WO2010032023A1

WO2010032023A1 - Tuneable planar dielectric resonator

Info

Publication number: WO2010032023A1
Application number: PCT/GB2009/002252
Authority: WO
Inventors: Oleg Yurevich Buslov; Vladimir Nikolayevich Keis; Andrei Borisovich Kozyrev; Aleksei Yurevich Shimko; Neil Mcneill Alford; Peter Krastev Petrov
Original assignee: Imperial Innovations Limited
Priority date: 2008-09-19
Filing date: 2009-09-18
Publication date: 2010-03-25
Also published as: GB0817215D0

Abstract

The invention relates to a planar dielectric resonator (50) for use in high frequency electromagnetic wave devices. Apparatus and methods are provided for a tuneable planar dielectric resonator having a single substrate (120), a tuneable planar dielectric resonator having a single metallized layer (100) and a tuneable planar dielectric resonator comprising a tuning conductor (520) disposed in the hole (110) of the resonator and coupled to the conductive layer (100) of the resonator by a tuning element (510).

Description

TUNABLE PLANAR DIELECTRIC RESONATOR

The application relates to the field of high frequency electromagnetic wave devices, such as resonators.

Background of the invention

Dielectric Resonators are key components in a number of microwave subsystems which are used in a range of consumer and commercial market products. These products include Satellite TV receiver modules and mobile telecommunications base stations. In microwave communication technology, dielectric resonators are commonly used in filters, low phase noise oscillators and frequency standards.

By combining multiple resonators, it is possible to construct microwave filters, for example band-pass filters. The construction of the resonators must provide a high Q-factor for this to be successful (the Q-factor of a resonator is determined by dividing its resonant frequency by the bandwidth measured between -3dB gain points above and below the resonant frequency) and in order that the filter may have a narrowband filter characteristic (Δf/f ~ 1%). This is because the filter cut-off slope will be sharp and also the insertion losses will be small, allowing multiple stages to be placed in series.

Whether used alone or singly, it is often necessary to tune the resonant frequency of a resonator. In a filter application, this is often necessary in order to arrive at a desired filter characteristic. Known resonators often incorporate adjustment means (such as an adjustment screw which can be used to alter the physical geometry of the resonator in order to change its resonant frequency) to allow an operator to adjust the resonant frequency of the resonator. If such manual adjustment means is employed, it can be very time consuming, inconvenient, and costly, to tune the filter to produce a desired filter characteristic. It is not always convenient or cost-effective for an operator to travel to the site of the equipment in need of adjustment, and often equipment must be packed into a compact space which allows little room for access. In some applications, the site where the equipment is housed may even be hazardous to an operator.

In addition, considerable skill on the part of the operator is required to process information, received hy the operator from test_^ equipment, and __arriye L<ϊiJhe required adjustment. In practice, the adjustment is often carried out by the operator using trial and error, which can result in non-optimal adjustment.

The above factors mean that it is often impractical to carry out filter adjustments as accurately or as regularly as might otherwise be desirable, a consequence of which is that equipment incorporating known resonators is often adjusted during the commissioning of an equipment and then not readjusted for some considerable time (if at all) afterwards.

Furthermore, changes in temperature or other factors can result in a change in the resonant frequency of known resonators, and the resonant frequency may resultantly drift over time. Equipment is thus sometimes operated in a maladjusted state leading to degraded pei foi inancc and possibly even contravention of radio spectrum usage regulations.

An application for a resonator is in mobile equipment. Mobile equipment, which may roam across different territories, is sometimes required to operate in different frequency bands, depending on the territory in which it currently resides. Known resonators, which are non- tuneable or are manually tuned, if employed in such mobile equipment would result in the equipment being fixed to a particular frequency band related to the resonant frequency of the resonator(s) employed. If multiple frequency bands were required to be supported, then multiple resonators would need to be incorporated. This would increase space requirements and cost.

Another application for a resonator is in telecommunications base station equipment which may comprise multiple transceiver channels. When multiple transceiver channels are operated side by side, each must commonly operate on a different frequency band so as avoid interfering with its neighbours. Redundant channels are often provided to provide back-up if a transceiver channel fails, however each redundant channel is set to a particular frequency band by the tuned resonant frequency of its associated resonators. If known resonators, which are non-tuneable or are manually tuned, are employed in a redundant channel it can be difficult or inconvenient to re-tune the redundant channel's frequency band so as to render the redundant channel suitable for operation in place of the failed channel). In this case it might be necessary to provide multiple redundant channels, one for each frequency band, adding to space requirements and cost.

A further problem with known resonators is that spurious resonant modes are often unintentionally excitable. A spectral graph of the resonant frequencies of a resonator can be produced by sweeping the frequency of an excitation signal on one axis and plotting the measured amplitude of the resonator output on another axis. Such a spectral graph produced with known resonators can show spurious resonant peaks which do not correspond to well defined resonant modes of the resonator and are often closely spaced in frequency. Because of the presence of spurious resonant modes and the resultant close spacing of the resonant modes in known resonators, it can be difficult in known resonators to ensure that the desired resonant mode, or only the desired resonant mode, is excited. Furthermore, although it can be desirable to excite multiple resonant modes in a single resonator (so as to reduce the total number of resonators required to produce a given filter cliaiacteiislic), the possibility of exciting spurious resonant modes in known resonators can make it difficult to take advantage of multiple excitation modes.

