US-12618927-B2 - Loran transmitter, receiver, system and method of operating same

US12618927B2US 12618927 B2US12618927 B2US 12618927B2US-12618927-B2

Abstract

A transmitter includes a Loran pulse generator, a dispersion filter, an equalizer, a power amplifier, an antenna tuner, and an antenna. The Loran pulse generator is configured to generate a Loran pulse signal. The dispersion filter is coupled to the Loran pulse generator, and is configured to generate a dispersed signal responsive to the Loran pulse signal. The equalizer is coupled to the dispersion filter, and is configured to generate an equalized dispersed signal responsive to the dispersed signal. The power amplifier is coupled to the equalizer, and configured to generate an amplified signal responsive to the equalized dispersed signal. The antenna tuner is coupled to the power amplifier, and is configured to generate a tuned signal responsive to the amplified signal. The antenna is coupled to the antenna tuner, and is configured to radiate a transmitted signal responsive to the tuned signal.

Inventors

David L. Hershberger

Assignees

CONTINENTAL ELECTRONICS CORP.

Dates

Publication Date: 20260505
Application Date: 20210818

Claims (20)

1 . A transmission system comprising: a transmitter comprising: a Loran pulse generator configured to generate a Loran pulse group, wherein a Loran pulse group comprises a sequence of multiple Loran signals spaced apart in time; a dispersion filter coupled to the Loran pulse generator, and configured to be concurrently applied to the Loran pulse group in order to generate a dispersed signal responsive to the Loran pulse group, wherein the dispersed signal is adapted to have a lower peak envelope power and to subject at least one antenna to a voltage stress that is reduced relative to a Loran pulse group that is not subjected to the dispersion filter; an equalizer coupled to the dispersion filter, and configured to generate an equalized dispersed signal responsive to the dispersed signal; a power amplifier coupled to the equalizer, and configured to generate an amplified signal responsive to the equalized dispersed signal; and an antenna tuner coupled to the power amplifier, and configured to generate a tuned signal responsive to the amplified signal; and the at least one antenna coupled to the transmitter, and configured to radiate a transmitted signal responsive to the tuned signal, wherein the at least one antenna is configured to present reactive impedances at certain frequencies of the transmitted signal to the transmitter such that the transmitter's output current or voltage increases while radiated power does not increase.
2 . The transmitter of claim 1 , wherein the dispersion filter comprises: a Hilbert transform device configured to receive the Loran pulse group, and to generate a first signal and a second signal offset from the first signal by a phase of 90 degrees; a first multiplier coupled to the Hilbert transform device, and configured to generate a frequency shifted signal in response to at least a first carrier signal, the first signal and the second signal; a decimator coupled to the first multiplier, and configured to generate a down-sampled signal in response to the frequency shifted signal; a first filter coupled to the decimator, and configured to generate a filtered down-sampled signal in response to the down-sampled signal; an interpolator coupled to the first filter, and configured to generate an up-sampled signal in response to the filtered down-sampled signal; and a second multiplier coupled to the interpolator, and configured to generate the dispersed signal in response to at least the up-sampled signal and a second carrier signal, the second carrier signal being a conjugate of the first carrier signal.
3 . The transmitter of claim 2 , wherein the decimator comprises: a low pass filter coupled to the first multiplier, and configured to generate a first filtered signal in response to the frequency shifted signal, the first filtered signal having a first sample frequency; and a first circuit coupled to the low pass filter, and configured to delete N−1 samples of N samples of the first filtered signal thereby generating the down-sampled signal, wherein N is an integer, and the down-sampled signal has a second sample frequency equal to the first sample frequency divided by the N samples.
4 . The transmitter of claim 2 , wherein the interpolator comprises: a first circuit coupled to the first filter, and configured to add N−1 zeros to the filtered down-sampled signal thereby generating a first signal, wherein N is an integer, the first signal has a first sample frequency, and the filtered down-sampled signal has a second sample frequency equal to the first sample frequency divided by the N samples; and a low pass filter coupled to the first circuit, and configured to generate a first filtered signal in response to the first signal.
