A multi-channel high isolation receiving system

Abstract

This invention discloses a multi-channel high-isolation receiving system, comprising four input channels, a combining module, a filtering module, a coupling module, a high-isolation microwave switch module, a mixing module, a local oscillator module, and two output channels. The four input channels include two adjustable-gain channels and two low-noise amplification channels. The high-isolation microwave switch module, composed of cascaded three-stage single-pole single-throw switch chips, has an isolation greater than 100dB, achieving an overall turn-off isolation of over 85dB for the receiving front-end, effectively preventing transmitted leakage signals from entering the receiver. High gain and high isolation are achieved by passing the main signal through the high-isolation microwave switch; simultaneously, a branch signal is branched from the coupling module and output through an independent mixing channel. This branch does not contain switching devices, eliminating switching delay and allowing continuous operation. The main channel handles long-range detection, while the branch compensates for near-range blind spots during switch turn-off; their collaborative operation achieves seamless coverage across the entire range.

Description

Technical Field

[0001] This invention relates to a multi-channel high-isolation receiving system. Background Technology

[0002] With the technological advancements in wireless communication, radar detection, and electronic countermeasures, the radio frequency (RF) receiver front-end, as the core entry point of the system, directly determines the sensitivity, dynamic range, and anti-interference capability of the entire system. Especially in complex applications such as phased array radar and multi-channel communication systems, the receiver front-end needs to simultaneously process multiple RF signals from different antenna elements.

[0003] Existing multi-channel receiver front-end designs typically integrate multiple low-noise amplifiers, mixers, and other circuits. To improve isolation between channels, traditional methods often rely on inserting ferrite isolators between different circuit stages. However, the isolation of typical isolators is only 20dB to 40dB. In environments with limited space and an increasing number of channels, leakage signals between transmit and receive channels, radiation of the local oscillator signal, and crosstalk between channels become increasingly prominent. Leakage signals enter the receiver link as noise and are amplified, sometimes even blocking the receiver, drowning out the target signal, and preventing subsequent signal processing systems from detecting it correctly.

[0004] Furthermore, to improve transmit / receive isolation, existing technologies often introduce microwave switches in the receiver link to achieve time-division multiplexing. However, the isolation of a single-stage microwave switch is limited (typically around 60dB), and the switching on and off has rising and falling edges. This inevitably creates a "near-range blind zone" in applications such as radar detection, meaning that close-range targets cannot be detected. How to achieve high isolation and high dynamic range in a multi-channel receiver front-end under limited space and cost constraints, and solve the near-range blind zone problem, is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this invention is to address the issue that existing single-receiver, single-transmitter systems can no longer meet the needs of transceiver systems, and that increasing the number of channels inevitably affects the isolation between channels. This invention provides a multi-channel, high-isolation receiver front-end design method. Based on the multi-channel processing of the RF signal received by the antenna, including amplification, attenuation, filtering, conduction switching, and frequency conversion, a high-isolation microwave switch module is internally developed. By controlling the microwave switch, the signal is turned off, preventing the transmitted signal from leaking into the receiving system.

[0006] The technical solution of this invention: A multi-channel high-isolation receiving system includes four input channels, a combining module, a filtering module, a coupling module, a high-isolation microwave switch module, a mixing module, a local oscillator module, and two output channels; The four input channels include two adjustable gain channels and two low noise amplification channels. The synthesis module combines the four input signals into one, which is then separated into a main signal and a coupled branch signal after passing through a filtering module and a power divider. The main signal is connected to the main mixer module via a low-noise amplifier and a high-isolation microwave switch module, and the coupled branch signal is directly connected to the branch mixer module. The local oscillator module provides a local oscillator signal to the mixing module, and after mixing, it forms a first output channel RFout1 and a second output channel RFout2 respectively. The high-isolation microwave switch module is composed of three cascaded single-pole single-throw switch chips with an isolation greater than 100dB and a receiver front-end turn-off isolation of not less than 85dB. The adjustable gain channel includes a limiter, two-stage amplifiers, two-stage digitally controlled attenuators, a single-stage fixed attenuator, and a control power supply module. The control power supply module provides +5V power to the two-stage amplifiers and provides TTL control signals to the digitally controlled attenuators.

