阅读说明：本技术 一种基于零反射网络的辐射计 (Radiometer based on zero reflection network ) 是由 毕晓君 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种基于零反射网络的辐射计,包括：多级低噪声放大器和零反射网络；多级低噪声放大器包括：N个级联的单级低噪声放大单元,依次记为第一级低噪声放大单元、……、第i级低噪声放大单元、……和第N级低噪声放大单元,用于将射频输入信号进行放大,零反射网络用于将多级低噪声放大器的输出阻抗进行匹配,并将带外反射信号进行吸收以实现端口无反射信号；混频器可以设置于基于零反射网络的外差式辐射计的最后一级；检波器可以设置于基于零反射网络的直检式辐射计的最后一级。本发明通过零反射网络的引入,提升了辐射计系统的线性度、灵敏度和稳定性,同时减小了电路尺寸。(The invention discloses a radiometer based on a zero reflection network, which comprises: a multi-stage low noise amplifier and a zero reflection network; the multistage low noise amplifier includes: the N cascaded single-stage low-noise amplification units are sequentially marked as a first-stage low-noise amplification unit, … …, an i-th-stage low-noise amplification unit, … … and an N-th-stage low-noise amplification unit and are used for amplifying a radio frequency input signal, and the zero reflection network is used for matching the output impedance of the multi-stage low-noise amplifier and absorbing an out-of-band reflection signal to realize no-reflection signal at a port; the mixer can be arranged at the last stage of the heterodyne radiometer based on the zero reflection network; the detector can be arranged at the last stage of the direct-detection radiometer based on the zero-reflection network. The invention improves the linearity, sensitivity and stability of the radiometer system and reduces the circuit size by introducing the zero reflection network.)

1. A radiometer based on a zero reflection network, comprising: a multi-stage low noise amplifier and a zero reflection network;

the multistage low noise amplifier includes: n cascaded single-stage low-noise amplification units, which are sequentially marked as a first-stage low-noise amplification unit, … …, an ith-stage low-noise amplification unit, … … and an Nth-stage low-noise amplification unit, are used for amplifying a radio-frequency input signal,

the zero reflection network is used for matching the output impedance of the multistage low noise amplifier and absorbing out-of-band reflection signals to realize no-reflection signals at a port;

wherein N represents the number of the single-stage low-noise amplification units, i represents the serial number of the single-stage low-noise amplification units, N is an integer greater than or equal to 2, and i is greater than or equal to 1 and less than or equal to N.

2. The radiometer of claim 1, wherein said zero reflection network is connected to the output of said nth stage low noise amplification unit for matching in-band impedance and absorbing out-of-band reflected signals.

3. The radiometer of claim 1, wherein the zero reflection network is disposed between any two of the N single-stage low noise amplification units.

4. The radiometer of claim 1, wherein the radiometer includes M zero-reflection networks, each disposed at an output of a respective one of the low-noise amplification units. Any zero reflection network can be arranged between the Nth-stage low noise amplification unit or the ith-stage low noise amplification unit and the (i + 1) th-stage low noise amplification unit in common (2)^N-1) a derivative architecture; wherein M is more than or equal to 1 and less than or equal to N, and i is more than or equal to 1 and less than or equal to N-1.

5. The radiometer of any of claims 1-4, wherein the zero reflection network comprises: the L-stage matching circuit is sequentially connected in series, and the resistive element is connected with the L-stage matching circuit in parallel;

the matching circuit is used for converting the input complex impedance into a parallel impedance value of a port impedance and a resistive element in a pass band and converting the parallel impedance value into a value approaching infinity in a stop band;

the resistive element is used for further transforming infinite impedance generated outside the band into a matching state and dissipating absorbed reflected signals, the resistance value of the resistive element is selected near the impedance value of the output port, and the impedance approaching the infinite impedance outside the band is matched to the impedance of the output port through parallel connection, so that the output port has no reflected signals in the full frequency band;

wherein, L represents the number of the matching circuits and takes the value of a positive integer which is more than or equal to 1.

6. The radiometer of claim 5, wherein the matching circuit comprises: a matching unit disposed at a previous stage, and an impedance converter disposed at a subsequent stage and multiplexed;

the matching unit is used for realizing complex impedance matching in a passband;

the impedance transformer is multiplexed and generates an out-of-band tending infinite impedance that is transformed to a matched state by the resistive element and dissipates the absorbed reflected signal through the resistive element.