5 . The transmitter of claim 2 , wherein the first filter comprises: a finite impulse response (FIR) filter; an infinite impulse response (IIR) filter; or a fast Fourier transform (FFT) filter.
6 . The transmitter of claim 5 , wherein the IIR filter corresponds to an all-pass filter having randomly generated coefficients.
7 . The transmitter of claim 6 , wherein the IIR filter comprises: a first time reversal circuit configured to generate a first time-reversed signal responsive to a first received signal, the first received signal corresponding to the down-sampled signal; a first circuit coupled to the first time reversal circuit, and configured to generate a conjugate of the first time-reversed signal responsive to the first time-reversed signal; a first filter coupled to the first circuit, and configured to filter the conjugate of the first time-reversed signal thereby generating a filtered first signal; a second circuit coupled to the first filter, and configured to generate a conjugate of the filtered first signal responsive to the filtered first signal; and a second time reversal circuit coupled to the second circuit, and configured to generate a second time-reversed signal responsive to the conjugate of the filtered first signal, the second time-reversed signal corresponding to the filtered down-sampled signal.
8 . The transmitter of claim 5 , wherein the FIR filter, the IIR filter or the FFT filter includes fixed filter coefficients for each of the multiple Loran signals.
9 . The transmitter of claim 5 , wherein the FIR filter, the IIR filter or the FFT filter includes dynamic filter coefficients that are time varying over the multiple Loran signals.
10 . A Loran system comprising: a transmitter comprising: a Loran pulse generator configured to generate a Loran pulse group, wherein a Loran pulse group comprises a sequence of multiple Loran signals spaced apart in time; an equalizer coupled to the Loran pulse generator, and configured to generate an equalized pulse group responsive to the Loran pulse group; a dispersion filter coupled to the equalizer, and configured to be concurrently applied to the Loran pulse group in order to generate a dispersed Loran signal responsive to the equalized pulse group, wherein the dispersed signal is adapted to have a lower peak envelope power and to subject at least one first antenna to a voltage stress that is reduced relative to a Loran pulse group that is not subjected to the dispersion filter; a power amplifier coupled to the dispersion filter, and configured to generate an amplified signal responsive to the dispersed Loran signal; and an antenna tuner coupled to the power amplifier, and configured to generate a tuned signal responsive to the amplified signal; the at least one first antenna coupled to the transmitter, and configured to radiate a transmitted signal responsive to the tuned signal, wherein the at least one antenna is configured to present reactive impedances at certain frequencies of the transmitted signal to the transmitter such that the transmitter's output current or voltage increases while radiated power does not increase; a receiver comprising: at least one second antenna configured to receive a received signal; an un-dispersion filter coupled to the at least one second antenna, and configured to generate an undispersed pulse group responsive to the received signal, the received signal corresponding to the transmitted signal; and a Loran receiver coupled to the un-dispersion filter, and configured to generate a Loran signals responsive to the undispersed pulse group.
11 . The Loran system of claim 10 , wherein the un-dispersion filter comprises: a Hilbert transform device configured to receive the received signal, and to generate a first signal and a second signal offset from the first signal by a phase of 90 degrees; a first multiplier coupled to the Hilbert transform device, and configured to generate a frequency shifted signal in response to at least a first carrier signal, the first signal and the second signal; a decimator coupled to the first multiplier, and configured to generate a down-sampled signal in response to the frequency shifted signal; a first filter coupled to the decimator, and configured to generate a filtered down-sampled signal in response to the down-sampled signal; an interpolator coupled to the first filter, and configured to generate an up-sampled signal in response to the filtered down-sampled signal; and a second multiplier coupled to the interpolator, and configured to generate the undispersed pulse signal in response to at least the up-sampled signal and a second carrier signal, the second carrier signal being a conjugate of the first carrier signal.