Spurious resonant modes in known resonators also complicate the adjustment task still further, making it still more difficult for an operator to perform manual adjustment.

US Patent Publication US2004/0021531A1 discloses that a Planar Dielectric Resonator (PDR) can be constructed in the form of a conductive cavity comprising a planar dielectric substrate having single or double side metallization. A circular or rectangular-shaped hole is etched out of the metal layer (if having single side metallization) or layers (if having double sided metallization). The resonant frequency spectrum is governed by the resonator's dimensions and the dielectric permittivity of the substrate material. However, the resonator described in that document is not tuneable (frequency agile) and, it is found, in at least some embodiments, suffers from spurious resonant modes. Brief description of the invention

The invention is set out in the claims.

In one aspect of the invention there is provided a resonator and a method for constructing a resonator, the resonator comprising a generally planar dielectric substrate, a conductive layer and a tuning element, the conductive layer having a hole in it (also referred to as a "resonator hole") and the tuning element being provided in a region of non zero electric field strength.

In another aspect of the invention there is provided a resonator and a method for constructing a resonator, the resonator comprising a generally planar dielectric substrate, a conductive layer, and a tuning element, the conductive layer having a resonator hole, the substrate having a first planar surface and a second planar surface, the conductive layer arranged on only one of said surfaces.

In a still further aspect of the invention there is provided a filter comprising at least one resonator according to the preceding aspects of the invention.

As a result of the invention it is possible to produce a tuneable (frequency agile) resonator which has the ability for its resonant frequency to be dynamically tuned (i.e. without a need for manual adjustment with a screwdriver by an opeiaLor). Such a tuneable resonator can have a relatively small size, a high Q-factor (as high as several thousands), be easy and relatively cheap to manufacture, and be suitable for combining to foππ a filter operable at, for example, microwave and/or millimetre wave frequencies. Additionally, such a resonator can have as few spurious resonant peaks in its frequency spectrum as possible so as to make excitation of desired (and only desired) resonant modes easier. Furthermore, such a resonator can be constructed using fewer manufacturing steps than known resonators, thus reducing costs.

Embodiments of the invention will now be described by way of example with reference to the attached Figures.

Fig. 1 shows plan and side views of a Uni-Planar Dielectric Resonator according to an embodiment of the invention.

Fig. 2 shows resonant frequency spectra for a Uni-Planar Dielectric Resonator and a prior art Planar Dielectric Resonator.

Fig. 3 shows electric field and magnetic field patterns for a main hybrid HEMl lδ mode excited in a Uni-Planar Dielectric Resonator.

Fig. 4a shows electric field excitation using a coplanar line ending inside the resonator.

Fig. 4b shows electric field excitation using a short-circuited co-planar line.

Fig. 5 shows a tuneable Uni-Planar Dielectric Resonator.

Fig. 6 shows a band-pass filter constructed from two tuneable Uni-Planar Dielectric Resonators. Fig. 7 shows the filter transmission characteristics of the filter of Fig. 6.

Fig. 8 shows a filter constructed from two tuneable Uni-Planar Dielectric Resonators, incorporating a co-planar line between input and output.

Fig. 9 shows a tuneable filter design incorporating four tuneable Uni-Planar Dielectric Resonators.

Fig. 10 shows a filter constructed with two stacked tuneable Uni-Planar Dielectric Resonators.

Fig. 11 shows a detailed view of the arrangement of the tuning element and the conductor extension, when the tuning element is surface mounted on the substrate.

Fig. 12 shows a tuneable resonator having means for excitation of two resonant modes simultaneously and which can be operated as a filter.

Fig. 13 shows a detailed view of the arrangement of the tuning element and the conductor extension, when the tuning element is embedded in the substrate.

Detailed Description

The present invention overcomes the disadvantages of known Planar Dielectric Resonators (PDRs) and improves on the prior art by the features which will now be briefly described with reference to the attached Figures.

In some embodiments according to the present invention, a PDR has only a single conductive layer (100), as shown in Fig. 1, which has been found to advantageously improve the resonant frequency characteristics of the resonator (the spurious resonant modes of conventional PDRs are avoided in the present invention) and to offer a simplified construction over the prior art. In other embodiments, a PDR comprises a single planar substrate (120) and thereby offers a less complex construction than that of known tuneable PDRs. Such embodiments may be termed herein Uni-Planar Dielectric Resonators (UPDRs).

Embodiments of the invention further include a tuneable UPDR, incorporating a tuning element. Further embodiments incorporate features which improve the coupling of the electrical and magnetic fields into the tuning element and thereby improve the tuneability of the tuneable UPDR.

The basic elements of a UPDR (10), as shown in Fig. 1 are a conductive box (130), and a substrate (120) having a conductive layer (100) disposed on it. The conductive layer (100) has a hole (110) in it (also referred to as a "resonator hole 110"). One or more resonant field modes (electric or magnetic) can be excited in region of the resonator hole (1 10). In a tuneable UPDR, as shown in Fig. 5, a tuning element (510), such as a varactor, is provided in a region of non-zero electric field strength and preferably relatively high or highest field strength. For example the tuning element (510) can be provided substantially co-planar with the conductive layer and in, or in the vicinity of the hole. Specific positioning of the tuning element comprises a compromise between placing it at the region of highest electric field, providing highest tuneability, and the reduction in Q factor at that position. The tuning element (510) is preferably coupled between a conductor extension (520), such as a co-planar line or a microstrip, and the conductive layer (100). The conductor extension (520) is arranged in the resonator hole (110). As shown in Fig. 6, multiple resonators can be coupled together by a diaphragm coupling (610) having an aperture (610), or "iris", which allows a electric and/or magnetic field to couple from one resonator hole (110) to another. A tuneable filter can be constructed having a band-pass characteristic using two UPDRs (its design and measured transmission characteristics being shown in Fig. 7). Fig. 6 shows an input coupled to the input conductor (400) of Fig. 4a. Also shown in Fig. 6 is an output conductor (630) having an output end (640) and coupled to an output (600).