7. The radiometer of claim 6, wherein said impedance transformer is implemented as a series capacitor or series coupled transmission line open at both ends.

8. The radiometer of any of claims 1-7, further comprising a mixer coupled to an output of the zero order reflection network for mixing the amplified radio frequency signal and the local oscillator signal and outputting an intermediate frequency signal.

9. A radiometer according to any of claims 1-7, wherein the radiometer further comprises a detector connected to the output of the zero order reflection network for converting the amplified radio frequency signal into a direct current signal and outputting it.

Technical Field

The invention belongs to the technical field of radiometers, and particularly relates to a radiometer based on a zero reflection network and a derivative framework thereof.

Background

Radiometers are devices designed for the radiation characteristics of objects, and receive thermal radiation from the environment for detection and imaging. Heterodyne architecture and direct detection architecture are widely used in radiometer design, the former mainly consisting of multiple Low Noise Amplifiers (LNAs) and mixers, and the latter mainly consisting of multiple low noise amplifiers and detectors. The maturity of silicon technology makes full integration, high performance millimeter wave radiometer possible, can be used for V wave band, W wave band and even higher frequency band. Typically, the ambient radiation signal is about-90 dBm, and the millimeter wave radiometer detects in the form of a large number of array elements, which places high demands on the sensitivity and dynamic range of the radiometer. However, the interstage signal reflection of each module in the radiometer can lead active devices such as an amplifier, a mixer and a detector to introduce extra intermodulation signals, increase gain fluctuation, reduce the dynamic range of the whole radiometer system, and even cause internal self-excitation and fail to work normally. Reducing interstage signal reflections from modules in the radiometer is therefore an effective means to improve stability and linearity.

Here, taking the heterodyne radiometer as an example, in order to reduce the interstage reflection, the conventional heterodyne radiometer architecture mainly has the following three types:

(1) as shown in fig. 1, a circulator is added between the multistage low noise amplifier and the mixer, and a forward signal is transmitted through the circulator, while a reflected signal generated at an input end surface of the mixer is absorbed by the circulator. However, due to the limitation of the process, the circulator cannot be integrated through silicon substrate, and the structure can be realized only by adopting a hybrid integration mode, so that the size and the power consumption of the system are increased;

(2) as shown in fig. 2, a silicon-based integrated attenuator is added between the multi-stage low noise amplifier and the mixer, the inter-stage reflected signal is absorbed by the attenuator to improve the isolation, but the attenuator also attenuates the forward wave at the same time, so that the system gain is inevitably reduced by the architecture, and the sensitivity of the overall system is not obviously improved or even deteriorated.

(3) As shown in fig. 3, a group of multistage low noise amplifiers is added, quadrature couplers are added before and after the two groups of multistage low noise amplifiers to form a balanced amplifier structure, and reflected signals from the amplifiers and the mixers pass through the quadrature couplers and are cancelled at a radio frequency input end, so that the reflected signals are reduced. However, the bandwidth of the quadrature coupler is limited, so the structure has the problems of narrow absorption bandwidth of the reflected signal, large circuit size, large power consumption and the like due to the introduction of the quadrature coupler.

The above is also applicable to a conventional direct-detection radiometer, and the mixer may be replaced with a detector.

In summary, the conventional radiometer is limited by device performance or circuit structure in reducing interstage reflection, and has the problems of narrow absorption bandwidth of reflected signals, reduced gain, incomplete integration, large circuit size, high power consumption and the like.

Disclosure of Invention

Aiming at the defects and the improvement requirements of the prior art, the invention aims to provide a radiometer based on a zero reflection network, and aims to solve the problems that the existing radiometer is limited by device performance or circuit structure in the technology of reducing interstage reflection, the absorption bandwidth of a reflection signal is narrow, the gain is reduced, the radiometer cannot be fully integrated, the circuit size is large or the power consumption is high, and the stability and the linearity of a system are further improved.

