A microwave ceramic filter with wide temperature range and high stability

Abstract

The application relates to the technical field of radio frequency communication, and discloses a wide-temperature-range high-stability microwave ceramic filter, which comprises a metalized shielding cavity, a composite ceramic resonator array and a self-adaptive input-output coupling network. The metalized shielding cavity is internally provided with a plurality of resonant cavities which are separated by metal partition ribs. The composite ceramic resonator array comprises positive temperature coefficient resonators and negative temperature coefficient resonators which are arranged in an interlaced mode, and the frequency drift amounts generated by the two under heat are superposed and offset on a cascaded transmission path. The self-adaptive input-output coupling network is arranged at a port, differential double-metal probes of the self-adaptive input-output coupling network are driven to generate mechanical deformation by environmental thermal stress, and the physical gap and the equivalent coupling capacitance between the suspended end of the probe and the resonator are dynamically adjusted. Through the double-passive self-generated frequency stabilization mechanism of internal dielectric complementation and external capacitance compensation, the frequency drift phenomenon under the wide-temperature-range alternating environment is eliminated, and the stability of a radio frequency system is improved.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication technology, specifically to a wide-temperature-range, high-stability microwave ceramic filter. Background Technology

[0002] Microwave ceramic filters are key passive components in mobile communication base stations, radar, and satellite radio frequency (RF) front-end systems, primarily used for frequency band selection and out-of-band spurious suppression of RF signals. In actual outdoor working environments, RF front-end systems often face harsh high and low temperature alternating climatic conditions. Drastic changes in ambient temperature cause alterations in the dielectric constant of microwave ceramic materials and thermal expansion and contraction of the device's physical dimensions, leading to a shift in the filter's center frequency and distortion of the passband bandwidth.

[0003] To control temperature drift, conventional techniques involve adjusting the internal composition of a single microwave dielectric ceramic material to minimize its resonant frequency temperature coefficient. However, due to the intrinsic physical properties of the material, a single material cannot maintain an ideal zero temperature coefficient state over a wide temperature range. When the microwave ceramic filter is exposed to environments with significant temperature fluctuations, the residual minute frequency drift will accumulate and amplify within the resonant network, ultimately leading to the derailment of the overall frequency selection network and increased signal transmission loss.

[0004] To address the limitations of intrinsic material properties, some radio frequency (RF) systems opt for external active temperature compensation circuits. These solutions typically rely on temperature sensors to collect environmental data, with a control unit driving heating components or varactor diodes for compensation. This active intervention method requires an additional power supply network and control chip, significantly increasing the physical size and power consumption of the RF front-end system. Furthermore, there are time lags in the acquisition of ambient temperature, the processing of electrical signals, and the physical heating process. Under transient thermal shock conditions, this response lag can cause momentary frequency misalignment, compromising the continuous and stable transmission of high-speed communication signals.

[0005] Furthermore, existing microwave ceramic filters typically employ rigid metal probes with fixed structures at the RF input and output ports for electromagnetic energy feeding and output. When the ambient temperature changes, the difference in the coefficients of linear expansion between the metal cavity, the rigid probe, and the ceramic resonator causes unintended relative displacement of the physical gap between the probe and the resonator. Since the fixed rigid probe cannot adaptively adjust to thermal stress, the equivalent coupling capacitance at the port changes with ambient temperature fluctuations, leading to port impedance mismatch and deterioration of the standing wave ratio (VSWR), directly impacting the signal transmission quality of the entire communication link. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a wide-temperature-range, high-stability microwave ceramic filter, which solves the problem that existing microwave ceramic filters are prone to center frequency drift and port impedance mismatch in wide-temperature-range alternating environments, thus leading to a decrease in the signal transmission quality of radio frequency systems.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a wide-temperature-range, high-stability microwave ceramic filter, comprising: A metallized shielded cavity contains multiple continuously arranged resonant chambers, with adjacent chambers separated by metal ribs. The metal ribs have internal cascaded coupling windows. A composite ceramic resonator array, installed inside the metallized shielded cavity, includes staggered positive temperature coefficient (PTC) and negative temperature coefficient (NTC) resonators, each fixed to the center of the bottom surface of its corresponding chamber. An adaptive input / output coupling network is located at the RF signal input and output ends of the metallized shielded cavity, including a differential bimetallic probe. The first end of the differential bimetallic probe is connected to an external connector, and the second end is suspended above the first or last order resonator, forming a physical gap and equivalent coupling capacitance. The frequency drift generated by the PTC and NTC resonators cancels each other out along the cascaded transmission path. The differential bimetallic probe undergoes mechanical deformation driven by thermal stress, adjusting the equivalent coupling capacitance.

[0008] Furthermore, the substrate of the positive temperature coefficient resonator is made of titanate-based microwave dielectric ceramic material, and the substrate of the negative temperature coefficient resonator is made of barium-zinc-tantalum-based microwave dielectric ceramic material. According to the physical relationship model of resonant frequency temperature coefficient, the resonant frequency of the positive temperature coefficient resonator shifts positively with increasing ambient temperature, and the resonant frequency of the negative temperature coefficient resonator shifts negatively with increasing ambient temperature. When the radio frequency signal is processed by the multi-order resonant network, the frequency shift components introduced by each single-order resonator are algebraically superimposed in the macroscopic topology network to achieve spontaneous cancellation of frequency shift within the system.

[0009] Furthermore, the differential bimetallic probe is formed by composite processing of a first metal conductor and a second metal conductor to form a cantilever beam structure; the first metal conductor is made of an alloy material with a large coefficient of linear expansion, and the second metal conductor is made of an alloy material with a small coefficient of linear expansion; the first end of the differential bimetallic probe passes through the side wall of the metallized shielded cavity for insulating connection, and the second end is directly opposite the top surface coupling region of the first-order resonator or the last-order resonator.

[0010] Furthermore, when the ambient temperature changes, the difference in the linear expansion coefficients of the first metal conductor and the second metal conductor generates an asymmetric thermal expansion within the differential bimetallic probe, driving the suspended end to generate a physical displacement in a direction perpendicular to the resonator surface. This physical displacement changes the physical gap between the lower surface of the suspended end and the coupling area of ​​the top surface of the resonator, and synchronously adjusts the equivalent coupling capacitance of the external port according to the dynamic change model of the equivalent coupling capacitance.

[0011] Furthermore, the metallized shielding cavity is precision machined from Invar alloy material; the inner surface of the metallized shielding cavity and the surface of the internal metal ribs are covered with a conductive metal plating layer, which is composed of a bottom copper plating structure and a top silver plating structure.

[0012] Furthermore, the metallized shielded cavity is equipped with a cross-coupling structure between non-adjacent resonant chambers; the cross-coupling structure includes a secondary coupling window opened on a specific metal rib or an introduced metal coupling rod, which is used to construct an auxiliary electromagnetic energy transmission channel that is different from the main transmission path; when the radio frequency signal is transmitted in the main transmission path and the auxiliary electromagnetic energy transmission channel, the phase difference accumulates and destructive interference occurs, thereby generating a finite transmission zero point.

