CN115332817B - Resonance-free broadband terahertz partition plate circular polarizer - Google Patents

Abstract

The invention discloses a wideband terahertz partition plate circular polarizer without resonance, which belongs to the technical field of terahertz devices and has a plane symmetrical structure, wherein the wideband terahertz partition plate circular polarizer comprises a pair of input rectangular waveguides manufactured by adopting E-plane waveguide center subdivision, a pair of in-line rectangular waveguide-semicircular waveguide impedance converters manufactured integrally, a stepped partition plate and an output public circular waveguide; the pair of input rectangular waveguides are respectively connected with the output common circular waveguide through corresponding in-line rectangular waveguide-semicircular waveguide impedance converters; the stepped partition board is positioned in the position corresponding to the gap between the pair of in-line rectangular waveguide and the semicircular waveguide impedance transformer in the output common circular waveguide, has the same thickness as the gap, and is connected with the input end of the output common circular waveguide. The invention avoids mode resonance caused by splitting the slit between the stepped partition board and the output public circular waveguide, and realizes the non-mode resonance transmission with low loss and high amplitude consistency in a broadband.

Description

A resonance-free broadband terahertz spacer circular polarizer

Technical Field

The invention belongs to the technical field of terahertz devices, and in particular relates to a non-resonant broadband terahertz partition circular polarizer.

Background Art

Waveguide circular polarizers are important components in dual-polarization antenna feeding systems and radial power combining networks based on circular polarization modes. Circular polarizers usually require excellent broadband performance, simple and compact structure, but these characteristics are difficult to exist in the same component. The rotating grating orthogonal mode converter is considered to be a broadband structure, but its size is too large and complex. Although a folded compact design has been proposed, it will increase the complexity of the structure and the difficulty of manufacturing, and is not suitable for submillimeter wave and terahertz applications.

The baffle circular polarizer has a simple and compact structure and is suitable for high-frequency applications, but its operating bandwidth is relatively narrow. When this concept was first proposed, a fractional bandwidth of 15% was achieved by using inclined baffles and square common circular waveguides. Later, stepped baffles and step-thickness baffles were proposed, respectively, to obtain a fractional bandwidth of 20%, which is close to the theoretical single-mode bandwidth limit. Later, a circular waveguide baffle circular polarizer with a 15% fractional bandwidth was proposed. Due to the single-mode bandwidth limitation of different port shapes, the bandwidth of the circular waveguide is narrower than that of the square waveguide. Therefore, a broadband baffle circular polarizer with a triangular common port was proposed, which achieved a fractional bandwidth of 37.8%, but the uneven distribution of the electric field in the triangular port would affect the radiation pattern. In order to expand the working bandwidth and maintain the uniformity of the electric field, some people set anti-parallel double baffles in the widened rectangular waveguide. Although its bandwidth can reach 40%, mode resonance will occur. In addition, the addition of additional precise structures inside the waveguide makes it unfavorable to expand to the submillimeter and terahertz bands.

In addition to adjusting the port shape or adding additional structures inside the waveguide to broaden the theoretical single-mode bandwidth, another approach is to allow the circular polarizer to operate at frequencies outside the single-mode bandwidth. By carefully optimizing the common waveguide and baffle dimensions, the level of higher-order modes can be reduced. The advantage is that this does not increase the difficulty of manufacturing and can be applied to higher frequency bands. At present, it is relatively easy to realize a resonance-free broadband baffle circular polarizer in the microwave band, because the manufacturing error is negligible compared to the wavelength, and the consistency between the test and simulation results is high. However, the baffle circular polarizers reported in the millimeter-wave band still have resonances at certain frequencies, making it difficult to expand to higher frequencies. Therefore, it is still very challenging to realize a broadband resonance-free baffle circular polarizer at terahertz frequencies.

