Spurious Response Suppression in Hairpin Filter Using DMS Integrated in Filter Structure

Abstract

Abstract-In this paper, several Defected Microstrip Structure (DMS) are used to suppress the first and second spurious responses in microstrip hairpin filters. The DMSs are integrated in filter structure, and therefore this method keeps the filter size unchanged. The DMS interconnection disturbs the current distribution only across the strip, thereby giving a modified microstrip line with certain stop band. The undesired spurious harmonics are suppressed through multiple transmission zeros which are added at these frequencies by designed DMSs. Experimental results verify that 25 dB suppression for the first harmonic and 40 dB suppression for the second harmonic, respectively, without affecting the main passband response. There is a good agreement between the simulated and measured results.

Harmonic Suppression by Using T-shaped Spur-Line in a Compact Hairpin-Line Bandpass Filter

“…Table 2 highlights the comparative study with fractional bandwidth (FBW, %), stopband rejection level (SRL, dB), insertion loss (IL, dB), stopband rejection bandwidth (SBW, GHz) and Size in terms of λ 0  λ 0 . It has been noted that there has been an improvement in the stopband rejection level better than [7][8][9][10][11]. Moreover, the sizes of the proposed filters are more compact than [7], [8], and [10].…”

“…By following the same method, the equivalent chain matrix of a double T-shaped spur-line as shown in Fig. 6(c), (d) has been determined as (7). The equivalent |S 21 | has been derived by the parameters conversion and expressed as (8) (1 2 sin ) 1 2 sin where…”

“…However, the introduction of a low-pass filter has increased the overall filter size greatly. In this context, the harmonic suppressed hairpin-line filters have been designed with Koch fractals [5] (stopband rejection level of 29 dB up to 2f 0 where f 0 is the center frequency), splitmode excitations [6] (20 dB up to 8.33f 0 ), Defected Microstrip Structure (DMS) [7] (33 dB up to 3.4f 0 ), and Minkowski fractals [8] (30 dB up to 2f 0 ). However, the design and fabrication difficulties are increasing as the iteration order of these types of perturbations increases.…”

“…However, the design and fabrication difficulties are increasing as the iteration order of these types of perturbations increases. Although the harmonic suppression characteristics of the above filters [5][6][7][8] are satisfactory, the sizes of the filters are quite large due to their conventional hairpin-line filter structures, restricting their applications. Afterward, in [9] λ/4 and λ/2 stepped-impedance resonators have been employed to design a 96% size reduced compact filter with a wide stopband of rejection level of 30 dB up to 3f 0 .…”

A Compact Band-Pass Filter with High Selectivity and Second Harmonic Suppression

“…In [26] two quarter wavelength open ended stubs are attached at the edges of the resonators in the main coupling path in order to have harmonic suppression, but this implies additional circuit elements against compact filter design. Another interesting alternative, such as using a continuous modulation in the coupled section of the filter [27,28] and using Koch fractal geometry [29], have also been considered, but both are time consuming due to the need of many parameters optimization. In this contribution, defected ground structures (DGS) are used to act as a low-pass filter.…”