A method and apparatus for measuring a resonance frequency response of passive microwave devices

Abstract

A method for measuring a resonance frequency response of passive microwave devices PMD 316 e.g. dielectric resonator includes transmitting RF signals through the passive microwave device, and measuring the resonance frequency response. One or more dielectric lossless mediums are placed within a distance of the passive microwave device. The distance may be adjusted, or the thickness of the dielectric lossless medium, or the effective permittivity of the dielectric lossless medium may be altered by subjecting it to an electric field. This modifies the effective permittivity of the PMD without directly modifying the PMD itself, which produces a frequency shift the PMD. Measuring the responses before and after this modification enables the resonance frequency response to be determined. An apparatus 300 includes a housing 302 for the PMD 316 and dielectric lossless media 308. A positioning mechanism 310 alters the distance between them. The thickness can be varied by dielectric stacking (611,612,613 Figure 6B). A digital signal processing unit 318 determines the resonance frequency response.

Description

FIELD This disclosure relates to a method and apparatus for measuring the resonance frequency response of passive microwave components. More specifically, the invention relates to the wideband measurement of frequency response using low power. BACKGROUND Typical radio frequency (RF) measurement devices may consist of a signal generator, test ports, receivers, and analysers. Such measurement devices are used to measure specific electromagnetic properties of other components or devices, such as Passive Microwave Devices (PMDs). PMDs are commonly found in microwave circuits, filters, antennas or sensors. PMDs are designed to store and manipulate electromagnetic energy within the microwave frequency range by using the phenomenon of resonance. The structure of the PMD can store standing waves, which may be oscillating patterns of electromagnetic fields that reflect within the PMD. The specific resonance frequency of a PMD is dependent on the physical dimensions and type of material of the PMD. Measurement devices for measuring the frequency response inherit several design challenges, such as medium interruption, power management, frequency range extension, and miss-matching networks. Solutions to these problems often increase their cost and design complexity. Signal generation and its analysis involves complex digital signal processing (DSP) algorithms, which further increase the hardware constraints followed by power management challenges. The frequency measurement range of these devices is a crucial parameter to consider while designing. To some extent, the concept of Software-Defined Radio (SDR) solves the frequency range problem, but noise floor and similar challenges still exist while designing such large bandwidth SDRs. Classical SDRs typically involve an RF front end, which contains several essential components of the RF transmitter and receiver, and an RF backend, typically a DSP unit that monitors and controls the whole operation of this device. Several architectures of SDRs have been proposed for specific applications. Those architectures focus on the RF back-end using different types of modulation techniques, power measurement, minimising miss-matching errors, etc. These challenges are overcome by VNA instruments, which are typically used for the accurate and precise frequency measurement of RF devices. However, instruments to measure the frequency response, such as the VNA, are costly and the design complexity increases with various frequency range variants. There is accordingly scope for improvement. The preceding discussion of the background is intended only to facilitate an understanding of the present disclosure. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY According to the disclosure there is provided a method for determining a resonance frequency response of a passive microwave device (PMD), the method comprising the steps of: positioning at least one dielectric lossless medium at a first distance from the PMD, where the dielectric lossless medium has a first relative permittivity and a first thickness; generating a first radio frequency signal, applying the first radio frequency signal to the PMD, and measuring a first signal transmission response; varying any combination of one or more parameters of the dielectric lossless medium to shift the resonance frequency response of the PMD, the parameters including; a distance between the PMD and the at least one dielectric lossless medium; a thickness of the at least one dielectric lossless medium, and an effective or relative permittivity of the at least one dielectric lossless medium; generating a second radio frequency signal, applying the second radio frequency signal to the PMD, and measuring a second signal transmission response; and, determining, via a digital signal processing (DSP) unit, the resonance frequency response of the passive microwave device from the first and second signal transmission measurements. The distance parameter may be varied by changing the distance between the dielectric lossless medium and the PMD from the first distance to a second distance. In one embodiment, the PMD is placed within a housing and the dielectric lossless medium is positioned above the PMD and is moved within the enclosure to change the distance between