[0013] Furthermore, the overall center frequency drift of the microwave ceramic filter conforms to the overall drift physical equilibrium equation. In the physical equilibrium equation, the overall frequency deviation trend generated by the thermal disturbance of the dielectric characteristics of each order resonator in the composite ceramic resonator array interacts algebraically with the frequency shift compensation function generated by the dynamic change of the equivalent coupling capacitance caused by the thermomechanical deformation of the adaptive input-output coupling network, thereby maintaining the overall center frequency drift of the microwave ceramic filter in a stable state.

[0014] Furthermore, the base and sidewalls of the metallized shielding cavity are made of surface-metallized polymer carbon fiber composite material, and conductive metal layers are attached to the inner and outer surfaces of the polymer carbon fiber composite material; or, the microwave ceramic filter embeds the composite ceramic resonator array and the adaptive input-output coupling network as a whole into the interior of a low-temperature co-fired ceramic multilayer substrate, and the positive temperature coefficient resonator and the negative temperature coefficient resonator are distributed on different green ceramic layers of the low-temperature co-fired ceramic.

[0015] Furthermore, the adaptive input / output coupling network replaces the differential bimetallic probe with a stepped bimetallic slider structure. The stepped bimetallic slider structure includes a fixed base rail and a bimetallic stacked slider that slides along the rail. The thermal stress caused by changes in ambient temperature drives the stepped end of the slider to translate and slide horizontally along the fixed base rail. According to the physical relationship model of the effective electromagnetic coverage area change, the translation and sliding change the effective electromagnetic coverage area of ​​the slider end facing the top surface of the composite ceramic resonator array, thereby adjusting the equivalent coupling capacitance of the port.

[0016] Furthermore, the adaptive input / output coupling network is configured as a butterfly bimetallic elastic sheet structure to replace the differential bimetallic probe; the butterfly bimetallic elastic sheet is rolled from two metals with different coefficients of linear expansion, and the center of the butterfly bimetallic elastic sheet is anchored on the feed or output base of the radio frequency signal. The cantilever arms on both sides of the butterfly bimetallic elastic sheet extend to the top surface area of ​​the adjacent resonator in a symmetrical fan-shaped geometric shape; under heated conditions, the cantilever arms on both sides are driven to produce symmetrical vertical bending deformation to adjust the physical gap.

[0017] This invention provides a wide-temperature-range, high-stability microwave ceramic filter. It has the following advantages: 1. This invention utilizes the contrasting dielectric constant temperature characteristics of titanate and barium zinc tantalum ceramic materials by arranging positive and negative temperature coefficient resonators alternately inside a metallized shielded cavity. This allows the frequency drift generated by each single-order resonator when the ambient temperature changes to be algebraically superimposed in the cascaded topology network. This enables the frequency deviation to be spontaneously canceled out on the main transmission path of the radio frequency signal, avoiding the data sampling and calculation delay of the external active temperature compensation control circuit and maintaining the center frequency stability of the radio frequency system in a wide temperature range alternating environment.

[0018] 2. This invention sets up an adaptive input-output coupling network composed of metals with different coefficients of linear expansion at the RF signal feed-in and feed-out ends. It utilizes the asymmetric thermal expansion of the differential bimetallic probe when heated to drive the probe's suspended end to generate a vertical physical displacement, thereby changing the physical gap between it and the resonator surface. This simultaneously adjusts the equivalent coupling capacitance of the port. By changing the impedance matching state at the port, it externally compensates for the residual frequency deviation of the internal array, eliminating the transient frequency misalignment and signal attenuation problems caused by transient changes in ambient temperature.

[0019] 3. The metallized shielded cavity of this invention is formed from Invar alloy material and configured with a cross-coupling structure. The low thermal expansion characteristics of Invar alloy provide a stable mechanical reference for the physical spacing of the internal resonant network and the position of the coupling interface, preventing thermal deformation of the shell from disrupting the passive temperature compensation balance at the system level. An auxiliary electromagnetic energy transmission channel is constructed using a secondary coupling window or metal coupling rod, causing destructive interference of the radio frequency signal and generating a finite transmission zero point. This improves the rectangular coefficient of the passband edge and enhances the filter's ability to suppress out-of-band spurious signals. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the algorithm flow of the present invention; Figure 2 This is a schematic diagram of the system architecture of the present invention; Figure 3 This is a schematic diagram of the multi-temperature frequency response of the filter of the present invention; Figure 4 This is a schematic diagram showing the comparison curves of the center frequency drift of the present invention with changes in ambient temperature. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See attached document Figure 1 This invention provides a wide-temperature-range, high-stability microwave ceramic filter, which is applied in an RF front-end system. The RF front-end system includes an antenna unit, a microwave ceramic filter, and an RF transceiver link.

[0023] A microwave ceramic filter is connected in series between the antenna element and the RF transceiver link. In the receive link, the input of the microwave ceramic filter is connected to the antenna element, and the output is connected to the low-noise amplifier in the RF transceiver link. In the transmit link, the input of the microwave ceramic filter is connected to the power amplifier in the RF transceiver link, and the output is connected to the antenna element. The microwave ceramic filter is configured to perform frequency band selection and out-of-band spurious suppression on the RF signals in the RF front-end system.

[0024] See attached document Figure 2 The microwave ceramic filter may include a metallized shielded cavity, a composite ceramic resonator array, an internal cascaded coupling window, and an adaptive input-output coupling network.

[0025] The metallized shielded cavity constitutes the external mechanical support and electromagnetic shielding shell of the microwave ceramic filter. Multiple continuously arranged resonant chambers are housed within the metallized shielded cavity, with adjacent resonant chambers separated by metal ribs. Internal cascaded coupling windows are located on the metal ribs, establishing electromagnetic energy transmission paths between adjacent resonant chambers.

[0026] The composite ceramic resonator array is installed inside a metallized shielded cavity. The array comprises staggered positive temperature coefficient (PTC) and negative temperature coefficient (NTC) resonators. The PTC and NTC resonators are fixed to the center of their respective cavity floor surfaces. Radio frequency (RF) signals pass sequentially through each PTC resonator, NTC resonator, and the internal cascaded coupling window to form a bandpass filter response.

[0027] An adaptive input / output coupling network is positioned at the RF signal feed and output ends of the metallized shielded cavity. The adaptive input / output coupling network includes a differential bimetallic probe. The first end of the differential bimetallic probe connects to an external RF coaxial connector or microstrip transmission line, while the second end of the differential bimetallic probe is suspended above the first or last resonator of the composite ceramic resonator array, forming a physical gap and equivalent coupling capacitance between the differential bimetallic probe and the resonator surface.

