Atomic clock system

Abstract

The atomic clock system includes a sealed waveguide cavity containing a gas enclosed therein. The waveguide cavity has a length approximately equal to an integral multiple of half wavelengths of the resonant frequency of the gas between two states. An oscillator system generates an RF signal through the waveguide cavity. The RF signal has a signal frequency approximately equal to the resonant frequency of the gas. A detection system measures a characteristic of the RF signal passing through the waveguide cavity to detect a maximum transition between the two states of the gas, and based on detecting the maximum transition, provides a feedback signal to the oscillator system to lock the signal frequency of the RF signal to the resonant frequency of the gas. The detection system provides a frequency reference output signal based on the signal frequency of the RF signal.

Description

Technical Field

[0001] The present disclosure generally relates to a time reference system, and more specifically to an atomic clock system.

Background Art

[0002] An atomic clock can be implemented as a very accurate and stable frequency reference for use in aerospace applications, among others. As an example, an atomic clock can be used in other navigation and positioning systems such as bistatic radar systems, Global Navigation Satellite systems (GNSS), and satellite systems. An atomic clock can also be used in communication systems such as cellular phone systems. An atomic clock is typically realized by providing a signal (e.g., an optical signal or an RF signal) to an atomic material and exciting the atomic material to different excited states based on the very accurate frequency of the signal required to do so. Examples of atomic clocks include coherent population trapping (CPT) atomic clocks, thermal beam atomic clocks, alkali vapor cell atomic clocks, and various other atomic clocks.

Summary of the Invention

[0003] One embodiment includes an atomic clock system including a waveguide cavity that is sealed and contains a gas enclosed therein. The waveguide cavity has a length that is an integer multiple of approximately half the wavelength of the resonant frequency of the gas between two states. An oscillator system generates an RF signal through the waveguide cavity. The RF signal has a signal frequency that is approximately equal to the resonant frequency of the gas. A detection system measures the characteristics of the RF signal passing through the waveguide cavity to detect a maximum transition between two states of the gas, and based on detecting the maximum transition, provides a feedback signal to the oscillator system to lock the signal frequency of the RF signal to the resonant frequency of the gas. The detection system provides a frequency reference output signal based on the signal frequency of the RF signal.

[0004] Another embodiment includes a method for providing a stable frequency-referenced output signal. The method includes generating an RF signal having a signal frequency approximately equal to the resonant frequency of ammonia gas, and radiating the RF signal through a transmitting antenna through a waveguide cavity containing and sealed ammonia gas. The waveguide cavity may have a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between two states. The method also includes receiving the RF signal at a receiving antenna on the opposite side of the transmitting antenna through the waveguide cavity, and measuring the characteristics of the RF signal at the receiving antenna to detect the maximum transition between the two states of ammonia gas. Based on the detection of the maximum transition, the method also includes generating a feedback signal associated with the difference between the signal frequency and the resonant frequency of the gas, and adjusting the signal frequency of the RF signal to be approximately equal to the resonant frequency in response to the feedback signal. The method further includes providing a stable frequency-referenced output signal based on the signal frequency of the RF signal.

[0005] Another embodiment includes an atomic clock system. The system includes a waveguide cavity containing ammonia gas that is sealed and enclosed therein. The waveguide cavity may have a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between two states. The system also includes an oscillator system configured to generate an RF dither signal between a first signal frequency and a second signal frequency and to provide the RF dither signal through the waveguide cavity via a transmitting antenna. The RF dither signal may have a center frequency approximately equal to the resonant frequency of the ammonia gas. The system further includes a detection system configured to measure the characteristics of the RF dither signal received at a receiving antenna opposite the transmitting antenna through the waveguide cavity at each of the first and second signal frequencies to detect the maximum transition between the two states of the ammonia gas, and to provide a feedback signal to the oscillator system based on the detection of the maximum transition to lock the center frequency of the RF signal to the resonant frequency of the ammonia gas. The detection system may be configured to provide a frequency reference output signal based on the center frequency of the RF signal. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 shows an example of an atomic clock system. [Figure 2] Figure 2 shows an example of a waveguide cavity. [Figure 3] Figure 3 shows an example of a power absorption frequency spectrum. [Figure 4] Figure 4 shows another example of a power absorption frequency spectrum. [Figure 5] Figure 5 shows another example of a power absorption frequency spectrum. [Figure 6] Figure 6 shows another example of a power absorption frequency spectrum. [Figure 7] Figure 7 shows another example of a power absorption frequency spectrum. [Figure 8] Figure 8 shows another example of a power absorption frequency spectrum. [Figure 9] Figure 9 shows an example of an integrated atomic clock system. [Figure 10] Figure 10 shows an example of a method for providing a stable frequency reference output signal. [Modes for carrying out the invention]

[0007] This disclosure relates in general to time reference systems, and more specifically to atomic clock systems. The atomic clock system can be implemented to adjust the frequency of a local oscillator, such as a quartz oscillator, which provides a stable frequency reference, thereby improving the stability and accuracy of the local oscillator. The atomic clock system described herein can provide state transitions for the maximum population of gas molecules by implementing a radio frequency (RF) signal having a signal frequency approximately equal to the resonant frequency of a gas (e.g., ammonia gas, NH3). Since the resonant frequency of a gas is very precise under a defined set of conditions, a stable frequency reference can be generated from the signal frequency of an RF signal by locking the signal frequency to be equal to the resonant frequency of the gas.

[0008] As an example, an atomic clock system may include a waveguide cavity containing a gas, selected to have a length approximately equal to an integer multiple of half the wavelength of the gas's resonant frequency (e.g., half the wavelength). The waveguide cavity includes a transmitting antenna located at one end of the waveguide cavity and a receiving antenna located at the opposite end, providing an RF signal through the waveguide cavity. As an example, the RF signal may be generated by an oscillator system including a frequency controller. The frequency controller may provide the RF signal as a dither signal oscillating between a first frequency and a second frequency, so that the center frequency of the dither signal can correspond to a signal frequency locked to the gas's resonant frequency. The received RF signal can be monitored by a detection system to determine the difference between the signal frequency and the resonant frequency, for example, based on the power of the received RF signal. Thus, the detection system can generate a feedback signal provided to the oscillator system to adjust the signal frequency of the RF signal to be equal to the gas's resonant frequency, thereby locking the signal frequency to the resonant frequency.

[0009] As described herein, atomic clock systems can be implemented to accommodate frequency instabilities caused by temperature changes, such as those arising from cavity pulling, and can accommodate fluctuations in the pressure of the gas confined in the waveguide cavity. For example, the frequency controller of an oscillator system can periodically determine the resonant frequency of the waveguide cavity. Thus, the detection system can include a stub tuner configured to adjust the electrical length of the waveguide cavity in response to changes in the physical length of the waveguide cavity, so that the electrical length of the waveguide cavity matches an appropriate fraction of the gas's resonant frequency. As another example, the detection system can include a detection processor configured to measure the pressure of the gas enclosed in the waveguide cavity based on changing the frequency offset from the center frequency of the dither signal. Thus, in response to changes in the gas pressure, and therefore changes in the gas's resonant frequency, the detection processor can adjust a stable frequency reference to accommodate the changes in the gas's resonant frequency.