A more detailed description of the various embodiments of the invention now follows with references to the attached Figures.

Fig. 1 shows a preferred embodiment of a Uniplanar Dielectric Resonator (UPDR) (10) having a single substrate (120) and a single conductive layer (100). The conductive layer (100) is arranged on the substrate (120) or closely Iocaled Io i|, and the conductive layer (100) incorporates a resonator hole (1 K)). The substrate (120) and conductive layer (100) are contained in a conductive container (for example, a box) (130). The conductive layer (100) is arranged in electrical contact with the box (130) and is usually grounded (at zero potential). As shown in Fig. 4a, an input conductor (400) has an input end (405) and an excitation end (420) which extends into the resonator hole (110). The input conductor (400) is, for example, a conductive line which is co-planar with the conductive layer (100) of the resonator (10), or a microstrip. It can be convenient to arrange the input conductor (400) co-planarly with the conductive layer (100), but the conductor does not have to be co-planar with the conductive layer and could, for example be arranged on the opposite side of the substrate (120) to the conductive layer (100).

An alternative arrangement is shown in Fig. 4b, where a short-circuited input conductor (410) has an input end (405) and a short-circuited end (430), the short-circuited end (430) being short-circuited to the conductive layer (100) at the edge of the resonator hole (110).

As shown in Fig. 5, a tunable Uniplanar Dielectric Resonator (50) incorporates the features of a Uniplanar Dielectric Resonator and further comprises a conductor extension (520) (for example a microstrip or co-planar line) and a tuning element (510). The conductor extension (520) is arranged within the resonator hole (1 10) of the conductive layer (100). The tuning element (510) is coupled between the conductor extension (520) and the conductive layer (100). In a preferred embodiment, the tuning element (510) is a semiconductor, ferroelectric or MEMS (Micro-Electro-Mechnical System) varactor.

A bias conductor (550) is coupled by a low pass filter (540) to a bias application port (530). The bias conductor (550) is coupled to the conductor extension (520). The low pass filter (540) is shown as being co-planar with the conductive layer but could be constructed according to any appropriate approach as will be well known to the skilled reader. As shown in Figs. 6, 8, 9 and 10, two or more resonators can be combined to form more complex filters, such as a band-pass filter (60), shown in Fig. 6.

Fig. 6 shows a first UPDR (61) on the left of the Figure, having an input (500) which is coupled to an input conductor (400) having an excitation end (420) and arranged to excite a resonant electric field in the resonator hole (110) of the first resonator (61). The two UPDRs are coupled by a diaphragm coupling

(610). An aperture, or "iris" (620) is arranged in the diaphragm coupling (610).

Optionally, one or more of the UPDRs can incorporate an output (600) coupled to an output conductor (630) having a drain end (640). Each UPDR (61 , 62) has a tuning element (510) arranged as previously described.

As shown in Fig. 8, a feed conductor (800), having a feed drain end (810) and a feed excitation end (820), can be arranged between first (61) and second (62) UPDRs to enable a portion of the alternating electric or magnetic field of a second or subsequent UPDR (62) to be fed back into a first (or earlier than the subsequent UPDR in a sequence of UPDRs) UPDR (61) and thereby enable additional 'zeroes' to be introduced into the frequency response of a filter constructed accordingly. The feed drain end (810) of the feed conductor (800) is arranged close to the resonator hole (1 10) of the second UPDR (62) and the feed excitation end (820) is arranged close to the resonator hole (110) of the first UPDR (61). An elliptical filter response can be realised using this feature.

As shown in Fig. 9, four resonators can be combined side by side. The input conductor (400) and output conductor (630) shown in Fig. 9 are arranged to each incorporate a 90 degree angled bend, such that the conductors can have a first portion arranged radially with respect to the resonator hole (1 10) and a second portion arranged parallel to a tangent of the resonator hole. Fig. 10 shows two resonator holes (110) located substantially uni-axially (with the centre of each resonator hole co-axial with the other), although other constructions could incorporate any spaced-plane (also referred to as "stacked") arrangement, for example an off- axial arrangement. This 'stacked' embodiment can be advantageous in terms of packaging.

Fig. 11 shows in detail the arrangement of the conductive layer (100) which can incorporate the bias application port (530), low pass filter (540), bias conductor (550) and conductor extension (520). The conductor extension (520) (which is, for example, a co-planar line, microstrip or transmission line) is arranged inside the resonator hole (110) and is spaced from the conductive layer (100). The conductor extension (520) is connected to the bias conductor (550) which is in turn connected to the low pass filter (540) and bias application port (530), all of which are unconnected to the conductive layer (100). The conductive layer is grounded and is connected to the conductive box (130). The tuning element (510) is connected between the conductor extension (520) and the conductive layer (100). An alternative arrangement is shown in Fig. 13 and also conforms to the above description.