[0028] In the adaptive input-output coupling network of this invention, the dynamic compensation process of the differential bimetallic probe is a purely non-contact displacement. When conventional filters use sliding contacts or threaded adjustment structures, the nonlinear contact resistance of the metal contact surface leads to severe passive intermodulation degradation. In this embodiment, the second end of the differential bimetallic probe is always suspended above the first or last order resonator, relying on the air dielectric gap to form an equivalent coupling capacitance. When RF energy is fed in, the strong electric field (E-field) is mainly concentrated in the air gap between the lower surface of the probe's suspended end and the coupling area on the top of the ceramic. To avoid the phenomenon of strong electric field tip discharge, the edges of the differential bimetallic probe are all treated with three-dimensional rounded corner polishing. This strong electromagnetic energy coupling of pure air dielectric combined with the seamless cold-pressing composite process of the probe body completely eliminates the nonlinear mechanical contacts on the current path, so that the third-order passive intermodulation (IMD3) index of the microwave ceramic filter remains stable below -160dBc during wide-temperature dynamic deformation, meeting the requirements of multi-carrier base station systems for extremely low intermodulation.

[0029] Based on the above system architecture, the workflow of the RF front-end system includes the following steps: RF signals are transmitted to the external port of the microwave ceramic filter via the RF transceiver link or antenna unit. The differential bimetallic probe in the adaptive input-output coupling network receives the RF signals and feeds the RF energy into the metallized shielded cavity using the coupling capacitance between its floating end and the first-order resonator.

[0030] Radio frequency (RF) signals propagate along a predetermined cascaded topology path within the composite ceramic resonator array. The RF signals generate electromagnetic resonance alternately between positive and negative temperature coefficient (TTC) resonators via internal cascaded coupling windows. The composite ceramic resonator array selectively transmits the RF signals based on its center frequency and bandwidth settings, and reflects out-of-band spectral components.

[0031] When the microwave ceramic filter is in an operating environment with varying temperatures, the system triggers a passive compensation process. Changes in ambient temperature cause the dielectric constants of the positive temperature coefficient resonator and the negative temperature coefficient resonator to change in opposite directions. The frequency drift generated by the positive and negative temperature coefficient resonators superimposes on the cascaded transmission path and achieves internal cancellation.

[0032] Simultaneously, changes in ambient temperature affect the adaptive input-output coupling network at both ends of the microwave ceramic filter. The differential bimetallic probe undergoes mechanical bending deformation due to the difference in the linear expansion coefficients of its constituent materials. This mechanical deformation drives a physical displacement of the suspended end of the differential bimetallic probe in a direction perpendicular to the resonator surface, thereby altering the physical gap between the probe and the resonator. This change in physical gap synchronously adjusts the equivalent coupling capacitance value of the port, providing external compensation for temperature-induced port impedance shifts.

[0033] After internal frequency compensation of the composite ceramic resonator array and port impedance compensation of the adaptive input-output coupling network, the frequency-stabilized RF signal is output through the differential bimetallic probe above the last-order resonator and fed to the subsequent low-noise amplifier or antenna unit.

[0034] In the actual assembly process of microwave ceramic filters, in order to eliminate the interfacial micro-shear stress caused by the difference in residual thermal expansion coefficients between the composite ceramic resonator array and the bottom surface of the metallized shielded cavity, this embodiment provides a stress-buffered welding layer between the bottom surface of the ceramic substrate and the metal cavity. This stress-buffered welding layer is made of indium-based alloy solder with high ductility (such as In-Sn or In-Ag system), and its thickness is controlled between 20µm and 40µm.

[0035] During high and low temperature alternating cycles, the low yield strength of indium-based alloys allows them to absorb and dissipate transverse thermal stress at the ceramic-metal interface through their own microscopic plastic deformation, thereby preventing microcracks or peeling of the conductive metal plating on the ceramic bottom surface. Simultaneously, this indium-based alloy solder possesses excellent radio frequency conductivity, ensuring a high-frequency, low-impedance connection between the ceramic resonator and the metal cavity ground potential, preventing passive intermodulation (PIM) interference at the contact surface.

[0036] See attached document Figure 3 This embodiment details the material structure and topology configuration of the composite ceramic resonator array.

[0037] The composite ceramic resonator array consists of both positive temperature coefficient (PTC) and negative temperature coefficient (NTC) resonators. The substrate of the PTC resonator is made of titanate-based microwave dielectric ceramic material. The substrate of the NTC resonator is made of barium-zinc-tantalum-based microwave dielectric ceramic material. By adjusting the internal composition ratio of these two types of ceramic materials, their respective dielectric constant temperature coefficients and linear expansion coefficients are determined.

[0038] Temperature coefficient of resonant frequency of a single microwave ceramic resonator Temperature coefficient of dielectric constant of material and coefficient of linear expansion The physical relationship satisfies the following formula: ; Based on the above formula, the material properties are configured such that the resonant frequency of the positive temperature coefficient (PTC) resonator shifts positively with increasing ambient temperature, while the resonant frequency of the negative temperature coefficient (NTC) resonator shifts negatively with increasing ambient temperature. Both PTC and NTC resonators are cylindrical or rectangular block structures. The outer surface of each resonator is covered with a conductive metal layer. This conductive metal layer is solidified onto the ceramic substrate surface using high-temperature sintering silver paste or electroplating copper. An exposed area without the conductive metal layer is reserved at the center of the top end face of each resonator, forming a coupling zone on the top surface. A tuning blind hole, not penetrating the bottom of the substrate, is opened at the central axis position of each resonator to cut the material and set the initial center frequency of the single-order resonator.

[0039] Inside the metallized shielded cavity, positive temperature coefficient (PTC) resonators and negative temperature coefficient (NTC) resonators are physically interleaved along the direction of RF signal transmission. In the preset system-level topology sequence, resonators of adjacent orders are made of materials with opposite temperature coefficients. Taking a fifth-order bandpass filter architecture as an example, the first, third, and fifth-order resonators are PTC resonators, while the second and fourth-order resonators are NTC resonators.

[0040] The radio frequency (RF) signal establishes a resonant mode in the cascaded network of the aforementioned resonators. Adjacent positive temperature coefficient (PTC) and negative temperature coefficient (NTC) resonators are electromagnetically cross-linked using cascaded coupling windows on the internal ribs of the metallized shielded cavity. The spatial position of the cascaded coupling windows determines the properties of the electromagnetic coupling and controls the energy transfer efficiency of the RF signal between adjacent resonators.

[0041] When the ambient temperature changes, the frequency drift generated by a positive temperature coefficient resonator is opposite in sign to that generated by a negative temperature coefficient resonator. The physically interleaved cascaded topology causes these two opposite frequency drifts to be distributed throughout the overall electromagnetic transmission path of the filter. When the RF signal is processed by a multi-order resonant network, the frequency shift components introduced by each single-order resonator are algebraically superimposed within the macroscopic topology, achieving spontaneous cancellation of the frequency offset within the system.