[0010] Figure 1 shows an example of an atomic clock system 100. The atomic clock system 100 can be implemented in any of the various applications requiring a very stable frequency reference, such as inertial navigation systems (INS) for aerospace vehicles. As will be described in more detail herein, the atomic clock system 100 adjusts the frequency of an oscillator system 102, such as a local oscillator operating within it, to produce a stable frequency reference output signal f OUT It can be implemented to provide this. For example, the atomic clock system 100 can be manufactured as an integrated atomic clock system based on any of the various integrated circuit (IC) manufacturing technologies.

[0011] The atomic clock system 100 includes a waveguide cavity 104 containing a gas 106 encapsulated therein. As an example, the gas 106 may be, but is not limited to, ammonia gas (NH3). In the example of FIG. 1, the oscillator system 102 provides a radio frequency (RF) signal f CTL to a transmitting antenna (“TX antenna”) 108 to propagate the RF signal f CTL through the waveguide cavity 104 and thus through the gas 106. Accordingly, the RF signal f CTL can be received via a receiving antenna 110 at an end of the waveguide cavity 104 opposite the transmitting antenna 108. The oscillator system 102 includes a frequency controller 112 configured to control the signal frequency of the RF signal f CTL . As described herein, the atomic clock system 100 can operate to lock the signal frequency of the RF signal f CTL to be approximately equal to the resonance frequency of the gas, and thus the frequency at which the maximum population of the gas molecules exhibits a transition between two energy states. As described in more detail herein, the signal frequency of the RF signal f CTL can refer to the center frequency of a dither signal including an offset frequency, and the signal frequency of the RF signal f CTL can be a time-averaged frequency approximately equal to the resonance frequency of the gas 106. By locking the signal frequency of the RF signal f CTL to the resonance frequency, the atomic clock system 100 can provide a stable frequency reference f CTL based on the signal frequency of the RF signal f OUT as described in more detail herein.

[0012] As an example, the waveguide cavity 104 can have a length that is an integer N times half the wavelength of the resonance frequency of the gas 106. For example, the integer N can be made equal to 1 such that the length of the waveguide cavity 104 is half the wavelength of the resonance frequency of the gas 106. In the example where the gas 106 is ammonia gas, 10 -3 Torr (about 133.322×10 -3The resonant frequency under defined conditions, such as a vapor pressure of Pa, is approximately 22.8 GHz. Therefore, the waveguide cavity 104 can have a length of approximately 34.8 millimeters. However, the integer multiple N is not limited to 1, and other multiples can be implemented instead. Thus, the waveguide cavity 104 can exhibit a resonant frequency related to the resonant frequency of the gas 106.

[0013] Figure 2 shows an exemplary diagram of waveguide cavity 202. Waveguide cavity 202 can correspond to waveguide cavity 104 in the example of Figure 1. Waveguide cavity 202 is shown as including a transmitting antenna 204 at a first end of waveguide cavity 202 and a receiving antenna 206 at a second end of waveguide cavity 202 opposite the first end. Thus, indicated by 208, the RF signal f in the example of Figure 1 CTL The corresponding RF signal is supplied to the transmitting antenna 204 (for example, from the oscillator system 102), propagates through the waveguide cavity 202, and can be received by the receiving antenna 206. As described above in the example of Figure 1, the waveguide cavity 202 may be filled with a gas, shown as ammonia gas in the example of Figure 2. The molecules of ammonia gas are shown in the first state at 210 in the example of Figure 2. Thus, the RF signal 208 is supplied through the volume of ammonia gas.

[0014] The waveguide cavity 202 is shown to have a length of N*λ / 2, where N is an integer, equal to 1 (N=1) in the example of Figure 2, and λ is the wavelength of the resonant frequency of the ammonia gas. Thus, the RF signal 208 is shown to have wave antinodes in each of the transmitting antenna 204 and receiving antenna 206 so as to transmit the RF signal 208 from the transmitting antenna 204 to the receiving antenna 206 to provide the maximum signal-to-noise ratio (SNR). Thus, the RF signal 208 having a signal frequency approximately equal to the resonant frequency of the ammonia gas, shown as approximately 22.8 GHz in the example of Figure 2, can result in the largest collection of ammonia gas experiencing an inversion transition between a first state at 210 and a second state at 212 where nitrogen atoms are inverted relative to the plane of hydrogen atoms. The inversion transition of ammonia gas atoms between state 210 and state 212 consumes power from the RF signal 208. Therefore, as an example, the measured power of the RF signal 208 received by the receiving antenna 206 can indicate a population of ammonia gas exhibiting an inversion transition, and thus can indicate the signal frequency of the RF signal 208.

[0015] Figure 3 shows an exemplary diagram of the power absorption frequency spectrum 300. The power absorption frequency spectrum plots the power of the RF signal 208 through the waveguide cavity 202, measured at the receiving antenna 206, as a function of the signal frequency of the RF signal 208. As shown in the example in Figure 3, diagram 300 shows a pair of low absorption peaks 302 where the measured power of the RF signal 208 is maximum, thus exciting an inversion transition of ammonia gas for the smallest population of ammonia gas. Diagram 300 also shows an inversion peak 304 located at approximately 22.8 GHz. Inversion peak 304 is therefore located at the resonant frequency of ammonia gas, indicating the maximum absorption of power of the RF signal 208 and providing an inversion transition of ammonia gas between two states 210 and 212 for the largest population of ammonia gas.

[0016] The low absorption peak 302 and the inversion peak 304 may be symmetrical around the inversion peak 304, and therefore around the resonance frequency of the ammonia gas. The power absorption frequency spectrum can be known a priori from experiments, and the symmetry of the power absorption frequency spectrum and the RF signal f CTL The relationship between the measured power and frequency can be identified by the detection processor 116. Thus, as will be described in more detail herein, the atomic clock system 100 detects the RF signal f CTL It operates to lock the signal frequency to the resonant frequency of ammonia gas, and a stable frequency reference f is established based on the signal frequency of RF signal 208. OUT To provide.

[0017] Returning to the example in Figure 1, the atomic clock system 100 propagates through the gas 106 and receives an RF signal f at the receiving antenna 110, which is shown as the signal PWR in the example in Figure 1. CTL The system includes a detection system 114 configured to measure the RF signal f. CTL It also monitors the RF signal f CTL The detection processor 116 is configured to compare the signal frequency of the RF signal f with the resonant frequency of the gas 106. For example, the detection processor 116 compares the RF signal f with the inversion transition of the ammonia gas, as described above in the example in Figure 3. CTL Detecting power absorption of RF signals f CTL It can be configured to monitor the power of the RF signal f. In the example in Figure 1, the detection processor 116 detects the RF signal f. CTL It is configured to generate a feedback signal FDBK that indicates the difference between the signal frequency and the resonant frequency of gas 106. The feedback signal FDBK is provided to the oscillator system 102, thereby the frequency controller 112 generates an RF signal f corresponding to the difference. CTL This can provide adjustment for the signal frequency of the RF signal f. CTL The signal frequency can be locked to the very stable resonant frequency of gas 106.

