295results about How to "Improve frequency selectivity" patented technology

A diversity transmitter for use in an OFDM transmission protocol which diversity transmitter comprises: a diversity generator (2) for receiving and diversifying OFDM transmit symbols, and outputting diversified OFDM symbol matrices (DOSM), DOSM symbols within each DOSM being divided into at least two primary streams each comprising different DOSM symbols, a transmit processor for receiving said at least two primary streams of DOSM symbols, and for transforming said each DOSM symbol from the frequency domain into the time domain, and outputting time domain OFDM symbols (TDOSs), a cyclic delay circuit (41 . . . 4P) for dividing at least one of said primary streams of TDOSs into at least two branches of identical TDOSs, each branch for supplying a respective spatial channel for transmission to a receiver, the arrangement being such that, in use, said cyclic delay circuit (41 . . . 4P) applies a cyclic time shift to a TDOS symbol in at least one of said branches before transmission.

The invention discloses a CPU (Central Processing Unit) realizing method based on amplitude-comparison direction finding of a multi-frequency point omnibearing passive radar. A CPU and GPU (Graphic Processing Unit) heterogeneous hardware platform is adopted; a processing module with strong parallelism and the processing module with strong logicality are respectively realized on the GPU and the CPU; the platform is simple and high in use ratio; a system is simple in operation and strong in flexibility when being expanded; the coagulation and the angle measurement are carried out in the CPU; specifically, a coagulating-while-comparing amplitude angle measuring method is adopted; trace point coagulation is combined with amplitude-comparison angle measurement, so that the time for recombining the data after coagulation is omitted; the coagulation and angle measurement processes are embedded in multithreading, so that the time is further saved; and a target point containing the angle information is transferred to a terminal display control platform. According to the CPU realizing method provided by the invention, the problems that a target positioning effect of a single-frequency passive radar detecting system is inferior, the multi-frequency precision is high but the calculated quantity is large and the consumed time is long are solved. The CPU realizing method has the advantages of high processing speed, high angle measuring precision, and wide angle measuring scope, and can be applied to the target detection and positioning for the passive radar.

The invention discloses a stacked type three-order substrate integrated waveguide filter. The stacked type three-order substrate integrated waveguide filter comprises a top surface metal layer, a first dielectric substrate, a first middle metal layer, a second dielectric substrate, a second middle metal layer, a third dielectric substrate and a bottom surface metal layer which are stacked and distributed in sequence, wherein a first resonant cavity, a second resonant cavity and a third resonant cavity are formed in the first dielectric substrate, the second dielectric substrate and the third dielectric substrate respectively; an input port is formed in the top surface metal layer; an output port is formed in the bottom surface metal layer; the first middle metal layer is used for adjusting the magnetic coupling coefficient between the first resonant cavity and the second resonant cavity to obtain a first transmission zero point; and the second middle metal layer is used for adjusting the magnetic coupling coefficient between the second resonant cavity and the third resonant cavity to obtain a second transmission zero point. The stacked type three-order substrate integrated waveguide filter provided by the invention, by adjusting the electromagnetic coupling strength and obtaining extra transmission zero points, greatly improves frequency selection and harmonic suppression characteristics without changing the existing dimensions.

An antenna system includes an antenna element and an electromagnetic bandgap element proximate the antenna element wherein the electromagnetic bandgap element is optimized for narrow bandwidth operation thereby providing radiofrequency selectivity to the antenna system. Preferably the electromagnetic bandgap element is tunable such as through use of a bias-alterable dielectric substrate or other tuning mechanism. The design approach also provides a means of creating an ultra-thin low-profile narrowband tunable channel selective antenna system suitable for low frequency applications.

The utility model discloses a planar capacitance resonator and the related preparation method, comprising a resonance body, a sensor electrode, a driving electrode and a related supporting substrate. The resonator is a suspended structure, and is fixed on the substrate through an anchor point; each of the sensor electrode and the driving electrode comprises an electrode plate and a solder pad, the electrode plates of the sensor electrode and the driving electrode are arranged on the two side of the resonance body separately and keep a clearance from the resonance body, the clearance between the plates performs as the media to form the capacitor structure; the solder pads of the sensor electrode and the driving electrode are fixed on the insulating medium layer, and the solder pads are provided with metal electrodes; the insulating medium layer are fixed on the substrate. The clearance between the any two electrodes of the capacitors is narrower than 100nm. The utility model has the advantages of extremely high dynamic performance, the harmonic resonance frequency exceeding 100 MHz, and the Q factor up to 105.