[0042] See attached document Figure 4 This embodiment details the mechanical structure and capacitance compensation principle of the adaptive input / output coupling network. The adaptive input / output coupling network is positioned at the RF signal input and output ports of the metallized shielded cavity to establish a signal interaction path between the external RF connector and the internal composite ceramic resonator array.

[0043] The adaptive input-output coupling network mainly consists of a differential bimetallic probe. The differential bimetallic probe is fabricated from a first metal conductor and a second metal conductor. The first metal conductor is made of an alloy material with a high coefficient of linear expansion, such as beryllium copper alloy. The second metal conductor is made of an alloy material with a low coefficient of linear expansion, such as iron-nickel alloy. The first and second metal conductors are tightly bonded together using a cold-pressing composite process or a laser cladding process to form a cantilever beam structure with thermomechanically sensitive properties.

[0044] The differential bimetallic probe is spatially divided into a fixed end and a floating end. The fixed end of the differential bimetallic probe passes through the insulating dielectric ring on the sidewall of the metallized shielded cavity and is directly soldered to the inner conductor of the external RF coaxial connector. The floating end of the differential bimetallic probe extends into the metallized shielded cavity and is directly opposite the top surface coupling region of the first-order or last-order resonator. A predetermined initial physical distance is maintained between the lower surface of the floating end of the differential bimetallic probe and the top surface coupling region of the resonator, and the two form an initial equivalent coupling capacitance through the air dielectric.

[0045] When the ambient temperature changes, the differential bimetallic probe undergoes bending deformation driven by thermal stress. The difference in the coefficients of linear expansion between the first and second metal conductors results in asymmetric thermal expansion within the differential bimetallic probe. This asymmetric expansion causes a physical displacement of the probe's levitating end along a direction perpendicular to the resonator surface. This physical displacement The calculation formula is as follows: ; In the formula, This represents the effective physical length of the cantilever portion of the differential bimetallic probe. The coefficient of linear expansion of the first metallic conductor. The coefficient of linear expansion of the second metallic conductor. This represents the relative change in ambient temperature.

[0046] The physical displacement generated by the levitated end of the differential bimetallic probe directly alters the physical distance between the coupling region of the lower surface of the levitated end and the top surface of the resonator. This dynamic adjustment of the physical distance causes a synchronous change in the equivalent coupling capacitance at the port. The dynamic change in the equivalent coupling capacitance... The following formula relationship must be satisfied: ; In the formula, Represents the vacuum permittivity. This represents the effective facing area between the suspended end of the differential bimetallic probe and the coupling region on the top surface of the resonator. This represents the initial physical distance between the two. The adaptive input-output coupling network utilizes the aforementioned dynamic capacitance change mechanism to spontaneously adjust the impedance matching state at the port, thereby offsetting the external port impedance mismatch caused by temperature changes.

[0047] This embodiment elaborates in detail on the material reference anchoring configuration of the metallized shielded cavity and the stray suppression mechanism of the internal cascaded coupling structure.

[0048] The metallized shielded cavity, serving as the mechanical reference platform for the entire microwave ceramic filter, is precision-machined from Invar alloy material, which has an extremely low coefficient of linear expansion. Under wide-temperature alternating environmental conditions, the physical properties of Invar alloy material suppress the tendency for the physical dimensions of the metallized shielded cavity to change drastically with temperature. The metallized shielded cavity provides a stable three-dimensional spatial anchor point for the internal composite ceramic resonator array and the adaptive input / output coupling networks at both ends. This stable reference platform prevents unexpected physical displacements in the spacing between internal resonators and the positions of coupling interfaces caused by shell deformation, ensuring that the physical reference of the passive temperature compensation mechanism within the composite ceramic resonator array remains constant.

[0049] The inner surface of the metallized shielded cavity and the surface of the internal metal ribs are both covered with a conductive metal plating. This conductive metal plating consists of a bottom copper plating structure and a top silver plating structure. The bottom copper plating structure enhances the physical adhesion between the entire conductive metal plating and the Invar alloy substrate. The top silver plating structure reduces the RF surface resistance of the inner surface of the metallized shielded cavity, minimizing electromagnetic losses caused by the skin effect when RF signals propagate through the inner wall of the metallized shielded cavity. The configuration of the conductive metal plating improves the overall quality factor of the metallized shielded cavity, maintaining extremely low insertion loss transmission of the composite ceramic resonator array during bandpass filtering and frequency selection.

[0050] Multiple resonant chambers within the metallized shielded cavity are physically separated by metal ribs, each with an internal cascaded coupling window. The three-dimensional geometry of these internal cascaded coupling windows controls the spatial electromagnetic field distribution between adjacent positive and negative temperature coefficient resonators. By adjusting the physical width and height parameters of these internal cascaded coupling windows, the electromagnetic coupling coefficient along the main transmission path is set. When the radio frequency signal passes through these internal cascaded coupling windows, the physical obstruction of the metal ribs and the field constraint of the window area create a passband transmission characteristic with a preset bandwidth.

[0051] To further suppress radio frequency interference signals from adjacent communication frequency bands, a cross-coupling structure is configured inside the metallized shielded cavity between non-adjacent resonant chambers. This cross-coupling structure creates an auxiliary electromagnetic energy transmission channel distinct from the main transmission path. By opening secondary coupling windows on specific metal ribs or introducing metal coupling rods, electromagnetic energy is distributed between the main transmission path and the auxiliary electromagnetic energy transmission channel.

[0052] The phase difference accumulated during the transmission of radio frequency (RF) signals in the main transmission path and the auxiliary electromagnetic energy transmission channel causes destructive interference in a specific out-of-band stopband region, thus generating a finite transmission zero. By setting the physical dimensions and insertion depth of the cross-coupling structure, the capacitive or inductive properties of this auxiliary electromagnetic energy transmission channel can be adjusted. The setting of the capacitive or inductive properties determines whether the finite transmission zero is located at the low-frequency or high-frequency edge of the passband. The introduction of the cross-coupling structure alters the rectangularity coefficient of the microwave ceramic filter's passband edge, enhancing the RF front-end system's ability to suppress out-of-band spurious signals.

