A kind of ultra wide band bandpass filter with trap wave point
Technical field
The utility model relates to a kind of band pass filter, particularly relates to a kind of ultra wide band bandpass filter with trap wave point, can be used for filtering in radio ultra wide band system.
Background technology
In the various fields such as communication system, radar, imaging, super-broadband tech occupies very important position.FCC (Federal Communication Commission-FCC) in 2002 the business application of allowing 3.1-10.6GHz, super-broadband tech starts to be subject to extensive concern.Ultra-wide band filter also becomes the focus of research.Yet in the commercial scope of FCC definition, UWB signal is subject to the interference of the signals such as WiAX (3.5GHz), WLAN (5.2GHZ, 5.8GHZ), RFID (6.8GHz).The filter therefore with trap characteristic has very high researching value.
The major design method of ultra-wide band filter has: high-pass and low-pass filter combined method, multimode the resonance method, short circuit branch collimation method.Because the filter size of high low pass combined method and the collimation method design of short circuit branch is larger, be unfavorable for application, the method for people's first Application multimode resonance in document (Ultra-wideband (UWB) Bandpass Filters Using Multiple-mode Resonator) in 2005 such as Lei Zhu realizes the design of ultra-wide band filter.But this filter transition band is wider, it is not precipitous that edge suppresses.2007, Hussein Shaman, Jia-Sheng Hong has realized the UWB filter with trap in document (Ultra-Wideband (UWB) Bandpass Filter With Embedded Band Notch Structures).The edge steepness of this structure is also not high enough.After this multiple multimode resonator structure and multiple trap structure are suggested in succession.How to realize edge precipitous, with the ultra-wide band filter of trap, be the difficult point facing at present.
Utility model content
It is wider that the utility model main purpose is to overcome traditional broadband filter transition band, edge is precipitous not, in free transmission range interference signal cannot filtering etc. technical problem, proposed a kind of simple in structure, edge is precipitous, have the ultra wide band bandpass filter of a trap wave point.
For solving this technical problem, the technical scheme the utility model proposes is as follows:
A kind of ultra wide band bandpass filter with trap wave point, this ultra wide band bandpass filter comprises medium substrate 1, be formed at the etched circuit layer 3 of medium substrate upper surface and be formed at the ground metal layer 2 of medium substrate lower surface, described etched circuit layer 3 comprises a stepped impedance line 6 and a resonant ring 7, this resonant ring is positioned at etched circuit layer 3 middle and upper part, stepped impedance line 6 be positioned at resonant ring 7 under and be connected with resonant ring 7.
In such scheme, described etched circuit layer 3 also comprises two 50 ohm of matched lines 4 and four sections of coupled microstrip lines 5, two 50 ohm of matched lines 4 are symmetrically distributed in the left and right sides of stepped impedance line 6 and resonant ring 7 junctions, and each 50 ohm of matched line 4 is all being connected with two sections of coupled microstrip lines 5 near stepped impedance line 6 and a side of resonant ring 7 junctions.
In such scheme, described resonant ring 7 is square, and described resonant ring 7 is rectangle resonant ring or square resonant ring.
In such scheme, described stepped impedance line 6 is open-circuit line, by one section of high impedance line, is loaded on low-impedance line and is formed.
The ultra wide band bandpass filter that the utility model provides is compared with traditional broadband band-pass filter, and edge steepness has had further improvement, and with a trap wave point, the interference signal in can filtering passband.This filter is single-sided structure, be easy to other microwave circuits integrated, simple in structure, be easy to processing.
Accompanying drawing explanation
Fig. 1 is the structural representation of the ultra wide band bandpass filter with trap wave point that provides of the utility model.
Fig. 2 is the schematic diagram according to the ultra wide band bandpass filter with trap wave point of the utility model embodiment.
Fig. 3 is emulation and the measured result according to the ultra wide band bandpass filter with trap wave point of the utility model embodiment.