An apparatus, having as an input an analog signal, is provided. The apparatus comprises a first circuit comprising an impedance transferring circuit configured to band pass filter the input signal, obtaining a filtered signal; the impedance transferring circuit comprising: a transconductance amplifier (1102), and a switching arrangement (1106, 1108) and an impedance circuit (404) connected in series, the switching arrangement being configured to switch the impedance of the impedance circuit of the impedance transferring circuit from base band to the frequency of the input signal. The apparatus further comprises a second circuit (1112) configured to perform down mixing to the filtered signal obtaining a base band signal and a feedback loop connecting the base band signal to the switching arrangement (1114, 1116) and the impedance circuit, the signal of the feedback loop configured to control the properties of the first circuit.

According to the present invention, a transmitter includes: multiple antennas 15-1, 15-2; a DFT unit 04 configured to transform a time domain signal into a frequency domain signal; a cluster mapping unit 05 configured to divide the frequency domain signal into clusters and to assign the clusters to frequencies on the basis of cluster assignment information; an IDFT unit 06 configured to transform a mapped frequency domain signal into a time domain signal; and cyclic delay setting units 11-1, 11-2 configured to set, for the respective multiple antennas, a cyclic delay amount to the IDFT-transformed time domain signal.

The invention discloses a multiple-substrate integrated waveguide filtering power divider. The multiple-substrate integrated waveguide filtering power divider comprises three dielectric substrates and four layers of metal, wherein the four layers of metal are located on the upper surface of the uppermost substrate, on the lower surface of the lowermost substrate and between the substrates respectively. A rectangular metallization through hole array is formed by metallization holes in the four edges. A rectangular resonant cavity is formed by the rectangular metallization through hole array and the two layers of metal between the substrates. An input port is formed in the left side of the rectangular resonant cavity and an output port is formed in the right side of the rectangular resonant cavity. A one-to-four filtering power divider and a one-to-two same-phase or opposite-phase filtering power divider can be flexibly designed. A substrate-integrated waveguide inductive window filter is embedded between the input port and the output port. The multiple-substrate integrated waveguide filtering power divider has the advantages of being broad in band, low in insertion loss, good in input voltage standing wave ratio, good in consistency of amplitudes of output signals, low in amplitude unbalance and the like. The multiple-substrate integrated waveguide filtering power divider can be applied to a microwave and millimeter wave antenna feed network and the like and has wide application prospect in microwave and millimeter wave systems such as a communication system and radar.

The invention discloses a tunable band-stop filter of constant absolute bandwidth based on a modular structure, which comprises a micro-band structure in the upper layer, a medium substrate in the middle layer and a grounded metal plate in the lower layer. The filter can consist of one module unit or a plurality of module units, each of which comprises two resonators and a main transmission line;the two resonators are both half-wavelength resonators which have the same structure, and the two resonators are symmetrical about a central vertical axis in the micro-band structure; the main transmission line comprises a coupling part and a non-coupling part; the coupling part consists of a seventh micro-band line, an eighth micro-band line and a ninth micro-band line, and the lines are sequentially connected to form an n-shaped structure which is arranged at the inside of an n-shaped structure of the coupling part of the resonators; variable capacitance diodes of the two resonators are setwith the same bias voltage; and the filter can be applied to various reconfigurable radio frequency front-end circuits and has the characteristics of constant absolute bandwidth when the frequency istuned. By cascading two or more module units, a tunable band-stop filter of constant absolute bandwidth can be obtained, the frequency selectivity of which is higher.

The present invention discloses a 2.5-dimensional ultra-wide band mobile communication radome of a grid square ring loading via hole structure. The radome is a periodism frequency selective surface mainly formed by a plurality of same period unit arrays, each period unit is mainly formed by upper and lower dielectric layers, metal pasters arranged on the dielectric layers, metal via hole and an air gap layer arranged between the two dielectric layers; the electromagnetic field in the space is incident into the radome and is subjected to the selection filtering through the upper dielectric layer, the air gap layer and the lower dielectric layer in order, and the electromagnetic field with the required frequency band is outputted from the lower dielectric layer to inhibit the energy of the clutter in the condition of changing the incident angle of the electromagnetic wave. The 2.5-dimensional ultra-wide band mobile communication radome of the grid square ring loading via hole structure is suitable for the design of the ultra-wide band mobile communication radome, is wide in the passband bandwidth, very small and stable in the in-band insertion loss, especially, is stable in the wideband performance and good in the frequency selection performance when the incident electromagnetic wave is subjected to big-angle changing, and has a huge application value in the fields such as mobile communication, radar and electromagnetic shielding and the like.