Fig 12 shows a UPDR which has two tuning elements (510) and which is suitable for excitation of two resonant modes simultaneously. A coupling conductor (1200) is placed at a 45 degree angle relative to input (500) and output (600). The coupling conductor is preferably placed in a region of nonzero electric field strength and preferably relatively high or highest field strength. Alternatively, an ellipse shaped resonator hole (1 10) (not shown) can be featured instead of the coupling conductor (1200). UPDRs as described herein are thus relatively easy to manufacture and integrate because they use conventional Printed Circuit Board (PCB) technology, and can use inexpensive single-sided PCB technology. Furthermore, only a single substrate is required for a UPDR. Preferably, no post-assembly of multiple substrates is required. These features allow UPDRs to be manufactured cheaply, in bulk, and using standard production facilities.

The resonator hole (110), bias application port (530), low pass filter (540), bias conductor (550) and conductor extension (520) can be patterned in the conductive layer (100) on the substrate (120) using such commonly used printed circuit board manufacturing techniques as photo-sensitive masking, chemical etching, laser etching, machining and screen printing. The substrate (120) and conductive layer (100) having a resonator hole (110) can be enclosed in a conductive box (130). The conductive box (130) can be pressed into shape, die cast or formed in other well-known ways.

The tuning element is a variable capacitance element and is preferably a varactor, and this includes semiconductor types of varactor, Micro-Electro- Mechanical Systems (MEMS) and ferroelectric types of varactor. Other known types of variable capacitor which vary their capacitance in response to an applied signal (such as, for example a voltage) can also be used. Ferroelectric varactors generally have higher power handling capability and offer greater tuning speed than Micro-Electro-Mechanical Systems (MEMS). Conversely, semiconductor varactors and Micro-Electro-Mechanical Systems (MEMS) generally offer greater tuneability (range of tuning) than ferroelectric varactors. Other known varactors have properties which may be chosen for their advantageous characteristics in certain embodiments. As shown in Fig. 1 1, the tuning element (510) can be surface mounted onto the conductive layer (100) and the conductor extension (520), which in turn are supported by the substrate (120). This mode of construction can be realised using very commonly available and cheap PCB manufacturing methods. In other embodiments, the tuning element (510) can be mounted onto the substrate (120) and connected to the conductive layer (100) and to the conductor extension (520) using a "flip chip" arrangement which is well known in the art. A "flip-chip" mode of construction can allow more compact constructions because the tuning element does not require a "package" around it ("packages" are commonly made of plastic or ceramic and used to surround the active element of a device and to support solder terminals used for mounting the component onto, for example a printed circuit board or "PCB"). Alternatively, the tuning element (510) can be embedded in the substrate, or on the substrate in the gap between the conductor extension (520) and the conductive layer (100) as shown in Fig. 13. Yet further the function of the tuning element (510) can be achieved by doping the substrate in the vicinity of the resonator hole (110), for example in the region between or surrounding the conductor extension (520) and conductive layer (100). The doping can be any appropriate material, for example ferroelectric or semiconductor material such as silicon.

In a preferred embodiment, the substrate is a microwave (MW) ceramic (or alumina). An alumina substrate can be fabricated by commonly known techniques such as sintering and pressing. An example of a suitable conductive layer (100) material is copper, which can be rolled and bonded to the substrate (120), or can be sputtered, or attached to the substrate (120) using other commonly used manufacturing techniques. Although alumina is specifically mentioned as a substrate (120) material, other high frequency ceramic or flexible circuit materials can be used for the substrate (120), such as Rogers Materials: RO 3xxxx or RO 4xxxx series. Suitable materials preferably have low electrical conductivity so as to avoid electrical losses (and thereby retain a high Q-factor), and stable mechanical properties so as to provide a stable support for the conductive layer, such that the conductive layer dimensions do not change with temperature or applied force in such as way as to significantly degrade resonator properties or allow them to change undesirably.

Suitable materials for the conductive layer have high conductivity and are preferably metals such as copper, silver or gold, but other metals or conductive materials could be used, such as for example carbon-loaded polymers or conductive paint. In certain embodiments, it is envisaged that semiconductor materials could be used for the conductive layer.

In operation, the resonator hole (1 10) and conductive layer (100) as shown in Fig. 1 form a Planar Dielectric Resonator (PDR) (10) in conjunction with a conductive box (130) which is usually grounded at zero potential. As is well known to the skilled person the dimensions of the PDR (the conductive box (130) has a height H, and length/width a, the substrate (120) has a thickness h, and the resonator hole (110) in the conductive layer (100) has a diameter D), the quality factor Q and the dielectric permittivity of the substrate (120), influence the frequency of the one or more resonant modes (200) in a frequency spectrum (220) of the resonator as shown in Fig. 2 (a graphical plot of resonant mode position on the frequency axis when the PDR is driven/excited by an input sinusoid signal of swept frequency). PDRs possess high quality factor (Q-factor), which can be as high as several thousands, making them suitable for use in narrowband microwave filters.

As shown in Figure 2, there are a large number of resonant modes (200, 210) that can be excited in a PDR, classified by the direction of the electric and magnetic fields relative to a coordinate system. These modes include:

Transverse Electric (TEnpg) (240, 260), Transverse Magnetic (TMnpg) (280), and Hybrid modes (200, 250, 270), designated as Hybrid Electric (HEMnpg) and EHnpg, where n and p are integers that describe the standing wave pattern, and g is used to denote the number of half- wavelength variations in the axial direction.