[0018] In the example above, the detection processor 116 receives the RF signal f CTL Monitor the power of the RF signal f CTL An example is given in which the signal frequency of the RF signal f is compared to the resonant frequency of gas 106. However, the RF signal f CTL Other characteristics of the ammonia gas can also be monitored for the detection of the inversion transition. For example, the detection processor 116 monitors the RF signal f CTL By monitoring the phase of the RF signal f, and similarly as above, detecting the maximum inversion transition, the RF signal f CTL The signal frequency may be configured to lock to the resonant frequency of the ammonia gas.

[0019] In the example shown in Figure 1, the detection processor 116 generates a stable frequency reference output signal f OUT It is also configured to generate the RF signal f. CTL Based on the signal frequency, a stable frequency reference output signal f OUT It can generate an RF signal f CTL The signal frequency is locked to the very stable resonant frequency of gas 106, thus providing a stable frequency output signal f OUT Similarly, it can be provided as having a very stable and accurate frequency. As an example, the detection processor 116 receives the RF signal f CTL The signal frequency is downsampled to create a stable frequency output signal f with a more manageable frequency range, such as the megahertz range (e.g., 5 MHz). OUT The atomic clock system 100 may be configured to provide a stable frequency output signal f such that it arises from temperature fluctuations in the waveguide cavity 104 and / or pressure fluctuations in the gas 106. As described in more detail herein, the atomic clock system 100 provides a stable frequency output signal f such that it arises from temperature fluctuations in the waveguide cavity 104 and / or pressure fluctuations in the gas 106. OUT External perturbations that could affect the system can be mitigated. Therefore, the atomic clock system 100 can exhibit superior accuracy and stability compared to conventional atomic clock systems that similarly provide a frequency reference based on gas state transitions.

[0020] As mentioned above, RF signal f CTLThis can be provided from the oscillator system 102 as a dither signal including the offset frequency. Figure 4 shows another exemplary diagram 400 of the power absorption frequency spectrum. Diagram 400 shows the same power absorption frequency spectrum as shown in diagram 300 in the example of Figure 3. Thus, in the following description of the example of Figure 4, the examples of Figures 1 and 3 will be referenced.

[0021] In the example in Figure 4, the RF signal f generated by the oscillator system 102 is shown. CTL This is shown as a dither signal. For example, the frequency controller 112 uses an RF signal f with an offset frequency δ around the center frequency. CTL It may be configured to provide the following: The center frequency is the RF signal f locked to the resonant frequency of gas 106. CTL It can handle the signal frequency of the RF signal f CTL The corresponding dither signal may have a time-averaged frequency equal to the center frequency. During the first time interval, the frequency controller 112 generates an RF signal f having a first frequency + δ. CTL This can be provided, thereby adding an offset frequency δ to the center frequency locked to the resonant frequency of gas 106. During a second time interval approximately equal to the first time interval, the frequency controller 112 provides an RF signal f having a second frequency -δ. CTL This can be provided, thereby subtracting an offset frequency δ from the center frequency locked to the resonant frequency of gas 106. The offset frequency δ can be selected as a small offset to identify the slope on each side of the inverted peak 304 in the power absorption frequency spectrum. Thus, in the example of Figure 4, the first frequency +δ and the second frequency -δ can be associated with portions of the power absorption frequency spectrum that are approximately half the height of the inverted peak 304, respectively.

[0022] Figure 5 shows another exemplary diagram 500 of the power absorption frequency spectrum. Diagram 500 shows an enlarged portion of the same power absorption frequency spectrum shown in diagrams 300 and 400 in the respective examples of Figures 3 and 4. Thus, in the following description of the example in Figure 5, the examples in Figures 1, 3 and 4 will be referenced.

[0023] The power absorption frequency spectrum is magnified so that only peak 302 and inverted peak 304 are shown in the example in Figure 5. As described above, the detection system 114 detects the RF signal f propagated through the gas 106 in the waveguide cavity 104. CTL It is configured to monitor the power of the gas 106, thereby the detection processor 116 detects the RF signal f for the resonant frequency of the gas 106. CTL The signal frequency can be determined. Therefore, the detection processor 116 determines the RF signal f for the resonant frequency of gas 106. CTL A feedback signal FDBK is generated that indicates the difference in signal frequencies, and the signal frequency can be adjusted by this difference, thereby locking the signal frequency to the resonant frequency of gas 106.

[0024] The example in Figure 5 shows the RF signal f, indicated by frequency cf. CTL This shows an example where the center frequency is shifted relative to the resonant frequency of the gas, which is denoted as frequency rf. In the example in Figure 5, the center frequency cf is shown as being slightly smaller than the resonant frequency rf by a frequency difference Δf. As described above in the example in Figure 4, the frequency controller 112 uses the RF signal f as a dither signal between frequencies +δ and -δ in each of the two equal time intervals. CTL The system provides that during the first time interval, if the dither signal has a frequency of +δ and is therefore greater than the center frequency cf by an offset frequency δ, the detection system 114 detects the received RF signal f CTL The power amplitude PWR1 is detected. During the second time interval, if the dither signal has a frequency -δ and is therefore smaller than the center frequency cf by an offset frequency δ, the detection system 114 detects the received RF signal fCTL The power amplitude PWR2 is detected.

[0025] Therefore, based on the symmetry of the power absorption frequency spectrum, the difference between the measured power amplitudes PWR1 and PWR2 represents the frequency difference Δf between the center frequency cf and the resonant frequency rf. Thus, the detection processor 116 can determine the frequency difference Δf based on the difference between the measured power amplitudes PWR1 and PWR2. This allows the detection processor 116 to generate a feedback signal FDBK that represents the frequency difference Δf. Thus, in response to the feedback signal FDBK, the frequency controller 112 generates the RF signal f CTL The center frequency cf can be adjusted by a frequency difference Δf. In the example in Figure 5, the frequency controller 112 adjusts the RF signal f CTL The center frequency cf is increased by the frequency difference Δf, and the RF signal f CTL The center frequency cf can be made to be approximately equal to the resonant frequency rf. Therefore, the RF signal f received by the receiving antenna 110 CTL Through continuous measurement of the power, the power difference between the measured powers PWR1 and PWR2 should become approximately zero. Therefore, the atomic clock system 100 will use the RF signal f CTL The signal frequency (e.g., center frequency cf) can be locked to the resonant frequency rf of ammonia gas 106.