The invention provides an integrated waveguide filter of a medium loaded foldable substrate. The integrated waveguide filter comprises a first metal layer, a first medium layer, a second metal layer, a second medium layer and a third metal layer from top to bottom, wherein a high-dielectric-constant and high-Q-value medium block is embedded into the first medium layer; and a metalized through hole and a blind hole array, which respectively penetrate through the whole structure and the second medium layer, are additionally arranged. The whole body is formed by three main parts including resonant cavity structures, a feeder line structure and a coupling structure. The quantity of the resonant cavity structures is the same as that of the step quantity of the filter; and each resonant cavity structure is formed by a metalized through hole group embedded into the periphery of a medium block and covering parts of the first metal layer and the second metal layer. The feeder line structure can be used for realizing loading land coplanar waveguide on a groove at the edge of the first metal layer. The coupling structure is divided into an inter-digital electric coupling structure for realizing electric coupling and an induction window magnetic coupling structure for realizing magnetic coupling, and is specifically adopted between adjacent resonant cavities according to the design requirements of the filter. The integrated waveguide filter has the characteristics of miniaturization, low inserting loss, high-frequency selectivity, easiness for machining and the like.

The invention discloses a broadband dual-polarization base station filter antenna unit without an external filter circuit and an array thereof. The antenna unit is arranged in the middle of the reflector. The antenna comprises an oscillator arm, a balun and two parasitic metal rings. The vibrator arm is provided with a microstrip line branch, is connected through the balun, and is fed through thebalun, and the balun is provided with a feeder line. The upper part and the lower part of the vibrator arm are respectively provided with parasitic metal rings. The antenna unit has the characteristics of compact and simple structure. The invention realizes good out-of-band rejection effect and has good frequency selectivity without cascading filter, thus avoiding filter insertion loss. The invention realizes high polarization isolation, and realizes stable pattern in wide frequency band at the same time.

The present invention provides a multilayer structure filtering antenna and a microwave communication system. The multilayer structure filtering antenna comprises a first dielectric substrate, a second dielectric substrate and a third dielectric substrate which are overlapped from down to up; the lower surface of the first dielectric substrate is provided with a microstrip feeder; the lower surface and the supper surface of the second dielectric substrate are respectively provided with a first metal layer and a second metal layer, an entirety formed by the first metal, the second dielectric substrate and the second metal layer is provided with a plurality of metallization through holes in rectangular arrangement mode, the first metal layer, the second metal layer and a plurality of metallization through holes commonly form a rectangular resonant cavity, the first metal layer is provided with a coupling slot, and the second metal layer is provided with two opposite radiation slots; and the third dielectric substrate comprises a rectangular main body portion and two extension bodies, and the main body portion is provided with a radiation metal layer. The multilayer structure filtering antenna and the microwave communication system realize high-frequency selectivity, high gain and bandwidth improvement effects, solve the problem that the whole gain of the antenna id decreased caused by a non-radiation resonator, and realize assembling of a filtering antenna through the antenna itself.

The invention discloses an aim satellite and data receiving circuit for a satellite communication receiver, belonging to the technical field of electronic communication. A satellite beacon signal or data signal is subject to down-conversion by a first mixer so that a first intermediate-frequency signal is obtained; the first intermediate-frequency signal successively passes through a band-pass filter, a first amplifier, a numeral control attenuator and a temperature-compensating attenuator, and then is subject to the down-conversion by a second mixer so that a second intermediate-frequency signal is obtained; and after the second intermediate-frequency signal successively passes through a low pass filter and a second amplifier, a one-way signal is output by the through output end of a coupler to be used for subsequent processing, and the other one-way signal is output by the coupling end of the coupler is filtered by a crystal band-pass filter and then is converted into a direct current voltage signal by a logarithmic detector. In the invention, the detector is arranged in the receiver so that the beacon signal is converted into a direct current voltage convenient for measurement, thereby being convenient for finishing aim satellite in the wild; and when the aim satellite work is completed, the circuit can also be utilized to receive the data signal. The circuit disclosed by the invention has the characteristics of good sensitivity, dynamic range, small noise jamming and the like, and is convenient for carrying.