As already described, a Uni-Planar Dielectric Resonator (UPDR) (10) has a conductive layer (100) on only one side of a substrate (120), as shown in Fig. 1. In operation, this construction improves the performance of a UPDR (10) compared to that of a conventional PDR. As shown in the upper part of Fig. 2, a UPDR frequency spectrum (220) has fewer spurious resonant peaks (210) than a frequency spectrum of a conventional PDR (230) (shown in the lower part of Fig. 2).

It has been found that in conventional PDRs having at least 2 conductive layers, spurious resonances can be excited in the bulk of the dielectric substrate between the two metal layers. These spurious resonances result in many of the spurious resonant peaks (210) shown in the lower part of Fig. 2. The presence of these spurious resonant peaks (210) is problematic, in that they make it more likely that an unintended resonant mode will be excited when operating a conventional PDR. If a filter were constructed using conventional PDRs, such an unintended excitation of a spurious resonant mode (210) could result in signal passing through the filter at an unintended frequency. This could lead to noise entering a receiver (with the result of reduced receiver performance), or noise exiting a transmitter (with the result of possibly contravening radio spectrum usage rules).

The Uniplanar Dielectric Resonator (UPDR) (10) of the present invention is advantageous over prior art resonators because when only a single conductive layer is incorporated, spurious resonant frequency peaks (210) in the frequency spectrum of the resonator (220) are avoided. The frequency spectrum of such a UPDR (10) is more spectrally pure than that of a conventional PDR. Filters constructed using UPDRs (10) can be made which have a frequency response (730), as shown in Fig. 7, which is closer to a particular desired frequency response. The output signal of such a filter is spectrally purer, having less undesired frequency components (210), thus enabling enhanced system performance.

Furthermore, it is possible to simultaneously excite more than one of the resonant modes (200, 240-290) shown in Fig.2. For example, two separate modes (200, 240) could be excited in a single PDR or UPDR. This can allow, for example, a filter comprising two resonant modes (such as a band-pass filter) to be constructed from a single UPDR. Alternatively, this can allow more complex filters to be constructed from a fewer number of resonators (10) than would otherwise be possible. However, it is important to ensure that only specific required modes are excited in this way, in order that the desired filter characteristic can be obtained.

It is difficult to ensure that only specific modes are excited in a conventional PDR, due to the close spacing (relative to that of a UPDR) of spurious modes (210) to the desired modes (200, 240). It is easier to excite only specific desired resonant modes in a UPDR than it is in a conventional PDR, due to the lower number of spurious resonant modes (210) (lower modal density) and the resultant greater spacing between the remaining resonant modes (200, 240- 290). A UPDR is therefore advantageous over a conventional PDR when attempting to excite multiple desired resonant modes in a single resonator.

As shown in Fig. 3, in operation the electric (300) and magnetic (310) fields excited in the resonator hole (1 10) are at a normal angle to each other and the magnetic field is circular. The electric field (300) lies parallel to the plane of the conductive layer (100), whilst the magnetic field (310) extends above and below the substrate (120) in a circular fashion.

The arrangement shown in Fig. 4a having an input conductor (400) having an excitation end (420) can be used to excite a resonant electric field (300) in the resonator hole (1 10), the field (300) being oriented in the direction from the input conductor (400) to the co-planar line end (420), and parallel to the plane of the conductive layer (100). In operation, the input conductor (400) carries an input signal from an input end (405) into the resonator hole (1 10), and excites a resonant electric field mode in the resonator hole (110) (the electric and resulting magnetic fields being shown in Fig. 3). The input conductor (400) and excitation end (420), also shown in Fig. 5, can be arranged for excitation of a hybrid HEMl lδ resonant mode (200) according to techniques well known to the skilled reader. The Hybrid HEM mode is advantageous as it is the lowest frequency mode in the spectra. There are no low frequency spurious modes, while the high frequency spurious modes are far away.

In contrast, the arrangement shown in Fig. 4b having a short circuited input conductor (410) can be used to excite a resonant electric field (300) in the resonator hole (110), the field being oriented at a 90 degree angle to the direction from the input end (405) to the short circuited end (430), and parallel to the plane of the conductive layer (100).

Furthermore, the input conductor (400) shown in Fig. 9 which has a 90 degree angled bend in it, can be used to excite a magnetic field (HEM l lδ) in the resonator hole (110).

As shown in Fig. 5, in operation, the conductor extension (520) couples at least one of the alternating ("a.c") electric and magnetic fields of the resonator hole (HO) into the tuning element (510). The location of the conductor extension

(520), inside the resonator hole (110) (and in a region of non-zero electric field strength and or highest field strength), results in more effective coupling of fields in the resonator hole (110) and the tuning element (510), compared with known tuneable PDRs. This increases the magnitude of the tuning effect and thereby the range of tuning control. This is particularly effective when the HEMl 16 mode, is excited as in a preferred embodiment of the present invention.

Furthermore, the tuneability of the UPDR of the present invention allows it to be used to realise tuneable microwave filters (for example tuneable band-pass microwave filters).