the PMD and the dielectric lossless medium. A thickness parameter may be varied by combining a plurality of dielectric lossless media together, thereby changing the combined thickness of all dielectric lossless media to a second thickness different than the first thickness. An effective permittivity parameter may be varied by subjecting the at least one dielectric lossless medium to an electric field. The electric field may be formed by applying an electrical voltage to at least two electrodes, with the electrodes arranged such that an electric field forms between the electrode pair when an electrical voltage is applied. The first and second radio frequency signals may be generated by a radio frequency transmitter, and a radio frequency receiver may measure the first and second signal transmissions through the PMD. In one example, the DSP unit sends signals to the radio frequency transmitter device and receives signals from the radio frequency receiver device. The DSP unit may use a mapping algorithm for determining the resonance frequency response of the PMD. The first radio frequency signal and the second radio frequency signal may be equivalent. The disclosure extends to an apparatus for determining a resonance frequency response of a passive microwave device (PMD); comprising: a positioning mechanism configured to position at least one dielectric lossless medium at a distance relative to the PMD; a communication system, including a radio frequency transmitter that is configured to generate a first and second radio frequency signal, and a radio frequency receiver that is configured to measure a first and second signal transmission response; a digital signal processing (DSP) unit configured to determine the resonance frequency response of the PMD from at least two signal transmission responses; and, a housing configured to accommodate the PMD, positioning mechanism, communication system, and DSP unit. The positioning mechanism may be configured to change the relative distance between one or more dielectric lossless mediums and the PMD. The apparatus may include at least two electrodes, configured such that an electric field forms between the electrodes when an electrical voltage is applied to the electrodes. The dielectric lossless mediums may be positioned in the electric field between the electrodes, such that the relative permittivity of the dielectric lossless mediums is changed by the electric field. The DSP may be configured to send the first and second radio frequency signal values to the radio frequency transmitter and may be configured to receive the first and second signal transmission response values from the radio frequency receiver. The apparatus may include a voltage source configured to generate and apply an electrical voltage to the electrodes. The housing may be an enclosure surrounding the PMD, and may include a lid, where the positioning mechanism is attached to the lid and inserted into the housing. Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is an illustration of electromagnetic waves being reflected, absorbed or transmitted through a medium; Figure 2 is an illustration of a graph of the magnitudes of the normalised resonance frequency under the influence of varying effective permittivity; Figure 3 is an illustration of an embodiment of the apparatus; Figure 4 is a schematic diagram of a communication system indicating the flow of signals; Figure 5 is a flow diagram of a method for measuring a resonance frequency response; Figure 6A is an illustration of a distance parameter between a passive microwave device and a dielectric lossless medium; Figure 6B is an illustration of a thickness parameter between a passive microwave device and a plurality of dielectric lossless medium; Figure 6C is an illustration of an effective permittivity parameter of a dielectric lossless medium and a pair of electrodes; and, Figure 7 is an illustration of a graph of the magnitudes of the normalised resonance frequency at two finely space frequency points within a narrow frequency band. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS An apparatus and a method for measuring a wideband resonance frequency response of passive microwave components is disclosed. The apparatus and method may be suitable for linear devices. The method takes advantage of the effects that dielectric materials have on electromagnetic wave propagation. A resonance frequency response of a dielectric resonator device, also referred to as a passive microwave device (PMD), is influenced by a relative permittivity and a thickness of the PMD. A PMD may comprise three layers; a ground, a substrate, and a conductor. The conductor may be the top surface layer of the PMD. Once the PMD has been manufactured, it is no longer possible to modify the thickness or relative permittivity of the PMD, and therefore, the resonance frequency response of the PMD cannot be altered. The PMD may be a passive two-port device. Figure 1 illustrates the propagation of an electromagnetic wave through a material medium. The propagation of electromagnetic waves is predominantly characterised by a relative permittivity and a thickness of the material medium. An incident wave (106) approaches a medium (102), it passes from free space to the material medium. The incident wave (106) may propagate through the medium (102), be absorbed (108) by the medium (102) and be transmitted (110) out of the medium (102). The incident wave (106) may also be reflected (112) away from