Low frequency ultra-wideband four-ridged horn feed

Abstract

The application discloses a low-frequency ultra-wideband four-ridge horn feed source, the aperture of the feed source is greater than 500 mm, and the feed source comprises a feed source skirt structure section, a transition section, a feed source coupling section and four ridge sheets located at the bottom of the feed source, and the bottom of the feed source is sealed; a heat insulation joint is arranged between the feed source coupling section and the transition section. The low-frequency ultra-wideband four-ridge horn feed source separates the current continuous four-ridge horn feed source into sections, separates the smaller volume but larger heat loss rear section of the feed source from the larger volume but smaller heat loss front section, optimizes the high-noise part of the feed source and the specific structure of the refrigeration Dewar, and finally realizes partial refrigeration of the low-frequency ultra-wideband feed source, greatly reduces the noise of a receiver system, improves the sensitivity of a telescope, and further improves the ability of the telescope to discover dim and weak celestial bodies.

Description

Technical Field

[0001] This invention relates to a low-frequency ultrawideband four-ridged horn feed, and more particularly to a low-frequency ultrawideband four-ridged horn feed for radio telescopes. Background Technology

[0002] Currently, the urgent need for real-time ultra-wideband observations by major radio telescopes worldwide, including FAST, is driving ultra-wideband receivers to gradually replace traditional single-octave receivers. This places more stringent demands on the overall performance of the core components of ultra-wideband receivers. The ultra-wideband feed is one of the core components of an ultra-wideband receiver, and its frequency coverage, radiation pattern, reflection loss, and polarization isolation directly affect the operating bandwidth, aperture efficiency, microwave link matching, and telescope polarization performance of the ultra-wideband receiver and even the entire telescope system. Previous research used log-periodic feed technology to achieve frequency coverage exceeding a 6:1 relative bandwidth. However, due to the inherent properties of log-periodic antennas, log-periodic ultra-wideband feeds can only be applied to reflector antennas with specific focal diameter ratios, severely limiting their widespread application in different telescopes. Furthermore, log-periodic ultra-wideband feeds require the use of low-noise differential amplifiers to achieve single-polarization phase matching and gain equalization. Compared to low-noise single-ended amplifiers, current research on low-noise differential amplifiers lags significantly. Their performance in terms of bandwidth, noise, and cryogenics fails to meet the requirements for widespread application in ultra-wideband receivers, severely limiting the application of log-periodic ultra-wideband feeds. In recent years, ultra-wideband feeds based on quad-ridged flared horn technology have been extensively studied. Quad-ridged flared horn feeds can achieve frequency coverage exceeding 6:1, have adjustable beamwidths, can be matched with different types of reflector antennas, and require only a single-port low-noise amplifier. These characteristics have led to widespread research on ultra-wideband quad-ridged flared horn feeds, promoting the development of ultra-wideband receivers for radio telescopes, such as the 0.27-1.62 GHz ultra-wideband receiver for the FAST telescope. Multi-octave ultra-wideband receivers are gradually replacing traditional single-octave receivers and are driving the development of real-time multi-octave ultra-wideband astronomical observations, which is of great significance. However, the four-ridged horn ultrawideband feed faces a prominent problem in low-frequency applications at 100 MHz: the feed's aperture and volume are large, making it impossible to cool it at low temperatures. The feed can only be used in normal temperature environments, resulting in a noise temperature of more than 5 times higher than that of a low-temperature feed, which significantly affects the overall noise performance of the receiver. Summary of the Invention

[0003] The purpose of this invention is to provide a low-frequency ultrawideband four-ridged horn feed source with a novel and unique structure, convenient use, and effective improvement of the overall noise performance of the receiver; the specific technical solution is as follows: A low-frequency ultra-wideband four-ridged horn feed source has a feed source diameter greater than 500 mm and includes a feed source skirt structure section, a transition section, a feed source coupling section, and four ridges located at the bottom of the feed source. The bottom of the feed source is sealed. A heat insulation seam is provided between the feed source coupling section and the transition section. A heat insulation film material coated with a gold film is bonded to the heat insulation seam using conductive adhesive. The gold film thickness is less than 35 micrometers. During bonding, the gold-plated side is placed close to the inner wall of the feed source to utilize the conductivity of the gold film.

[0004] Furthermore, the width of the thermal insulation joint is 1 to 2 millimeters.

[0005] Furthermore, the feed skirt structure segment and the transition segment are separately configured.