12 . The Loran system of claim 11 , wherein the decimator comprises: a low pass filter coupled to the first multiplier, and configured to generate a first filtered signal in response to the frequency shifted signal, the first filtered signal having a first sample frequency; and a first circuit coupled to the low pass filter, and configured to delete N−1 samples of N samples of the first filtered signal thereby generating the down-sampled signal, wherein N is an integer, and the down-sampled signal has a second sample frequency equal to the first sample frequency divided by the N samples.
13 . The Loran system of claim 11 , wherein the interpolator comprises: a first circuit coupled to the first filter, and configured to add N−1 zeros to the filtered down-sampled signal thereby generating a first signal, wherein N is an integer, the first signal has a first sample frequency, and the filtered down-sampled signal has a second sample frequency equal to the first sample frequency divided by the N samples; and a low pass filter coupled to the first circuit, and configured to generate a first filtered signal in response to the first signal.
14 . The Loran system of claim 11 , wherein the first filter comprises: a finite impulse response (FIR) filter; an infinite impulse response (IIR) filter; or a fast Fourier transform (FFT) filter.
15 . The Loran system claim 14 , wherein the FIR filter, the IIR filter or the FFT filter includes dynamic filter coefficients that are time varying over the multiple Loran signals.
16 . The transmitter of claim 14 , wherein the FIR filter, the IIR filter or the FFT filter includes fixed filter coefficients for each of the multiple Loran signals.
17 . The Loran system of claim 14 , wherein the FFT filter comprises: a first circuit configured to perform an FFT on a first signal thereby generating an FFT signal, the first signal corresponding to the down-sampled signal; a second circuit coupled to the first circuit, and configured to add weighted filter coefficients to samples of the FFT signal thereby generating a weighted FFT signal; and a third circuit coupled to the second circuit, and configured to perform an inverse FFT on the weighted FFT signal thereby generating a second signal, the second signal corresponding to the filtered down-sampled signal.
18 . A method, the method comprising: generating, by a Loran pulse generator, a Loran pulse group, wherein a Loran pulse group comprises a sequence of multiple Loran signals spaced apart in time; generating, by a dispersion filter concurrently applied to the Loran pulse group, a dispersed Loran signal based on the Loran pulse group such that the dispersion filter reduces voltage stress on at least one antenna relative to an undispersed Loran pulse signal, wherein the dispersed signal is adapted to have a lower peak envelope power; generating, by a power amplifier, an amplified signal based on the dispersed Loran signal; generating, by an antenna tuner coupled to the power amplifier, a tuned signal responsive to the amplified signal; and radiating, by the at least one antenna coupled to the transmitter, a transmitted signal responsive to the tuned signal, wherein the at least one antenna is configured to present reactive impedances at certain frequencies of the transmitted signal to the transmitter such that the transmitter's output current or voltage increases while radiated power does not increase.
19 . The method of claim 18 , further comprising: generating, by an equalizer, an equalized signal responsive to the Loran pulse group; and wherein generating the dispersed Loran signal comprises: generating the dispersed Loran signal responsive to the equalized signal, wherein the equalizer is coupled between the Loran pulse generator and the dispersion filter; and wherein generating the amplified signal comprises: generating the amplified signal responsive to the dispersed Loran signal.
20 . The method of claim 18 , further comprising: generating, by an equalizer, an equalized signal responsive to the dispersed Loran signal; and wherein generating the dispersed Loran signal comprises: generating the dispersed Loran signal responsive to the Loran pulse signal; and wherein generating the amplified signal comprises: generating the amplified signal responsive to the equalized signal, wherein the equalizer is coupled between the dispersion filter and the power amplifier.