The invention provides a radiometer based on a zero reflection network, which comprises: a multi-stage low noise amplifier and a zero reflection network; the multistage low noise amplifier includes: the N cascaded single-stage low-noise amplification units are sequentially marked as a first-stage low-noise amplification unit, … …, an ith-stage low-noise amplification unit, … … and an Nth-stage low-noise amplification unit and are used for amplifying a radio-frequency input signal, and the zero reflection network is used for matching the output impedance of the multi-stage low-noise amplifier and absorbing an out-of-band reflection signal to realize no-reflection signal at a port; wherein N represents the number of the single-stage low-noise amplification units, i represents the serial number of the single-stage low-noise amplification units, N is an integer greater than or equal to 2, and i is greater than or equal to 1 and less than or equal to N.

In the invention, the zero reflection network is used as an output impedance matching network of the multi-stage low noise amplifier and is also used as a reflection signal absorption network to absorb the reflection signal generated by the rear-stage mixer, thereby improving the stability and the linearity of front and rear-stage devices. And the multistage low noise amplifier is formed by cascading N single-stage low noise amplification units, and can provide enough high gain for a link.

The zero reflection network is a passive network, adopts a simple lumped element and transmission line structure, can be integrated on a silicon substrate compared with a circulator and an attenuator, has small circuit size and low loss, and avoids the reduction of system gain. In addition, the zero reflection network not only matches the in-band impedance, but also absorbs the out-of-band reflection signal to realize that the port has no reflection signal.

Furthermore, the zero reflection network is connected to the output end of the Nth-stage low-noise amplification unit and is used for matching in-band impedance and absorbing out-of-band reflection signals, so that the stability and the linearity of the front-stage low-noise amplifier are improved, and the conversion gain of the rear-stage mixer is increased.

Furthermore, the zero reflection network is arranged between any two low-noise amplification units in the N single-stage low-noise amplification units; the zero reflection network is used as an output matching network or an input matching network of the single-stage low-noise amplifier to form the zero reflection low-noise amplifier, and absorbs a reflection signal from a rear-stage circuit or a front-stage circuit.

In the embodiment of the invention, the zero reflection network can be selected from different positions, and the heterodyne radiometer architecture based on the zero reflection network and the direct detection radiometer architecture based on the zero reflection network have N forms respectively.

Furthermore, the radiometer includes M zero reflection networks, which are respectively referred to as a first zero reflection network, a second zero reflection network, … … and an mth zero reflection network, wherein any zero reflection network can be added after the nth low noise amplifier unit or between the ith and (i + 1) th low noise amplifiers, and there can be 2^N-1 derivative architecture. The zero reflection network is used for replacing each traditional interstage 50 omega matching network, so that the interstage reflection can be eliminated, and the stability and the linearity of the system are further improved; wherein M is more than or equal to 1 and less than or equal to N, and i is more than or equal to 1 and less than or equal to N-1.

Further, the zero reflection network includes: the L-stage matching circuit is sequentially connected in series, and the resistive element is connected with the L-stage matching circuit in parallel; the matching circuit is used for converting the input complex impedance into a parallel impedance value of a port impedance and a resistive element in a pass band and converting the parallel impedance value into a value approaching infinity in a stop band; the resistive element is used for further transforming infinite impedance generated outside the band into a matching state and dissipating absorbed reflected signals, the resistance value of the resistive element is selected near the impedance value of the output port, and the impedance approaching the infinite impedance outside the band is matched to the impedance of the output port through parallel connection, so that the output port has no reflected signals in the full frequency band; wherein, L represents the number of the matching circuits and takes the value of a positive integer which is more than or equal to 1.

Wherein, the matching circuit includes: a matching unit disposed at a previous stage, and an impedance converter disposed at a subsequent stage and multiplexed; the matching unit is used for realizing complex impedance matching in a passband; the impedance transformer is multiplexed and generates an out-of-band tending infinite impedance that is transformed to a matched state by the resistive element and dissipates the absorbed reflected signal by the resistive element.

Further, the impedance transformer is implemented using a series capacitor or a series capacitive structure of a coupled transmission line open at both ends.

Further, the radiometer may be classified into a heterodyne radiometer and a direct sensing radiometer, and when the radiometer is a heterodyne radiometer, the above-described structure further includes a mixer, which is located at the last stage of the radiometer, for mixing the amplified radio frequency signal and the local oscillator signal and outputting an intermediate frequency signal. When the radiometer is a direct-detection radiometer, the structure described above further includes a detector, which is located at the last stage of the radiometer and is used for converting the amplified radio-frequency signal into a direct-current signal and outputting the direct-current signal.

