Near zero intermediate frequency (NZIF) compensation of local oscillator leakage
In an embodiment, a communications system includes a first transmitter electrically coupled to a first antenna of a phased array antenna, the first transmitter configured to receive an input signal, apply a first baseband frequency shift to the input signal to generate a first baseband frequency shifted input signal, generate a first modulated signal based on the first baseband frequency shifted input signal and transmit the first modulated signal by the first antenna. The communications system includes a second transmitter electrically coupled to a second antenna of the phased array antenna. The second transmitter configured to receive the input signal, apply a second baseband frequency shift, different from the first baseband frequency shift, to the input signal to generate a second baseband frequency shifted input signal, generate a second modulated signal based on the second baseband frequency shifted input signal, and transmit the second modulated signal by the second antenna.
1 . A communications system comprising:
a first transmitter electrically coupled to a first antenna of a phased array antenna, wherein the first transmitter is configured to receive an input signal to be transmitted, apply a first baseband frequency shift to the input signal to generate a first baseband frequency shifted input signal, generate a first modulated signal based on the first baseband frequency shifted input signal, and transmit the first modulated signal by the first antenna, wherein a frequency of the first baseband frequency shifted input signal comprises a near zero intermediate frequency (NZIF); and
a second transmitter electrically coupled to a second antenna of the phased array antenna, wherein the second transmitter is configured to receive the input signal to be transmitted, apply a second baseband frequency shift, different from the first baseband frequency shift, to the input signal to generate a second baseband frequency shifted input signal, generate a second modulated signal based on the second baseband frequency shifted input signal, and transmit the second modulated signal by the second antenna.
2 . The communications system of claim 1 , wherein:
a frequency of the first baseband frequency shifted input signal is greater than zero hertz (Hz) or DC frequency; and
to generate the first modulated signal based on the first baseband frequency shifted input signal, a first modulation section is configured to up convert the first baseband frequency shifted input signal based on a first local oscillator frequency.
3 . The communications system of claim 2 , wherein the first local oscillator frequency equals a carrier frequency minus the first baseband frequency shift.
4 . The communications system of claim 3 , wherein:
a frequency of the second baseband frequency shifted input signal is greater than zero Hz or DC frequency; and
to generate the second modulated signal based on the second baseband frequency shifted input signal, a second modulation section is configured to up convert the second baseband frequency shifted input signal based on a second local oscillator frequency, different from the first local oscillator frequency.
5 . The communications system of claim 4 , wherein the second local oscillator frequency equals the carrier frequency minus the second baseband frequency shift.
6 . The communications system of claim 5 , wherein the second baseband frequency shift is a multiple of the first baseband frequency shift.
7 . The communications system of claim 6 , wherein the second local oscillator frequency equals the carrier frequency minus the second baseband frequency shift.
8 . The communications system of claim 1 , wherein:
the first transmitter is included in a first integrated circuit (IC) chip of a plurality of IC chips;
the second transmitter is included in a second IC chip of the plurality of IC chips;
a maximum baseband frequency separation between a highest shifted baseband frequency and a lowest shifted baseband frequency associated with the plurality of IC chips is less than a frequency bandwidth of the first modulated signal.
9 . The communications system of claim 1 , wherein:
the first transmitter is included in a first IC chip of a plurality of IC chips;
the second transmitter is included in a second IC chip of the plurality of IC chips;
the first IC chip includes a first digital mixer for generating the first baseband frequency shifted input signal; and
the second IC chip includes a second digital mixer for generating the second baseband frequency shifted input signal, wherein the first digital mixer and the second digital mixer actuate in synchronization with each other.
10 . The communications system of claim 9 , wherein the first digital mixer includes a baseband frequency shift generator electrically coupled to each of a first mixer associated with a complex-valued signal I component and a second mixer associated with a complex-valued signal Q component.
11 . The communications system of claim 10 , wherein:
the first IC chip includes a first reference clock signal counter configured to count cycles of a reference clock;
the second IC chip includes a second reference clock signal counter configured to count cycles of the reference clock;
the first digital mixer is configured to actuate at a first particular value of the first reference clock signal counter; and
the second digital mixer is configured to actuate at a second particular value of the second reference clock signal counter, wherein the first particular value of the first reference clock signal counter and the second particular value of the second reference clock signal counter are equal.
12 . The communications system of claim 1 , wherein the communications system comprises a satellite communications system.
13 . The communications system of claim 1 , wherein:
the first transmitter is included in a first IC chip of a plurality of IC chips; and
the first IC chip further comprises one or more digital beamforming components configured to encode the input signal to generate an encoded input signal, wherein the encoded input signal is frequency shifted to generate the first baseband frequency shifted input signal.
14 . A method comprising:
receiving an input signal to be transmitted;
applying a first baseband frequency shift to the input signal to generate a first baseband frequency shifted input signal, wherein a frequency of the first baseband frequency shifted input signal comprises a near zero intermediate frequency (NZIF);
generating a first modulated signal based on the first baseband frequency shifted input signal;
transmitting the first modulated signal by a first antenna;
receiving the input signal to be transmitted,
applying a second baseband frequency shift, different from the first baseband frequency shift, to the input signal to generate a second baseband frequency shifted input signal,
generating a second modulated signal based on the second baseband frequency shifted input signal, and
transmitting the second modulated signal by a second antenna.
15 . The method of claim 14 , wherein:
a frequency of the first baseband frequency shifted input signal is greater than zero hertz (Hz) or DC frequency; and
to generate the first modulated signal based on the first baseband frequency shifted input signal, a first modulation section is configured to up convert the first baseband frequency shifted input signal based on a first local oscillator frequency.
16 . The method of claim 15 , wherein the first local oscillator frequency equals a carrier frequency minus the first baseband frequency shift.
17 . The method of claim 16 , wherein a frequency of the second baseband frequency shifted input signal is greater than zero Hz or DC frequency, the method comprising: up converting the second baseband frequency shifted input signal based on a second local oscillator frequency, different from the first local oscillator frequency.
18 . The method of claim 17 , wherein the second local oscillator frequency equals the carrier frequency minus the second baseband frequency shift.
19 . The method of claim 18 , wherein the second baseband frequency shift is a multiple of the first baseband frequency shift.