CN104466320A - Ka wave band broadband band-pass filter utilizing cut-off waveguide - Google Patents

Abstract

The invention relates to a Ka wave band broadband band-pass filter utilizing a cut-off waveguide. According to the Ka wave band broadband band-pass filter, the design method combining the cut-off waveguide theory, the low-pass filter theory and the waveguide gradual change theory is adopted, and a Ka wave band 32-40GHz waveguide broadband filter is designed by the adoption of the design method. When a broad side of a waveguide port is selected, under the condition that the length is fixed, it needs to be guaranteed that the cut-off frequency is smaller than the band-pass low-frequency point of the filter, and low-frequency out-of-band rejection also needs to be guaranteed. According to linear gradual change transition of the wide and narrow sides of the waveguide, when the frequency is higher than and approximate to the cut-off frequency of the waveguide, the wavelength of the waveguide approaches infinite length, and ratio between the waveguide impedance and standard waveguide outlet impedance approaches approximately infinite. The Ka wave band broadband band-pass filter utilizing the cut-off waveguide achieves the filter performance in a broadband transmitter and a broadband transmitting-receiving assembly in an electronic countermeasure.

Description

The Ka band broadband band pass filter of application cut-off waveguide

Technical field

The invention belongs to ECM (Electronic Countermeasures) field, be specifically related to a kind of Ka band broadband band pass filter applying cut-off waveguide.

Background technology

In Millimeter wave countermeasure equipment, the generation that broadband millimeter-wave transmits comes from frequency multiplication and the mixing of low frequency signal, therefore attached various spurious signal, in wideband transmitter, broadband transmitting-receiving subassembly, we need to adopt broadband filter to suppress harmonic wave and spurious signal.At millimeter wave frequency band, filter has the structure such as micro-band, SIW, waveguide.Microstrip filter and SIW filter (substrate integral wave guide filter) due to loss excessive, be not suitable for the output filtering of millimeter wave broadband transmitter, broadband transmitting-receiving subassembly; Waveguide filter has the advantages such as power capacity is large, loss is little, passband is wide, is suitable for the wideband filtered application of millimeter wave broadband transmitter, broadband transmitting-receiving subassembly.In waveguide bandpass filter, traditional structure is the mode that waveguide resonator and coupled structure combine, and this fabric bandwidths is maximum reaches about 15%, when bandwidth is wide, crosses senior general be difficult to realize due to difficulty of processing.In order to the waveguide broad-band band pass filter of design bandwidth 22%, we propose to apply the method for designing design millimeter wave broadband waveguide filter that cut-off waveguide is theoretical, low-pass filtering is theoretical and waveguide gradual change theory combines.

Summary of the invention

The technical problem solved

In order to avoid the deficiencies in the prior art part, the present invention proposes a kind of Ka band broadband band pass filter applying cut-off waveguide, realizes the filtering performance in electronic countermeasures middle width strip transmitter and broadband transmitting-receiving subassembly.

Technical scheme

Apply a Ka band broadband band pass filter for cut-off waveguide, it is characterized in that comprising waveguide lowpass and waveguide transition line; Connect waveguide transition line at the two ends of waveguide lowpass, the broadside size Selection of connectivity port must meet condition: basic mode TE ₁₀mould cut-off frequency is less than the low frequency of filter passband, and basic mode TE ₁₀mould cut-off frequency is higher than the outer low frequency inhibition point of band; And higher mode TE ₂₀mould cut-off frequency leads to high frequency points higher than band, basic mode TE ₁₀mould cut-off frequency is lower than the low frequency of filter passband; The narrow limit size Selection of connectivity port must meet condition: higher mode TE ₁₁mould cut-off frequency higher than band passband high-frequency suppressing point, and meets the requirement of working ability; The size of another port of waveguide transition line matches with the bore of the standard waveguide be connected.