[0053] When constructing an auxiliary electromagnetic energy transmission channel, the physical form of the cross-coupling structure determines the frequency domain location of the finite transmission zeros. Specifically, when a secondary coupling window is opened on a specific metal rib (e.g., between the first and third order resonant chambers), the auxiliary channel exhibits significant capacitive properties because electric field spatial coupling mainly occurs between the ceramic resonators. Capacitive cross-coupling causes phase reversal and destructive interference between the auxiliary and main path signals on the high-frequency side of the passband, generating a steep transmission zero at the right edge of the passband, greatly improving the suppression of high-frequency spurious signals. Conversely, when a metal coupling rod is introduced (i.e., an isolated slender conductor inserted into the rib hole), the radio frequency signal induces a high-frequency surface current on the rod, and the auxiliary channel changes from being dominated by an electric field to being dominated by a magnetic field, exhibiting strong inductive properties. Inductive cross-coupling causes the transmission zero to be generated at the low-frequency edge of the passband. Based on the actual anti-interference requirements of the RF system for uplink and downlink adjacent channel signals, capacitive windows and inductive rods can be flexibly combined to achieve a quasi-elliptic function filtering response, optimizing the out-of-band rectangular coefficients without increasing the overall order and physical volume of the filter.

[0054] For harsh coastal or shipboard deployment environments characterized by high salt spray and high humidity, wide-range temperature alternation can easily induce trace amounts of water vapor condensation inside the metallized shielding cavity. Water vapor adhering to the surface of the differential bimetallic probe can lead to changes in dielectric constant and metal oxidation. Therefore, in this embodiment, a nanoscale parylene conformal coating is uniformly coated on the outer surface of the differential bimetallic probe. The thickness of this conformal coating is controlled at 1–2 µm and is prepared using a vacuum chemical vapor deposition (CVD) process.

[0055] Wide-temperature environments not only induce physical dimensional deformation but also significantly alter the surface conductivity of metallic materials. In high-temperature environments (+85°C and above), the decrease in metal conductivity leads to an increase in the microwave surface skin depth. If the coating thickness is insufficient, electromagnetic waves will penetrate the highly conductive layer and enter the underlying high-loss Invar substrate, causing a sharp drop in the filter's unloaded quality factor (Qu).

[0056] In this embodiment, both the inner surface of the metallized shielding cavity and the surface of the metal ribs are treated with a multi-layer composite electroplating process, comprising, in sequence: a 1-2 µm alkaline copper undercoat for enhanced adhesion, a 2-3 µm nickel barrier layer for inhibiting ion diffusion, and a 15-20 µm thick high-purity dense bright silver layer. The thickness of this bright silver layer is strictly set to 4 to 5 times the high-temperature skin depth at the filter's lowest operating frequency. By controlling this thickness threshold, deep electromagnetic field dissipation caused by high-temperature conductivity deterioration is completely blocked. Combined with high-Q composite ceramics, this achieves Q-value locking performance of less than 0.15 dB insertion loss increment at extreme high temperatures.

[0057] The parylene coating not only exhibits extremely low microwave dielectric loss (loss tangent <0.0002) but also does not alter the mechanical stress characteristics of the bimetallic probe, perfectly isolating it from moisture and corrosive ions. Furthermore, this flexible polymer coating provides microscopic-level mechanical damping when the probe undergoes thermomechanical bending or external high-frequency mechanical oscillations, rapidly absorbing the residual vibrational kinetic energy of the probe's cantilever beam structure and preventing rebound oscillations during thermal shock. This further improves the smoothness of the dynamic capacitance compensation process and the transient stability of the RF signal.

[0058] This embodiment details the joint physical response mechanism of the composite ceramic resonator array and the adaptive input-output coupling network during the operation of a microwave ceramic filter. When the temperature of the operating environment of the microwave ceramic filter shifts, the material dielectric complementarity mechanism of the internal composite ceramic resonator array and the physical deformation capacitance compensation mechanism at both ends are activated simultaneously. The overall drift of the system's center frequency is... The drift state is jointly controlled by the internal resonant frequency shift of each single-order resonator and the external compensation frequency shift introduced by the deformation of the external adaptive coupling network. The overall drift state of this system level satisfies the following physical equilibrium equation: ; In the above equilibrium equations, Defined as the total order of the microwave ceramic filter. Representing the Electromagnetic weighting coefficients assigned to a first-order resonator in a multi-order interleaved cascaded electromagnetic topology network. The intrinsic center frequency of this resonator is calibrated under standard room temperature conditions. Refers to the first The temperature coefficient of the resonant frequency of the ceramic unit is pre-configured as a positive or negative value based on the specific material composition ratio in step one. Record the relative change in ambient temperature. The first summation term on the right-hand side of the equation characterizes the overall frequency deviation trend of the composite ceramic resonator array when the dielectric properties of its internal materials are thermally disturbed. This is achieved through the staggered cascading of positive and negative temperature coefficient resonators in physical space and the electromagnetic weights of each order. With the allocation of the summation term, the background residual deviation of the output is suppressed to a very small numerical range.

[0059] The right side of the equilibrium equation Characterizing the thermomechanical deformation of the differential bimetallic probe in the adaptive input-output coupling network, the dynamic change of the equivalent coupling capacitance is expressed. This is mapped to the frequency shift compensation function of the entire frequency selection system. When the internal resonator array exhibits the aforementioned residual bias over a wide temperature range, the vertical mechanical displacement generated by the differential bimetallic probe synchronously reconstructs the impedance matching state between the RF input and RF output ports. The capacitance impedance adjustment process at the external ports directly alters the overall phase shift characteristics of the filter network, thereby generating a compensation frequency shift opposite to the direction of the residual bias in the internal summation term. The system maintains the overall drift through the algebraic cancellation effect between the internal dielectric complementary summation structure and the external capacitance compensation function. It is in a stable state that is close to zero.

[0060] Due to the batch-to-batch dispersion of materials with positive and negative temperature coefficients, microwave ceramic filters require a two-stage precise tuning strategy before leaving the factory to achieve strict alignment of the physical equilibrium equations.

[0061] The first stage is room temperature intrinsic frequency response tuning: at a standard room temperature of 25°C, a miniature high-speed CNC spindle is used to perform micro-cutting on the tuning blind holes reserved in the center of each ceramic resonator, changing the volume ratio of the equivalent inductance to capacitance of the resonator, and precisely tuning the center frequency, out-of-band rejection and return loss of the multi-order interleaved topology network to the design nominal value.

[0062] The second stage is thermal slope matching tuning: the filter is connected to a vector network analyzer and placed in a high and low temperature chamber, where a temperature scan is performed in the range of -40℃ to +85℃, and the initial drift slope of the center frequency is recorded. The control system calculates the required compensation equivalent capacitance change based on the extracted drift slope, and then uses a nanosecond-level ultraviolet laser to perform micro-nano-level ablation etching (Laser Trimming) on ​​the side edges of the differential bimetallic probe. This etching process precisely reduces the effective physical length of the first and second metal conductors ( (or width, changing its thermomechanical bending sensitivity until the overall drift detected by the vector network analyzer.) Approaching zero value. This two-stage tuning strategy ensures the consistency of compensation effect during mass production.