[0026] Referring back to the example in Figure 1, as mentioned above, the waveguide cavity 104 can be manufactured to have a length approximately equal to an integer multiple of the wavelength (e.g., half the wavelength) of the resonant frequency of the gas 106. Such dimensions of the waveguide cavity 104 are suitable for low-order cavity modes TE 102This facilitates the use of low-order cavity modes. Such low-order cavity modes offer several advantages compared to the use of higher-order modes, as implemented in conventional atomic clock systems. Advantages of using low-order cavity modes include Dicke confinement, reduced mode-pulling, and improved temperature-compensated fidelity. Since gas 106 is confined within waveguide cavity 104 at a distance comparable to the transition wavelength of the resonant frequency of gas 106, Dicke confinement can cause Doppler narrowing of the transition of gas 106. Also, adjacent TE 101 Mode and TE 103 The relatively large frequency separation between modes can suppress line-pulling of gas 106 transitions by adjacent modes. Furthermore, as will be described in more detail below, the increased free spectral range (FSR) of the lower-order modes in waveguide cavity 104 provides a passive temperature compensation scheme that more readily addresses cavity pulling than in the case of higher-order cavities.

[0027] While the length of the waveguide cavity 104 offers the aforementioned advantages, temperature fluctuations can alter the physical length of the waveguide cavity 104. Therefore, the physical length of the waveguide cavity 104 can be greater than or less than an integer multiple of the wavelength of the resonant frequency of the gas 106. However, as described below, the atomic clock system 100 is configured to accommodate variations in the physical length of the waveguide cavity 104, thereby adjusting the RF signal f to the resonant frequency of the gas 106. CTL The stability of the signal frequency lock, and therefore the frequency reference output signal f OUT It can maintain stability.

[0028] As a first example, in the example of Figure 1, the waveguide cavity 104 includes a temperature sensor 118 configured to monitor the temperature of the waveguide cavity 104, and the detection system 114 includes a stub tuner 120. The temperature sensor 118 is shown as providing the stub tuner 120 with an indication of the temperature of the waveguide cavity 104, indicated as a signal TMP. As an example, a relationship between the temperature of the waveguide cavity 104 and the physical length of the waveguide cavity 104 can be modeled and / or tested. Thus, the detection processor 116 and / or the stub tuner 120 can be configured to identify variations in the physical length of the waveguide cavity 104 based on the measured temperature TMP. In response to a change in the temperature of the waveguide cavity 104, as indicated by the signal TMP, the stub tuner 120 can provide a signal TN to provide a reactive load to the transmitting antenna 108. As an example, a reactive load provides adjustment to the capacitance and / or inductance of the transmitting antenna 108, thereby controlling the RF signal f transmitted by the transmitting antenna 108. CTL A phase shift can be induced. As a result, the reactive load provided to the transmitting antenna 108 provides adjustment to the electrical length of the waveguide cavity 104. Thus, a change in the electrical length of the waveguide cavity 104 can compensate for a change in the physical length of the waveguide cavity 104. Thus, the waveguide cavity 104 can compensate for temperature-induced cavity pulling based on the temperature sensor 118 and the stub tuner 120.

[0029] As a second example, the temperature sensor 118 can be omitted from the waveguide cavity 104, and the RF signal f CTL A passive temperature compensation scheme can be implemented based on a periodic frequency sweep. An example of this passive temperature compensation scheme is shown in Figure 6.

[0030] Figure 6 shows another exemplary diagram 600 of the power absorption frequency spectrum. Diagram 600 shows the first power absorption frequency spectrum 602 and the second power absorption frequency spectrum 604. The first power absorption frequency spectrum 602 is shown as the same power absorption frequency spectrum as shown in diagram 300 in the example of Figure 3. Thus, in the following description of the example of Figure 6, the examples of Figures 1 and 3 will be referenced.

[0031] The first power absorption frequency spectrum 602 can correspond to the steady-state operation of the atomic clock system 100 where the resonant frequency of the waveguide cavity 104 is approximately equal to the resonant frequency of the gas 106. In the example in Figure 6, the resonant frequency of the waveguide cavity 104 is indicated by a virtual peak 606 located in the center between the low absorption peaks 302. Thus, the virtual peak 606 is located at approximately the same position as the inverted peak 304, indicating that the resonant frequencies of the waveguide cavity 104 and the gas 106 are approximately equal. Therefore, the first power absorption frequency spectrum 602 is shown to be symmetrical with respect to the inverted peak 304, as described above. By making the resonant frequencies of the waveguide cavity 104 and the gas 106 approximately equal, the RF signal f CTL This realizes the low-order modes of propagation and provides a stable frequency reference output signal f OUT It can be generated accurately.

[0032] As described above, the frequency controller 112 uses the RF signal f to determine the resonant frequency of the waveguide cavity 104. CTL The frequency can be configured to sweep periodically. The periodic sweep of the frequency is shown as a sweep of the frequency between a first frequency -Δ and a second frequency +Δ. As an example, the frequencies -Δ and +Δ are the RF signal f CTLThis can correspond to large offset frequencies with respect to the center frequency and / or the resonant frequency of gas 106. The first frequency -Δ corresponds approximately midway through the rising portion of the power absorption frequency spectrum smaller than the first low absorption peak 302, and the second frequency +Δ corresponds approximately midway through the falling portion of the power absorption frequency spectrum larger than the second low absorption peak 302. Thus, the periodic sweep of frequencies between the first frequency -Δ and the second frequency +Δ is a broad frequency band across the power absorption frequency spectrum with frequency boundaries across the portion of power approximately equal across the first power absorption frequency spectrum 602.

[0033] As described above, the resonant frequency of the waveguide cavity 104 can change based on temperature fluctuations. Therefore, temperature can be easily compensated for by determining the resonant frequency of the waveguide cavity 104 and adjusting it to be approximately equal to the resonant frequency of the gas 106. The second power absorption frequency spectrum 604 shows the shift of the resonant frequency of the waveguide cavity 104, shown as frequency fc, with respect to the resonant frequency of the gas 106, shown as frequency fg. In the example in Figure 6, the resonant frequency fg of the gas 106 is shown as being slightly smaller than the resonant frequency fc of the waveguide cavity 104 by a frequency difference Δf. Therefore, the virtual peak 606 is shown as shifted with respect to the inverted peak 304, resulting in asymmetry in the power absorption frequency spectrum.

[0034] When the frequency controller 112 performs a frequency sweep, the detection system 114 detects the RF signal f received at the first frequency-Δ. CTL The power amplitude PWR1 can be detected, and the RF signal f received at the second frequency +Δ can be detected. CTLThe power amplitude PWR2 can be detected. Therefore, based on the asymmetry of the second power absorption frequency spectrum 604, the difference between the measured power amplitudes PWR1 and PWR2 represents the frequency difference Δf between the resonant frequency fg of the gas 106 and the resonant frequency fc of the waveguide cavity 104. Thus, the detection processor 116 can determine the frequency difference Δf based on the difference between the measured power amplitudes PWR1 and PWR2. Thus, the detection processor 116 can provide the stub tuner 120 with instructions to change the electrical length of the waveguide cavity 104, as described above in the first example of temperature compensation.