In addition, mode resonance is affected by waveguide segmentation and manufacturing methods, especially for the popular metal segmentation technology, poor contact between modules will introduce variable air gaps. In existing technologies, the waveguide impedance transformers of almost all baffle circular polarizers are not in the same straight line with their common ports, which means that the baffle circular polarizer can only be segmented at the top, middle or side of the common circular waveguide to adapt to metal precision processing technology. However, these segmentation methods will result in air gaps in the common port and impedance transformer parts. In the terahertz frequency band, the waveguide segmentation gaps are comparable to the working wavelength, and these gaps will cause serious electromagnetic leakage. In addition, due to the size sensitivity of the baffle part of the broadband baffle circular polarizer, the air gaps generated by the traditional segmentation method introduce discontinuities, making it very easy to excite higher-order modes outside the single-mode bandwidth and produce mode resonances.

Summary of the invention

The purpose of the present invention is to provide a non-resonant broadband terahertz partition circular polarizer to address the problems in the above-mentioned prior art, reduce the splitting leakage of the partition circular polarizer in the terahertz frequency band, avoid the mode resonance caused by the splitting gap, and have the advantages of simple and compact structure, high orthogonal mode amplitude consistency, low loss, large working bandwidth and no mode resonance.

The technical solution adopted by the present invention is as follows:

A non-resonant broadband terahertz partition circular polarizer, characterized in that it comprises a pair of input rectangular waveguides, a pair of in-line rectangular waveguide-semicircular waveguide impedance converters, a stepped partition and an output common circular waveguide;

The broadband terahertz partition circular polarizer is a planar symmetrical structure, a pair of input rectangular waveguides are respectively connected to the output common circular waveguide through corresponding in-line rectangular waveguide-semicircular waveguide impedance converters, and the spacing between the pair of in-line rectangular waveguide-semicircular waveguide impedance converters is the same as the thickness of the stepped partition; the stepped partition is located inside the output common circular waveguide at a position corresponding to the gap between the pair of in-line rectangular waveguide-semicircular waveguide impedance converters, and is connected to the input end of the output common circular waveguide;

The pair of input rectangular waveguides are manufactured by adopting the metal block technology of E-plane waveguide center splitting, and the pair of in-line rectangular waveguide-semicircular waveguide impedance transformers, stepped partitions and output common circular waveguide are manufactured by integrating them from the in-line rectangular waveguide-semicircular waveguide impedance transformer end and the output common circular waveguide end to the center.

Furthermore, the pair of in-line rectangular waveguide-semicircular waveguide impedance converters each include at least three orders of rectangular waveguide units with rounded corners on four sides; the length of each order of rectangular waveguide units is 1/4 wavelength; the narrow side size of the last order of rectangular waveguide units is equal to the radius of the connected output common circular waveguide, and the narrow side sizes of the other orders of rectangular waveguide units decrease in an arithmetic progression starting from the input rectangular waveguide; the wide side size of each order of rectangular waveguide units decreases in sequence or is equal to the previous order, and the overall transition is from the wide side size of the input rectangular waveguide to the diameter size of the output common circular waveguide; the inner side of each order of rectangular waveguide units is located in the same plane as the inner side of the corresponding input rectangular waveguide, and the radii of the rounded corners of the two inner edges are consistent and are the processing limit value; the radii of the rounded corners of the two outer edges of each order of rectangular waveguide units increase in sequence, and the radii of the rounded corners of the two outer edges of the last order of rectangular waveguide units are larger than the radius of the connected output common circular waveguide. The above dimensions are preferred dimensions, and the actual dimensional error caused by processing is within an acceptable range of ±0.01 times the wavelength.

Furthermore, the stepped partition includes at least 3 steps, and the thickness is 1/16 to 1/8 of the wavelength.

Furthermore, when the stepped partition has 4 steps, the lengths of the steps are 0.08, 0.24, 0.34 and 0.37 times the wavelength respectively, and the height difference between adjacent steps is 0.07 to 0.13 times the wavelength. The above dimensions are preferred dimensions, and the actual dimensional error caused by processing is within an acceptable range of ±0.01 times the wavelength.