The invention discloses a wide-stop-band LTCC band-pass filter based on the frequency selectivity coupling technology. The wide-stop-band LTCC band-pass filter comprises two quarter-wave resonators, a metal floor and a pair of feeder line structures. The resonators and the feeder lines are distributed on four conductor layers. The feeder lines transmit energy to the resonators in a broadside-coupled mode, and the resonators transmit energy to each other in a side-coupled mode. According to the wide-stop-band LTCC band-pass filter based on the frequency selectivity coupling technology, the frequency selectivity coupling technology is achieved by selecting a proper coupling interval, and therefore third harmonics can be effectively restrained; meanwhile, weak coupling, namely, source-load coupling, is introduced between the two feeder lines, two transmission zeros are generated near a pass band, and therefore good frequency selectivity is achieved; besides, a transmission zero is also generated on a stop band, and therefore the restraint level of the stop band is enhanced. The wide-stop-band LTCC band-pass filter based on the frequency selectivity coupling technology has the advantages of being capable of restraining the third harmonics, high in selectivity, multiple in transmission zero and compact in structure.

The invention belongs to the field of high resolution remote sensing image processing and particularly relates to a high resolution remote sensing image local feature extraction method based on 2D-Gabor. According to the method provided by the invention, a scale space pyramid expression of an image is firstly established; accelerated partition testing features of different feature scales are searched in the scale space, and a maximum value inhibition method is utilized to obtain a feature point and to determine the position and the scale of the feature point; then a local feature descriptor based on a binary system is established; and finally, a Hamming distance is used in a similarity measurement method to perform feature matching of images of the same scene under different perspective conditions, then an RANSAC algorithm is adopted to perform feature purification, and error matching point pairs are removed. The method provided by the invention can accurately simulate cognitive features of the visual cortex and the retina of human beings. In the feature detection process, an invariance property for change in brightness and scale is achieved, and optimal performances can be obtained at the same time in the time domain and the frequency domain.

The invention discloses a broadband dual-polarized filtering dipole antenna without an additional circuit, which is characterized in that two pairs of mutually perpendicular radiation array sub-arms are printed on a horizontal dielectric substrate, and the two pairs of mutually perpendicular radiation array sub-arms are horizontally placed; two vertical dielectric substrates are respectively equipped with baluns to feed the radiation array sub-arms, and the balun includes a slot line, two closed stubs and an inverted L-shaped feeder line with the tail end being open-circuited; the two vertically intersecting vertical dielectric substrates are arranged on a reflecting plate; the closed stubs are close to the middle position of the vertical dielectric substrates on the top and connected withthe radiation array sub-arms on the horizontal dielectric substrate through extending upwards so as to constitute a short-circuit inverted L-shaped resonator together; and the horizontally placed radiation array sub-arms and the part which does not extend upward at the top of each closed stub constitute resonant groove together. The invention realizes a broadband filtering antenna operating at 1.7-2.8GHz, and has the excellent performance such as high isolation, weak cross polarization and good filtering and radiation characteristics.

The invention relates to a submillimeter wave FSS (frequency selective surface) with a loading fractal structure, wherein the submillimeter wave FSS has double frequency band-pass characters, the first central operating frequency is 424GHz, and the 3dB operating frequency is 387-452GHz; the second central operating frequency is 556GHz, and the 3dB operating frequency is 538-593GHz; the device is realized by an array consisting of multiple periodic resonance units, the center of each periodic resonance unit is provided with a Y-shaped three-arm seam, and one three-arm fractal seam pattern is loaded around each Y-shaped seam at every 120 degrees; and the FSS comprises a first silicon material layer, a first metal layer, a second silicon material layer, a second metal layer and a third silicon material layer, the structures of the five layers are cascaded, and the adjacent layers are tightly adhered.

The invention discloses a filtering antenna array based on a multi-mode resonator. The filtering antenna array comprises four same dual-layer stacked microstrip patch antennas arranged symmetrically and a power distribution network with a one-to-four distributor, wherein each dual-layer stacked microstrip patch antenna comprises a first microstrip patch antenna and a second microstrip patch antenna, the power distribution network with the one-to-four distributor comprises an impedance conversion microstrip, a reverse-phase power distribution microstrip, a tapping coupling microstrip, a branch loaded dual-mode resonator and an in-phase power distribution T-type microstrip. The invention designs the filtering power distribution network with filtering and power distribution functions, the dual-layer stacked microstrip patch antenna is used as the last order of a filter network, the filter order is improved, and meanwhile edge selectivity is enhanced. Meanwhile, the antenna is relatively compact in structure, high in gain and good in filter property.

