Near-field communications with multiple transmit and multiple receive antennae
Near-field communication (NFC) system provides a plurality of transmit antennae. The transmit antennae of the plurality have at least two different polarizations. A plurality of receive antennae have polarizations arranged to receive signals from respective antennae of the transmit antennae, such that each polarization of the transmit antennae has a receive antennae with a corresponding polarization. The transmitters are tuned to a transmit frequency and each have a dimension. A distance between the receive and the transmit antennae is no greater than a greater of twice a maximum dimension squared of the transmit antennae divided by a wavelength of transmission and a wavelength of transmission divided by 2π.
1. A communications system, comprising:
a plurality of transmit antennae, wherein the plurality of transmit antennae have at least two different polarizations, and wherein each of the transmit antennae have a respective largest physical dimension (Di), and a greatest of the respective largest physical dimensions (Di) of the plurality of transmit antennae is a maximum dimension (D), wherein each of the transmit antennae are configured to transmit a respective modulated signal that encodes a respective data stream, at a wavelength (λ);
a plurality of receive antennae, wherein the plurality of receive antennae have at least one receive antennae with a polarization matching a polarization of the plurality of transmit antennae, and wherein each receive antenna is spaced from all of the transmit antennae by a distance less than a greater of 2D^2/λ and λ/2π;
a plurality of receivers, coupled to one or more respective receive antennae to recover data streams from signals received at the respective coupled receive antennae; and
a data recovery unit coupled to the plurality receivers to recover data from the recovered data streams.
2. The communications system of claim 1 , wherein the plurality of transmit antennae are configured for single input/single output (SISO) operation.
3. The communications system of claim 1 , wherein the plurality of transmit antennae are configured for Multiple Input/Multiple Output (MIMO) operation.
4. A communications systems method, comprising:
transmitting, from a plurality of transmit antennae, a respective modulated transmit signal that encodes a respective data stream at a wavelength (λ), wherein the plurality of transmit antennaes have at least two different polarizations, and each of the transmit antennae have a largest physical dimension (Di) and a greatest of the respective largest physical dimensions (Di) of the plurality of transmit antennae is a maximum dimension (D);
receiving, by at least one respective receive antenna, each of the transmit signals; and
during the transmitting and the receiving, maintaining the plurality of transmit antennae and the at least one respective receive antenna within a distance of each other that is less than a greater of 2D^2/λ and λ/2π.
5. The method of claim 4 , further comprising adjusting polarizations of the transmit signals based on signal quality.