[0063] When handling transient thermal shock conditions, microwave ceramic filters rely on the aforementioned intrinsic structural deformation and the evolution of basic material properties to achieve spontaneous frequency stabilization at the system level. Conventional external active temperature compensation systems rely on temperature sensors to collect data and instruct control units to drive external components to heat up. The signal sampling, transmission, and heating cycle inevitably introduces a time lag in the system's thermodynamic response. Microwave ceramic filters integrate frequency compensation logic into the polarization changes of the microparticles in the dielectric ceramic material and the thermal expansion behavior of the probe alloy lattice.

[0064] When the external ambient temperature undergoes a drastic change, the transient change in the dielectric constant of the material layer within the positive and negative temperature coefficient resonator is synchronously triggered by the physical dimensional expansion and contraction of the differential bimetallic probe structure. This physical mechanism avoids the cross-level transmission and processing time of external electrical signal commands. This zero-delay passive compensation closed loop, constructed using the intrinsic properties of materials and structures, eliminates the transient frequency misalignment and impedance mismatch encountered by the microwave RF front-end system during sudden temperature changes, maintaining the signal transmission continuity of the RF communication link under wide-temperature alternating shocks.

[0065] This embodiment details the system compatibility expansion methods of microwave ceramic filters in different application scenarios, as well as alternative solutions for cavity and coupling structures.

[0066] To address the stringent weight limitations imposed on airborne radar or spaceborne microwave RF front-end systems, metallized shielded cavities are equipped with lightweight alternative structures. In the first lightweight alternative structure, the base and sidewalls of the metallized shielded cavity are made of surface-metallized high-polymer carbon fiber composite material. This high-polymer carbon fiber composite material provides mechanical and physical strength similar to metal alloys while significantly reducing the overall density of the cavity structure. A dense conductive metal layer is chemically plated onto the inner and outer surfaces of the high-polymer carbon fiber composite material to maintain the electromagnetic shielding effectiveness and internal ground potential reference required for RF communication.

[0067] In the second lightweight alternative structure, the microwave ceramic filter abandons the independent external packaging cavity, embedding the composite ceramic resonator array and adaptive input / output coupling network integrally within a low-temperature co-fired ceramic multilayer substrate. Positive and negative temperature coefficient resonators are distributed across different green ceramic layers of the low-temperature co-fired ceramic, forming internal functional patterned regions. Each green ceramic layer is fused into a single substrate component through multilayer lamination and high-temperature sintering. The internal cascaded coupling windows are replaced by a three-dimensional electromagnetic boundary constructed from the metallized via array and planar wiring layers within the multilayer substrate, achieving a highly miniaturized integration of the system-level architecture.

[0068] The differential bimetallic probe structure in the adaptive input-output coupling network also exhibits mechanical evolution and replacement solutions. In sensor communication systems dealing with drastic thermal gradient changes, the adaptive input-output coupling network replaces the original cantilever beam probe with a stepped bimetallic slider structure. The stepped bimetallic slider structure includes a fixed base rail and a bimetallic stacked slider sliding along the rail. Changes in ambient temperature induce a linear thermal expansion difference within the bimetallic stacked slider. This thermal stress drives the stepped end of the slider to translate horizontally along the base rail. This horizontal translational sliding directly alters the effective electromagnetic coverage area of ​​the slider end facing the top surface of the composite ceramic resonator array. The physical relationship between temperature and ambient temperature satisfies the following formula: ; In the formula, The fixed horizontal physical width representing the stepped bimetallic slider. Represents the initial overlap coverage length at standard temperature. This represents the horizontal sliding displacement driven by the thermal expansion difference between the two types of metallic materials. The stepped bimetallic slider structure changes the equivalent coupling capacitance at the port by adjusting the coverage area. Its mechanical structure extends the travel distance of the thermomechanical physical displacement, accommodating a wider range of temperature fluctuations and impedance compensation requirements.

[0069] The adaptive input / output coupling network can also be configured as a butterfly bimetallic elastic sheet structure. The center of the butterfly bimetallic elastic sheet is physically anchored to the feed or output base of the RF signal, with its two cantilever arms extending in a symmetrical fan-shaped geometry to the top surface region of the adjacent resonator. The butterfly bimetallic elastic sheet is rolled from two metals with different coefficients of linear expansion. Under heat, this structure drives the two cantilever arms to produce completely symmetrical vertical bending deformation. This symmetrical deformation mechanism ensures structural stress balance during the dynamic adjustment of the physical gap, suppresses micro-nano-level mechanical resonance phenomena caused by asymmetric cantilever structures under strong external mechanical vibration, and improves the mechanical reliability of the dynamic compensation process.

[0070] The wide-temperature-range passive temperature adaptive compensation mechanism constructed by microwave ceramic filters supports reuse in the architecture of multi-band and multi-mode RF front-end systems. In microwave duplexer and microwave multiplexer architectures, the transmit and receive link channels are independently deployed in the aforementioned composite ceramic resonator interleaved arrays. The adaptive input-output coupling networks of different frequency band channels are aggregated to a single antenna feed interface through a common matching node. Each independent frequency band channel executes its own internal dielectric complementarity and external capacitance compensation mechanism under wide-temperature-range alternating environments. In large-scale multiple-input multiple-output antenna array systems, multiple identical microwave ceramic filters are integrated in parallel on the same metallized shielded cavity base. The parallel integrated filter array reuses the mechanical-thermal-physical reference of the overall substrate to constrain the consistency of the RF signal phase deflection and frequency offset of each independent transmit and receive channel under complex thermal environments, maintaining the multi-channel signal alignment accuracy of high-order modulation and demodulation communication systems.

[0071] Specific application examples: To aid in understanding the technical solution of this invention, this section provides a specific application embodiment for a radio frequency remote unit in a fifth-generation mobile communication base station. This embodiment constructs a microwave ceramic filter operating in the 3.5 GHz band, with a designed ambient temperature range covering -40°C to +85°C.

[0072] In this application embodiment, the composite ceramic resonator array employs a fifth-order Chebyshev bandpass response topology. The first, third, and fifth-order resonators are made of positive temperature coefficient ceramic materials, with a preset resonant frequency temperature coefficient of +10 ppm / ℃. The second and fourth-order resonators are made of negative temperature coefficient ceramic materials, with a preset resonant frequency temperature coefficient of -15 ppm / ℃. A metallized shielded cavity, machined from Invar steel using a CNC machine tool, is used to anchor the physical cascade spacing between the resonators of each order. The differential bimetallic probe in the adaptive input / output coupling network is constructed by cold-pressing beryllium copper alloy conductors and iron-nickel alloy conductors. The cantilever physical length of the probe is configured to be 15 mm, and the initial physical distance between the suspended end and the top surface of the first and last order resonators is configured to be 0.8 mm.

