Masthead Amplifier Diversity Feedback Suppression
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Solution Overview
Problem
In two-way radio communication systems, the feedback loop between the receiving and transmitting branches in the antenna mast causes high attenuation requirements for the transmit filter, leading to large and expensive filter designs due to the need for significant attenuation of the feedback path, which affects the efficiency and heating of the power amplifier.
Innovation Solution
The amplifier unit in the antenna mast is redesigned with a configuration where the feedback path of the signal amplified in the receiving branch circulates via both radiators and airspace, increasing the attenuation of the leak signal, allowing for a reduction in the attenuation requirements of the transmit filter by summing the isolation between radiators with the feedback path attenuation, thus enabling smaller and cheaper filter designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the transmit filter is designed with high attenuation in the receive band to suppress feedback from the receiving branch, then the feedback signal attenuation is improved, but the filter size and complexity increase significantly
Solution Approach 1:
The patent introduces a new spatial dimension by routing the feedback path through the antenna radiators and free space rather than through the cable infrastructure. This dimensional change adds antenna isolation (typically 30-60 dB) to the feedback attenuation, allowing the transmit filter to have lower attenuation requirements in the receive band while achieving the same overall feedback suppression.
Solution Approach 2:
The antenna radiators and free space act as intermediaries in the feedback path. Instead of directly connecting the receive and transmit branches through cables, the signal must pass through the radiators and propagate through free space, which provides natural isolation and attenuation without requiring large, complex filters.
2Reliability
If separate intermediate cables are used for transmitting and receiving branches, then the signal transmission is improved, but the system cost increases considerably
Solution Approach 1:
The patent merges the transmit and receive paths by using a single shared intermediate cable from the mast to the base station equipment. The feedback suppression is achieved not through separate cables but through the amplifier unit's internal configuration and the antenna isolation, eliminating the need for expensive separate cable infrastructure while maintaining signal transmission quality.
3Loss of energy
If the amplifier unit is placed close to the antenna in the mast, then the receive signal attenuation is reduced, but the feedback loop between receive and transmit branches is created
Solution Approach 1:
The patent extracts the feedback path from the cable infrastructure and redirects it through the antenna radiators and free space. By taking out the feedback loop from the traditional cable-based path and routing it through the radiation elements, the system maintains low receive signal attenuation while achieving feedback suppression through antenna isolation.
Solution Approach 2:
The patent converts the potentially harmful feedback loop into a beneficial arrangement by using the antenna isolation as part of the feedback suppression mechanism. The same antenna elements that transmit and receive signals also provide natural isolation for feedback suppression, turning a potential problem into a solution.
Data Source
AI summary
An amplifier unit to be placed in an antenna mast and belonging to a two-way radio system. The amplifier unit comprises two front stages for implementing diversity, each front stage comprising a receiving branch with an amplifier and a transmitting branch including a transmit bandpass filter. In both front stages the output of the receiving branch and the input of the transmitting branch are coupled together and further to a base station (BT1, BT2) by an intermediate cable. There is at least one pair of antenna radiators. One radiator of the pair is coupled to the input of the receiving branch of the first front stage and the output of the transmitting branch of the second front stage, and the other radiator to the input of the receiving branch of the second front stage and the output of the transmitting branch of the first front stage. Then, the feedback path of the signal amplified in the receiving branch circulates for the part of both front stages via both radiators and the airspace. Because of isolation between the radiators, the attenuation of the feedback path increases, in which case the transmit bandpass filters can be made smaller and cheaper.