Broadside size and the narrow limit size of described waveguide transition line convert simultaneously, and waveguide width limit linear gradient formula is as follows:

${\mathrm{\Γ}}_{f_0}=\frac{1}{2}\underset{z=0}{\overset{z=L_0}{\∫}}{e}^{-2\mathrm{jz}\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\sqrt{1-{\left(\frac{\mathrm{\λ}}{2(a_0+z\frac{{a-a}_0}{L_0})}\right)}^2}\right)}\frac{d}{\mathrm{dz}}\ln (\frac{1}{Z_0}\×\frac{b_0+z\frac{b-b_0}{L_0}}{a_0+z\frac{{a-a}_0}{L_0}}\×\frac{1}{\sqrt{1-{\left(\frac{\mathrm{\λ}}{2(a_0+z\frac{{a-a}_0}{L_0})}\right)}^2}})\mathrm{dz}$

Wherein: a, b, be the waveguide port before conversion, a ₀, b ₀, be the waveguide port after conversion, L ₀for the length of waveguide transition line, λ is frequency f ₀the air wavelength at place.

Described waveguide transition line and waveguide lowpass connecting portion are provided with a chamfering r.

Described chamfering r is 0.5mm.

The low frequency of described filter passband is 32GHz.

Described outer low frequency inhibition point 30GHz.

Described band passband high-frequency suppressing point 40GHz.

The length of described waveguide transition line is 25mm.

Beneficial effect

A kind of Ka band broadband band pass filter applying cut-off waveguide that the present invention proposes, proposes the Novel Filter method for designing in conjunction with cut-off waveguide theory, low-pass filtering theory and waveguide gradual change theory.When applying cut-off waveguide and being theoretical, control the size of nonstandard waveguide port, application of low-pass Theoretical Design waveguide lowpass, and transform to standard waveguide mouth by waveguide width sideline property grading structure.The present invention, when waveguide port broadside is selected, in length one timing, should ensure that cut-off frequency is less than the low frequency of filter passband, needs again to ensure low frequency Out-of-band rejection.In the property gradual transition of waveguide width sideline, frequency higher than and close to waveguide cutoff frequency time, guide wavelength is close to endless, and waveguide impedance and standard waveguide mouth impedanoe ratio are close to infinitely great.A kind of Ka wave band of the present invention 32-40GHz waveguide broad-band filter, realizes the filtering performance in electronic countermeasures middle width strip transmitter and broadband transmitting-receiving subassembly.

Accompanying drawing explanation

Fig. 1: waveguide broad-band bandpass filter structures figure

1-standard waveguide, 2-waveguide transition line, 3-waveguide lowpass.

Fig. 2: waveguide width sideline property graded junction composition

Fig. 3: waveguide low-pass filter structure figure

Fig. 4: waveguide broad-band band pass filter simulation result figure

Embodiment

Now in conjunction with the embodiments, the invention will be further described for accompanying drawing:

In the present invention, waveguide broad-band band pass filter comprises waveguide port selection, the transition of waveguide transition line, waveguide low-pass filter structure three aspects.Waveguide port will ensure that the outer low frequency of band pass filter band suppresses, and therefore applies cut-off waveguide theoretical, ensure during design waveguide mouth broadside size the cut-off frequency of waveguide higher than and away from the outer low frequency inhibition point of band; When signal enters the waveguide segment identical with waveguide port broadside, will pass through smoothly higher than cut-off frequency signal, lower than cut-off frequency signal, namely waveguide has serious mismatch by showing forceful electric power resistance, and reflection causes very greatly most of power not transmit and to decay.And the size that decays is relevant with the length of cut-off waveguide to the size of propagation constant imaginary part.Propagation constant imaginary part is larger, waveguide length is longer, fixed frequency decays larger.When waveguide port broadside is less, propagation constant imaginary part is larger; Waveguide port broadside is less, and waveguide cutoff frequency is larger.Therefore, when waveguide port broadside is selected, in length one timing, should ensure that cut-off frequency is less than the low frequency of filter passband, need again to ensure low frequency Out-of-band rejection.

