Methods and devices for surge protection in RF systems

Abstract

Microwave, RF or electronic equipment can suffer damage from large variations in the current and / or voltage of a signal coupled to the equipment which may comprise lightning strikes, surges, transients, noise, incorrect connections or other abnormal conditions or malfunctions. These may result in large DC signals being applied to the equipment thereby overloading or damaging the RF circuitry. Accordingly, a microwave or radio-frequency (RF) surge suppression device, also known as a RF surge protector, may protect this equipment where it is beneficial for such devices to be compact, have a low insertion loss and low voltage standing wave ratio (VSWR).

Description

METHODS AND DEVICES FOR SURGE PROTECTION IN RF SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of priority to U.S. Provisional Patent Application 63 / 718,317 filed November 8, 2024; the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION

[0002] This patent application relates to microwave and radio-frequency (RF) systems and more particularly to surge protectors with low loss, good microwave match over the target frequency range and providing DC supply for external active devices and low frequency interference signal blocking protectors with low loss, good microwave match over the target frequency range and providing DC supply for external active devices and low frequency interference signal blocking..BACKGROUND OF THE INVENTION

[0003] A microwave or radio-frequency (RF) surge suppression device (protector) (RF surge protector) protects microwave, RF or electronic equipment from damage arising from large variations in the current and / or voltage of the signal coupled to the equipment arising from lightning strikes, surges, transients, noise, incorrect connections or other abnormal conditions or malfunctions that would otherwise result in large DC signals being applied to the equipment either overloading or damaging the RF circuitry. Ideally, an RF surge protector would have a compact size, a low insertion loss and a low voltage standing wave ratio (VSWR).

[0004] The inventors have established a novel design for an RF surge protector with improved microwave performance with a compact single cavity design upon an RF circuit board.

[0005] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to mitigate limitations within the prior art relating to microwave and radio-frequency (RF) systems and more particularly to surge protectors with low loss, good microwave match over the target frequency range and providing DC supply for external active devices and low frequency interference signal blocking.

[0007] In accordance with an embodiment of the invention there is provided a surge protector for an RF circuit comprising: an input port for receiving RF signals; a first circuit disposed between the input port and an output port wherein the first circuit comprises a filter circuit which blocks DC and low frequency signals; and a second circuit disposed between the input port and the output port wherein the second circuit comprises one or more surge protection elements; wherein an end of the second circuit is coupled to an end of the first circuit via an inductor; a distal end of the second circuit is coupled to a distal end of the first circuit via another inductor.

[0008] In accordance with an embodiment of the invention there is provided a method comprising: providing a surge protector for an RF circuit comprising a filter circuit disposed in parallel to a surge protection circuit; wherein the filter circuit comprises a transmission line segment to which an inductor is coupled at one end and ground at its distal end; and the transmission line segment within the filter circuit has a different design to those other transmission line segments which couple the filter circuit to an input port of the surge protector and an output port of the surge protector.

[0009] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

[0011] Figure 1 depicts a capacitive RF surge protector circuit according to the prior art;

[0012] Figure 2 depicts a capacitive RF surge protector circuit with improved matching according to an embodiment of the invention;

[0013] Figure 3 depicts microwave performance and a CAD schematic of the capacitive RF surge protector circuit according to Figure 2;

[0014] Figure 4 depicts a DC blocking - radiofrequency(RF) matching circuit according to an embodiment of the invention exploiting additional transmission line elements;

[0015] Figure 5 depicts microwave performance of the DC blocking - RF matching circuit according to Figure 4;

[0016] Figure 6 depicts an RF surge protector according to an embodiment of the invention exploiting the DC bias path - RF matching circuit according to Figure 4;

[0017] Figure 7 depicts a CAD layout of the RF surge protector according to Figure 6;

[0018] Figure 8 depicts a photograph of an assembled circuit according to Figure 6 and its measured RF performance;

[0019] Figure 9 depicts an RF surge protector according to an embodiment of the invention exploiting the DC blocking - RF matching circuit according to Figure 4 with modified transmission line geometry within the DC blocking - RF matching circuit;

[0020] Figure 10 depicts a photograph of an assembled RF surge protector exploiting the circuit depicted in Figure 9 and its measured RF performance; and

[0021] Figure 11 depicts measured RF performance of a variant design of the RF surge protector depicted in Figure 9.

[0022] DETAILED DESCRIPTION

[0023] The present description is directed to microwave and radio-frequency (RF) systems and more particularly to surge protectors with low loss, good microwave match over the target frequency range and providing DC supply for external active devices and low frequency interference signal blocking.

[0024] The ensuing description provides representative embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the embodiment(s) will provide those skilled in the art with an enabling description for implementing an embodiment or embodiments of the invention. It is understood that various changes can be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. Accordingly, an embodiment is an example or implementation of the inventions and not the soleimplementation. Various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention can also be implemented in a single embodiment or any combination of embodiments. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the invention.