the medium (102) at the incident surface (104). The transmission (110), absorption (108), and reflection (112) may occur as the electromagnetic wave experiences a change of wave impedance at the interface between two mediums. The degree of change may depend upon the medium's relative permittivity and thickness. Both the relative permittivity and thickness of the PMD relate inversely to the normalised resonance frequency. Variations in the normalised resonance frequency with a change in thickness and relative permittivity is shown in Figure 2. A normalised frequency graph (200) illustrates the magnitude of the electromagnetic wave response on the vertical axis and the normalised frequency along the horizontal axis. A first frequency curve (202) of the material medium is illustrated for a PMD. The normalised frequency of the same material but of a different thickness is illustrated by a second frequency curve (204), and the normalised frequency of a different material with a different relative permittivity, but of a same thickness as the first frequency curve material, is illustrated by a third frequency curve (206). The present disclosure describes an apparatus and method for changing and measuring the normalised frequency response of the PMD without directly modifying the PMD itself. The method and apparatus may exploit the mentioned phenomenon of electromagnetic wave propagation by utilising a dielectric lossless medium to modify an effective permittivity in the vicinity of the PMD. The dielectric lossless medium is a material or medium in which electromagnetic waves can propagate without attenuation or energy dissipation (at least to any substantial extent). The dielectric lossless medium may have a permittivity value different to the surrounding material. Therefore, if an incident wave (106) reaches the surface (104) of the dielectric lossless medium, a change to a frequency, an amplitude, or a wavelength may occur. However, these changes will not occur as the electromagnetic wave travels through the dielectric lossless medium. If a PMD is exposed to a dielectric lossless medium within a proximity to the surface of the PMD, the dielectric lossless medium may produce a frequency shift in the PMD. The magnitude of a frequency shift in the PMD may depend on the dielectric lossless medium’s relative permittivity and thickness. If a dielectric lossless medium is placed with the vicinity of a PMD, the normalised resonance frequency (202) may shift to a new normalised frequency (204,206), depending on the properties of the dielectric lossless medium. Figure 3 illustrates an embodiment of an apparatus (300) for measuring the resonance frequency response of a PMD. The apparatus may include a housing structure (302), which may further comprise an enclosure (304) and a lid (306). The enclosure may be a cubic enclosure. The apparatus (300) may be configured to accept a PMD (316) within a testing area in the housing structure (302) of the apparatus (300). The apparatus (300) may be configured to accept at least one dielectric lossless medium (308) within a positioning mechanism (310). The positioning mechanism (310) may be configured to position the at least one dielectric lossless medium (308) at a first distance apart from the PMD. The apparatus (300) may include at least one pair of electrodes fixed to one or more guiding arms (312). The guiding arms (312) may be affixed to the lid (306). The guiding arms (312) may be configured to fit into a cutout (314) of the housing structure (304) when the lid (306) is positioned onto the housing structure (304) to close the apparatus. The cutout (314) may guide the guiding arms (312) such that the dielectric lossless medium would be positioned directly above the PMD (316). The cutout (314) may include an electrical connection, such that electrical power is only provided to the electrodes when the lid (306) and housing structure (304) are configured together in a testing mode. In another embodiment, the electrodes may be incorporated into the positioning mechanism (310) such that the electrodes are alongside the one or more dielectric lossless medium (308). The electrodes may be in direct contact with the dielectric lossless medium (308). In a further embodiment, the electrodes may be incorporated into the housing structure (304). The electrodes may be arranged parallel to each other. The electrodes may be configured to accept an electrical voltage, which may induce an electrical field to form between the electrodes. The electrodes may be arranged on opposite sides of the dielectric lossless medium (308) such that, when an electrical voltage is applied to the electrodes, the dielectric lossless medium (308) is positioned in the resulting electric field. The electrodes may be configured such that they extend across the entire height of all dielectric lossless medium or media that the positioning mechanism can retain. The dielectric lossless medium (308) may be held in place by guiding rails of the positioning mechanism (310). The dielectric lossless medium (308) may be held in place by a friction fit. The dielectric lossless medium (308) may be inserted through an opening in the lid (306). The height of the dielectric lossless medium (308) may be adjusted vertically be raising or lowering the guiding rails of the positioning mechanism (310). The height of the positioning mechanism (310) may be adjusted in predefined increments designed into the guiding rails. Spacers may be inserted between the