[0007] The first output channel is formed by the main signal through microwave switching, mixing, and attenuation; the second output channel is formed by the coupled branch signal through mixing and attenuation, and there are no switching devices in the second output channel.

[0008] The signal link of the adjustable gain channel includes, in sequence: RF input → limiter → first-stage amplifier → first-stage digitally controlled attenuator → fixed attenuator → second-stage amplifier → second-stage digitally controlled attenuator → RF output.

[0009] The low-noise amplification channel is equipped with a low-noise amplifier with a noise figure of less than 1.8dB and a built-in DC blocking capacitor; each low-noise amplification channel has an isolator at its input.

[0010] The filtering module is a parallel-coupled microstrip bandpass filter with an insertion loss of less than 3.5 dB, out-of-band rejection greater than 30 dB, and in-band unevenness of less than 0.5 dB.

[0011] The coupling module has a coupling degree of 10dB, and divides the filtered signal into a main path and a coupling branch.

[0012] The high-isolation microwave switch module includes an RF link and a control power supply link. The RF link of the high-isolation microwave switch module is as follows: RF input → Limiter → First-stage switching chip → Second-stage switching chip → Electrically adjustable attenuator → Third-stage switching chip → Amplifier → Attenuator → RF output; The control power supply chain is as follows: a +5V power supply powers the DC-DC module, operational amplifier, and driver chip; the driver chip is connected to a TTL signal to provide drive control signals for the switching chip; and the operational amplifier is connected to a DTK signal to provide control signals for the electrically adjustable attenuator.

[0013] In the main signal link, isolators are provided after the coupling module, before the low-noise amplifier, and between the low-noise amplifier and the microwave switch module.

[0014] The input signals of the adjustable gain channel and the low noise amplification channel come from the antenna, and the four input signals are multiplexed by the synthesis module for subsequent circuits.

[0015] The beneficial effects of this invention are: The high-isolation microwave switch module, which is composed of three-stage single-pole single-throw switch chips cascaded together, has an isolation of more than 100dB, enabling the overall turn-off isolation of the receiving front end to reach more than 85dB, effectively preventing transmitted leakage signals from entering the receiver.

[0016] The main signal is transmitted through a high-isolation microwave switch to achieve high gain and high isolation. Simultaneously, a branch signal is split from the coupling module and output via an independent mixing channel. This branch contains no switching devices, eliminating switching delay and allowing for continuous operation. The main signal handles long-range detection, while the branch compensates for near-range blind spots during switch-off periods. Working together, they achieve seamless coverage across the entire range.

[0017] Balancing high dynamic range and high sensitivity: This invention employs a four-input channel design, with two channels being adjustable gain channels containing two-stage digitally controlled attenuators, enabling wide-range gain control to adapt to large dynamic input signals; the other two are low-noise amplification channels using ultra-low noise amplifiers (noise figure <1.8dB), ensuring sensitivity for receiving extremely weak signals. The four signals are multiplexed by a synthesis module for subsequent circuitry, satisfying the reception requirements for signals of varying strengths while optimizing circuit complexity and cost. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the principle of the present invention.

[0019] Figure 2 This is a schematic diagram of the adjustable gain module of the present invention.

[0020] Figure 3 This is a schematic diagram of the principle of the microwave switch of the present invention.

[0021] Figure 4 This is a schematic diagram of the cavity layout structure of the present invention.

[0022] Figure 5 This is a schematic diagram of the external connection of the switch cable of the present invention.