The invention discloses a four-order cross-coupling band pass filter which comprises input and output feeder lines, bandstop structures and first and second resonators, wherein the first and the second resonators are oppositely arranged; a double-mold third resonator is coupled in the first and the second resonators; the first and the second resonators are in the completely same open-loop structure and are used for realizing the coupling of interstage signals; the third resonator is a center loading resonator and comprises an open type microstrip line and a T-shaped structure, wherein the length of the open type microstrip line is the semi-wave length of the center frequency of the filter; the third resonator is embedded in the first and the second resonators to form cross coupling; the input and the output feeder lines are respectively connected to the first and the second resonators; and the two same bandstop structures are loaded on the input and the output feeder lines. According to the invention, the double-mold resonator is embedded between the two semi-wave resonators which are mutually coupled, and simultaneously, an asymmetrical feeding manner is adopted and the bandstop structure is increased, so that the filter has high-frequency selectivity and wide bandstop characteristics.

The invention discloses a micro-strip double-pass-band filter which is respectively applied to a broad-band system and a narrow-band system. The double-pass-band filter is formed on a dielectric substrate and comprises a first resonator, a second resonator, a third resonator, a fourth resonator, a first feeder line, a second feeder line, a first short circuit branch and a second short circuit branch. A three-order interdigital filter is formed by the first feeder line, the second feeder line, the first resonator, the second resonator and the third resonator and a broad-band pass band is generated. A dual-mode filter is formed by the first feeder line, the second feeder line, the first resonator, the third resonator and the fourth resonator and a narrow-band pass band is generated. Parameters of the two pass bands of the double-pass-band filter can be independently adjusted, the pass bands are high in frequency selectivity and isolation, the circuit structure is simple, and performance is good.

The invention discloses a high-isolation duplexer based on a coupled electromagnetic shunt. The high-isolation duplexer mainly solves the problem that an existing duplexer is large in volume and complex in structure and design. The high-isolation duplexer comprises a medium substrate and three ports, wherein a metal conduction band structure (2) is arranged on the front surface of the medium substrate, and an earth plate (3) is arranged on the back surface of the medium substrate; the ports are respectively connected with the metal conduction band structure; the metal conduction band structure is divided into a left part and a right part which are in the same shape and have different sizes, and two wave filters with different frequencies in the symmetrical structure are formed; each wave filter consists of an isosceles right-angled triangle micro-strip ring (7) with an open top, a curved micro-strip line section (8) and a broken line micro-strip line section (9) surrounding the lower part of a triangle; a magnetic coupling through hole (10) is formed in the middle position of the bottom edge of the triangle, an electric coupling opening (11) is formed in the middle of the broken line micro-strip line section (9), and two transmission zeros of each wave filter are respectively controlled by electric coupling and magnetic coupling. The high-isolation duplexer disclosed by the invention is high in isolation and simple in structure, and can be used for a small-scale radio frequency communication system.

The invention provides an ultra wide band filter which comprises a first metal patch (1), a second metal patch (2) and a dielectric substrate (3), wherein the two metal patches are respectively coated on the upper surface and the lower surface of the dielectric substrate, the first metal patch comprises a five-mode step impedance resonator (4), an input coupling feed line (5) and an output coupling feed line (6); the five-mode step impedance resonator (4) comprises one section of low-resistivity line (7), one sections of open-circuit stub lines (8) and two sections of open-circuit stub lines; tail ends of the two sections of open-circuit stub lines are respectively provided with metallization through holes; and the second metal patch is provided with metallization through holes corresponding to those of the first metal patch and is connected with the first metal patch through the metallization through holes. The novel ultra wide band micro-strip band pass filter is realized by adopting a stub line loaded five-mode resonator, and has the characteristics of novel structure, high frequency selectivity, easy regulation of resonance mode, small size and low cost.

The invention discloses a microstrip tri-band bandpass filter. The microstrip tri-band bandpass filter is small in integral size and independently controllable in bandpass characteristics. The microstrip tri-band bandpass filter comprises an upper metal layer, a medium substrate and a lower metal layer which are stacked sequentially from top to bottom. The upper metal layer is printed with a circuit structure, which is composed of a first resonator, a second resonator, a short circuit stub loading half-wavelength resonator, a first U-type half-wavelength resonator, a second U-type half-wavelength resonator, a first S-type half-wavelength resonator, a second S-type half-wavelength resonator, a first feeder and a second feeder. By means of the structure above, three independent filter units can be obtained, and the bandpass frequency and the bandwidth of every filter unit can be adjusted separately, and meanwhile, good frequency selectivity, high interband isolation, low insertion losses and wide attenuation band can be obtained; meanwhile, the microstrip tri-band bandpass filter is compact in structure, small in integral size and applicable to popularization and application in the technical field of microwave filters.