[0025] Reference in the specification to “one embodiment,” “an embodiment,” “some embodiments” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment, but not necessarily all embodiments, of the inventions. The phraseology and terminology employed herein is not to be constmed as limiting but is for descriptive purposes only. It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not to be constmed as there being only one of that element. It is to be understood that where the specification states that a component feature, stmcture, or characteristic “may,” “might,” “can” or “could” be included, that particular component, feature, stmcture, or characteristic is not required to be included.

[0026] Reference to terms such as “left,” “right,” “top,” “bottom,” “front” and “back” are intended for use in respect to the orientation of the particular feature, stmcture, or element within the figures depicting embodiments of the invention. It would be evident that such directional terminology with respect to the actual use of a device has no specific meaning as the device can be employed in a multiplicity of orientations by the user or users.

[0027] Reference to terms “including,” “comprising,” “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, integers or groups thereof and that the terms are not to be constmed as specifying components, features, steps or integers. Likewise, the phrase “consisting essentially of,” and grammatical variants thereof, when used herein is not to be constmed as excluding additional components, steps, features integers or groups thereof but rather that the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

[0028] It would be understood by one of skill in the art that whilst the embodiments of the invention described and depicted within this specification are directed to systems operatingwithin the frequency range of one of more global navigation satellite systems (GNSSs) that the methods and concepts presented may be applied to other operating frequency ranges without departing from the scope of the invention.

[0029] Table 1 below presents the operating frequencies for single and dual-band GNSS receivers of the Beidou, Galileo, GLONASS, GPS, and NAVIC GNSS systems. Beidou, Galileo, GLONASS and GPS provide dual-band operation in the frequency range 1150MHz- 1610MHz and define the frequency range within which embodiments of the invention were designed, manufactured and tested. Also depicted within Table 1 are the operating frequencies of satellite phone systems which could extend the bandwidth requirements of variants of the embodiments of the invention presented if a dual use system required an RF surge protector according to an embodiment of the invention.Table 1: Operating Frequencies of GNSS and Satellite Phone Systems (Nearest 1MHz)

[0030] RF surge protection devices are known in the art for protecting electronic equipment.These include capacitors, gas discharge tubes (GDTs), and metal oxide varistors (MOVs).

[0031] A capacitor blocks the flow of direct current (DC) and permits the flow of alternating current (AC) depending on the capacitor's capacitance and frequency of the current where atcertain frequencies the capacitor may also attenuate the AC signal. Typically, the capacitor is disposed in-line with an RF transmission line to block the de signal and undesirable surge transients.

[0032] A GDT contains hermetically sealed electrodes which ionize a gas during use wherein when the gas is ionized the gas tube becomes conductive and the breakdown voltage is lowered. The breakdown voltage varies and is dependent upon the rise time of the surge. Accordingly, depending on the surge, several microseconds may elapse before the gas tube becomes ionized, thus resulting in the leading portion of the surge passing the GDT and onto the subsequent RF circuitry. A GDT is disposed between the RF transmission line and a ground plane such the GDT diverts the surge current to ground.

[0033] An MOVs is typically utilized as a voltage limiting element as if voltage at the MOV is below its clamping or switching voltage the MOV exhibits a high resistance but once the voltage exceeds the clamping or switching voltage of the MOV then the MOV exhibits a low resistance. An MOV is a non-linear device functioning as a voltage dependent resistor with symmetrical (must be asymmetrical because MOV are voltage-current characteristics. As with a GDT a MOV is disposed between the RF transmission line and ground. A MOV is typically employed in conjunction with a GDT as the MOV has a fast response time and accordingly can manage the leading portion of the surge which passes a GDT before it becomes ionized.

[0034] Referring to Figure 1 there is depicted a capacitive RF surge protector Circuit 100 according to the prior art. As depicted the Circuit 100 comprises an Input Port 100A and Output Port 100B with first and second Transmission Line (TL) Sections 110 and 120 between the Input Port 100A and an In-Line Capacitor 130 and third and fourth Transmission Line (TL) Sections 140 and 150 between the In-Line Capacitor 130 and the Output Port 100B. A first Inductor 160 is disposed between a point between the first and second Transmission Line (TL) Sections 110 and 120 and ground. A second Inductor 180 is disposed between a point between the third and fourth Transmission Line (TL) Sections 140 and 150 and ground. Accordingly, the Circuit 100 provides for blocking of DC and low frequency signals between the Input Port 100A and Output Port 100B. The first and second Inductors 160 and 180 in conjunction with the In-Line Capacitor 130 provide a high pass filter such that in addition to DC blocking Circuit 100 blocks low frequency signals in dependence upon the values of the first and second Inductors 160 and 180 and the In-Line Capacitor 130.

