Compact lowpass filter with wide stopband using stepped impedance hairpin units

Abstract

A novel microstrip lowpass filter (LPF) with a wide stopband is presented. The basic resonator is composed of two stepped impedance hairpin units with one embedded in another, which can obtain two more transmission zeros and extend a wide stopband. Based on the proposed resonator, a demonstration LPF of compact size, sharp transition and wide stopband has been designed, fabricated and measured. The proposed filter exhibits a small size of 0.081λg × 0.113λg, where λg is the waveguide length at the cutoff frequency of 1.6 GHz. Results show good agreement with simulations and the 20 dB rejection stopband can be extended to more than 15 GHz.Introduction: Compact size and high-performance planar lowpass filters (LPFs) are widely applied in microwave systems. However, such filters inherently have a spurious response. Addressing this problem, several methods [1-4] have been introduced. The compact microstrip resonant cell, using a one-dimensional photonic bandgap cell, exhibits slow-wave and stopband characteristics [1]. In [2], a defected ground structure with an ultra-wide stopband is proposed. Other structures, such as the asymmetric parallel-coupled co-planar waveguide stage and the step-impedance resonator have been studied [3,4]. To obtain a wide stopband response, many conventional filters need more resonators, which will increase the filter size and insertion loss.The microstrip hairpin, because of its advantages of small size and easy fabrication, has been attracting much attention for LPF application. In [5], a class of microstrip coupled-line hairpin units was presented and characterised for the design of compact LPFs with expanded upper stopbands. An elliptic-function LPF [6] using a multiple cascaded stepped impedance hairpin shows a very sharp cutoff frequency response and low insertion loss. To obtain a sharp roll-off and wide stopband, a stub-loaded coupled-line hairpin unit was proposed [7]. In [8], a filter based on a modified stepped impedance hairpin resonator obtained compact size and a broad stopband.In this Letter, a compact microstrip resonator using stepped impedance hairpin units with one embedded in another is proposed. Without increasing the size, the structure exhibits low insertion loss, a wide stopband and two more transmission zeros (TZs) compared with a traditional resonator. On the basis of the proposed resonator, a LPF has been designed. The exact dimensions of the filter are designed by the EM-simulator (high-frequency structure simulator (HFSS)). Measured results indicate that the filter has a better than 20 dB stopband rejection from 1.9 to more than 15 GHz, which achieves 10th harmonic suppression. The size of the filter is only 12.01 × 16.2 mm 2 .

New design of an adjustable compact microstrip lowpass filter using Z‐shaped resonators with low VSWR

“…LPFs play a key role in wireless communication systems owing to their tasks in eliminating unwanted harmonics and noise 3 . Growing demands for these elements motivate scientists to design LPFs with diverse structures and specifications 4‐19 . C‐shaped structures along with complementary split‐ring resonators were used to design an LPF 4 .…”

A sharp‐selective micro strip triplexer with hairpin resonators for long‐term evolution (LTE)

“…All the proposed structures have complicated configuration and the design procedure is not simple. Stepped‐impedance hairpin resonators are widely used for compact size filter implementations . Coupled stepped‐impedance hairpin resonator, trisection hairpin‐shaped resonator for a compact dual‐band, and band‐pass filter realization are reported.…”

“…Stepped-impedance hairpin resonators are widely used for compact size filter implementations. 6 Coupled stepped-impedance hairpin resonator, 7 trisection hairpin-shaped resonator for a compact dual-band, and band-pass filter realization 8 are reported. The transmission line resonators, which are used in the proposed diplexer, have many applications in sensors.…”

Design and fabrication of a compact microstrip lowpass-bandpass diplexer with high isolation for telecommunication applications

“…15 20,30,31 coupled-stub loaded resonator (CSLR), 21 Greek-cross fractal resonator (GCFR), 22 multimode resonator (MMR), 23,33 dual-band resonant junction (DBRJ), 24 meander-loop and square-loop resonators, 26 right-/left-handed, 28 quintuple-mode stub-loaded resonator, 29 and quad-/penta-/sext-mode resonant 32 have been offered to produce compact BPF with good performance. All the LPFs reviewed in the articles above [6][7][8][9][10][11][12][13][14][15][16][17][18] are not tunable. With the development of microwave telecommunication systems, the need for tunable filters has been increased.…”