A tuning bias signal (for example, a non-alternating, substantially stable, or "d.c", voltage, or an alternating low frequency "a.c." voltage) is applied to the UPDR (10) at a bias application port (530), and is coupled to the conductor extension (520) via a low pass filter (540) and a bias conductor 550. The tuning bias signal sets up an electric field across the tuning element (510) and thereby influences the capacitance of the tuning element (510) (which is, for example, a varactor). The tuning bias signal can be varied so as to vary the capacitance of the tuning element (510) and thereby tune the resonant frequency of at least one of the electric and magnetic field resonant modes (for example 200, 240, 260, 280) of the UPDR (50), in particular the HEM modes The tuning bias signal is typically lower in frequency than the lowest resonant frequency mode of the UPDR. Thereby, the tunable UPDR (50) can be tuned, for example by application of a tuning bias signal (for example, a voltage) to the bias application port (530). The length of the conductor extension (520) can be varied in order to influence the range of tuneability of the UPDR.

The low pass filter (540) prevents alternating signal from the conductor extension (520) (induced in it by the alternating magnetic and electric field in the resonator hole), from exiting the UPDR (10) at the bias application port (530) via the bias conductor (550). The low pass filter (540) also helps to stabilise the low frequency or non-alternating ("d.c") tuning bias signal at the conductor extension (520) and thereby the component of the electric field across the tuning element (510) resulting from the tuning bias signal.

In operation of an alternative embodiment, as shown in Fig. 6, a pair of UPDRs (61, 62) which are coupled by a diaphragm coupling (610) are shown in Fig. 6. The first or input UPDR (61) on the left of Fig. 6 is excited by the excitation end (420) of the input conductor (400) coupled to the input (500) The second or output UPDR (62) on the right of Fig. 6 is coupled to the first UPDR by the magnetic field of the first UPDR (61) through the aperture (or iris) (620) to the second UPDR (62), but not the electric field in view of its orientation. Alternatively, the UPDRs can be coupled using transmission lines (622) as can be seen in Fig 9. The output conductor (630), with its drain end (640), couples the electrical and/or magnetic fields from the resonator hole (110) of the second resonator (62) to the output (600). A signal passing from the input (400) via the UPDRs (61 , 62) to the output (600) is thereby influenced by the resonant characteristics of both UPDRs.

In addition to the previously mentioned influence that the resonator dimensions have on resonator frequency characteristics (and therefore on filter frequency response, as shown in Fig. 7), the dimensions of the iris (620) also influence the filter frequency characteristics (shown in Fig. 7), the response being varied by adjusting the iris dimensions, as will be well known to the skilled reader, for example using a regulation screw (not shown). Each resonator (61, 62) has a tuning element (510) arranged to be controlled by a tuning bias signal (for example a voltage) applied at a bias application port (530) via a low pass filter (540), so as to alter at least the main (fundamental) resonant frequency (200) of each of the resonators (61, 62).

A band-pass filter characteristic can be produced by a suitable arrangement of two or more resonators. Furthermore, it will also be described how a band-pass filter characteristic can be produced using a single UPDR according to the present invention.

As shown in Fig. 7, multiple resonators can be combined to produce complex filters, having more complex frequency characteristics (730) than that of a single resonator, for example a band-pass filter or an elliptical filter. Fig. 7 shows the frequency characteristic (730) of the filter apparatus shown in Fig. 6 which employs two tuneable UPDRs (61, 62). Each resonant mode of a UPDR (61,62) is associated with a resonant peak (710) in the frequency response (730). Fig. 7 shows an elliptical filter response and shows a first resonant peak (710) of a UPDR (50) when a first tuning bias signal is applied to the bias application port (530), and a second resonant peak (720) of a UPDR (50) when a second tuning bias signal is applied to the bias application port (530). Fig. 7 thus illustrates the range of tuneability of the UPDR used to obtain the results in Fig. 7, as being the difference between the resonant frequency of the first resonant peak (710) and the resonant frequency of the second resonant peak (720) when the tuning bias signal is varied from a minimum value to a maximum value.

Additional 'zeroes' (700) in the frequency response (730), where the filter gain drops significantly from unity gain (OdB), can be introduced by features such as the feed conductor (800) shown in Fig. 8, which can feed back a portion of the alternating electrical or magnetic field energy of a second UPDR (62) to a first UPDR (61) (for example, by coupling the output of a second UPDR to the input of a first UPDR). The feed conductor (800) has a feed drain end (810) which receives electromagnetic energy from the second UPDR (62) and couples it to the first UPDR (61), where the feed excitation end (820) radiates the energy into the first UPDR. The shape and length of the feed conductor (800) and its ends (810, 820), and their proximity to the resonator holes (110) can be altered to obtain desired phase and amplitude characteristics for the feedback.

As shown in Fig. 9 (which shows a tuneable filter design based on four UPDRS), in operation, the shape, length and orientation of the input and output conductors (400, 630) and their ends (420, 640) which influence the direction of the electric and magnetic fields in the resonator holes (110). The excitation is provided by the open end (420) of the input conductor (400) which can be formed in the conductive layer (100) outside the resonator hole (110). As shown, each of input and output conductors, has a first and a second portion (400a, 400b) which are shown meeting at a right angled corner but can be at any orientation and can meet at a curve, the length of the second portion (400b) principally influencing the excited field. Each first portion is connected to its respective input or output (500, 600)

As is well known to the skilled reader, by the use of either straight or angled input conductor (400), the electric and magnetic fields can be set up in a direction which is most effective for coupling through irises (620) to resonators in a filter combination. For example, in Fig. 6, the electric field in the leftmost resonator (61) is aligned between the input conductor (400) and the tuning element (510). In contrast, in Fig. 9, the electric field in the lower left hand resonator (900) is aligned approximately between the tuning element (510) and the opposite side of the resonator hole (110). The UPDRs are magnetically coupled through the apertures (620) (or irises) in the diaphragm couplings (610), although alternatively, transmission lines (622) can perform the coupling function.