[0006] Furthermore, it includes the aforementioned low-frequency ultra-wideband four-ridged horn feed; it also includes a Dewar; the feed coupling section is disposed within the Dewar.

[0007] Furthermore, a feed support cooling platform is provided inside the Dewar; the feed coupling section is fixedly connected to the feed support cooling platform.

[0008] Furthermore, a cold screen and a cold screen support cooling platform are provided inside the Dewar; the cold screen is fixedly connected to the cold screen support cooling platform; the top of the feed coupling section is lower than the top surface of the cold screen.

[0009] Furthermore, the inner cavity of the feed source is provided with an insulating and heat-insulating sealant to block the transition section, and the top surface of the insulating and heat-insulating sealant is not higher than the top surface of the Dewar.

[0010] This invention relates to a low-frequency ultra-wideband four-ridged horn feed, which segments the current continuous four-ridged horn feed. It separates the smaller but heat-lossy rear section of the feed from the larger but heat-loss-reducing front section. Furthermore, it optimizes the design of the high-noise section of the feed and the cooling Dewar specific structure. Ultimately, it achieves partial cooling of the low-frequency ultra-wideband feed, significantly reducing receiver system noise, improving telescope sensitivity, and thus enhancing the telescope's ability to detect fainter celestial objects. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the low-frequency ultra-wideband four-ridged horn feed structure of the present invention; Figure 2 for Figure 1 A half-section view; Figure 3 Schematic diagram of the installation structure for a low-frequency ultra-wideband four-ridged horn feeder; Figure 4 The simulation results for the feed return loss are shown in the figure.

[0012] In the diagram: 1. Low-frequency ultra-wideband four-ridged horn feed; 101. Feed coupling section; 102. Transition section; 103. Feed skirt structure section; 104. Ridge; 2. Dewar; 3. Cold shield; 4. Feed support cooling platform; 5. Cold shield support cooling platform; 6. Insulating and heat-insulating sealing body; 601. Supporting foam; 602. Vacuum sealing film. Detailed Implementation

[0013] The invention will now be described more fully by way of examples. The invention can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments described herein.

[0014] For ease of explanation, spatial relative terms such as “up,” “down,” “left,” and “right” may be used herein to describe the relationship of one element or feature shown in the figure relative to another element or feature. It should be understood that, in addition to the orientation shown in the figure, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figure is inverted, an element described as being “down” of another element or feature would be positioned “up” of that other element or feature. Therefore, the exemplary term “down” can encompass both up and down orientations. The device may be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0015] like Figure 1 , Figure 2 As shown, in this embodiment, the low-frequency ultra-wideband four-ridged horn feed 1 has an aperture greater than 500 mm. The feed includes a feed skirt structure section 103, a transition section 102, a feed coupling section 101, and four ridge plates located at the bottom of the feed. The bottom of the feed is sealed. The feed coupling section 101 and the transition section 102 are separately arranged. After assembly, a heat insulation seam is provided between the feed coupling section 101 and the transition section 102. The heat insulation seam can significantly reduce the heat conduction between the feed coupling section 101 and the transition section 102, keeping the feed coupling section 101 at a low temperature.

[0016] The width of the insulation seam should not be too narrow to avoid affecting the insulation effect; nor should it be too wide to avoid affecting the outward propagation of the electromagnetic wave signal of the feed coupling section 101; the range should be controlled within 1 to 2 millimeters.

[0017] To reduce signal loss, conductive adhesive can be used to bond a gold-plated insulating film to the isolation seam. The gold film thickness should be less than 35 micrometers. This utilizes the conductivity of the gold film while minimizing heat conduction. Of course, when bonding, the gold-plated side should be close to the inner wall of the feed source.

[0018] Alternatively, the feed skirt structure section 103 and the transition section 102 can be set separately; this facilitates the precise installation of the transition section 102 and the feed coupling section 101.

