RU2821837C1 - Terahertz band-pass waveguide filter - Google Patents

Abstract

FIELD: microwave equipment.

SUBSTANCE: invention relates to microwave engineering, namely to filters. Terahertz band-pass waveguide filter includes two main sections of rectangular waveguide connected to two resonators. Filter has a central waveguide section. Each resonator has the shape of an elliptical cylinder, the bases of which are located in the planes of narrow walls of the main sections of the rectangular waveguide. Ratio of the semi-axes of the ellipse is selected to provide a single resonance in the pass band. Length of the central section is selected so that in the operating frequency band there is only one resonance corresponding to the operating mode TE _1,0,1. Sequentially arranged the first main section of the rectangular waveguide, the first resonator, the central waveguide section, second resonator and second main section of rectangular waveguide have electrodynamic coupling through narrowed sections of rectangular waveguide. Width of the wide wall of which is equal to the width of the wide wall of the main sections of the rectangular waveguide, and the height of the narrow wall of the narrowed sections is not more than 20% of the height of the narrow wall of the main sections of the rectangular waveguides. Main sections of rectangular waveguide, resonators, section of central waveguide and narrowed sections of rectangular waveguide are made as cavities in metal housing.

EFFECT: providing the presence of only one operating resonance in the required frequency band and increasing the transmission coefficient at the resonant frequency.

1 cl, 3 dwg

Description

The invention relates to microwave technology, namely to the submillimeter wavelength range, and can be used in waveguide paths to measure the radiation frequency of powerful microwave devices, for example, relativistic surface wave generators (SWGs) and high-power pulsed gyrotrons, as well as to suppress out-of-band parasitic oscillations .

The design of a waveguide band-pass filter is known (CN 102856615 “Waveguide band-pass filter suitable for 380 – 390 GHz frequency range”, IPC H01P1/208, H01P11/00, published 01/02/2013), made of silicon dioxide coated gold. The waveguide resonator consists of an input section, an output section and 3-7 resonant cavities located between the input and output sections. The lengths of the resonant cavities in the center of the filter are greater than the lengths of the resonant cavities located at the input and output edges of the filter. The widths of the resonant cavities in the center of the filter are smaller than the widths of the resonant cavities located at the input and output edges of the filter. The waveguide bandpass filter is designed to operate in the frequency range 380 – 390 GHz. Significant disadvantages of this filter are the small operating frequency range (10 GHz), low quality factor and complexity of manufacturing this device.

A bandpass filter (US 11223095 “Waveguide filter”, IPC H01P1/20, H01P1/208, H01P1/211, H01P1/213, published 01/11/2022) was selected as a prototype, which provides, compared to the above filter design, work in a wider range of operating frequencies. The filter is implemented in the K-band and W-band frequency ranges. In the W-band range, the filter consists of two resonant diaphragms, six narrowing waveguides of standard cross-section and three vertically mounted rectangular resonators. In the K-band band, the filter design is based on two resonant diaphragms and three rectangular resonators. The significant disadvantages of this filter are its low quality factor, the complexity of manufacturing this device, and operation in the cm and mm ranges.

The problem to be solved by this invention is the development of a bandpass waveguide filter in the terahertz range, ensuring the presence of only one operating resonance in the required frequency band and a sufficiently high transmission coefficient at the resonant frequency.

The technical result is achieved due to the fact that the developed filter, just like the prototype filter, is a resonant system composed of several selective elements: a section of a rectangular waveguide connected via communication channels to two resonators. The characteristic dimensions of all elements are on the order of the wavelength. What is new in the developed filter is that the electrodynamic characteristics of the filter are adjusted using the parameters of these resonators and the length of the central waveguide section. Each resonator has the shape of an elliptical cylinder, the bases of which are located in the planes of the narrow walls of the main sections of the rectangular waveguide, and the ratio of the semi-axes of the ellipse is chosen such that a single resonance in the passband is ensured. The length of the central section is selected in such a way that there is only one resonance in the operating frequency band, corresponding to the operating mode TE 1,0,1. Moreover, the sequentially located first main section of the rectangular waveguide, the first resonator, the section of the central waveguide, the second resonator and the second main section of the rectangular waveguide have an electrodynamic connection through narrowed sections of the rectangular waveguide, the width of the wide wall of which is equal to the width of the wide wall of the main sections of the rectangular waveguide, and the height of the narrow wall narrowed sections is no more than 20% of the height of the narrow wall of the main sections of the rectangular waveguide. In this case, all elements of the device are made in the form of cavities in a common metal filter housing. The filter housing is composed of two halves, mirror-symmetrical relative to the plane passing through the middle of the wide walls of the main sections of the rectangular waveguide, connected by threaded and pin connections.

The invention is illustrated by the following figures.

Figure 1 shows the design of the proposed bandpass waveguide filter.

Figure 2 shows the magnetic field distributions on the side surface of the filter obtained using the finite element method: a) field structure at the resonance frequency, b) field structure in the stopband.

Figure 3 shows the results of measurements of frequency dependences: a) transmission coefficient T , b) reflection coefficient R of the bandpass filter.