In figure: 1. medium substrate, the 2. etched circuit layer of medium substrate upper surface, the 3. ground metal layer of medium substrate lower surface, 4.50 ohm of matched lines, 5. coupled microstrip line, 6. stepped impedance line, 7. resonant ring.
Embodiment
For making method for designing of the present utility model, technical scheme more cheer and bright, below in conjunction with specific embodiment, and with reference to accompanying drawing, the utility model is described in further detail.
As shown in Figure 1, the ultra wide band bandpass filter with trap wave point that the utility model provides, comprise medium substrate 1, be formed at the etched circuit layer 3 and the ground metal layer 2 that is formed at medium substrate lower surface of medium substrate upper surface, wherein etched circuit layer 3 comprises two 50 ohm of matched lines 4, four sections of coupled microstrip lines 5, a stepped impedance line 6 and a resonant ring 7, this resonant ring 7 is square, be positioned at etched circuit layer 3 middle and upper part, stepped impedance line 6 be positioned at resonant ring 7 under and be connected with resonant ring 7, stepped impedance line 6 is open-circuit line, by one section of high impedance line, be loaded on low-impedance line and form.Two 50 ohm of matched lines 4 are symmetrically distributed in the left and right sides of stepped impedance line 6 and resonant ring 7 junctions, and each 50 ohm of matched line 4 is all being connected with two sections of coupled microstrip lines 5 near stepped impedance line 6 and a side of resonant ring 7 junctions.
The effect of resonant ring 7 is to produce wider bandwidth, and by adjusting length and width and the impedance of resonant ring 7, the position of each mode of resonance of capable of regulating, makes it to be evenly distributed in free transmission range, realizes the pass band width of 3.1-10.6.
By adjusting length and the impedance ratio of stepped impedance line 6, can regulate the position of each transmission zero, thereby reach the effect of trap.In the utility model embodiment, by adjusting length and the impedance ratio of stepped impedance line 6, three transmission zero f shown in adjustable Fig. 3
z1, f
z2, f
z3position.Regulate transmission zero f
z2, make it to be positioned at the position of required trap wave point.Regulate another two transmission zero f
z1, f
z3, make it to lay respectively at upper and lower stopband and near the position of passband, can realize precipitous edge.Finally regulate length and width and the gap of coupled microstrip line 5, ripple in free transmission range is reduced, reach smooth.
Application the utility model, free transmission range and the trap wave point of first definite filter, select pcb board material, defines relative dielectric constant and the thickness of sheet material.Regulate length and width and the impedance of resonant ring, reach required free transmission range.Regulate stepped impedance line length wide, reach trap effect and brink.Adjusting coupling line makes in filter passband smooth.
The filter that the utility model provides can directly be printed on frequency PCB plate.The live width of practical filter, line length be with pass band width scope, the difference of the position of trap wave point and pcb board material and difference.
Embodiment
Designing a passband is 3.1GHz-10.6GHz, the filter that trap wave point is 5.7GHz.Used medium substrate is Rogers RO4350, and its relative dielectric constant is 3.5, and thickness is 1.524mm.Through theory, calculate and optimize and obtain the final size (unit: mm) shown in Fig. 2.
The size of the present embodiment is 26.28mm * 19.02mm (not comprising 50 ohm line).Fig. 3 is emulation and the measured data of this embodiment.S
21for insertion loss parameter, S
11for return wave loss parameter.As shown in the figure, the 3dB cut-off frequency of this example is 3.05GHz-10.4GHz, and the insertion loss maximum of the 5.6-5.8GHz of trap place reaches 10.3dB.Upper stopband edge rate of descent is 29.2dB/GHz, and lower stopband edge rate of descent is 79.26dB/GHz.This filter edge is precipitous.
Above-described specific embodiment; the purpose of this utility model, technical scheme and beneficial effect are further described; be understood that; the foregoing is only specific embodiment of the utility model; be not limited to the utility model; all within spirit of the present utility model and principle, any modification of making, be equal to replacement, improvement etc., within all should being included in protection range of the present utility model.