In the property gradual transition of waveguide width sideline, frequency higher than and close to waveguide cutoff frequency time, guide wavelength is close to endless, and waveguide impedance and standard waveguide mouth impedanoe ratio are close to infinitely great.Therefore in this regard, waveguide cutoff frequency need away from frequency low in filter passband.The design of waveguide port broadside will consider above three aspects.In the property gradual transition of waveguide width sideline, during waveguide transition, waveguide width limit converts simultaneously, and waveguide width limit linear gradient formula is as follows:

${\mathrm{\Γ}}_{f_0}=\frac{1}{2}\underset{z=0}{\overset{z=L_0}{\∫}}{e}^{-2\mathrm{jz}\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\sqrt{1-{\left(\frac{\mathrm{\λ}}{2(a_0+z\frac{{a-a}_0}{L_0})}\right)}^2}\right)}\frac{d}{\mathrm{dz}}\ln (\frac{1}{Z_0}\×\frac{b_0+z\frac{b-b_0}{L_0}}{a_0+z\frac{{a-a}_0}{L_0}}\×\frac{1}{\sqrt{1-{\left(\frac{\mathrm{\λ}}{2(a_0+z\frac{{a-a}_0}{L_0})}\right)}^2}})\mathrm{dz}$

Wherein: a, b, be the waveguide port before conversion, a ₀, b ₀, be the waveguide port after conversion, L ₀for the length of waveguide transition line, λ is frequency f ₀the air wavelength at place.

By theory deduction pole location and simulation optimization transition length designed in conjunction, ensure that the feasibility of transition.

When according to low pass filter Theoretical Design low pass filter, realize by inductance capacitance.In waveguide lowpass, these go out waveguide lowpass by waveguide height low-impedance line Approximate Design.Now when low pass filter waveguide height Low ESR is similar to, be that the impedance of applying basic mode is similar to reactance component, therefore Narrow Wall of Waveguide limit is maximum, and minimum dimension is suitable, ensure that the impact of higher mode is unlikely to various numerical value and far departs from evaluation when applying waveguide basic mode, ensure processing request again.Therefore, under reactance original cost numerical value is determined, waveguide port impedance is as normalized impedance value, and the narrow limit of waveguide port is selected to ensure above two aspects.Under port is suitable, design applicable waveguide lowpass.

Specific embodiment:

If Fig. 1 is Ka wave band waveguide broad-band bandpass filter structures.Its structure comprises the Ka wave band standard waveguide mouth at two ends, is of a size of a × b, realizes interconnected by this standard waveguide mouth and outside.Be L by length ₀the limit linear transformation of waveguide width realize standard waveguide mouth and transform to nonstandard waveguide mouth, be of a size of a ₀× b ₀, as shown in Figure 2.With the waveguide lowpass that this nonstandard waveguide mouth design cut-off frequency is 40GHz, as shown in Figure 3.

Nonstandard waveguide mouth broadside a ₀design synthesis considers following aspect:

1 is theoretical according to cut-off waveguide, basic mode TE ₁₀mould cut-off frequency is less than the low frequency of filter passband, is namely in this case less than 32GHz.

2 is theoretical according to cut-off waveguide, basic mode TE ₁₀mould cut-off frequency is higher than the outer low frequency inhibition point 30GHz of band, and TE ₁₀mould cut-off frequency is selected to ensure that low frequency suppresses index request.Higher by frequency, low frequency inhibition is better.

3 is theoretical according to cut-off waveguide, higher mode TE ₂₀mould cut-off frequency, higher than band passband high frequency points 40GHz, ensures that in passband be single mode.And higher mode TE ₂₀mould cut-off frequency is higher, and single mode transport frequency band is wider, and effect is better.

4 according to waveguide width sideline property gradual transition, and because operating frequency is the closer to by frequency, guide wavelength is more close to endless, and waveguide impedance is close to infinity.For ensureing that transition is smooth, basic mode TE ₁₀mould cut-off frequency need be less than the low frequency of filter passband, and be namely in this case less than 32GHz, and cut-off frequency is less, in passband, transition effect is better.

The narrow limit b of nonstandard waveguide mouth ₀design synthesis considers following aspect:

1 according to single mode transport requirement, and the narrow limit of any waveguide segment ensures higher mode TE ₁₁mould cut-off frequency higher than and away from band passband high-frequency suppressing point 40GHz.

