mm-Wave Antennas with Large Effective Receiving Area Over a Wide Angular Range

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Wireless communication links at high frequencies (mm-wave and above) are severely restricted by the strongly increasing pathlosses of the links. In contrast to the common and accepted wording that this increase is caused by an increase of the propagation or free-space pathloss, this is actually not really the cause. The true cause of the pathloss increase is the decrease of the effective receiving areas of the used receiving antennas at increasing frequencies. Increasing the effective receiving area will substantially increase the gain of the antennas, but for the disadvantage that the beamwidth of the antennas becomes very narrow. This makes large receiving area antennas hard to align and restricts their usability within multiple input multiple output (MIMO) configurations. To overcome these limitations, it is proposed to investigate and realize receiving antennas which have a large effective area and a large beamwidth at the same time. It is clear that this requirement violates reciprocity. Therefore, the proposed concept utilizes a frequency conversion to a lower frequency band, where, however, no local oscillator signal delivered by the receiver is used for conversion. The goal of maintaining a large beamwidth is achieved by mixing the signal with itself, e.g. in a square detector, and by coherently combining the signals of various antenna elements within the lower frequency range after down-conversion. The mixing process in the receiver can be assisted by transmitting a signal with a particular carrier as known from the ancient amplitude modulation. However, more sophisticated signal forms shall also be investigated and particularly designed. The proposed concept will overcome some of the limitations of wireless links at mm-wave frequencies and above on the way to ultra high-speed communications and it will lead at the same time to relatively simple receiver frontends, since no local oscillator signals need to be generated and distributed. Moreover, the often hard to fulfill spacing requirements in antenna arrays will be considerably relieved. In contrast to a “conventional” digital beamforming solution, which needs e.g. in the 60 GHz band more than 100 complete receive channels (one per antenna element) with mixer, local oscillator, low-noise amplifier and analog to digital converter in order to achieve the desired effective receiving aperture, the proposed antenna concept would need only one receive channel with low-noise amplifier and analog to digital converter together with the square detectors for every antenna elements. For MIMO, several of the proposed receiving antennas would be realized, independent from each other or possibly interlaced with each other, where one receive channel would be needed for every MIMO channel.