[0023] In the diagram: 1-First adjustable gain module, 2-Second adjustable gain module, 3-One-way isolator A, 4-One-way isolator B, 5-Low noise amplifier A, 6-Low noise amplifier B, 7-Combiner A, 8-Combiner B, 9-Combiner C, 10-One-way isolator C, 11-Bandpass filter, 12-One-way isolator D, 13-One-way isolator E, 14-Low noise amplifier C, 15-Microwave switch, 16-One-way isolator F, 17-Coupler A, 18-π-type filter A, 19-One-way isolator G, 20-Coupler B, 21-π-type filter B, 22-Combiner D, 23-Block, 24-Separation cavity, 25-External cable, 26-Signal output terminal, 27-Signal input terminal, 28-Power divider. Detailed Implementation

[0024] like Figure 1 As shown, the receiving front end of the present invention includes: four input channels, a synthesis module, a filtering module, a coupling module, a high-isolation microwave switch module, a mixing module, a local oscillator module, and two output channels.

[0025] Specifically, the four input channels include a first adjustable gain channel, a second adjustable gain channel, a first low-noise amplification channel, and a second low-noise amplification channel. The technical advantage lies in the fact that the adjustable gain channel is used to process input signals with a large dynamic range, while the low-noise amplification channel is used to process extremely weak input signals. The combination of these two channels allows the receiving front-end to withstand both strong signal desaturation and weak signal sensitivity, greatly expanding the system's dynamic range.

[0026] like Figure 1 and Figure 3 As shown, the signal link of the adjustable gain channel sequentially includes: RF input → limiter → first-stage amplifier → first-stage digitally controlled attenuator → fixed attenuator → second-stage amplifier → second-stage digitally controlled attenuator → RF output. The limiter protects the subsequent circuitry from overload damage. The two-stage amplifier provides sufficient gain. The two-stage digitally controlled attenuator, in conjunction with the first-stage fixed attenuator, achieves wide-range, high-precision gain control, providing the system with flexible link budget allocation capabilities. The control power supply module provides +5V power to the two-stage amplifier and TTL control signals to the digitally controlled attenuator. This link structure, while ensuring high gain, optimizes the linearity and noise figure of each stage of the circuit through distributed attenuation control, enabling the entire adjustable gain channel to maintain excellent signal quality at different attenuation levels.

[0027] like Figure 1As shown, the low-noise amplification channel is equipped with a low-noise amplifier with a noise figure below 1.8dB and a built-in DC blocking capacitor. This ultra-low noise figure is crucial for ensuring the receiver's high sensitivity. The built-in DC blocking capacitor blocks any DC components that may be introduced by the preceding stage, preventing amplifier saturation. Furthermore, each low-noise amplification channel has an isolator at its input. This isolator absorbs reflected signals from the antenna and provides a stable source impedance for the low-noise amplifier, ensuring optimal noise figure.

[0028] The synthesis module combines four input signals into one. By combining the four input signals into one, only one set of subsequent expensive filtering, local oscillator, and mixing circuits is needed, achieving circuit reuse and greatly reducing the complexity, size, and cost of the system.

[0029] The synthesized signal undergoes out-of-band interference suppression via a filtering module. In this embodiment, the filtering module is a parallel-coupled microstrip bandpass filter with an insertion loss of less than 3.5 dB, out-of-band rejection greater than 30 dB, and in-band flatness less than 0.5 dB. Low insertion loss ensures that the useful power of the signal is not lost; high out-of-band rejection effectively filters out spurious signals such as image frequencies and local oscillator leakage; and good in-band flatness ensures that the signal waveform remains undistorted after passing through the filter, providing a clean input signal for subsequent mixing.

[0030] The filtered signal is amplified and then enters the coupling module. The coupling module has a coupling degree of 10dB, dividing the filtered signal into a main path signal and a coupled branch signal. The technical effect is that the 10dB coupling degree means that most of the energy (approximately 90%) enters the main path to achieve a high-gain, high-isolation main receiving channel; a small portion of the energy (approximately 10%) enters the coupled branch to achieve a different but related auxiliary receiving channel. The correlation effect will be explained below in conjunction with the output channel.