[0035] For example, the stub tuner 120 provides a signal TN to provide a reactive load to the transmitting antenna 108, and the RF signal f transmitted by the transmitting antenna 108. CTL A phase shift can be induced. As a result, the reactive load provided to the transmitting antenna 108 provides adjustment to the electrical length of the waveguide cavity 104. Thus, a change in the electrical length of the waveguide cavity 104 can compensate for a change in the physical length of the waveguide cavity 104, which results in an offset between the resonant frequency fg of the gas 106 and the resonant frequency fc of the waveguide cavity 104. Thus, by changing the electrical length of the waveguide cavity 104, the resonant frequency fc of the waveguide cavity 104 and the resonant frequency fg of the gas 106 can be made to approximately match. Thus, the waveguide cavity 104 can compensate for cavity pulling due to temperature based on performing a periodic frequency sweep between a first frequency -Δ and a second frequency +Δ, and implementing a stub tuner 120 to change the electrical length of the waveguide cavity 104.

[0036] In addition to responding to frequency changes, the atomic clock system 100 can also respond to changes in the pressure of the gas 106 in the waveguide cavity 104. For example, temperature fluctuations can negatively affect not only the resonant frequency of the waveguide cavity 104 but also the pressure of the gas 106 sealed within it. The pressure of gas 106 can affect its resonant frequency, and as a result, fluctuations in the pressure of gas 106 can cause the signal frequency to lock into an inaccurate frequency value. Consequently, a stable frequency reference output signal f OUT Without pressure compensation, this may include errors.

[0037] Figure 7 shows another exemplary diagram 700 of the power absorption frequency spectrum. Diagram 700 shows the first power absorption frequency spectrum 702 and the second power absorption frequency spectrum 704. The first power absorption frequency spectrum 702 is shown as the same power absorption frequency spectrum as shown in diagram 300 in the example of Figure 3. Thus, in the following description of the example of Figure 7, the examples of Figures 1 and 3 will be referenced.

[0038] The first power absorption frequency spectrum 702 can correspond to the steady-state operation of the atomic clock system 100 at a first pressure of ammonia gas in the waveguide cavity 104. A change in the pressure of the ammonia gas can result in a change in the separation of the low absorption peak 302 in the power absorption frequency spectrum. Such a change in the separation of the peaks can result in a change in the slope of the inverted peak 304. In the example of Figure 7, the second power absorption frequency spectrum 704 can correspond to the steady-state operation of the atomic clock system 100 at a second pressure of ammonia gas in the waveguide cavity 104, where the second pressure is different from the first pressure.

[0039] The pressure of the ammonia gas has a direct correlation with the resonant frequency of the ammonia gas sealed within the volume of the waveguide cavity 104. Therefore, the inversion peaks in the first power absorption frequency spectrum 702 and the second power absorption frequency spectrum 704 are shown at the resonant frequency fr corresponding to the largest population of ammonia gas molecules exhibiting the inversion transition between the first state 210 and the second state 212. As described above, about 10 -3 Torr (approximately 133.322 × 10 -3 For a pressure of Pa, the resonant frequency fr is approximately 22.8 GHz. However, the resonant frequency fr may drift in response to changes in pressure. Therefore, if the change in the resonant frequency fr is not recognized, the detection processor 116 will not detect the RF signal f CTL The signal frequency is locked to the changed resonant frequency, resulting in a stable frequency reference output signal f OUT A frequency error occurs. However, as illustrated in the example in Figure 8, the detection processor 116 can detect and compensate for fluctuations in the pressure of the gas 106 in the waveguide cavity 104.

[0040] Figure 8 shows another exemplary diagram 800 of the power absorption frequency spectrum. Diagram 800 includes the first power absorption frequency spectrum 802, which corresponds to the enlarged region 706 of the first power absorption frequency spectrum 702 in the example of Figure 7. Diagram 800 also includes the second power absorption frequency spectrum 804, which corresponds to the enlarged region 708 of the second power absorption frequency spectrum 704 in the example of Figure 7. Thus, in the following description of the example of Figure 8, the examples of Figures 1, 3, and 7 will be referenced.

[0041] As illustrated in the examples in Figures 4 and 5, the RF signal f generated by the oscillator system 102 CTLThe dither signal can be provided as a center frequency with an offset frequency δ added to and subtracted from it. To detect the pressure of the gas 106 in the waveguide cavity 104, the detection processor 116 can measure the slope of the inverted peak 304 based on the dither signal. As an example, the frequency controller 112 can provide a dither signal during a first duration by adding and subtracting a first offset frequency δ1 to the center frequency, and during a second duration by adding and subtracting a second offset frequency δ2 to the center frequency, where the second offset frequency δ2 is greater than the first offset frequency δ1.

[0042] As described above in the examples in Figures 4 and 5, the detection processor 116 receives the RF signal f during each of the two dither frequency time intervals +δ and -δ. CTL By measuring the power PWR, the center frequency can be locked to the resonant frequency. During steady-state operation, each iteration of the measurement can bring the time-averaged difference of the power measurement to approximately zero, thus indicating that the center frequency is approximately equal to the resonant frequency of gas 106. The power measurements PWR1 and PWR2 are based on the power absorption on each side of the inversion peak 304 at dither frequencies +δ and -δ, respectively. By adjusting the dither frequencies from +δ1 and -δ1 to +δ2 and -δ2, the power measurements PWR1 and PWR2 differ based on the portion of the inversion peak aligned with the dither frequencies +δ2 and -δ2.

[0043] In the example in Figure 8, in each of the first power absorption frequency spectrum 802 and the second power absorption frequency spectrum 804, the center frequencies are the same for the dither frequencies from +δ1 and -δ1 and +δ2 and -δ2, and are approximately equal to the resonant frequency of gas 106. In the first power absorption frequency spectrum 802, the dither frequencies +δ1 and -δ1 provided during the first duration correspond to portions of the power absorption frequency spectrum having power Pδ1, respectively (e.g., PWR1=PWR2=Pδ1). Thus, during the first duration, the dither frequencies are provided as +δ1 and -δ1 to measure the respective powers PWR1 and PWR2 with respect to power Pδ1. During the second duration, the dither frequencies +δ2 and -δ2 correspond to portions of the power absorption frequency spectrum having power Pδ2, respectively (e.g., PWR1=PWR2=Pδ2). Therefore, during the second duration, the dither frequencies are provided as +δ2 and -δ2 to measure the respective powers PWR1 and PWR2 with respect to power Pδ2.

[0044] Based on the slope of the inversion peak 304 in the first power absorption frequency spectrum 802, power Pδ2 is greater than power Pδ1. The difference between powers Pδ1 and Pδ2, and the difference between relative offset frequencies δ1 and δ2, can determine the slope of the inversion peak 304. Thus, the detection processor 116 can calculate the pressure of gas 106 in the waveguide cavity 104 based on the known relationship between the pressure of gas 106 and the power absorption frequency spectrum of gas 106. Thus, the pressure of gas 106 can indicate the resonant frequency of gas 106 based on the known relationship between the pressure of gas 106 and the resonant frequency.