Furthermore, the area where the stepped partition plate meets the inner wall of the output common circular waveguide is rounded, and the radius is a processing limit value.

Furthermore, the pair of input rectangular waveguides each include a first straight waveguide, a first 45° bent waveguide, a second straight waveguide, a second 45° bent waveguide and a third straight waveguide in sequence, which are bent 90° in total, so that the input ports of the pair of input rectangular waveguides are opposite and the output ports are parallel.

Furthermore, when the broadband terahertz clapboard circular polarizer operates in a single-mode frequency band, the radius R of the output common circular waveguide satisfies the single-mode transmission condition of the main mode TE ₁₁ mode, that is,

When the broadband terahertz clapboard circular polarizer operates in a non-single-mode frequency band, the radius R of the output common circular waveguide satisfies:

Wherein, λ _c1 is the cutoff wavelength of the main mode TE ₁₁ mode; λ _c2 is the cutoff wavelength of the first high-order mode TM ₀₁ mode.

The working principle of the resonance-free broadband terahertz partition circular polarizer of the present invention is as follows: according to the basic principle of electromagnetic field, any linear polarized wave can be vector-decomposed into two orthogonal components. The linearly polarized TE ₁₀ mode input from the input rectangular waveguide can also be vector-decomposed into two orthogonal components. In the output common circular waveguide, the rectangular waveguide TE ₁₀ mode is transformed into the circular waveguide TE ₁₁ mode, wherein the asymmetric stepped partition realizes the function of vector decomposition and makes the two orthogonal TE ₁₁ modes produce a phase difference of 90°, thereby generating the circularly polarized TE ₁₁ mode in the circular waveguide.

When the operating frequency of the broadband terahertz partition circular polarizer exceeds the frequency range of single-mode transmission, there will be a risk of high-order mode excitation outside the single-mode bandwidth. By carefully optimizing the dimensions of the stepped partition and the output common circular waveguide, high-order mode excitation can be avoided outside the single-mode bandwidth. When the dimensions of the stepped partition and the output common circular waveguide are unreasonable or additional discontinuities are introduced, high-order modes will be excited and reflected multiple times between the output common circular waveguide and the input rectangular waveguide, causing mode resonance. In the terahertz frequency band, the waveguide splitting gap caused by metal block processing is comparable to the operating wavelength. The discontinuity introduced by the metal block processing splitting method cannot be ignored. The integrated manufacturing of the size-sensitive output common circular waveguide part and the in-line rectangular waveguide-semicircular waveguide impedance converter can avoid the introduction of discontinuities, thereby effectively preventing mode resonance, while reducing transmission loss and achieving mode-free resonance transmission in a wide band.

The beneficial effects of the present invention are:

The present invention proposes a resonance-free broadband terahertz partition circular polarizer. By arranging an in-line rectangular waveguide-semicircular waveguide impedance converter, a transition from an input rectangular waveguide to an output common circular waveguide is achieved. The in-line rectangular waveguide-semicircular waveguide impedance converter is integrated with a size-sensitive stepped partition and an output common circular waveguide, so that no splitting gap is generated and no additional discontinuity is introduced, thereby avoiding electromagnetic leakage and mode resonance caused by the splitting process. By accurately optimizing the sizes of the stepped partition and the output common circular waveguide, the partition circular polarizer in the terahertz frequency band is achieved without high-order mode resonance in a wide frequency band. The polarizer has the advantages of simple and compact structure, high orthogonal mode amplitude consistency, low loss, large working bandwidth and no mode resonance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a three-dimensional diagram of the block-integrated processing of the resonance-free broadband terahertz partition circular polarizer provided in Example 1 of the present invention;

FIG2 is an external three-dimensional stereogram of an electromagnetic signal path in a non-resonant broadband terahertz partition circular polarizer provided in Example 1 of the present invention;

FIG3 is a partial perspective view of FIG2;