[0031] like Figure 1 and Figure 5As shown, the main signal is connected to the main mixer module via a low-noise amplifier and a high-isolation microwave switch module. The high-isolation microwave switch module is the core component of this invention for achieving high transmit / receive isolation. Its RF link is: RF input → limiter → first-stage switch chip → second-stage switch chip → electrically adjustable attenuator → third-stage switch chip → amplifier → attenuator → RF output. Its control and power supply link is: +5V power supplies the DC-DC module, operational amplifier, and driver chip; the driver chip receives a TTL signal to provide drive control signals to the switch chips; the operational amplifier receives a DTK signal to provide control signals to the electrically adjustable attenuator. Through the cascading of three single-pole single-throw switch chips, the switching isolation can be accumulated, easily exceeding 100dB for the entire module. The front-end limiter protects the switch chips from burnout by high-power leakage signals. The internal electrically adjustable attenuator can fine-tune the link gain according to the control signal when the switch is on, increasing design flexibility. Based on this high-performance switching module, the receiving path can be completely shut off when the receiving front end is not working, so that the overall shutdown isolation of the receiving front end reaches more than 85dB, effectively eliminating the impact of transmission leakage noise on the receiver.

[0032] The coupled branch signal is directly connected to the branch mixer module without any switching. The local oscillator module provides the two mixer modules with the same local oscillator signal through a power divider. After mixing, the main signal forms the first output channel RFout1, and the coupled branch signal forms the second output channel RFout2. As described in claim 2: the first output channel is formed by the main signal through microwave switching, mixing, and attenuation; the second output channel is formed by the coupled branch signal through mixing and attenuation, and there are no switching devices in the second output channel; solving the "near-range blind zone" problem: The first output channel (main path) uses a high-isolation microwave switch in series, which physically cuts off the receiving path during the switch-off period (e.g., during radar pulse transmission), achieving extremely high transmit-receive isolation. However, any switch has a nanosecond-level on and off time. During this transition period, the receiving front end cannot function properly, resulting in the inability to receive reflected echoes from nearby targets, creating a "blind zone."

[0033] The second output channel (branch) is specifically designed to address this problem. This channel contains no switching devices and is therefore always on. Its signal comes from the coupling module, and although its gain is relatively lower than the main channel, it can continuously receive signals, including during the transmit pulse and the transition time between switch switching.

[0034] Therefore, the main path and branch paths work together: the main path is responsible for high-isolation, high-gain long-range detection; the branch paths are responsible for continuous, blind-spot-free short-range coverage. Their output characteristics differ and complement each other, thus completely eliminating short-range detection blind spots caused by switching, achieving seamless detection capability across the entire range.

[0035] Finally, in terms of structural layout, the present invention employs multiple isolation measures to ensure the realization of the aforementioned circuit performance.

[0036] Cavity-separated layout: Radio frequency signals and low-frequency signals (such as power and control signals) are separated to prevent low-frequency noise from being coupled into the radio frequency link through spatial coupling or common power ground.

[0037] Pre- and post-stage small cavity isolation: The pre- and post-stage circuits use separate small cavities and are separated by partitions, which can effectively cut off the path of signal feedback from the output to the input through spatial radiation, preventing amplifier self-oscillation, which is especially important for high-gain links.

[0038] In the main signal link, isolators are installed after the coupling module, before the low-noise amplifier, and between the low-noise amplifier and the microwave switching module. These isolators ensure impedance matching between each stage of the circuit, absorb reflected signals from subsequent stages (such as filters and switches), and ensure that devices such as the low-noise amplifier in the preceding stage operate stably without performance degradation due to load pull.