Further, in the heterodyne radiometer architecture based on the zero reflection network, the zero reflection network may be located between the multi-stage low noise amplifier and the mixer, i.e., after the nth stage low noise amplification unit, or may be located between the multi-stage low noise amplifier stages, i.e., between the ith stage and the (i + 1) th stage low noise amplifier; the zero reflection network can replace the traditional 50 omega matching network and be used as an output matching network or an input matching network of a single-stage low-noise amplifier to form the zero reflection low-noise amplifier and absorb a reflection signal from a post-stage circuit or a front-stage circuit; the direct detection type radiometer based on the zero reflection network has the same structure. Wherein i is more than or equal to 1 and less than or equal to N-1.

Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:

(1) the zero reflection network provided by the invention is a passive network, is composed of a concentration element and a transmission line structure, and is easier to integrate, smaller in circuit size and lower in power consumption compared with a circulator, an attenuator and an orthogonal coupler.

(2) The zero reflection network is seamlessly integrated in the radiometer, the zero reflection low-noise amplifier can be directly used as an output matching network of a front-stage amplification unit or an input matching network of a rear-stage amplification unit to form the zero reflection low-noise amplifier, an additional 50 omega matching network is not required to be added for interstage matching, the circuit size and the loss are further reduced, and the gain of the whole radiometer system is improved.

(3) The radiometer provided by the invention adopts the zero reflection network as the matching network and the undersea network, realizes in-band impedance matching and out-of-band reflection signal absorption, increases the bandwidth for absorbing interstage reflection signals, covers the full wave band in the absorption range, greatly enhances the linearity and stability of front and rear active devices, and does not increase extra noise coefficient, thereby improving the stability and dynamic range of the whole radiometer system.

Drawings

FIG. 1 is a diagram of a prior art heterodyne radiometer architecture based on a ferrite circulator;

FIG. 2 is a diagram of a prior art attenuator-based heterodyne radiometer architecture;

FIG. 3 is a diagram of a heterodyne radiometer architecture for a prior art quadrature coupler;

FIG. 4 is a diagram of a heterodyne radiometer architecture based on a zero reflection network according to the present invention;

FIG. 5 is an architecture diagram derived from the heterodyne radiometer architecture proposed by the present invention based on a zero reflection network as an output matching network for any stage of amplification unit;

FIG. 6 is an architecture diagram derived from the heterodyne radiometer architecture proposed by the present invention based on a zero reflection network as an input matching network for any stage of amplification unit;

FIG. 7 is an architecture diagram derived from the heterodyne radiometer architecture proposed in the present invention based on zero reflection networks, where more than one zero reflection network is used as the output matching network for multiple amplification units;

FIG. 8 is a possible zero reflection network architecture proposed by the present invention;

FIG. 9 is a simulation result of S-parameters for a zero reflection network as a multi-stage low noise amplifier output matching network;

FIG. 10 is | | c_out|-r_out| a graph of the calculated results of the pass band and the stop band;

FIG. 11 is a graph of the effect of harmonic amplitude on radiometer linearity.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Fig. 4 is a heterodyne radiometer based on a zero reflection network, which belongs to one of the radiometer architectures based on the zero reflection network proposed in the present invention, and includes: the system comprises a multistage low noise amplifier, a zero reflection network and a mixer;

the multistage low noise amplifier includes: the N cascaded single-stage low-noise amplification units are sequentially marked as a first-stage low-noise amplification unit, … …, an ith-stage low-noise amplification unit, … … and an Nth-stage low-noise amplification unit and are used for amplifying a radio-frequency input signal and providing sufficient gain for a system link;

wherein N represents the number of the single-stage low-noise amplification units, i represents the serial number of the single-stage low-noise amplification units, N is an integer greater than or equal to 2, and i is greater than or equal to 1 and less than or equal to N

The single-stage low noise amplifier comprises an input matching network and an amplifying unit, wherein the inter-stage matching network adopts a traditional 50 omega matching network and is used for matching in-band input impedance.