[0045] For example, in response to a change in the pressure of gas 106 based on a change in the temperature of the waveguide cavity 104, gas 106 may change from exhibiting a power absorption frequency spectrum 702 to a power absorption frequency spectrum 704. Therefore, the detection processor 116 can calculate the change in slope, and consequently the change in pressure, and can identify the change in the resonant frequency of gas 106.

[0046] In the second power absorption frequency spectrum 804, the dither frequencies +δ1 and -δ1 provided during the first duration correspond to the portion of the power absorption frequency spectrum having power Pδ1, respectively (e.g., PWR1=PWR2=Pδ1). Therefore, during the first duration, the dither frequencies are provided as +δ1 and -δ1 to measure the respective powers PWR1 and PWR2 with respect to power Pδ1. During the second duration, the dither frequencies +δ2 and -δ2 correspond to the portion of the power absorption frequency spectrum having power Pδ2, respectively (e.g., PWR1=PWR2=Pδ2). Therefore, during the second duration, the dither frequencies are provided as +δ2 and -δ2 to measure the respective powers PWR1 and PWR2 with respect to power Pδ2.

[0047] Similar to what was described above with respect to the first power absorption frequency spectrum 802, the detection processor 116 can calculate the slope of the inversion peak 304. For example, the difference between powers Pδ1 and Pδ2, and the difference between relative offset frequencies δ1 and δ2, can determine the slope of the inversion peak 304 in the second power absorption frequency spectrum 804. However, the detection processor 116 can identify the change in slope between the first power absorption frequency spectrum 802 and the second power absorption frequency spectrum 804. In particular, the difference between powers Pδ1 and Pδ2 in the first power absorption frequency spectrum 802 is greater than the difference between powers Pδ1 and Pδ2 in the second power absorption frequency spectrum 804. Therefore, the detection processor 116 can monitor the change in the slope of the inversion peak at each of the two durations to calculate the change in the pressure of the gas 106.

[0048] As described above, the detection processor 116 provides a feedback signal FDBK to lock the center frequency to the resonant frequency of gas 106. This continues even when the resonant frequency of gas 106 shifts based on changes in the pressure of gas 106. However, based on identifying the change in the pressure of gas 106, and therefore the amount of resonant frequency drift resulting from the pressure change, the detection processor 116 provides a stable frequency reference output signal f OUT The system is configured to mathematically compensate for changes in the resonant frequency when providing the signal. For example, the detection processor 116 provides the downsampled frequency reference output signal f OUT By changing the denominator in the calculation, the change in the numerator of the resonant frequency can be proportionally compensated. Therefore, the frequency reference output signal f OUT This can be provided as a stable frequency reference regardless of changes in the resonant frequency of gas 106.

[0049] Figure 9 shows an example of an integrated atomic clock system 900. The integrated atomic clock system 900 can correspond to the atomic clock system 100 in the example in Figure 1. Therefore, the example in Figure 1 will be referenced in the following description of the example in Figure 9.

[0050] The integrated atomic clock system 900 can be manufactured by any of the various methods using integrated circuit manufacturing techniques. The integrated atomic clock system 900 includes a waveguide cavity 902 and transmitting antennas 904 and receiving antennas 906 positioned at opposite ends of the waveguide cavity 902. The integrated atomic clock system 900 includes a circuit section 908 which includes an oscillator system 102 and a detection system 114. Microstrip lines or other RF signal transmission conductors can be routed between the circuit section 908 and antennas 904 and 906. Thus, the integrated atomic clock system 900 can be formed into an integrated package with a compact form factor to provide a stable frequency reference, such as for implementation in an INS or other precision device.

[0051] Considering the structural and functional features described above, methods according to various aspects of the present invention will be better understood with reference to Figure 10. For the sake of simplicity, the methods in Figure 10 are shown and described as being performed sequentially, but it should be understood and recognized that the present invention is not limited by the illustrated order, as some aspects may occur in a different order than those shown and described herein, and / or simultaneously with other aspects, according to the present invention. Furthermore, not all illustrated features are required to carry out a method according to one aspect of the present invention.

[0052] Figure 10 shows a stable frequency reference output signal (for example, a stable frequency reference output signal f OUT An example of method 1000 for providing ) is shown. In 1002, an RF signal (for example, an RF signal f) having a signal frequency approximately equal to the resonant frequency of ammonia gas is provided. CTL ) is generated. In 1004, the RF signal is radiated through a waveguide cavity (e.g., waveguide cavity 104) containing ammonia gas sealed and enclosed therein via a transmitting antenna (e.g., transmitting antenna 108). The waveguide cavity can have a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between the two states. In 1006, the RF signal is received through the waveguide cavity at a receiving antenna (e.g., receiving antenna 110) on the opposite side of the transmitting antenna. In 1008, the characteristics of the RF signal at the receiving antenna are measured to detect the maximum transition between the two states of the ammonia gas. In 1010, a feedback signal (e.g., feedback signal FDBK) associated with the difference between the signal frequency and the resonant frequency of the gas is generated based on the detection of the maximum transition. In 1012, the signal frequency of the RF signal is adjusted in response to the feedback signal to be approximately equal to the resonant frequency. In 1014, a stable frequency reference output signal is generated based on the signal frequency of the RF signal.

