Calibration system for satellite radio receivers operation
A radio calibration system includes an FPGA that generates a calibration signal by a pseudo noise generator and mixes the calibration signal with a carrier generated by a carrier generator. The FPGA injects the calibration signal into an analog electronic device which couples the calibration signal into a receiver channel. The receiver channel measures calibration signal power, group delay, and phase, and performs calibration based on these measurements. A reference clock synchronizes the pseudo noise generator, the carrier generator and the receiver channel.
1. A radio calibration system, comprising:
a field-programmable gate array (FPGA) including:
a pseudo noise generator configured to generate a calibration signal, and
a carrier generator configured to generate a carrier to be mixed with the calibration signal to generate a plurality of harmonics of the calibration signal,
an analog electronic device including:
a high pass filter configured to select one or more harmonics of the calibration signal from the plurality of harmonics at a select frequency;
an attenuator configured to attenuate a power level of the select harmonic of the calibration signal;
a coupler configured to inject the attenuated calibration signal into a receiver channel that receives a signal from an antenna input; and
a receiver channel configured to:
measure power, group delay, and phase of the calibration signal,
determine a ratio of power, group delay and phase corrections of the calibration signal,
perform power calibration based on the determined ratio of power,
perform instrumental delay calibration based on the group delay and the phase corrections, and
a reference clock configured to synchronize the pseudo noise generator, the carrier generator and the receiver channel.
2. The radio calibration system of claim 1 , wherein the select frequency is a GPS L1 frequency.
3. The radio calibration system of claim 1 , wherein the carrier generator is a square wave generator.
4. The radio calibration system of claim 1 , wherein the radio calibration system calibrates a GPS system and a GNSS system.
5. The radio calibration system of claim 1 , wherein the coupler includes a power splitter configured to split the calibration signal into a plurality of receiver channels, and a plurality of discrete directional couplers that couple the calibration signals to one or more of the receiver channels.
6. The radio calibration system of claim 1 , wherein the coupler includes a middle layer and a top layer of a printed circuit board, the middle layer receiving the calibration signal 0 and 90 degrees out of phase, and the top layer receiving the signal from the antenna input, the calibration signal being coupled to the signal from the antenna input due to physical arrangement of the middle layer and the top layer.
7. The radio calibration system of claim 1 , wherein the coupler includes microstrip lines of a printed circuit board that are orthogonally crossed and run on two different layer heights, forming a coupling.
8. The radio calibration system of claim 1 , wherein the receiver channel measures properties of the calibration signal against a known noise model used by the pseudo noise generator.
9. The radio calibration system of claim 1 , wherein the receiver channel extracts from the calibration signal one or more of the following observables to determine instrumental delays: power, carrier phase, and group delay.
10. The radio calibration system of claim 1 , wherein the receiver channel is configured to calibrate differences in input gain, noise figure, and path length.
11. The radio calibration system of claim 1 , wherein the receiver channel uses the calibration signal to measure variations in gain, phase and group delay.
12. A calibration method for calibrating a radio system, comprising:
generating a calibration signal by a pseudo noise generator of an field-programmable gate array FPGA;
mixing the calibration signal with a carrier generated by a carrier generator of the FPGA to generate a plurality of harmonics of the calibration signal;
selecting a harmonic of the calibration signal of a select frequency from the plurality of harmonics using a high pass filter;
attenuating the select harmonic of the calibration signal by an attenuator;
coupling the attenuated calibration signal with signals received from antenna inputs in receiver channels;
measuring power by one or more receiver channels;
determining a ratio of power of the receiver channels based on the measured power of the calibration signal; and
performing calibration based on the determined ratio of power.
13. The calibration method of claim 12 , wherein the coupling of the attenuated calibration signal with the signals received from the antenna inputs is performed at least by one or more discrete directional coupler.
14. The calibration method of claim 12 , wherein the coupling of the attenuated calibration signal with the signals received from the antenna inputs is performed at least by orthogonally crossed microstrips that run on different layer heights of a printed circuit board.
15. The calibration method of claim 12 , further comprising:
measuring phase and group delay of the calibration signal;
determining phase corrections; and
performing instrumental delay calibration based on the group delay and the phase corrections.