FIG4 is a diagram showing S-parameter simulation results of the non-resonant broadband terahertz clapboard circular polarizer provided in Example 1 of the present invention when the waveguide is not sliced and processed and applied to the frequency band of 190 to 270 GHz;

FIG5 is a three-dimensional diagram of conventional dissection processing of a non-resonant broadband terahertz partition circular polarizer provided in Example 1 of the present invention;

FIG6 is a diagram showing the S-parameter simulation results of the non-resonant broadband terahertz partition circular polarizer provided in Example 1 of the present invention when conventional splitting processing ( FIG5 ) is used in the frequency band of 190 to 270 GHz;

FIG7 is a diagram showing the S-parameter simulation results of the non-resonant broadband terahertz partition circular polarizer provided in Example 1 of the present invention when the block-integrated combined processing ( FIG1 ) is applied to the frequency band of 190 to 270 GHz;

The descriptions of the symbols in the accompanying drawings are as follows:

1: a pair of input rectangular waveguides; 101: the third straight waveguide of the first input rectangular waveguide; 102: the third straight waveguide of the second input rectangular waveguide; 2: a pair of in-line rectangular waveguide-semicircular waveguide impedance transformers; 201: the first in-line rectangular waveguide-semicircular waveguide impedance transformer; 202: the second in-line rectangular waveguide-semicircular waveguide impedance transformer; 3: stepped partition; 4: output common circular waveguide.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Example 1

The present embodiment provides a non-resonant broadband terahertz baffle circular polarizer operating in the frequency band of 190 to 270 GHz, the structure of which is shown in FIGS. 1 to 3 , and includes a pair of input rectangular waveguides 1 (i.e., a first input rectangular waveguide and a second input rectangular waveguide), a pair of in-line rectangular waveguide-semicircular waveguide impedance transformers 2 (i.e., a first in-line rectangular waveguide-semicircular waveguide impedance transformer 201 and a second in-line rectangular waveguide-semicircular waveguide impedance transformer 202), a stepped baffle 3 and an output common circular waveguide 4.

The broadband terahertz partition circular polarizer is a planar symmetrical structure, the first input rectangular waveguide is connected to the output common circular waveguide 4 through the corresponding first in-line rectangular waveguide-semicircular waveguide impedance converter 201, the second input rectangular waveguide is connected to the output common circular waveguide 4 through the corresponding second in-line rectangular waveguide-semicircular waveguide impedance converter 202, the spacing between the first in-line rectangular waveguide-semicircular waveguide impedance converter 201 and the second in-line rectangular waveguide-semicircular waveguide impedance converter 202 is the same as the thickness of the stepped partition 3; the stepped partition 3 is located inside the output common circular waveguide 4 at a position corresponding to the gap between the first in-line rectangular waveguide-semicircular waveguide impedance converter 201 and the second in-line rectangular waveguide-semicircular waveguide impedance converter 202, and is connected to the input end of the output common circular waveguide 4.

The first input rectangular waveguide and the second input rectangular waveguide are both WR-4.3 rectangular waveguides (1.092mm*0.546mm), including a first straight waveguide, a first 45° curved waveguide, a second straight waveguide, a second 45° curved waveguide and a third straight waveguide in sequence, which are bent 90° in total, so that the input ports of the first input rectangular waveguide and the second input rectangular waveguide are opposite, and the output ports are parallel. The third straight waveguide 101 of the first input rectangular waveguide and the third straight waveguide 102 of the second input rectangular waveguide are respectively connected to the corresponding first in-line rectangular waveguide-semicircular waveguide impedance converter 201 and the second in-line rectangular waveguide-semicircular waveguide impedance converter 202.

The radius of the output common circular waveguide 4 is 0.496 mm.

