A tunable dual-band bandpass filter using asymmetrical varactor-loaded HWRs and defected ground structure

Abstract

In this paper, a tunable dual-band bandpass filter using asymmetrical varactor-loaded half-wavelength resonators (HWR) and defected ground structure (DGS) is proposed. First, varactors are added at the end of the conventional HWRs to change their resonant frequencies. And to determine the bandwidth of the passbands, the coupling coefficients are calculated to the requirements based on the theoretical analyses. However, the isolation will deteriorate if the passbands are tuned close to each other. Then in order to solve this problem, a pair of circular DGS is introduced at the ground plane of the filter. This structure can prevent electromagnetic energy from propagating at some certain frequency point and if it is designed between the passbands, the isolation will be improved. In our design, the proposed dual-band bandpass filter using varactor-loaded HWRs and DGS is simulated and fabricated. The simulated results and measured results are in good agreement and the proposed filter can be applied in microwave circuits and communication systems.

A compact dual-band bandpass filter for 2.4/5.2 GHz WLAN application

“…9, in the first passband, the group [3] 0:35g  0:33g 6.1%/7.3% Ref. [4] Not given Not given Ref. [5] 0:28g  0:13g 3%/2.16% This work 0:15g  0:09g 7.7%/7.1%…”

“…Where g is the transmission group delay, φ is the phase of S21, ω is the angular frequency. Equation (5) shows that the linear phase will cause a flat group delay response. Therefore, the fluctuation of the group delay is the basis for measuring the linearity of the phase response.…”

“…Wolff first demonstrated a microstrip dual-mode filter in 1972 [1] and therefore, the number of resonators had been reduced by half, resulting in a compact size. Since then [2,3,4,5,6], multi-mode filters have been widely used in wireless communications systems [7,8,9,10,11,12,13,14,15,16]. On the other hand, high performance, light weight, good outband rejection and low cost can't be ignored for filter designers.…”

Millimeter‐wave substrate integrated waveguide bandpass filters based on stepped‐impedance E ‐shaped defected ground structure s

“…Recent years, the defected ground structure (DGS) 1 has attracted more and more research interest due to the wide applications at microwave, millimeter-wave, and terahertz bands. For example, it can be used to improve the electromagnetic wave manipulating performances of passive and active microwave/millimeter-wave components, including the high-performance antenna, [2][3][4][5][6][7][8][9] filter, [10][11][12][13][14][15][16][17][18][19][20][21][22] transmission line, 23 power division network, 24 wireless power transfer, 25 oscillator, 26 and low noise amplifier. 27 Specifically, for antenna application, circular dumbbell-shaped DGS is used to contribute additional resonance and miniaturize the antenna size, 2 full-length resonant-type and asymmetric DGS can reduce the cross-polarized radiation, 3,4,9 Fractal DGS can reduce the mutual coupling of coplanar spaced microstrip antenna elements 5 and also generate circularly polarized radiation, 6 S-shaped DGS is used to achieve the ultra-wideband antenna with multiple band-rejection properties, 7 and Г-shaped DGS can be used to improve the impedance matching property for the magnetoelectric dipole antenna.…”

Compact tunable dual-band bandpass filter with independently tunable passbands and high selectivity

“…In [12,13,14,15], the designed filters offered only one tunable passband, while the other passband was static at a fixed frequency. To overcome this, several tunable dual-band filters with two independently controlled passbands were presented using various resonators [16,17,18,19,20,21,22,23]. For example, in [18], a tunable dual-band BPF using varactor-loaded stub-loaded resonators was reported.…”