[0039] Unique microwave switch input / output layout: The microwave switch input is located at the bottom of the cavity, and the output is located at the top of the cavity, connected by an external cable. This layout completely separates the high-power, stray-rich input signal from the sensitive output signal in physical space, avoiding electromagnetic coupling between them on the same plane. Experiments have shown that this connection method provides more than 5dB higher isolation than the conventional same-side layout, which is an important structural guarantee for improving the isolation of the switch module itself, thereby ensuring that the overall shutdown isolation reaches 85dB. Structurally, the use of a cavity-separated layout, isolation between front and rear small cavities, and layered input / output ports connected by external cables minimizes crosstalk between channels and between internal and external systems.

Claims

1. A multi-channel high-isolation receiving system, characterized in that: It includes four input channels, a synthesis module, a filtering module, a coupling module, a high-isolation microwave switch module, a mixer module, a local oscillator module, and two output channels; The four input channels include two adjustable gain channels and two low noise amplification channels. The synthesis module combines the four input signals into one, which is then separated into a main signal and a coupled branch signal after passing through a filtering module and a power divider. The main signal is connected to the main mixer module via a low-noise amplifier and a high-isolation microwave switch module, and the coupled branch signal is directly connected to the branch mixer module. The local oscillator module provides a local oscillator signal to the mixing module, and after mixing, it forms a first output channel RFout1 and a second output channel RFout2 respectively. The high-isolation microwave switch module is composed of three cascaded single-pole single-throw switch chips with an isolation greater than 100dB and a receiver front-end turn-off isolation of not less than 85dB. The adjustable gain channel includes a limiter, two-stage amplifiers, two-stage digitally controlled attenuators, a single-stage fixed attenuator, and a control power supply module. The control power supply module provides +5V power to the two-stage amplifiers and provides TTL control signals to the digitally controlled attenuators.

2. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The first output channel is formed by the main signal through microwave switching, mixing, and attenuation; the second output channel is formed by the coupled branch signal through mixing and attenuation, and there are no switching devices in the second output channel.

3. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The signal link of the adjustable gain channel includes, in sequence: RF input → limiter → first-stage amplifier → first-stage digitally controlled attenuator → fixed attenuator → second-stage amplifier → second-stage digitally controlled attenuator → RF output.

4. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The low-noise amplification channel is equipped with a low-noise amplifier with a noise figure of less than 1.8dB and a built-in DC blocking capacitor; each low-noise amplification channel has an isolator at its input.

5. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The filtering module is a parallel-coupled microstrip bandpass filter with an insertion loss of less than 3.5dB, out-of-band rejection greater than 30dB, and in-band unevenness of less than 0.5dB.

6. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The coupling module has a coupling degree of 10dB and divides the filtered signal into a main path and a coupling branch.

7. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The high-isolation microwave switch module includes an RF link and a control power supply link. The RF link of the high-isolation microwave switch module is as follows: RF input → Limiter → First-stage switching chip → Second-stage switching chip → Electrically adjustable attenuator → Third-stage switching chip → Amplifier → Attenuator → RF output; The control power supply chain is as follows: a +5V power supply powers the DC-DC module, operational amplifier, and driver chip; the driver chip is connected to a TTL signal to provide drive control signals for the switching chip; and the operational amplifier is connected to a DTK signal to provide control signals for the electrically adjustable attenuator.

8. The multi-channel high-isolation receiving system according to claim 1, characterized in that: In the main signal link, isolators are provided after the coupling module, before the low-noise amplifier, and between the low-noise amplifier and the microwave switch module.

9. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The input signals of the adjustable gain channel and the low noise amplification channel come from the antenna, and the four input signals are multiplexed by the synthesis module for subsequent circuits.

10. The multi-channel high-isolation receiving system according to claim 1, characterized in that: The structure adopts a cavity layout: the radio frequency signal and the low frequency signal are arranged in separate sections, and the front and rear stage circuits are separated by small cavities and partitions; isolators are provided between the microwave switch and the mixer, and between the low noise amplifier and the filter input and output terminals; the microwave switch input terminal is located at the bottom of the cavity and the output terminal is located at the top of the cavity, and they are connected by an external cable. This connection method has a higher isolation of more than 5dB than the same-side layout.

Images