The zero reflection network includes: the L-stage matching circuit is sequentially connected in series, and the resistive element is connected with the L-stage matching circuit in parallel; the matching circuit is used for converting the complex impedance of the output end of the low-noise amplification unit into a parallel impedance value of the port impedance and the resistive element in a pass band and converting the complex impedance into a parallel impedance value approaching infinity in a stop band; the resistive element is used for further transforming infinite impedance generated outside the band to a matching state and dissipating the absorbed reflected signal, the resistance value of the resistive element is selected near the impedance value of the output port, and the impedance approaching the infinite impedance outside the band is matched to the impedance of the output port through parallel connection, so that the output port has no reflected signal in the full frequency band; wherein, L represents the number of the matching circuits and takes the value of a positive integer which is more than or equal to 1.

The zero reflection network is used as an output matching network of the multi-stage low noise amplifier and connected to the output end of the Nth-stage low noise amplification unit, in-band impedance can be matched, and out-of-band reflection signals from a rear-stage mixer are absorbed, so that introduction of intermodulation products is reduced, gain fluctuation is reduced, stability and linearity of the low noise amplifier and the mixer are improved, and conversion gain of the mixer is improved.

In an embodiment of the present invention, a matching circuit includes: a matching unit disposed at a previous stage, and an impedance converter disposed at a subsequent stage and multiplexed; the matching unit is used for realizing complex impedance matching in a passband; the impedance transformer is multiplexed and generates out-of-band tending infinite impedance that is transformed to a matched state by the resistive element and dissipates the absorbed reflected signal through the resistive element.

The matching circuit matches the complex impedance in the passband to the parallel resistance value of the output port impedance and the resistive element to realize the impedance matching of the signal in the passband.

Specifically, the matching circuit can select a structure of serially connecting a capacitor behind a parallel grounding microstrip transmission line or serially connecting a capacitor behind a series inductor to realize each stage of matching according to the numerical values of the input complex impedance under different frequencies.

As an embodiment of the present invention, the impedance transformer may be implemented by a series capacitor or a series capacitive structure with a coupled transmission line open at both ends.

The impedance converter simultaneously determines the impedance of the in-band signal and the out-of-band signal, and the capacitance value of the impedance converter meets the requirement of enabling the out-of-band impedance to be infinite and simultaneously ensures impedance matching in a passband.

In the embodiment of the invention, the mixer is positioned at the last stage of the heterodyne radiometer architecture based on the zero reflection network, and mixes a Radio Frequency (RF) signal and a Local Oscillator (LO) signal to output an Intermediate Frequency (IF) signal.

Further, as shown in fig. 5 and fig. 6, the zero reflection network may replace the conventional 50 Ω interstage matching network, and directly serve as an input matching network or an input matching network of the ith-stage amplification unit to form an ith-stage low noise amplifier, i.e., a zero reflection low noise amplifier.

Furthermore, there may be more than one zero reflection network, as shown in fig. 7, which includes M zero reflection networks respectively disposed at the output ends of the low noise amplification units. Any zero reflection network can be arranged between the Nth-stage low noise amplification unit or the ith-stage low noise amplification unit and the (i + 1) th-stage low noise amplification unit in common (2)^N-1) a derivative architecture; wherein M is more than or equal to 1 and less than or equal to N, and i is more than or equal to 1 and less than or equal to N-1. The output matching network of any amplifying unit is replaced by a zero reflection network to form a zero reflection low noise amplifier. The zero reflection network is simultaneously used as a reflection signal absorption network to absorb reflection signals from a rear-stage low-noise amplifier and a mixer, and can also play a role in improving the stability and linearity of the device, so that the stability and dynamic range of the whole radiometer system are improved.

In order to better illustrate the performance advantages of the radiometer based on the zero reflection network, the circuit architecture is shown in fig. 4, which mainly takes the V-band heterodyne radiometer based on the zero reflection network provided by the present invention as an example, and analyzes and illustrates the expansion of the absorption bandwidth by the zero reflection network and the improvement of the stability and linearity of the radiometer.

The invention provides a zero reflection netThe network structure is shown in FIG. 8 and comprises an in-band matching network and a reflection absorption network, wherein the in-band matching network comprises two stages of matching circuits connected in series with a transmission line TL_R1And a series capacitor C_R1Forming a first stage, parallel transmission line TL_R2And series capacitor CR₂And the second stage is formed and is used for replacing a traditional 50-omega output matching network and carrying out in-band impedance matching on the front-stage low-noise amplifier. In addition, the series capacitor CR of the second stage₂Meanwhile, in a reflection absorption network, out-of-band impedance is converted into infinite, and a parallel connection dissipative resistor R is combined_AAnd full-band matching is realized, so that reflected signals of the ports can be eliminated. S parameter simulation is carried out on the zero reflection network, and a simulation result is shown in fig. 9, so that the out-of-band return loss S22 is smaller than-20 dB and the in-band return loss is smaller than-10 dB in a frequency range of 0-110GHz, that the full frequency bands are in an impedance matching state is shown, reflection signals at an output port are absorbed, and the absorption bandwidth reaches more than 110 GHz.