dielectric lossless medium (308) to change the effective permittivity properties of the dielectric lossless medium or media (308). Each dielectric lossless medium may have different permittivity values. The apparatus may include a communication system that comprises a radio frequency transmitter (317) and a radio frequency receiver (319). A digital signal processing (DSP) unit (318) may form part of the communication system. The transmitter (317), receiver (319) and DSP unit (318) may be a single device that may perform the function of all three components. The radio frequency transmitter (317) and the radio frequency receiver (319) may be connected to the PMD via a cable. The radio frequency transmitter (317) and the radio frequency receiver (319) may be connected to an arrange of sensor equipment with the test bed of the housing, surrounding the PMD (316). The radio frequency transmitter (317) and the radio frequency receiver (319) may be connected to the DSP unit (318). The communication system may be placed outside of the housing structure (304). In a further embodiment, the communication system may be configured within the housing structure (304) such that it does influence the testing of the PMD (316). The radio frequency transmitter (317) may be configured to generate a radio frequency signal and to transmit the signal to the PMD (316). The radio frequency receiver (319) may be configured to measure a signal transmission response from the PMD (316). The transmitting and measuring of a signal are indicated in Figure 3 by the dotted lines extending from the radio frequency transmitter (317) to the PMD (316) and on towards the radio frequency receiver (319). The radio frequency signal and the signal transmission response may be a form of electromagnetic radiation, such as an electromagnetic wave within the radio frequency spectrum or any other suitable range within the electromagnetic spectrum. Figure 4 illustrates the function of the communication system (317, 318, 319) and the PMD (316) together. The DSP unit (318) may determine a normalised frequency value and send (410) the signal to the radio frequency transmitter (317). The radio frequency transmitter (317) may generate the first radio frequency signal and apply (412) the signal to the PMD (316). The radio frequency receiver (319) may measure (414) a signal transmission response of the PMD (316). The radio frequency receiver (319) may send (416) the measured signal to the DSP unit (318). The steps for carrying out the method of testing a PMD (316) is shown in Figure 5. The method may begin by setting up (502) the apparatus. The setting up may include; placing the PMD (316) within the housing structure, configuring the radio frequency transmitter (317) and radio frequency receiver (319) with the PMD (316), configuring the DSP unit (318) with the transmitter (317) and receiver (319) The DSP unit (318) may determine (504) a first radio frequency signal to be generated (504) by the transmitter (317). The transmitter (317) may apply (506) the first radio frequency signal to the PMD (316). The receiver (319) may measure (508) a first signal transmission response from the PMD (316). The receiver (319) may send (510) the first measured signal to the DSP unit (318). Once the first signal transmission response has been measured, a set of effective permittivity parameters may be adjusted (512) in the apparatus by changing any one of; a distance between the dielectric lossless media, adding or removing dielectric lossless media, or applying an electrical voltage to the electrodes. By changing the effective permittivity parameters, the resonance frequency response of the PMD (316) shifts, causing measurable changes in the transmission magnitude (vertical axis of Figure 2) and normalised frequency for each radio frequency signal. The DSP unit (318) may determine (514) a second radio frequency signal to be generated (514) by the transmitter (317). The transmitter (317) may apply (516) the second radio frequency signal to the PMD (316). The receiver (319) may measure (518) a second signal transmission response from the PMD (316). The receiver (319) may send (520) the second measured signal to the DSP unit (318). The DSP unit (318) may determine (522) a resonance frequency response. The DSP unit (318) may determine the frequency response by comparing the measured first and second signal transmission responses. The first and second radio frequency signals may be equal in order to measure a resonance frequency shift due to changes of the effective permittivity. The resonance frequency response may be a frequency curve as illustrated in Figure 2. The transmitter (317) may operate at a fixed frequency to monitor signal transmission through the PMD (316). The transmitter (317) may have a narrow radio frequency window, which allows for the measurement of the resonance frequency response of the PMD at a single frequency point at a time. Referring to Figure 7, the communication system may allow for precise control and sampling of the resonance frequency responses across a finely spaced set of frequencies (710), generating a collection of responses (712). A first resonance frequency response (702) may be shifted to a second resonance frequency response (704) by changing any of the one or more of the effective permittivity parameters. The collected signal transmission data may be processed by the DSP unit (318) using digital signal processing algorithms to determine the resonance frequency