[0019] like Figure 3 As shown, in use, the feed coupling section 101 of the feed in the embodiment should be placed inside the Dewar for cooling. The feed coupling section 101 is used to couple the TEM mode electromagnetic wave in the coaxial transmission line to the TE mode in the feed circular waveguide. 11 The thermal noise of the feed coupling section 101 accounts for more than 80% of the overall feed noise, mainly caused by the coaxial probe and ridge. This invention employs cryogenic cooling of the feed coupling section 101, utilizing the first-stage cold head of a cryogenic Dewar to cool the average physical temperature of the feed coupling section 101 to approximately 60K, thereby significantly reducing the overall physical temperature of the feed. To prevent external heat from being conducted through the upper (300K) and middle (300K) sections of the feed to the feed coupling section 101 (60K) (metal heat conduction), this invention proposes separating an appropriate gap (e.g., 2mm) between the middle and lower sections of the feed. First, the gap can block heat conduction; otherwise, the cryogenic Dewar cooler would be unable to cool the feed coupling section 101 due to the massive heat generated by the external metal thermal connection. Second, for the feed's operating frequency, the gap between the metal sections can be equivalent to a capacitor at high frequencies, and its capacitive reactance can be expressed by the formula... Xc =1 / jω C represents (where ω is the operating angular frequency and C is the gap capacitance). As the formula shows, at a given frequency (ω), a smaller gap is advantageous for achieving a higher capacitance (C), thus increasing the gap capacitive reactance. Xc The smaller the gap, the better for the electromagnetic performance of the feed source; however, with a fixed gap end area, the smaller the gap, the greater the heat radiation between the metal end faces at both ends of the gap, which is detrimental to the cooling of the feed source coupling section 101. But the heat transferred by this kind of heat radiation is extremely small. This invention proposes to minimize the separation end area of ​​the middle and lower sections of the feed source, and design the feed source wall thickness at the break point to be 1 mm, further reducing the amount of heat radiation.

[0020] A feed support cooling platform 4 is provided inside the Dewar 2; the feed coupling section 101 is fixedly connected to the feed support cooling platform 4; the upper end of the transition section 102 is brought close to the Dewar opening through the feed support cooling platform 4.

[0021] To reduce heat radiation, a cold shield 3 and a cold shield support cooling platform 5 are also provided inside the Dewar; the cold shield 3 is fixedly connected to the cold shield support cooling platform 5; after installation, the top of the feed coupling section 101 should be lower than the top surface of the cold shield. The cold shield is also cooled to an average physical temperature of approximately 60K.

[0022] An insulating and heat-insulating sealant 6 can also be provided inside the feed cavity to seal the transition section 102. The top surface of the insulating and heat-insulating sealant 6 is preferably not higher than the top surface of the Dewar flask to improve heat insulation performance. The insulating and heat-insulating sealant 6 can be a combination of a vacuum-sealed film 602 and a supporting foam 601. In use, the trapezoidal structure of the supporting foam 601 is strongly supported by the feed transition section 102 and provides sufficient support force to the vacuum-sealed film 602, which then vacuum-seals the supporting sealing layer. Both the vacuum-sealed film 602 and the supporting foam 601 are transparent to electromagnetic waves and do not affect the propagation of electromagnetic waves from the feed.

[0023] The lower end face of the feed skirt structure section 103 or the upper end face of the transition section 102 can be welded to the opening of the Dewar 2. When the lower end face of the feed skirt structure section 103 or the transition section 102 is set separately, the lower end face of the feed skirt structure section 103 and the upper end face of the transition section 102 are both welded to the opening of the Dewar 2 to form a continuous inner metal surface of the feed, ensuring the continuous transmission of electromagnetic waves.

[0024] To verify the overall electromagnetic performance of the segmented feed proposed in this invention, a return loss simulation was performed on a 0.5-3.3 GHz segmented ultra-wideband feed. The return loss results are shown in [Figure number missing]. Figure 4 As shown, within the ultra-wideband, the return loss is better than -10dB within 95% of the bandwidth, indicating that electromagnetic waves can be effectively transmitted through the slot capacitance, meeting application requirements.

[0025] The feed source in this embodiment significantly reduces the thermal noise of traditional feed sources operating at room temperature: taking a 1GHz operating frequency as an example, the ohmic loss of a traditional continuous surface ultrawideband four-ridged horn feed source is about 0.15dB, and the noise introduced at room temperature (300K) is calculated by the following formula (1):