[0073] See attached document Figure 3 To verify the reliability of the microwave ceramic filter in a real environment, the experimental evaluation system was constructed using a high-low temperature alternating test chamber and a vector network analyzer. The microwave ceramic filter was placed inside the high-low temperature alternating test chamber, and its external ports were connected to the vector network analyzer via a phase-stable RF coaxial cable. Figure 3 The input return loss and forward transmission coefficient curves of the microwave ceramic filter were recorded at three ambient temperature nodes: -40℃, +25℃, and +85℃. The data trajectory shows that after undergoing wide-temperature thermal shock cycling, the passband center frequency of the microwave ceramic filter did not physically shift, the signal insertion loss within the passband remained constant, and the cross-coupling transmission zero position in the stopband region did not drift. These test curves confirm that the dielectric complementarity mechanism of the internal composite ceramic resonator array and the capacitance deformation mechanism of the external adaptive input-output coupling network work synchronously to maintain the stability of the overall frequency domain response.

[0074] See attached document Figure 4 To isolate and verify the effect of the dual self-generated frequency stabilization mechanism, a control group filter that did not employ the scheme of this invention was simultaneously tested in the experiment. The control group filter used a ceramic resonator with a single positive temperature coefficient and was configured with a conventional rigid RF probe with no thermomechanical deformation characteristics. Figure 4 The absolute drift data of the center frequency of the experimental group and the control group were extracted within a continuous temperature scanning range from -40℃ to +85℃. The comparison trajectory showed that the center frequency of the control group filter exhibited a unidirectional linear shift as the ambient temperature increased. The center frequency drift trajectory of the microwave ceramic filter using this invention was constrained to near the zero baseline across the entire alternating temperature axis. Through passive intervention via physical structure evolution and material dielectric complementarity, the microwave ceramic filter eliminates impedance mismatch and frequency band shift caused by thermal gradients in the RF system, meeting the passive constant frequency operation requirements of the base station RF front-end under harsh external environments.

[0075] To further aid in understanding the broad applicability and technical advantages of this invention across various industrial sectors, three different embodiments are provided below: Example 1: Radio Frequency Remote Unit Applied to 5G Mobile Communication Base Stations (Conventional Base Station Scenarios) This embodiment constructs a microwave ceramic filter operating in the 3.5 GHz band, with an ambient temperature range of -40°C to +85°C.

[0076] The composite ceramic resonator array employs a fifth-order Chebyshev bandpass response topology. The first, third, and fifth-order resonators are made of positive temperature coefficient ceramics (+10ppm / ℃), while the second and fourth-order resonators are made of negative temperature coefficient ceramics (-15ppm / ℃). An Invar cavity provides the anchoring reference. The differential bimetallic probe cantilever has a physical length of 15mm, and the initial physical distance between the suspended end and the resonator surface is 0.8mm.

[0077] Under high-frequency, high-power continuous wave (CW) feeding conditions, the first-order resonator at the filter input, which bears the maximum RF power, experiences significantly higher Joule heating due to its dielectric loss compared to the last-order resonator. This dynamic thermal gradient within the cavity leads to inconsistent local temperatures sensed by the differential bimetallic probes in different regions, thereby disrupting the global capacitance compensation synchronization.

[0078] To eliminate this negative effect, the Invar shielding cavity of this invention does not employ a homogeneous single-layer structure. Instead, a high thermal conductivity isothermal substrate (such as copper-molybdenum alloy CuMo or aluminum silicon carbide AlSiC) is embedded or explosively laminated at the bottom of the cavity. This isothermal substrate has a thermal conductivity greater than 170 W / (m·K), enabling it to conduct the localized heat generated by the first-order resonator laterally to the entire bottom surface of the filter with extremely low thermal resistance. This three-dimensional heterogeneous metal cavity architecture with low-expansion sidewalls and a high thermal conductivity base plate ensures that even under peak power full-load operation, the temperature difference between each resonant cavity is forcibly clamped within 2°C, guaranteeing that all bimetallic probes always perform synchronous deformation on the same temperature baseline.

[0079] Joint testing using a high-low temperature alternating test chamber and a vector network analyzer showed that the passband center frequency of the microwave ceramic filter did not physically shift at three ambient temperature nodes: -40℃, +25℃, and +85℃. Comparative testing revealed that the control group filter, employing a traditional single positive temperature coefficient and a rigid probe, experienced unidirectional linear frequency derailment. In contrast, the center frequency drift trajectory of this embodiment was strictly constrained to near the zero-baseline (±0.5MHz) across the entire alternating temperature axis, perfectly meeting the stringent requirements of 5G high-capacity data transmission for crosstalk prevention at the frequency band edges.

[0080] Example 2: Application in Low Earth Orbit (LEO) Spaceborne Broadband Communication Systems (Lightweight / Extreme Temperature Difference Scenarios) Spaceborne microwave RF front-ends have extremely high requirements for device size, weight, and resistance to extreme thermal stress. This example constructs a microwave ceramic filter operating in the Ku band (12-18 GHz) in extreme deep space alternating environments with an operating temperature range of -55℃ to +125℃. In this example, the traditional metal shell cavity is abandoned, and the previously described low-temperature co-fired ceramic (LTCC) multilayer substrate embedded architecture is adopted. Positive and negative temperature coefficient microwave dielectric ceramics are formulated into pastes suitable for green ceramic tape casting processes and printed at different spatial positions on layers 3 to 8, forming a three-dimensional staggered resonant network. The adaptive input / output coupling network no longer uses independent mechanical probes but is composed of a bimetallic thin film layer (titanium alloy and copper alloy stack) embedded on the surface of the LTCC substrate. During the intense thermal cycling tests conducted on the satellite, which involved entering the shadow zone (-55°C) and the sunlit zone (+125°C), the heterogeneous ceramic layer within the LTCC substrate spontaneously offset most of the dramatic changes in dielectric constant caused by thermal expansion and contraction. Meanwhile, the surface bimetallic thin film layer underwent slight heat warping, dynamically fine-tuning the parasitic capacitance at the pad ports. This embodiment not only achieved zero frequency drift across a 100 MHz bandwidth but also reduced the overall device weight by 68% compared to traditional Invar cavity solutions, significantly saving on satellite launch payload costs. Furthermore, it eliminated the risk of cold solder joint failure that could occur in mechanically movable parts under the vacuum of space.

[0081] Specific application example 3: Applied to airborne phased array radar systems (high power / strong vibration / transient thermal shock scenarios) Airborne radar systems require filters that can withstand both the transient thermal shocks caused by high-power pulse signals and the strong mechanical vibrations during violent aircraft maneuvers. This embodiment constructs a microwave ceramic filter operating in the X-band (8-12 GHz).

[0082] To balance wide-temperature frequency stability and vibration resistance, the adaptive input / output coupling network in this embodiment adopts the butterfly-shaped bimetallic elastic sheet structure described above. Compared to the single-arm suspended differential bimetallic probe, the center of the butterfly-shaped elastic sheet is firmly anchored to the RF feed base, and the two sides extend in a symmetrical fan shape.