[0053] The above description is an example of the present invention. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of illustrating the present invention, but those skilled in the art will recognize that many further combinations and substitutions of the present invention are possible. Accordingly, the present invention is intended to encompass all such changes, modifications, and variations that fall within the scope of this application, including the appended claims. The technical concepts included in this disclosure are described below as an addendum. (Note 1) It is an atomic clock system, A waveguide cavity that is sealed and contains a gas therein, the waveguide cavity having a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the gas between two states, An oscillator system configured to generate an RF signal through the waveguide cavity, wherein the RF signal has a signal frequency approximately equal to the resonant frequency of the gas, A detection system configured to measure the characteristics of the RF signal passing through the waveguide cavity to detect the maximum transition between the two states of the gas, and to provide a feedback signal to the oscillator system based on the detection of the maximum transition to lock the signal frequency of the RF signal to the resonant frequency of the gas. An atomic clock system comprising the detection system, wherein the detection system is configured to provide a frequency reference output signal based on the signal frequency of the RF signal. (Note 2) The aforementioned gas is ammonia gas, as described in Appendix 1 of the atomic clock system. (Note 3) The atomic clock system according to Appendix 1, wherein the oscillator system includes a frequency controller configured to provide the RF signal as a dither signal between a first signal frequency and a second signal frequency, and the detection system is configured to provide the feedback signal to lock the center frequency of the dither signal to the resonant frequency of the gas. (Note 4) The atomic clock system according to Appendix 3, wherein the frequency controller is configured to provide the dither signal by adding a first offset frequency to the center frequency of the RF signal and subtracting the first offset frequency from the center frequency of the RF signal at substantially equal time intervals to determine the difference between the center frequency of the RF signal and the resonant frequency of the gas, and the detection system includes a detection processor configured to provide the feedback signal to adjust the center frequency to be substantially equal to the resonant frequency of the gas based on the measured difference in the characteristics between adding and subtracting the first offset frequency to the center frequency. (Note 5) The atomic clock system as described in Appendix 4, wherein the frequency controller is configured to provide the dither signal by adding and subtracting a first offset frequency to the center frequency for a first duration and by adding and subtracting a second offset frequency to the center frequency for a second duration, wherein the second offset frequency is greater than the first offset frequency, and the detection processor is configured to determine the resonant frequency of the gas based on the time-averaged difference of the measured characteristics of the RF signal in each of the first and second durations, and to adjust the frequency reference output signal based on the determined resonant frequency. (Note 6) The atomic clock system according to Appendix 5, wherein the detection processor is configured to determine the resonant frequency of the gas based on identifying the pressure of the gas in the waveguide cavity in response to the time-averaged difference of the measured characteristics of the RF signal in each of the first and second durations. (Note 7) The atomic clock system as described in Appendix 1, wherein the waveguide cavity includes a transmitting antenna at a first end of the waveguide cavity and a receiving antenna at a second end of the waveguide cavity opposite the first end, the transmitting antenna being configured to radiate the RF signal through the waveguide cavity to be received by the receiving antenna, and the detection system includes a stub tuner configured to provide a reactive load to the transmitting antenna to adjust the electrical length of the waveguide cavity in response to a change in the physical length of the waveguide cavity. (Note 8) The atomic clock system according to Appendix 7, wherein the waveguide cavity further includes a temperature sensor configured to measure the temperature of the waveguide cavity, and the stub tuner is configured to adjust the electrical length of the waveguide cavity in response to the change in the physical length of the waveguide cavity based on the temperature. (Note 9) The atomic clock system according to Appendix 7, wherein the oscillator system includes a frequency controller configured to periodically sweep a frequency range between a first frequency and a second frequency on either side of a power transmission peak in the power absorption frequency spectrum associated with the gas, and the stub tuner is configured to adjust the electrical length of the waveguide cavity in response to detecting the change in the physical length of the waveguide cavity in response to the periodic sweep of the frequency range. (Note 10) An integrated circuit (IC) equipped with the atomic clock system described in Appendix 1. (Note 11) A method for providing a stable frequency reference output signal, To generate an RF signal having a signal frequency approximately equal to the resonant frequency of ammonia gas, The RF signal is transmitted via a transmitting antenna through a waveguide cavity that is sealed and contains the ammonia gas contained therein, and has a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between the two states. The RF signal is received at the receiving antenna on the opposite side of the transmitting antenna through the waveguide cavity. The characteristics of the RF signal in the receiving antenna are measured to detect the maximum transition between the two states of the ammonia gas. Based on detecting the maximum transition, a feedback signal is generated that is associated with the difference between the signal frequency and the resonant frequency of the ammonia gas. In response to the feedback signal, adjust the signal frequency of the RF signal so that it is approximately equal to the resonant frequency. The stable frequency reference output signal is provided based on the signal frequency of the RF signal. Methods that include... (Note 12) The RF signal is generated by During the first time interval, a first offset frequency is added to the center frequency of the RF signal. Subtracting the first offset frequency from the center frequency in a second time interval that is approximately equal to the first time interval. Includes, The method according to Appendix 11, wherein generating the feedback signal includes generating the feedback signal associated with the difference between the center frequencies of the first and second offset frequencies and the resonant frequency of the ammonia gas, based on detecting the maximum transition. (Note 13) Adding and subtracting the first offset frequency to the center frequency includes adding and subtracting the first offset frequency to the center frequency during a first duration, and the method is During the first time interval of the second duration, a second offset frequency greater than the first offset frequency is added to the center frequency of the RF signal. During the second duration, subtract the second offset frequency from the center frequency in a second time interval that is approximately equal to the first time interval. The resonant frequency of the ammonia gas is determined based on the time-averaged difference of the measured characteristics of the RF signal during each of the first and second durations. Adjusting the stable frequency reference output signal based on the determined resonant frequency. The method described in Appendix 12, further including the method described in Appendix 12. (Note 14) To measure the temperature of the waveguide cavity, Based on the temperature, a change in the physical length of the waveguide cavity is detected. The reactive load of the transmitting antenna is changed to adjust the electrical length of the waveguide cavity to be approximately equal to the physical length of the waveguide cavity. The method described in Appendix 11, further including the method described in Appendix 11. (Note 15) The signal frequency of the RF signal is periodically swept within the frequency range between a first frequency and a second frequency on both sides of the power transmission peak on the power absorption frequency spectrum associated with the ammonia gas. To detect changes in the physical length of the waveguide cavity in response to a periodic sweep of the aforementioned frequency range, The reactive load of the transmitting antenna is changed to adjust the electrical length of the waveguide cavity to be approximately equal to the physical length of the waveguide cavity. The method described in Appendix 11, further including the method described in Appendix 11. (Note 16) An integrated atomic clock system, A waveguide cavity that is sealed and contains ammonia gas, the waveguide cavity having a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between two states, An oscillator system configured to generate an RF dither signal between a first signal frequency and a second signal frequency, and to provide the RF dither signal through the waveguide cavity via a transmitting antenna, wherein the RF dither signal has a center frequency substantially equal to the resonant frequency of the ammonia gas, A detection system configured to measure the characteristics of the RF dither signal received by a receiving antenna on the opposite side of the transmitting antenna through the waveguide cavity at each of the first and second signal frequencies to detect the maximum transition between the two states of the ammonia gas, and to provide a feedback signal to the oscillator system based on the detection of the maximum transition to lock the center frequency of the RF signal to the resonant frequency of the ammonia gas. An integrated atomic clock system comprising, wherein the detection system is configured to provide a frequency reference output signal based on the center frequency of the RF signal. (Note 17) The integrated atomic clock system as described in Appendix 16, wherein the oscillator system includes a frequency controller configured to provide the RF dither signal by adding a first offset frequency to the center frequency of the RF dither signal and subtracting the first offset frequency from the center frequency of the RF dither signal at substantially equal time intervals to determine the difference between the center frequency of the RF dither signal and the resonant frequency of the ammonia gas, and the detection system includes a detection processor configured to provide the feedback signal to adjust the center frequency to be substantially equal to the resonant frequency of the ammonia gas based on the measured difference in the characteristics between adding and subtracting the first offset frequency to the center frequency. (Note 18) The integrated atomic clock system as described in Appendix 17, wherein the frequency controller is configured to provide the RF dither signal by adding and subtracting a first offset frequency to the center frequency for a first duration and by adding and subtracting a second offset frequency to the center frequency for a second duration, wherein the second offset frequency is greater than the first offset frequency, and the detection processor is configured to determine the resonant frequency of the ammonia gas based on the time-averaged difference of the measured characteristics of the RF dither signal for each of the first and second durations, and to adjust the frequency reference output signal based on the determined resonant frequency. (Note 19) The integrated atomic clock system according to Appendix 16, wherein the waveguide cavity further includes a temperature sensor configured to measure the temperature of the waveguide cavity, and the detection system further includes a stub tuner configured to adjust the electrical length of the waveguide cavity in response to a change in the physical length of the waveguide cavity based on the temperature. (Note 20) The integrated atomic clock system according to Appendix 16, wherein the oscillator system includes a frequency controller configured to periodically sweep a frequency range between a first frequency and a second frequency on either side of a power transmission peak on the power absorption frequency spectrum associated with the ammonia gas, and the detection system further includes a stub tuner configured to adjust the electrical length of the waveguide cavity in response to detection of a change in the physical length of the waveguide cavity in response to the periodic sweep of the frequency range.