response of the PMD (316) across a large bandwidth. The bandwidth can be extended by sampling from different groups of finely spaced sets of frequencies (710). The digital signal processing algorithm may be a mapping algorithm. The apparatus (300) may vary the effective permittivity in the vicinity of the PMD by placing a dielectric lossless medium within a first distance of the PMD and altering the effective permittivity parameters. These parameters may include; a distance parameter, a thickness parameter, or an effective permittivity parameter. The distance parameter may be the distance between the dielectric lossless medium (602) and the PMD as shown in Figure 6A. Generally, a PMD may comprise a ground (608), a substrate (607), and a conductor layer (604). The PMD may be positioned in the housing structure with the dielectric lossless medium (602) placed at a height (606) above the PMD. The height (606) may be changed in order to alter the effective permittivity of the PMD. Electromagnetic waves travelling from a surface of the PMD, such as the conductor (604), towards a free space above the PMD exhibits a change in a field intensity as a function of height or distance from the surface. The field intensity is strongest at the surface and decreases with height from the surface to become weaker. By disturbing the near field intensity, such as by placing a dielectric lossless medium near the surface of the PMD, the resonance frequency response of the PMD is affected. A second parameter that may be changed is the thickness parameter, as shown in Figure 6B. The PMD, comprising the ground (618), the substrate (617), and the conductor (614), is placed below a plurality of dielectric lossless media (611, 612, 613). Each dielectric lossless medium may have a different relative permittivity value or may have the same relative permittivity value. A first thickness (615) of a single dielectric lossless medium (611) may be less than that of a second thickness (616) of a combination of dielectric lossless media (611, 612, 613). The combination of media results in dielectric stacking. Each dielectric lossless medium may be of the same thickness or may each be of a unique thickness. The amount of dielectric stacking may result in varying degrees of change of the resonance frequency response of the PMD. A third parameter that may be changed is the effective permittivity parameter, as shown in Figure 6C. The PMD, comprising the ground (628), the substrate (627), and the conductor (624), is placed below the dielectric lossless medium (622). The dielectric lossless medium (622) may be arranged between a pair of electrodes (623). The electrodes (623) are configured with an electrical voltage source (621). The electrical voltage source (621) may supply an electrical voltage to the electrodes, creating an electrical field between the electrodes (623). The electrodes (623) and dielectric lossless medium (622) are arranged such that the dielectric lossless medium (622) may be within the created electric field. The electric field may interact with the medium (622), changing the relative permittivity of the medium (622). The change in permittivity of the medium (622) affects the near field intensity of the PMD, changing the effective permittivity and subsequently, changing the resonance frequency response of the PMD. Using an electric field may be a more efficient way to vary the effective permittivity of the dielectric lossless medium, as well as provide more control to make small adjustments to the relative permittivity by changing the electrical voltage incrementally. In a further embodiment of the apparatus, the dielectric lossless medium may be placed on a sidewall of the housing structure, alongside of the PMD instead of above it. The positioning mechanism may be integrated into the sidewall instead of the lid. The dielectric lossless medium may be placed vertically to a left or right side of the PMD and moved closer or away from the PMD to vary the distance parameter. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 5 The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based 10 hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood 15 to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A method for determining a resonance frequency response of a passive microwave device 5 (PMD), the method comprising the steps of:positioning at least one dielectric lossless medium at a first distance from the PMD, where the dielectric lossless medium has a first relative permittivity and a first thickness;generating a first radio frequency signal, applying the first radio frequency signal to the PMD, and measuring a first signal transmission response;10 varying one or more parameters of the dielectric lossless medium to shift the resonancefrequency response of the PMD, the parameters being; a distance parameter which is a distance between the PMD and the at least one dielectric lossless medium; a thickness parameter which is a thickness of the at least one dielectric lossless medium, and a permittivity parameter which is an effective or relative permittivity of the at least one dielectric lossless medium;15 generating a second radio frequency signal, applying the second radio frequency signalto the PMD, and measuring a second signal transmission response; and,determining, via a digital signal processing (DSP) unit, the resonance frequency response of the passive microwave device from the first and second signal transmission measurements.