The first in-line rectangular waveguide-semicircular waveguide impedance converter 201 and the second in-line rectangular waveguide-semicircular waveguide impedance converter 202 both include 4-order rectangular waveguide units with rounded corners on all four sides; the length of each order rectangular waveguide unit is 0.31 mm, and from a pair of input rectangular waveguides 1 to an output common circular waveguide 4, the wide side dimensions are 1.092 mm, 1.092 mm, 1.05 mm, and 1.01 mm, respectively, and the narrow side dimensions are 0.524 mm, 0.503 mm, 0.481 mm, and 0.491 mm, respectively; the inner side of each order rectangular waveguide unit is located in the same plane as the inner side of the corresponding input rectangular waveguide, and the radius of the rounded corners of the two inner edges is consistent and is the processing limit value of 0.1 mm; the radius of the rounded corners of the two outer edges of each order rectangular waveguide unit increases successively, and is 0.2 mm, 0.3 mm, 0.38 mm, and 0.533 mm, respectively.

The stepped partition 3 includes 4 steps, the thickness of each step is 0.104mm, the lengths are 0.11mm, 0.317mm, 0.47mm, 0.503mm respectively, and the heights are 0.549mm, 0.407mm, 0.256mm, 0.125mm respectively; the area where the stepped partition 3 connects to the inner wall of the output common circular waveguide 4 is chamfered, and the radius is the processing limit value of 0.1mm.

This embodiment uses three-dimensional electromagnetic simulation software to accurately design the size of the non-resonant broadband terahertz baffle circular polarizer. In order to verify the performance and mode resonance of the terahertz baffle circular polarizer proposed in this embodiment, it is applied to the 190-270GHz frequency band for simulation. The simulation results are shown in Figure 4. In the working frequency band of 200-270GHz, the input return loss exceeds 20dB, the input port isolation exceeds 16dB, the orthogonal mode isolation exceeds 40dB, the amplitude difference of the orthogonal mode is less than 0.1dB, the relative bandwidth exceeds 30%, which is much higher than the 20% that can be achieved by the single-mode bandwidth, and no mode resonance occurs, realizing mode-free resonance transmission in a wide band.

In order to more intuitively highlight the beneficial effects proposed by the present invention, the broadband terahertz partition circular polarizer is manufactured by different splitting methods, and electromagnetic simulation is performed in the working frequency band of 190-270GHz, and a 20μm thick air cavity is used to simulate the gap caused by the splitting process. When the conventional splitting process is used for manufacturing (i.e., the metal block technology of the E-plane center splitting is used for the whole), the three-dimensional splitting schematic diagram is shown in Figure 5, and the simulation results are shown in Figure 6. It can be seen from the simulated S parameter results that there is a peak at the frequency of 247GHz, which proves that the conventional splitting process causes the partition circular polarizer to have a mode resonance. In addition, the value of S ₄₁ is significantly reduced, while S ₃₁ is basically unchanged, indicating that the splitting gap causes a component in the orthogonal mode to produce serious electromagnetic leakage, thereby deteriorating the amplitude consistency of the orthogonal mode. When the block-integrated combined processing method proposed in the present invention is adopted (i.e., a pair of input rectangular waveguides 1 are processed by the metal block technology of E-plane center segmentation, and a pair of in-line rectangular waveguide-semicircular waveguide impedance transformers 2, stepped partitions 3 and output common circular waveguide 4 are processed by an integrated process from the in-line rectangular waveguide-semicircular waveguide impedance transformer end and the output common circular waveguide end to the center respectively), its three-dimensional segmentation schematic diagram is shown in Figure 1, and the simulation results are shown in Figure 7. It can be seen from the simulated S parameter results that the curve is smooth, no resonance occurs, and there is no obvious deterioration in amplitude consistency, which proves the effectiveness of the block-integrated combined processing method.

In summary, the resonance-free broadband terahertz baffle circular polarizer proposed in this embodiment can effectively avoid the mode resonance and energy leakage problems caused by the split manufacturing of the broadband terahertz baffle circular polarizer, and has the advantages of simple and compact structure, high orthogonal mode amplitude consistency, low loss, large working bandwidth, and no mode resonance.