[0026] in, T e The feed source equivalent noise temperature; L dB For feed source dB Insertion loss in units; T p Feed source physical temperature. Calculations show that the equivalent noise temperature of the feed source at room temperature is approximately 10.5K. However, for the novel segmented feed source and its segmented cooling scheme proposed in this invention: the upper and middle sections of the feed source are connected to the outer metal wall of the cooling Dewar, and their physical temperature... T p The ambient temperature is 300K, and the upper and middle sections have smooth, continuous metallic waveguide inner surfaces, thus their insertion loss is... L dB Only 0.01 dB The introduced thermal noise can be calculated using formula (1) (10 0.01 / 10 -1) * 300K = 0.69K; Besides the smooth waveguide wall, the lower section of the feed also consists of metal ridges, resulting in a relatively high insertion loss of 0.14dB (0.15dB-0.01dB). This invention uses a cooling Dewar to cool the small-sized lower section of the feed to a low temperature of 60K (see...). Figure 3 Feed support cooling platform 4), the thermal noise introduced by the lower section of the feed is (10 0.14 / 10 -1) * 60K = 1.97K, so the overall thermal noise of the feedhorn is 0.69K + 1.97K = 2.66K. From the above calculations, it can be seen that this invention can reduce the thermal noise of the receiver front-end feedhorn by 7.84K, a reduction of 75%. Furthermore, a feedhorn operating at room temperature needs to be connected to a cryogenic Dewar (cooled first-stage cryogenic amplifier) ​​using a certain length (at least 250mm) of room-temperature coaxial cable. Therefore, at a frequency of 1GHz, the thermal noise of a 250mm long room-temperature coaxial transmission line is approximately 10.5K. However, using the feedhorn lower-stage cooling scheme of this invention, both the lower-stage feedhorn and the subsequent cryogenic amplifier are placed in a cryogenic Dewar. The average physical temperature of the interconnecting coaxial cable between the feedhorn output port (60K) and the cryogenic amplifier (10K) is only 35K, and the thermal noise is only (10... 0.15 / 10 -1) * 35K = 1.2K. In summary, the noise introduced by a traditional ultra-wideband feed and its downstream coaxial signal line at room temperature is 21K, while the overall noise introduced by the proposed solution is only 3.86K, a reduction of 17.14K, or 81.6%. The amount and percentage reduction in noise are undoubtedly significant. Taking the deployment of an ultra-wideband receiver on the FAST telescope (300m aperture parabolic reflector) as an example, its receiving area is 70650m². 2 With a telescope efficiency of 60%, the effective area is 42390m². 2 When a room-temperature ultra-wideband feed receiver is deployed, the telescope sensitivity is 42390m. 2 / (21K+10K(noise of the feed circuit))=1367m 2 When the segmented cooled ultra-wideband feed receiver proposed in this invention is deployed, the telescope sensitivity is 42390m. 2 / (2.66K+6.2K(noise of the feed stage circuit))=4784m 2 / K. It can be observed that by employing the segmented feed of this invention, the telescope sensitivity is improved by 3408 m. 2 / K is equivalent to increasing the diameter of a 300m parabolic reflector to 434m, increasing the reflector area by 77209m². 2 The cost would be in the hundreds of millions, making it virtually impossible to implement in practice, thus highlighting the value of this invention.

[0027] The above examples are only for illustrating the present invention. In addition, there are many other different implementations, which can be conceived by those skilled in the art after understanding the concept of the present invention. Therefore, they will not be listed one by one here.

Claims

1. A low-frequency ultra-wideband four-ridged horn feed, the feed having a diameter greater than 500 mm, comprising a feed skirt structure section, a transition section, a feed coupling section, and four ridges located at the bottom of the feed, the bottom of the feed being sealed; characterized in that, A heat insulation seam is provided between the feed coupling section and the transition section; a heat insulation film material coated with gold film is attached to the isolation seam with conductive adhesive, the gold film thickness being less than 35 micrometers; when attaching, the gold-plated side is placed close to the inner wall of the feed, utilizing the conductivity of the gold film.

2. The low-frequency ultra-wideband four-ridged horn feed as described in claim 1, characterized in that, The width of the thermal insulation joint is 1 to 2 millimeters.

3. The low-frequency ultra-wideband four-ridged horn feed as described in claim 1, characterized in that, The feed skirt structure section and the transition section are set separately.

4. A low-frequency ultra-wideband four-ridged horn feed system, characterized in that, It includes a low-frequency ultra-wideband four-ridged horn feed as described in any one of claims 1 to 3; it also includes a Dewar; the feed coupling section is disposed within the Dewar.

5. The feed system as described in claim 4, characterized in that, The Dewar is equipped with a feed support cooling platform; the feed coupling section is fixedly connected to the feed support cooling platform.

6. The feed system as described in claim 4, characterized in that, The Dewar contains a cold screen and a cold screen support cooling platform; the cold screen is fixedly connected to the cold screen support cooling platform; the top of the feed coupling section is lower than the top surface of the cold screen.

7. The feed system as described in claim 4, characterized in that, The inner cavity of the feed source is provided with an insulating and heat-insulating sealant to block the transition section, and the top surface of the insulating and heat-insulating sealant is not higher than the top surface of the Dewar.

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