A self-tuning filter that is well suited for use as a output digital filter in a direct conversion delta-sigma transmitter is constructed as a high pass finite impulse response filter having a cutoff frequency of twice the desired carrier frequency. The filter is clocked using the same clock as used for the commutatation within the transmitter. The aliasing effect of the digital filter produces a passband centered around the carrier frequency which allows the information contained in the spectrum around the passband to be transmitted, while effectively filtering out the quantization noise produced by the commutation. When the commutator clock frequency is changed in order to change the carrier frequency, the passband automatically moves to track the new carrier frequency. The output filter may be constructed using series connected flip-flops with analog taps and an analog summer connected to respective Q and {overscore (Q)} outputs, thereby producing an analog output.

The present invention belongs to the technical field of antennae, and discloses a frequency-reconfigurable filter antenna applied to a UWB / WLAN. The frequency-reconfigurable filter antenna applied to the UWB / WLAN comprises: a radiation structure, a feeding structure, a filter structure, a radio frequency control structure, a reflection structure and a dielectric substrate. The present invention can achieve band switching among an ultra wide band state, a 2.4GHz WLAN narrow band state and a 5.8GHz WLAN narrow band state. Due to integrated design of a filter, and by controlling on-off of a diode, the antenna can work under the switched wide band or narrow band state. Moreover, due to an integrated filter function, the narrow band state can achieve good frequency selectivity and high harmonic suppression characteristics.

The invention provides a double-frequency band-pass filter, which belongs to the design field of microwave and millimeter wave devices. The filter comprises a first metal patch, a second metal patch and a medium substrate, wherein the two metal patches are respectively wrapped on the upper surface and the lower surface of the medium substrate; the first metal patch consists of an input feeder line, an output feeder line and two three-mode stepped impedance resonators; the two resonators are respectively provided with three metallized through holes; and three metallized through holes corresponding to the first metal patch are arranged on the second metal patch. The double-frequency band-pass filter is designed by using two three-mode stepped impedance resonators which are loaded by stub lines; each resonator can generate and independently control a pass band; the bandwidths of the two pass bands are respectively 15.4 % and 10.2 %; four transmission zero points are generated, so that the band-pass filter has the characteristics of high frequency selection performance, independent pass band control, low cost, high performance, small size and adjustable pass band widths.

The invention relates to a broadband receiver circuit with adjustable impedance matching frequency, which belongs to the field of radio frequency integrated circuits. The broadband receiver circuit comprises a low-noise transconductance amplifier, two passive frequency mixers, a quadrature trans-impedance amplifier I path, a quadrature trans-impedance amplifier Q path, a feedback resistor, two double-pole double-throw switches and four variable resistors, wherein a radio frequency input signal is connected with an input end of the low-noise transconductance amplifier and is connected with an input end of the second passive mixer through using the feedback resistor; an output end of the low-noise transconductance amplifier is connected with a signal input end of the first passive mixer; clock input ends of the two passive mixers are connected with four-phase non-overlapping clock signals; a signal output end of the first passive mixer is connected with a differential input end of the Ipath and a differential input end of the Q path; differential output signal ends of the I path and the Q path are connected with a four-phase input end of the second passive mixer; and the four variable resistors are bridged at input ends and output ends of the I path and the Q path through using the two double-pole double-throw switches. The broadband receiver circuit is suitable for zero-intermediate-frequency and low-intermediate-frequency receiver schemes.

The invention discloses a multi-band tunable microstrip band-pass filter which comprises a three-layer structure: a front metal microstrip line, a middle dielectric plate layer, input and output ports and an earthing metal through hole, and a metal coating at the back of a dielectric plate, wherein the metal microstrip line is a symmetric resonator consisting of a half-wavelength uniform impedance line resonator and an open-loop dual-mode resonator; the two resonators share input and output coupling lines; and a variable capacitance diode is loaded between the tail end of the open-loop dual-mode resonator and the earthing metal through hole to form a tunable structure. The filter is compact in structure, low in passband insertion loss, steep in passband edge and high in selectivity, and meets a development trend of filter miniaturization.