Description

PRIORITY CLAIM The present application is a U.S. National Phase of International Application Number PCT/US2021/071225, filed Aug. 18, 2021, which claims the benefit of U.S. Provisional Application No. 63/067,015, filed Aug. 18, 2020. BACKGROUND Loran signals of some approaches include a number of short bursts of high amplitude pulses and are referred to as very “peaky.” The peak to average power ratio of Loran signals of some approaches is very high. In vacuum tube transmitters, vacuum tubes designed for pulse service were used to generate the high peak powers. The pulse durations were approximately 200 microseconds, which was shorter than the thermal time constants of vacuum tubes designed for pulsed service. Such vacuum tubes could produce very high power, but only for a short time period. Modern solid state transmitters of some approaches are generally peak power limited. Engineering solid state devices for pulse service is more difficult and less effective than doing so with vacuum tubes. The thermal time constant of a semiconductor power device of some approaches is much shorter than that of a pulse type vacuum tube. If a Loran pulse shape is retained, then the solid state transmitter used to produce the Loran pulse shape will have a relatively large number of power transistors for the produced average power. BRIEF DESCRIPTION OF THE DRAWINGS Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. FIGS. 1A-1B are block diagrams of transmitters, in accordance with some embodiments. FIG. 2 is a block diagram of a receiver, in accordance with some embodiments. FIG. 3 is a block diagram of a dispersion filter, in accordance with some embodiments. FIG. 4 is a block diagram of a decimator, in accordance with some embodiments. FIG. 5 is a block diagram of an interpolator, in accordance with some embodiments. FIG. 6A is a block diagram of an FIR filter, in accordance with some embodiments. FIG. 6B is a block diagram of an IIR filter, in accordance with some embodiments. FIG. 6C is a block diagram of an FFT filter, in accordance with some embodiments. FIG. 7A is a waveform diagram of a Loran pulse group, in accordance with some embodiments. FIG. 7B is a waveform diagram of a Loran pulse, in accordance with some embodiments. FIG. 7C is a waveform diagram of an RF power density spectrum of the pulse group signal, in accordance with some embodiments. FIG. 8A is a waveform diagram of an output of the Hilbert transform device, in accordance with some embodiments. FIG. 8B is a waveform diagram of the Hilbert transformed signal after being down converted to zero frequency, in accordance with some embodiments. FIG. 9 is a waveform diagram of an amplitude response and a group delay response of a dispersion filter, in accordance with some embodiments. FIG. 10A is a waveform diagram of an impulse response of a FIR filter, in accordance with some embodiments. FIG. 10B is a waveform diagram of a baseband signal at the output of the dispersion filter of FIG. 3, in accordance with some embodiments. FIG. 10C is a waveform diagram of a dispersed Loran signal envelope and an ideal Loran signal envelope, in accordance with some embodiments. FIG. 10D is an RF waveform diagram of a dispersed Loran pulse group, in accordance with some embodiments. FIG. 11A is a waveform diagram of a pulse group signal and an envelope of the pulse group signal, in accordance with some embodiments. FIG. 11B is a waveform diagram of the power density spectra of the ideal, un-dispersed Loran signal and the recovered Loran signals, in accordance with some embodiments. FIG. 12 is a block diagram of an all-pass filter, in accordance with some embodiments. FIG. 13 is a waveform diagram of a group delay response of a dispersion filter, in accordance with some embodiments. FIG. 14 is a waveform diagram of a Loran pulse group with random all-pass dispersion, in accordance with some embodiments. FIG. 15 is a diagram of a time reversed filter, in accordance with some embodiments. FIG. 16 is a schematic view of a controller usable in one or more of the transmitter of FIGS. 1A-1B, or the receiver of FIG. 2, in accordance with some embodiments. FIG. 17 is a flowchart of a method of operating a system, in accordance with some embodiments. DETAILED DESCRIPTION The following disclosure provides different embodiments, or examples, for implementing features of the provided subject matter. Specific examples of components, materials, values, steps, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not limiting. Other components, materials, values, steps, arrangements, or the like, are cont