The 2 narrow limits of any waveguide segment meet working ability.

In the limit linear transformation of waveguide width, by theory deduction pole location and simulation optimization transition length L designed in conjunction ₀, ensure that the feasibility of transition.

At this nonstandard waveguide mouth a ₀× b ₀design cut-off frequency is in the waveguide lowpass of 40GHz, according to chebyshev comprehensively in conjunction with the high Low ESR reactance principle of equal effects, is specifically of a size of 17 rank.The size on every rank as shown in Figure 3.

Utilize Ansoft HFSS electromagnetic simulation software, adopt waveguide broad-band band pass filter form shown in Fig. 1 to carry out simulation optimization to parameters, parameter optimization result is as shown in table 1.

As Fig. 4, simulation result shows: filter passband bandwidth 32-40GHz, echo S11<-20dB in passband band, during f=30GHz, during degree of suppression >=38dB, f=42GHz, and degree of suppression >=23dB.

Table 1 Ka band broadband filter parameter

a	b	a 0	b 0	L 0	r	b 1	b 2	b 3	b 4	b 5	b 6
												7.112	3.556	4.85	1	25	0.5	0.74	2.5	0.4	2.5	0.4	2.5
b 7	b 8	b 9	l 1	l 2	l 3	l 4	l 5	l 6	l 7	l 8	l 9
												0.4	2.5	0.4	0.77	1.02	0.82	1.35	0.98	1.40	1.04	1.39	1.06

Unit is mm.

Claims (8)

1. apply a Ka band broadband band pass filter for cut-off waveguide, it is characterized in that comprising waveguide lowpass and waveguide transition line; Connect waveguide transition line at the two ends of waveguide lowpass, the broadside size Selection of connectivity port must meet condition: basic mode TE ₁₀mould cut-off frequency is less than the low frequency of filter passband, and basic mode TE ₁₀mould cut-off frequency is higher than the outer low frequency inhibition point of band; And higher mode TE ₂₀mould cut-off frequency leads to high frequency points higher than band, basic mode TE ₁₀mould cut-off frequency is lower than the low frequency of filter passband; The narrow limit size Selection of connectivity port must meet condition: higher mode TE ₁₁mould cut-off frequency higher than band passband high-frequency suppressing point, and meets the requirement of working ability; The size of another port of waveguide transition line matches with the bore of the standard waveguide be connected.

2. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: broadside size and the narrow limit size of described waveguide transition line convert, and waveguide width limit linear gradient formula is as follows simultaneously:

${\mathrm{\&Gamma;}}_{f_0}=\frac{1}{2}\underset{z=0}{\overset{z=L_0}{\&Integral;}}{e}^{-2\mathrm{jz}\left(\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sqrt{1-{\left(\frac{\mathrm{\&lambda;}}{2(a_0+z\frac{a-a_0}{L_0})}\right)}^2}\right)}\frac{d}{\mathrm{dz}}\ln (\frac{1}{Z_0}\&times;\frac{b_0+z\frac{b-b_0}{L_0}}{a_0+z\frac{a-a_0}{L_0}}\&times;\frac{1}{\sqrt{1-{\left(\frac{\mathrm{\&lambda;}}{2(a_0+z\frac{a-a_0}{L_0})}\right)}^2}})\mathrm{dz}$

Wherein: a, b, be the waveguide port before conversion, a ₀, b ₀, be the waveguide port after conversion, L ₀for the length of waveguide transition line, λ is frequency f ₀the air wavelength at place.

3. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: described waveguide transition line and waveguide lowpass connecting portion are provided with a chamfering r.

4. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 2, it is characterized in that: described chamfering r is 0.5mm.

5. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: the low frequency of described filter passband is 32GHz.

6. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: described outer low frequency inhibition point 30GHz.

7. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: described band passband high-frequency suppressing point 40GHz.

8. apply the Ka band broadband band pass filter of cut-off waveguide according to claim 1, it is characterized in that: the length of described waveguide transition line is 25mm.