Duplexer Signal Cancellation for Simultaneous Radar Operation
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Solution Overview
Problem
Radar systems face challenges in achieving simultaneous transmit and receive operations due to transmit leakage and antenna port reflections, which overload the receive path and degrade sensitivity, as existing duplexers fail to provide adequate isolation and noise rejection.
Innovation Solution
The integration of high dynamic range (HDR) low noise amplifiers with a signal cancellation circuit topology, including a circulator, directional couplers, and amplifiers, to adaptively cancel leakage signals and enhance sensitivity, using gallium nitride or similar wide band gap semiconductor amplifiers, and a trimming circuit for amplitude and phase adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional duplexer is used to isolate transmitter and receiver, then isolation between transmit and receive paths is provided, but transmit leakage and antenna port reflections still overload the receive path and degrade sensitivity
Solution Approach 1:
The invention samples the transmit signal using directional couplers and feeds it through a cancellation amplifier to the cancellation port of a second directional coupler. This converts the harmful transmit leakage signal into a beneficial cancellation signal that subtracts from the receiver input, transforming the problem of transmit leakage into a solution that actively eliminates it.
Solution Approach 2:
The invention introduces a cancellation amplifier and trimming circuit as intermediary components between the transmitter and receiver paths. These intermediaries process the transmit signal to create an inverted copy that cancels leakage, and they provide the necessary gain and phase adjustment to enable effective cancellation without directly connecting the high-power transmit path to the sensitive receiver.
2Reliability
If transmit leakage cancellation is implemented using prior art circuits, then some isolation improvement is achieved, but receive signals near the transmit frequency are completely canceled making simultaneous operation impossible
Solution Approach 1:
The invention uses trimming circuits with variable attenuators and phase shifters to precisely control the amplitude and phase of the cancellation signal. By adjusting these parameters, the system achieves partial cancellation that reduces transmit leakage to acceptable levels while preserving enough of the receive signal near the transmit frequency to enable simultaneous operation, rather than attempting complete cancellation.
Solution Approach 2:
The invention incorporates trimming circuits that can dynamically adjust the cancellation signal parameters. This dynamic adjustment capability allows the system to adapt to different operating conditions and signal levels, enabling simultaneous transmit and receive operation by balancing the cancellation effect against the need to preserve receive signals.
3Device complexity
If no amplifier is placed between the antenna and receiver to reduce path losses, then device complexity is reduced, but sensitivity is degraded due to thermal noise added by losses
Solution Approach 1:
The invention introduces a low-noise amplifier as an intermediary component between the antenna and receiver. This amplifier compensates for path losses and prevents thermal noise from degrading sensitivity, while the trimming circuit and cancellation amplifier act as additional intermediaries to manage the transmit leakage without requiring multiple high-gain stages that would increase complexity.
Solution Approach 2:
The invention changes the noise figure parameter of the amplification system by using low-noise amplifiers with optimized noise characteristics. This allows the system to achieve the necessary sensitivity without requiring excessive gain from multiple amplifier stages, thereby maintaining relatively simple device architecture while improving measurement precision.
4Reliability
If directional couplers and cancellation circuits are added to reduce transmit leakage, then leakage rejection is improved, but device complexity increases due to additional components
Solution Approach 1:
The invention makes the cancellation amplifier serve multiple functions: it amplifies the sampled transmit signal, provides phase shifting through trimming circuits, and generates the cancellation signal for the directional coupler. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in device complexity while achieving effective transmit leakage cancellation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces transmit leakage by over 30 dB, enables greater sensitivity, and allows for simultaneous transmit and receive operations while minimizing AM/PM sideband residue, enabling the use of a wider range of amplifiers with less stringent dynamic range requirements in phased array antennas.
Implementation Method 1
A portion of the transmit signal is sampled with a directional coupler
Implementation Method 2
The main transmit signal is fed into a conventional circulator, which separates the transmit and receive paths
Implementation Method 3
Any losses between the antenna and the receiver (or first low noise amplification device) directly degrade sensitivity by adding thermal noise proportional to the losses directly into the receiver
Implementation Method 4
combined with the output of the first HDR amplifier using a second directional coupler. The gain of the second amplifier is adjusted so the leakage signals are canceled
Data Source
AI summary
An enhanced duplexer (1) which includes a combination of high dynamic range (HDR) amplifiers (11, 17) and a naovel signal cancellation circuit topology (15). Return signals from the circulator (3) are fed into the first HDR amplifier (11). A portion of the transmit signal is sampled with a directional coupler (7) and amplified with a second HDR amplifier (17) and then combined with the output of the first HDR amplifier (11) using a second directional coupler (13). The gain and phase of the second io amplifier (17) are adjusted so the leakage signals are canceled (19, 21) to enable a radar system to simultaneously transmit and receive signals to and from an antenna with increased sensitivity of operation.