The above embodiments only illustrate the principles and advantages of the present invention, and are not intended to limit the present invention. They are only intended to help understand the principles of the present invention. The protection scope of the present invention is not limited to the above configurations and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the disclosed technology without departing from the essence of the present invention, but they are still within the protection scope of the present invention.

Claims (5)

1. A wideband terahertz baffle plate circular polarizer without resonance is characterized by comprising a pair of input rectangular waveguides manufactured by adopting a metal blocking technology of E-plane waveguide center subdivision, a pair of in-line rectangular waveguide-semicircular waveguide impedance converters manufactured integrally and jointly, a stepped baffle plate and an output common circular waveguide; the pair of input rectangular waveguides comprise a first straight waveguide, a first 45-degree bent waveguide, a second straight waveguide, a second 45-degree bent waveguide and a third straight waveguide in sequence, and are bent for 90 degrees altogether; the integrated common manufacturing means integrated processing performed from the in-line rectangular waveguide-semicircular waveguide impedance transformer end and the output common circular waveguide end to the center respectively;

the broadband terahertz partition plate circular polarizer is of a plane symmetrical structure, a pair of input rectangular waveguides are respectively connected with an output public circular waveguide through corresponding in-line rectangular waveguide-semicircular waveguide impedance transformers, and the distance between the pair of in-line rectangular waveguide-semicircular waveguide impedance transformers is the same as the thickness of the stepped partition plate; the stepped baffle is positioned in the output common circular waveguide and corresponds to the gap between the pair of in-line rectangular waveguide and the semicircular waveguide impedance transformer, and is connected with the input end of the output common circular waveguide;

the broadband terahertz partition plate circular polarizer achieves a relative bandwidth of more than 30% in a 190-270 GHz frequency band.

2. The wideband terahertz spacer circular polarizer without resonance according to claim 1, wherein the pair of in-line rectangular waveguide-semicircular waveguide impedance transformers each include rectangular waveguide units with at least 3-order peripheral four edges rounded; the length of each step of rectangular waveguide unit is 1/4 wavelength; the size of the narrow side of the first-order rectangular waveguide unit is equal to the radius of the connected output public circular waveguide, and the sizes of the narrow sides of other various-order rectangular waveguide units are sequentially reduced in an equal-difference array from the input rectangular waveguide; the width dimension of each step of rectangular waveguide unit is sequentially reduced or equal to the width dimension of the previous step, and the whole is in transition from the width dimension of the input rectangular waveguide to the diameter dimension of the output common circular waveguide; the inner side of each step of rectangular waveguide unit and the inner side of the corresponding input rectangular waveguide are positioned on the same plane, the radiuses of the two edges of the inner side are consistent, and the processing limit value is adopted; the radius of the outer two-edge rounding angles of each step of rectangular waveguide units is sequentially increased, and the radius of the outer two-edge rounding angles of the final first step of rectangular waveguide units is larger than that of the connected output public circular waveguide.

3. The wideband terahertz spacer circular polarizer without resonance according to claim 1, wherein the stepped spacer includes at least 3 steps and has a thickness of 1/16 to 1/8 wavelength.

4. The wideband terahertz separator circularly polarizer without resonance according to claim 3, wherein when the stepped separator is 4 steps, the lengths of the steps are 0.08, 0.24, 0.34 and 0.37 times the wavelength in order, and the height difference of the adjacent steps is 0.07 to 0.13 times the wavelength.

5. The wideband terahertz-baffle circular polarizer without resonance according to claim 1, wherein when the wideband terahertz-baffle circular polarizer operates in a single-mode frequency band, the radius R of the output common circular waveguide satisfies:

When the broadband terahertz partition plate circular polarizer works in a non-single-mode frequency band, the radius R of the output common circular waveguide meets the following conditions:

wherein lambda _c1 is the cut-off wavelength of the main mode TE ₁₁ mode; lambda _c2 is the cutoff wavelength of the first higher order mode TM ₀₁ mode.