Claims

1. It is an atomic clock system, A waveguide cavity that is sealed and contains a gas therein, the waveguide cavity having a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the gas between two states, An oscillator system configured to generate an RF signal through the waveguide cavity, wherein the oscillator system includes a frequency controller configured to provide the RF signal as a dither signal between a first signal frequency and a second signal frequency, the RF signal having a center frequency between the first signal frequency and the second signal frequency, the center frequency being approximately equal to the resonant frequency of the gas, A detection system configured to measure the characteristics of the RF signal passing through the waveguide cavity to detect the maximum transition between the two states of the gas, and to provide a feedback signal to the oscillator system based on the detection of the maximum transition to lock the center frequency of the RF signal to the resonant frequency of the gas. An atomic clock system comprising, wherein the detection system is configured to provide a frequency reference output signal based on the center frequency of the RF signal.

2. The atomic clock system according to claim 1, wherein the gas is ammonia gas.

3. The atomic clock system according to claim 1, wherein the frequency controller is configured to provide the dither signal by adding a first offset frequency to the center frequency of the RF signal and subtracting the first offset frequency from the center frequency of the RF signal at substantially equal time intervals to determine the difference between the center frequency of the RF signal and the resonant frequency of the gas, and the detection system includes a detection processor configured to provide the feedback signal to adjust the center frequency to be substantially equal to the resonant frequency of the gas based on the measured difference in the characteristics between adding and subtracting the first offset frequency to the center frequency.

4. The atomic clock system according to claim 3, wherein the frequency controller is configured to provide the dither signal by adding and subtracting a first offset frequency to the center frequency for a first duration and by adding and subtracting a second offset frequency to the center frequency for a second duration, wherein the second offset frequency is greater than the first offset frequency, and the detection processor is configured to determine the resonant frequency of the gas based on the time-averaged difference of the measured characteristics of the RF signal in each of the first and second durations, and to adjust the frequency reference output signal based on the determined resonant frequency.

5. The atomic clock system according to claim 4, wherein the detection processor is configured to determine the resonant frequency of the gas based on identifying the pressure of the gas in the waveguide cavity in response to the time-averaged difference of the measured characteristics of the RF signal in each of the first and second durations.

6. The atomic clock system according to claim 1, wherein the waveguide cavity includes a transmitting antenna at a first end of the waveguide cavity and a receiving antenna at a second end of the waveguide cavity opposite the first end, the transmitting antenna is configured to radiate the RF signal through the waveguide cavity to be received by the receiving antenna, and the detection system includes a stub tuner configured to provide a reactive load to the transmitting antenna in order to adjust the electrical length of the waveguide cavity in response to a change in the physical length of the waveguide cavity.

7. The atomic clock system according to claim 6, wherein the waveguide cavity further includes a temperature sensor configured to measure the temperature of the waveguide cavity, and the stub tuner is configured to adjust the electrical length of the waveguide cavity in response to the change in the physical length of the waveguide cavity based on the temperature.

8. The atomic clock system according to claim 6, wherein the oscillator system includes a frequency controller configured to periodically sweep a frequency range between a first frequency and a second frequency on either side of a power transmission peak in the power absorption frequency spectrum associated with the gas, and the stub tuner is configured to adjust the electrical length of the waveguide cavity in response to detecting the change in the physical length of the waveguide cavity in response to the periodic sweep of the frequency range.

9. An integrated circuit (IC) comprising the atomic clock system according to claim 1.

10. A method for providing a stable frequency reference output signal, This includes generating an RF signal having a center frequency approximately equal to the resonant frequency of ammonia gas, and generating the RF signal is During the first time interval, an offset frequency is added to the center frequency of the RF signal. Subtracting the offset frequency from the center frequency in a second time interval that is approximately equal to the first time interval. The method includes, The RF signal is transmitted via a transmitting antenna through a waveguide cavity that is sealed and contains the ammonia gas contained therein, and has a length that is an integer multiple of approximately half a wavelength of the resonant frequency of the ammonia gas between the two states. The RF signal is received by a receiving antenna on the opposite side of the transmitting antenna through the waveguide cavity. The characteristics of the RF signal in the receiving antenna are measured to detect the maximum transition between the two states of the ammonia gas. Based on detecting the maximum transition, a feedback signal is generated that is associated with the difference between the center frequency and the resonant frequency of the ammonia gas. In response to the feedback signal, adjust the center frequency of the RF signal to be approximately equal to the resonant frequency. The stable frequency reference output signal is provided based on the center frequency of the RF signal. Methods that include...

11. Adding and subtracting the offset frequency to the center frequency includes adding and subtracting the first offset frequency to the center frequency during a first duration, and the method is During the first time interval of the second duration, a second offset frequency greater than the first offset frequency is added to the center frequency of the RF signal. During the second duration, subtract the second offset frequency from the center frequency in a second time interval that is approximately equal to the first time interval. The resonant frequency of the ammonia gas is determined based on the time-averaged difference of the measured characteristics of the RF signal during each of the first and second durations. Adjusting the stable frequency reference output signal based on the determined resonant frequency. The method according to claim 10, further comprising:

12. To measure the temperature of the waveguide cavity, Based on the temperature, a change in the physical length of the waveguide cavity is detected. The reactive load of the transmitting antenna is changed to adjust the electrical length of the waveguide cavity to be approximately equal to the physical length of the waveguide cavity. The method according to claim 10, further comprising:

13. The signal frequency of the RF signal is periodically swept within the frequency range between a first frequency and a second frequency on both sides of the power transmission peak on the power absorption frequency spectrum associated with the ammonia gas. To detect changes in the physical length of the waveguide cavity in response to a periodic sweep of the aforementioned frequency range, The reactive load of the transmitting antenna is changed to adjust the electrical length of the waveguide cavity to be approximately equal to the physical length of the waveguide cavity. The method according to claim 10, further comprising:

Images