In addition, if the input conductor (400) of Fig. 9 which incorporates a 90 degree angled bend, or the short-circuited input conductor (410) of Fig. 4a are employed, the conductor does not influence the field distribution inside the resonator hole (1 10), hence the conductor does not either influence the resonance frequency or Q-factor of the UPDR (10).

Another advantage of the input conductor (400) / output conductor (630) incorporating a 90 degree angled bend, as shown in Fig. 9, is that the spatial arrangement is improved from a physical packaging perspective, and it is thereby possible to construct more compact resonators and filters. Physical size, weight and cost can be advantageously reduced in this manner. As shown in the vertically "stacked" arrangement of Fig. 10, where two or more UPDRs (61, 62) are arranged with their substrates in spaced planes, an iris (620) in the diaphragm coupling (610) between the two resonator holes (110) allows electrical and magnetic fields to couple from one UPDR (61) to the other UPDR (62).

As shown in Fig. 12, a single UPDR can be operated so as to simultaneously excite more than one resonant mode. In this way, a band-pass filter characteristic can be produced using a single resonator. In operation, the input conductor (400) excites a resonant mode in a first field in the resonator hole

(1 10). Preferably a coupling conductor (1200) (for example, a co-planar line or microstrip) couples the first field (for example, an electrical field) to a second field which is orthogonal to the first field. The coupling conductor is spaced from and connected to or an extension of the conductive layer, receives energy from the first field and radiates energy in order to excite the second resonant field mode in the resonator hole (110). The output conductor (630) is thus arranged so as to couple the second field to the output (600). Optionally, an elliptical shaped resonator hole (110) can be used in which case a coupling conductor is not required. In such embodiments, two separate and orthogonal fields can be excited in a UPDR, as shown in Fig. 12, simultaneously. Such a UPDR can be used to implement a complex filter characteristic (for example a band-pass filter characteristic) without the need to couple more than one UPDR together. This has advantages in cost and space savings and of course reduces the number of components required. It will be appreciated that the purpose of the coupling conductor (1200) is to strengthen the field coupling but that coupling may be achieved even without it. Because the frequency spectrum of a UPDR (10) is more spectrally pure than that of a conventional PDR, it is easier to excite multiple resonances in a single resonator. In particular, it is easier to excite only those resonances which are necessary for a desired filter frequency characteristic (730) without inadvertently exciting spurious resonances.

The invention thus delivers multiple advantages, including tuneability, spectral purity, ease of manufacture, low cost, ease of physical packaging resulting in small size (for example when multiple resonators are combined such as shown in Figs. 6, 8, 9 and 10).

In addition, the electrical tuneability provided by the present invention (as opposed to other means such as mechanical tuneability) enables remote tuneability and dynamic tuneability.

Remote tuneability for example includes schemes such as where an internet terminal can be used to issue commands to a remote subsystem having internet connectivity, arranged to produce a tuning bias signal and connected to a UPDR of the present invention so as to drive the tuning bias signal into the bias application port (530) of the UPDR. In such a scheme, the UPDR could be tuned remotely by issuing commands over an internet connection.

Dynamic tuneability enables schemes such as automatic tuning (for example using a feedback control system to measure actual frequency characteristic and generate a tuning control signal for tuning the resonator characteristic such that the desired frequency characteristic is achieved). Dynamic tuneability also enables schemes such as dynamic reconfiguration of hardware resources, for example dynamic re-tuning of the frequency band of transceivers in a radio telecommunications base station. This has clear advantages in terms of best and most efficient use of hardware resources. Another possible advantage is the ability to provide redundancy capabilities in case of equipment failure, without a requirement to provide excessive (expensive, bulky) amounts of additional redundant hardware.

Although the input conductor (400), output conductor (630), conductor extension (520), bias conductor (550), feed conductor (800) and coupling conductor (1200) are preferably co-planar with the conductive layer, a significant portion of their function may still be achieved if they are spaced from the plane of the conductive layer and embodiments thus are considered to be within the scope of the present invention.

As mentioned, preferably the excitation mode in the resonator is the HEMl lδ mode. However, other electromagnetic excitation modes can be employed and are within the scope of the invention. Indeed, as already stated, it is possible for more than one resonant excitation mode to be excited simultaneously in a resonator according to the present invention.

The UPDR of the present invention can be made using any appropriate material having suitable properties, as already described, and can be used in any appropriate application having regard to the operating parameters (such as operating frequency and temperature), size, weight, cost and other factors which would be considered by a person skilled in the art. Although the invention has been described as being operable at microwave frequencies, any frequency of operation is encompassed which is compatible with a device of a practical size, weight and cost, the size being generally related to the operating frequency and materials used, the cost being generally related to the device size and materials used. Although the resonator hole (1 10) is shown in the Figures as being circular, the hole can be other shapes such as rectangular or an ellipse. The shape chosen can influence the resonant modes which predominate in a spectral graph of the resonator response. For example, an elliptical resonator hole (110) can aid coupling between more than one resonant mode in the resonator hole (110).