[0083] When the radar transmitter outputs a 500W peak radio frequency pulse, a rapid Joule heat buildup (transient thermal shock) occurs within the filter over milliseconds. At this time, the internal positive and negative temperature coefficient resonators undergo transient polarization cancellation; simultaneously, the butterfly-shaped bimetallic elastic sheet undergoes perfectly symmetrical vertical bending deformation due to heat. Because the deformation force is physically symmetrical, it not only instantly compensates for the port coupling capacitance, maintaining a stable VSWR (VSWR < 1.2) under high power, but also completely eliminates the microphonics effect that might occur during 9G overload maneuvers of fighter jets. Experimental results show that, under the dual harsh conditions of strong frequency sweep vibration and rapid thermal shock, the filter did not exhibit any phase noise degradation or frequency jumps, ensuring the high coherence of the radar target detection signal.

Claims

1. A wide-temperature-range, high-stability microwave ceramic filter, characterized in that, include: A metallized shielded cavity has multiple continuously arranged resonant chambers inside, and adjacent resonant chambers are separated by metal ribs, with internal cascaded coupling windows on the metal ribs. A composite ceramic resonator array, which is installed inside the metallized shielded cavity, includes staggered positive temperature coefficient resonators and negative temperature coefficient resonators, wherein the positive temperature coefficient resonators and the negative temperature coefficient resonators are respectively fixed to the center of the bottom surface of the corresponding resonant cavity. An adaptive input-output coupling network is disposed at the RF signal feed-in end and feed-out end of the metallized shielded cavity, including a differential bimetallic probe. The first end of the differential bimetallic probe is connected to an external connector, and the second end is suspended above the first-order resonator or the last-order resonator, forming a physical gap and an equivalent coupling capacitance. The frequency drifts generated by the positive temperature coefficient resonator and the negative temperature coefficient resonator are superimposed and cancel each other out on the cascaded transmission path. The differential bimetallic probe is driven by thermal stress to generate mechanical deformation and adjust the equivalent coupling capacitance.

2. The wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The substrate of the positive temperature coefficient resonator is made of titanate-based microwave dielectric ceramic material, and the substrate of the negative temperature coefficient resonator is made of barium-zinc-tantalum-based microwave dielectric ceramic material. According to the physical relationship model of resonant frequency temperature coefficient, the resonant frequency of the positive temperature coefficient resonator shifts positively with the increase of ambient temperature, and the resonant frequency of the negative temperature coefficient resonator shifts negatively with the increase of ambient temperature. When radio frequency signals are processed by a multi-order resonant network, the frequency shift components introduced by each single-order resonator are algebraically superimposed in the macroscopic topology network to achieve spontaneous cancellation of frequency offset within the system.

3. The wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The differential bimetallic probe is formed by composite processing of a first metal conductor and a second metal conductor to create a cantilever beam structure. The first metal conductor is made of an alloy material with a large coefficient of linear expansion, and the second metal conductor is made of an alloy material with a small coefficient of linear expansion. The first end of the differential bimetallic probe is insulated and fixed through the side wall of the metallized shielded cavity, and the second end is directly opposite the coupling region on the top surface of the first-order resonator or the last-order resonator.

4. The wide-temperature-range, high-stability microwave ceramic filter according to claim 3, characterized in that, When the ambient temperature changes, the difference in the coefficients of linear expansion between the first metal conductor and the second metal conductor generates an asymmetric thermal expansion within the differential bimetallic probe, driving the suspended end to generate a physical displacement in a direction perpendicular to the resonator surface. The physical displacement changes the physical gap between the lower surface of the suspending end and the coupling area of ​​the top surface of the resonator, and synchronously adjusts the equivalent coupling capacitance of the external port according to the dynamic change model of the equivalent coupling capacitance.

5. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The metallized shielding cavity is precision machined from Invar alloy material. The inner surface of the metallized shielding cavity and the surface of the metal ribs inside are both covered with a conductive metal plating layer, which is composed of a bottom copper plating structure and a top silver plating structure.

6. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The metallized shielded cavity has a cross-coupling structure between non-adjacent resonant chambers inside; The cross-coupling structure includes a secondary coupling window opened on a specific metal rib or an introduced metal coupling rod, used to construct an auxiliary electromagnetic energy transmission channel that is different from the main transmission path. When radio frequency signals are transmitted in the main transmission path and the auxiliary electromagnetic energy transmission channel, they accumulate phase difference and undergo destructive interference, thus generating finite transmission zeros.

7. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The overall center frequency drift of the microwave ceramic filter conforms to the overall drift physical equilibrium equation. In the physical equilibrium equation, the overall frequency deviation trend generated by the thermal disturbance of the dielectric characteristics of each order resonator in the composite ceramic resonator array interacts algebraically with the frequency shift compensation function generated by the dynamic change of the equivalent coupling capacitance caused by the thermomechanical deformation of the adaptive input-output coupling network, thereby maintaining the overall center frequency drift of the microwave ceramic filter in a stable state.

8. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The base and sidewalls of the metallized shielded cavity are made of surface-metallized polymer carbon fiber composite material, and conductive metal layers are attached to the inner and outer surfaces of the polymer carbon fiber composite material. Alternatively, the microwave ceramic filter may embed the composite ceramic resonator array and the adaptive input-output coupling network into the interior of a low-temperature co-fired ceramic multilayer substrate, with the positive temperature coefficient resonator and the negative temperature coefficient resonator distributed on different green ceramic layers of the low-temperature co-fired ceramic.

9. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The adaptive input-output coupling network replaces the differential bimetallic probe with a stepped bimetallic slider structure. The stepped bimetallic slider structure includes a fixed base guide rail and a bimetallic stacked slider that slides along the guide rail. The thermal stress caused by the change in ambient temperature drives the stepped end of the slider to translate and slide along the fixed base guide rail in the horizontal direction. Based on the physical relationship model of the effective electromagnetic coverage area change, the translational sliding changes the effective electromagnetic coverage area of ​​the slider end facing the top surface of the composite ceramic resonator array, thereby adjusting the port equivalent coupling capacitance.

10. A wide-temperature-range, high-stability microwave ceramic filter according to claim 1, characterized in that, The adaptive input-output coupling network is configured as a butterfly-shaped bimetallic elastic sheet structure to replace the differential bimetallic probe; The butterfly-shaped bimetallic elastic sheet is rolled from two metals with different coefficients of linear expansion. The center of the butterfly-shaped bimetallic elastic sheet is anchored on the feed-in or feed-out base of the radio frequency signal. The cantilever arms on both sides of the butterfly-shaped bimetallic elastic sheet extend to the top surface area of ​​the adjacent resonator in a symmetrical fan-shaped geometric shape. When heated, the two cantilever arms are driven to produce symmetrical vertical bending deformation to adjust the physical gap.

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