2. The method as claimed in claim 1, wherein the distance parameter is varied by changing the distance between the dielectric lossless medium and the PMD from the first distance to a second distance.

3. The method as claimed in claim 2, wherein the PMD is placed within a housing and the 25 dielectric lossless medium is positioned above the PMD and is moved within the enclosure to change the distance between the PMD and the dielectric lossless medium.

4. The method as claimed in claim 1, wherein the thickness parameter is varied by combining a plurality of dielectric lossless media together, thereby changing the combined thickness of all 30 dielectric lossless media to a second thickness different than the first thickness.

5. The method as claimed in claim 1, wherein the permittivity parameter is varied by subjecting the at least one dielectric lossless medium to an electric field.35 6. The method as claimed in claim 5, wherein the electric field is formed by applying anelectrical voltage to at least two electrodes, and the electrodes are arranged such that an electric field forms between the electrode pair when an electrical voltage is applied.

7. The method as claimed in any one of the preceding claims, wherein the first and second radio frequency signals are generated by a radio frequency transmitter.

8. The method as claimed in any one of the preceding claims, wherein a radio frequency receiver measures the first and second signal transmissions through the PMD.

9. The method of claim 7, wherein the DSP unit sends signals to the radio frequency transmitter device and receives signals from the radio frequency receiver device.

10. The method as claimed in any one of the preceding claims, wherein the DSP unit uses a mapping algorithm for determining the resonance frequency response of the PMD.

11. The method of any one of the preceding claims, wherein the first radio frequency signal and the second radio frequency signal are equivalent.

12. An apparatus for determining a resonance frequency response of a passive microwave device (PMD); comprising:a positioning mechanism configured to position at least one dielectric lossless medium at a distance relative to the PMD;a communication system, including a radio frequency transmitter that is configured to generate a first and second radio frequency signal, and a radio frequency receiver that is configured to measure a first and second signal transmission response;a digital signal processing (DSP) unit configured to determine the resonance frequency response of the PMD from at least two signal transmission responses; and,a housing configured to accommodate the PMD, positioning mechanism, communication system, and DSP unit.

13. The apparatus as claimed in claim 12, wherein the positioning mechanism is configured to change the relative distance between one or more dielectric lossless mediums and the PMD.

14. The apparatus as claimed in claim 12 and 13, wherein the apparatus includes at least two electrodes, configured such that an electric field forms between the electrodes when an electrical voltage is applied to the electrodes.

15. The apparatus as claimed in claim 14, wherein the dielectric lossless mediums are positioned in the electric field between the electrodes, such that the relative permittivity of the dielectric lossless mediums is changed by the electric field.

16. The apparatus as claimed in any one of claims 12 to 15, wherein the DSP is configured to send the first and second radio frequency signal value to the radio frequency transmitter.5 17. The apparatus as claimed in any one of claims 12 to 16, wherein the DSP is configured toreceive the first and second signal transmission response value from the radio frequency receiver.

18. The apparatus as claimed in claims 14 and 15, wherein the apparatus includes a voltage source configured to generate and apply an electrical voltage to the electrodes.1019. The apparatus as claimed in any one of claims 12 to 18, wherein the housing is an enclosure surrounding the PMD.

20. The apparatus as claimed in any one of claims 12 to 19, wherein the housing includes a 15 lid, and where the positioning mechanism is attached to the lid and inserted into the housing.24 01 25