Analysis from the stability aspect, the output echo reflection S of the conventional LNA due to mismatch in the stop band₂₂This leads to a reduction in stability and a tendency to cause problems such as low-frequency oscillation. The zero reflection network without bandwidth limitation is used as an output matching circuit of the low noise amplifier, and multiple reflection signals from the rear-stage frequency mixer can be absorbed in the full frequency band to obtain S which is matched in the full frequency band₂₂And absolute stability is realized. Therefore, for low noise amplification based on zero reflection network, when S₂₂0, input end echo reflection | S₁₁|<1, the formula of its output stability circle can be expressed as:c_outand r_outRespectively representing the center and radius of the output stability circle. For in-band signals, | S due to reverse isolation of the amplifier₁₂Is greater than the forward gain | S₂₁| so that | c |_out|-r_outIf is greater than 1, the absolute stability condition is satisfied, whereas for out-of-band signals, due to S₂₁Attenuation of | so that | c_out|-r_outI is also greater than 1 and,the absolute stability condition is satisfied, and thus, absolute stability can be achieved in the full frequency band. More specifically, a typical set of low noise S parameters may be taken as an example, assuming reverse isolation S₁₂Is-30 dB, in-band S₁₁Is-10 dB, out-of-band S₁₁Is-0.1 dB, in-band gain S₂₁20dB, out-of-band S₂₁Is-10 dB, when the output is no reflection, i.e. S₂₂Fig. 10 gives the calculated | c | |, 0_out|-r_outAnd the result graph shows that the result graph is absolutely stable in the full frequency band. On the other hand, the stability of the later mixer is also enhanced due to the cancellation of the reflected signal. According to the formula of the reflection coefficient of the output port of the mixerIt can be known that when there is no reflected signal at the input port, the gamma in the formula_s-mixCan be regarded as 0, therefore, the formula can be further simplified toDue to 0<|S₂₂ ^RF _-mix|<1, therefore, the output reflection coefficient of the mixer is always less than 1, and the absolute stability condition is met.

From the linearity analysis, for the heterodyne radiation architecture, assuming that an out-of-band sinusoidal interference signal is input simultaneously with the desired sinusoidal RF signal, amplified by the low noise amplifier, and then enters the mixer, the final output IF signal can be expressed as:

wherein alpha is_i(i-1, 2,3) represents a nonlinear coefficient, a_RFAnd A_INTRepresenting the voltage amplitude, omega, of the RF signal and of the interfering signal, respectively_RFAnd ω_INTRepresenting the frequencies of the RF signal and the interfering signal, respectively. Further, an input power 1dB compression point formula of the radiometer system can be obtainedAs can be seen from the equation, IP1dB decreases with increasing interfering signal amplitude, indicating that system linearity deteriorates with increasing out-of-band interfering signals. Compared with the traditional heterodyne architecture, the zero reflection network adopted in the architecture can absorb interstage reflection signals, and interference signal amplitude is reduced, so that system linearity is improved. In addition, IF the spurious effects caused by intermodulation products introduced by the RF and LO signals and their harmonics are considered, the output IF signal can be expressed as:

wherein A is_LOAnd ω_LORespectively representing the voltage amplitude and frequency, A, of the LO signal_RF(n) and A_LO(m) represents the voltage amplitude of the nth harmonic of the RF signal and the mth harmonic of the LO signal, respectively. This illustrates that the IF input of the heterodyne radiometer is not only affected by the RF and LO signals, but also related to their harmonics. Fig. 11 illustrates the effect of harmonic amplitude on radiometer linearity, and it can be seen that the harmonics cause the IP1dB point to transition from the ideal a point to the degraded B point, reducing system linearity. Compared with the traditional heterodyne architecture, the zero reflection network adopted in the architecture can effectively absorb the harmonic components at the input end of the mixer, so that the linearity of the system is improved.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.