The proposed terahertz bandpass waveguide filter (Fig. 1) includes a metal housing 1 with flanges 2, which consists of two mirror-symmetrical halves connected by threaded and pin connections. In the filter housing 1 there are cavities consisting of a sequentially located first main section 3 of a rectangular waveguide, a first resonator 4 in the form of an elliptical cylinder, a section of the central waveguide 5, a second resonator 6, a second main section 7 of a rectangular waveguide, connected by narrowed sections 8 of a rectangular waveguide. In this case, each of the resonators 4 and 6 has the shape of an elliptical cylinder, the bases of which are located in the planes of the narrow walls of the main sections 3 and 7 of the rectangular waveguide, and the ratio of the semi-axes of the ellipse is chosen such that a single resonance is provided in the passband. This system forms a common highly selective resonator consisting of the above elements. The length of the central waveguide 5 is chosen in such a way as to ensure selective excitation of the lowest mode of the common resonator.

The operating principle of the proposed bandpass waveguide filter can be explained as follows.

The width of the wide wall of the narrowed sections 8 is equal to the width of the wide wall of the main sections 3 and 7 of the rectangular waveguide. The height of the narrow wall of the narrowed sections 8 is no more than 20% of the height of the narrow wall of the main sections 3 and 7 of rectangular waveguides.

Height size $$\Delta$$ 1 narrowed sections 8, connecting resonators 4 and 6 in the form of an elliptical cylinder with a central waveguide 5 and two main sections 3 and 7 of a rectangular waveguide, determines the loaded quality factor of the overall system and the bandwidth. The key component of the proposed filter is the use of selective elements (resonators 4, 6), which, with optimally selected parameters, ensure effective reflection of the working wave. Thus, the operating oscillation field is concentrated in the area of the central waveguide section 5. Unlike the prototype, the proposed device uses only 3 elements, which makes the developed device more compact and attractive in terms of potential applications and ease of implementation.

The length of the central section is selected in such a way that there is only one resonance in the operating frequency band, corresponding to the operating mode TE 1,0,1.

The developed bandpass waveguide filter for the terahertz frequency range is intended for experimental studies of the spectral characteristics of generators of various types. For example, to study mode selection mechanisms in Cherenkov radiation sources based on supersized electrodynamic systems, it is necessary to conduct detailed studies of generation modes, including using the above filter. Such measurements are also in demand for the purpose of determining the mode composition of radiation in pulsed short-wave gyroresonance devices.

Figure 2 shows the amplitude distribution of the magnetic field on the side surface of the filter when solving a stationary problem based on the finite element method. The system was excited using a waveguide port located at the end on the left (see Fig. 2). Registration of the transmitted signal was carried out by the response port located on the right in Fig.2. As follows from Fig. 2a, at the resonant frequency in the electrodynamic system under consideration, the field is mainly concentrated between two resonators in the form of elliptical cylinders, which corresponds to the excitation of the working volumetric mode. Also in this figure, in the areas of the first and second main segments, fields with lower intensity are observed, corresponding to the transmitted and reflected waves. From Fig. 2 b it is clear that in the stopband the field in the second main segment is almost absent, and in the first it is a pronounced standing wave, which indicates a fairly large reflection coefficient.

The electrodynamic characteristics of the developed terahertz filter were studied experimentally on an Agilent panoramic source in the frequency range 220 – 325 GHz. It is shown that in this range there is a single resonance corresponding to the excitation of the operating mode (see Fig. 3). The calculation results show good agreement with experimental data, including a pass frequency of 312 GHz and an out-of-band suppression value of less than 25 dB. In Figure 3, the blue solid curve corresponds to the experimental data, and the red dashed curve corresponds to the 3D finite element simulation.

Thus, the proposed filter is characterized by the presence of only one resonance in the passband in the operating frequency range, which is achieved by choosing the characteristic dimensions of the device comparable to the wavelength, low losses at the operating frequency, a fairly narrow passband (about 0.25%) and a high coefficient passage in the passband (about -4 dB).

The filter is designed for diagnosing radiation in the terahertz frequency range. The system can be manufactured using 3D printing, CNC milling, and erosion.

Claims (1)

Terahertz bandpass waveguide filter, including two main sections of a rectangular waveguide connected to two resonators, characterized in that includes a section of a central waveguide, with each resonator having the shape of an elliptical cylinder, the bases of which are located in the planes of the narrow walls of the main sections of the rectangular waveguide, and the ratio of the semi-axes of the ellipse is selected to provide a single resonance in the passband, and the length of the central section is selected so that in the operating frequency band there was only one resonance corresponding to the operating mode T.E. _1,0,1, and the sequentially located first main section of the rectangular waveguide, the first resonator, the section of the central waveguide, the second resonator and the second main section of the rectangular waveguide have an electrodynamic connection through narrowed sections of the rectangular waveguide, the width of the wide wall of which is equal to the width of the wide wall of the main sections of the rectangular waveguide, and the height of the narrow the walls of the narrowed sections is no more than 20% of the height of the narrow wall of the main sections of rectangular waveguides, while the main sections of the rectangular waveguide, resonators, a section of the central waveguide and narrowed sections of the rectangular waveguide are made as cavities in a metal housing in a waveguide design, and the filter housing is composed of two mirror-symmetrical relative to the plane passing through the middle of the wide walls of the main sections of the rectangular waveguide, halves connected by threaded and pin connections.