Compact LTCC balanced bandpass filter using distributed‐element resonator

Abstract

Presented is a vertically and horizontally folded half-wavelength resonator in a three-dimension (3D) environment and its application to a balanced bandpass filter (BPF). Benefiting from the multilayered resonator based on the transmission line theory and low temperature co-fired ceramic (LTCC) technology, the proposed balanced BPF can obtain compact size and good performance. For demonstration, a LTCC balanced BPF centred at 2.45GHz has been designed using the proposed resonator, and the size of the circuit is 6.0 × 5.0 × 1.6 mm 3 .Introduction: With the rapid development of modern wireless communication systems, increasing demands for balanced circuits are arising. The balanced bandpass filter (BPF), as an essential passive component, usually occupies a very large area of the printed circuit board (PCB). As a result, it is very important to reduce the filter's size. In the developed balanced BPFs, planar topologies are in the majority [1,2]. They all have good performance, but they may suffer from bulky size, which would be an obstacle in practical applications. Recently, low temperature co-fired ceramic (LTCC) technology has attracted much attention as it can reduce the circuit's size significantly. Accordingly, many lumped-element or semi-lumped-element LTCC BPFs with compact size and good performance have been demonstrated [3,4]. However, as the frequency increases, the parasitic effect and unwanted coupling may influence the original characteristic of the lumped element. Therefore, the values of the lumped element cannot be accurately predicted and controlled. The distributed resonator and filter do not have the same problem except the relatively large sizes [5,6]. Hence, size reduction is a challenge in designing the LTCC distributed resonator and filter.In this Letter, a vertically and horizontally folded half-wavelength (λ g / 2, λ g is the guided wavelength at the centre frequency) resonator based on the transmission line theory is proposed. Accordingly, a balanced BPF constructed by a pair of the multilayered resonators has been designed and fabricated in LTCC technology. In this way, the proposed distributed-element LTCC balanced BPF can obtain the same performance and compact size as the LTCC balanced BPF based on lumped elements [4].

Microwave and Millimeter-Wave LTCC Filters Using Discriminating Coupling for Mode Suppression

“…According to (2) and (3), the voltage distributions on the feeding line at f 0 and 3 f 0 are plotted, as shown in Fig. 2…”

“…Compared with the designs in [2] and [20], the proposed BPF shows a compact size and a wider bandwidth. The designs in [3], [5], and [17] realize the wide stopband LTCC filter with a comparable electrical size.…”

Novel Narrow-Band Balanced Bandpass Filter Using Rectangular Dielectric Resonator

“…Over the past few years, several classes of balanced filters have been reportedly developed with good performance using the printed circuit board (PCB) technology [1]- [5], and the low temperature co-fired ceramic (LTCC) technology [6]. However, they are hardly employable in narrowband systems due to their low -factor limitation.…”

Balanced substrate integrated waveguide bandpass filter with high selectivity and common‐mode suppression

“…Some works based on lumped elements have been developed to achieve the compactness using the low-temperature co-fired ceramic technology [6][7][8]. More works about balanced filters are designed with distributed elements of transmission-line structures, such as one-layered microstrip line [9][10][11][12][13][14][15], multi-layer stripline [16], double-sided parallel-strip line [17,18] and hybrid microstrip/slotline [19][20][21][22][23]. Meanwhile, since the substrate integrated waveguide (SIW) [24] is a good candidate to develop microwave and millimetre-wave circuits operating at relatively higher frequencies because of its advantages of low loss, low cost, high power-handling capability and easy integration, several SIW balanced or balun filters have been studied in [25][26][27][28].…”