a single circuit, the most effective design method is to use PIN diodes to turn on or off the passband . Many reported planar switchable BPFs were realized by using the printed circuit board technology, but suffered from large circuit area.…”