Although the invention has been described in relation to its preferred embodiments, these are not intended to limit the scope of the invention. It will be understood by those skilled in the art that many other modifications and variations are possible without departing from the scope of the invention as claimed. Embodiments and features of embodiments may be juxtaposed or interchanged as appropriate.

Claims

1. A resonator, comprising a generally planar dielectric substrate, a conductive layer and a tuning element, the conductive layer having a resonator hole and the tuning element being provided in a region of non-zero electric field strength.

2. A resonator, comprising a generally planar dielectric substrate, a conductive layer, and a tuning element, the conductive layer having a resonator hole, the substrate having a first planar surface and a second planar surface, the conductive layer arranged on only one of said surfaces.

3. A resonator as claimed in claim 1, further comprising a conductor extension, at least a part of the conductor extension arranged in the resonator hole, and the tuning element coupled between the conductor extension and the conductive layer.

4. A resonator as claimed in claim 1 or 3 in which the tuning element is supported by the substrate.

5. A resonator according to claim 3 wherein the conductor extension is a microstrip.

6. A resonator according to claims 4 or 5 wherein the conductor extension is coupled to a bias conductor, the bias conductor carrying a tuning bias signal.

7. A resonator according to claim 6 wherein the bias conductor is coupled to a bias application port via a low pass filter.

8. A resonator according to any preceding claim wherein the tuning element is co-planar with the conductive layer or the substrate, or arranged on the conductive layer.

9. A resonator according to any preceding claim further comprising at least one of an input conductor and an output conductor, wherein at least one of the input conductor and output conductor is arranged on the substrate.

10. A resonator according to claim 9 wherein at least one of the input conductor and the output conductor is co-planar with the conductive layer.

11. A resonator according to claim 9 or 10 wherein the input conductor has an input end and an excitation end, and the excitation end projects into the resonator hole.

12. A resonator according to claim 9 or 10 wherein the input conductor has an input end and an excitation end, and the excitation end is short circuited to the conductive layer at the circumference of the resonator hole.

13. A resonator according to claims 9 to 12 wherein the input conductor comprises first and second portions, the first portion arranged parallel to a radius of the resonator hole, the second portion arranged parallel to a tangent of the resonator hole boundary.

14. A resonator according to claim 9 or 10 wherein the output conductor is co-planar with (he conductive layer.

15. A resonator according to claims 9 to 14 wherein at least one of the input conductor and output conductor is arranged to interact with at least one of an electrical and a magnetic field of the resonator hole.

16. A resonator according to any preceding claim wherein the tuning element comprises at least one of a ferroelectric tuning element, a micromachined (mems) tuning element and a semiconductor tuning element.

17. A resonator according to any preceding claim in which the primary resonant mode of the resonator comprises an axially oriented electrical field.

18. A resonator according to any preceding claim in which the primary resonant mode is the HEMl lδ mode.

19. A resonator according to any preceding claim, further incorporating a coupling conductor.

20. A resonator according to any preceding claim wherein each tuning element is arranged to influence the resonant frequency of an electric or magnetic field.

21. A resonator according to any preceding claim which is electrically tuneable under control of a tuning bias signal.

22. A resonator according to claim 21 wherein information comprised in the tuning bias signal is conveyed to the resonator from a remote location.

23. A filter comprising at least one resonator according to any preceding claim.

24. A filter according to claim 23 wherein the at least one resonator comprises at least first and second resonators, and the first resonator is coupled to the second resonator by a diaphragm coupling, the diaphragm coupling incorporating an aperture, or by a transmission line.

25. A filter according to claim 23 or 24 wherein the first and second resonators are arranged such that their respective substrates are substantially co-planar.

26. A filter according to claim 23 or 24 wherein the first and second resonators are arranged such that their respective substrates are arranged as spaced planes.

27. A filter according to claims 23 to 26 wherein the first and second resonators are arranged such that in use they are coupled together by electrical or magnetic field interaction.

28. A filter according to claims 25 to 27 wherein a feed conductor is arranged so as to feed back a portion of the electrical or magnetic field of the second resonator into the first resonator.

29. A filter according to claims 23 to 28 wherein the filter is a band pass filter.

30. An electromagnetic wave generator comprising a filter according to claims 23 to 29.

31. A modulator comprising a filter according to claims 23 to 29.

32. A method of constructing a resonator, comprising the steps of: providing a generally planar dielectric substrate, a conductive layer and a tuning element, the conductive layer having a resonator hole, and arranging the tuning element in a region of non-zero electric field strength.

33. A method of constructing a resonator, comprising the steps of: providing a generally planar dielectric substrate, a conductive layer and a tuning element, the conductive layer having a resonator hole, the substrate having a first planar surface and a second planar surface, and providing the conductive layer on only one of said surfaces.

34. A method of constructing a resonator according to claim 32, further comprising the steps of: providing a conductor extension, providing at least a part of the conductor extension in the resonator hole, and coupling the tuning element between the conductor extension and the conductive layer.

35. A method of tuning a resonator, the resonator having a generally planar dielectric substrate, a conductive layer, a tuning element, a conductor extension and a bias application port, the conductive layer having a resonator hole, at least a part of the conductor extension arranged in the resonator hole, and the tuning element coupled between the conductor extension and the conductive layer comprising: applying a tuning bias signal to the bias application port.

36. An apparatus or method substantially as described or shown in the Figures.