[0035] Circuit 100 is coupled between an RF circuit and another RF circuit in order to protect the another RF circuit from DC voltages being coupled to it from the RF circuit. However,whilst Circuit 100 blocks DC and low frequency signals its RF performance in the frequency range of the signals passed to the another RF circuit is sub-optimal with respect to at least one of insertion loss and impedance matching where the latter leads to low return loss. Accordingly, the inventors established Circuit 200 which depicts a capacitive RF surge protector circuit with improved matching according to an embodiment of the invention.

[0036] Circuit 200 incorporates a Matching Circuit 200A within Circuit 100 where the Matching Circuit 200A comprises In-Line Capacitor 130, another In-Line Capacitor 210 and a third Inductor 220 to ground disposed between the In-Line Capacitor 130 and another In- Line Capacitor 210. A CAD schematic of Circuit 200 is depicted in Schematic 300B in Figure 3 whilst the simulated performance is depicted in Graph 300A in Figure 3. As evident from Graph 300A the insertion loss (first plot 310) is below approximately 0.3dB over the frequency range 1150 MHz to 1650 MHz and return loss is above approximately 27 dB over the same frequency range. Over the 1500 MHz - 1600 MHz range which covers Beidou Bl, Galileo El, GPS LI the return loss is 30 dB or more.

[0037] Now referring to Figure 4 there is depicted a DC blocking - radiofrequency (RF) matching circuit (Circuit 400) according to an embodiment of the invention exploiting additional transmission line elements, first and second Filter TL Sections 410 and 420 within Matching Circuit 400A such that first Filter TL Section 410 is between In-Line Capacitor 130 and the connection to third Inductor 220 and second Filter TL Section 420 is between the connection to third Inductor 220 and the another In-Line Capacitor 21O.The simulated RF performance of Circuit 400 being depicted in first and second Graphs 500A and 500B respectively in Figure 5. As evident the insertion loss depicted in first Graph 500A is below 0.32dB over the frequency range 1150 MHz - 1650 MHz whilst the return loss is above 29 dB. However, over the 1500 MHz - 1600 MHz range which covers Beidou Bl, Galileo El, GPS LI the return loss is 40 dB or more.

[0038] Now referring to Figure 6 there is depicted an RF Surge Protector 600 according to an embodiment of the invention exploiting the DC blocking - RF matching Circuit 400 according to Figure 4 and Surge Circuit 600A. Surge Circuit 600A being coupled between the first Node 600B, between the first Inductor 160 and first Capacitor 170 and second Node 600C between the second Inductor 180 and second Capacitor 190. As depicted the Surge Circuit 600A comprises a GDT 640 disposed between the first Node 600B and ground, a pair of serially connected Unidirectional Transient-Voltage-Suppression (TVS) Diodes (UTVSDs), first and second UTVSDs650 and 660 disposed between the second Node 600Cand ground together with first to third Surge Inductors 610 to 630 respectively disposed between the first Node 200B and the second Node 200C.

[0039] A TVS Diode operates by shunting excess current when the induced voltage exceeds the avalanche breakdown potential of the diode and as such is a clamping device. A TVS Diode suppresses all over-voltages above its breakdown fixed voltage and automatically restores when the overvoltage goes away. In contrast to a MOV a TVS Diode clamps at a lower fixed voltage and does not degrade over time. Beneficially, TVS have lower breakdown voltage for the pulse in opposite direction and provide reliable protection from negative pulses.

[0040] Referring to Figure 7 there is depicted a CAD layout of populated printed circuit board (PCB) 700 which exploits the circuit of the RF Surge Protector 600 depicted in Figure 6. Accordingly, it is evident that the RF Surge Protector 600 can be implemented onto a single PCB 700 which can then be housed within a single housing with in-line RF connectors attached to the input and output Pads 700A and 700B respectively at either end of PCB 700. Such solution provides big advantage of inexpensive automated manufacturing. Figure 8 depicts a Photograph 800A of an assembled PCB 700 with input and output RF connectors according to the design of the RF Surge Protector 600 depicted in Figure 6. Graph 800B depicts the measured RF performance showing that the insertion loss varies from approximately 0.1 dB to 1.0 dB over the frequency range 1150 MHz - 1650 MHz whilst the return loss varies from approximately 16 dB to approximately 30dB over the frequency range.

[0041] Accordingly, the inventors analyzed the design and performance of the PCB) 700 implementing the RF Surge Protector 600 in order to ascertain a modified design basis for improved RF performance. Accordingly, referring to Figure 9 there is depicted an RF Surge Protector 900 according to an embodiment of the invention exploiting the Surge blocking / DC Bias path - RF matching circuit according to Figures 4 and 6 but now with modified transmission lines within the RF Signal path - RF matching circuit. Accordingly, rather than first and second Filter TL Sections 410 and 420 as depicted in Figure 4 the RF Surge Protection 900 has first and second Filter TL Sections 910 and 920 which have a different design than the other transmission line segments such as second and fourth TL Sections 120 and 140 respectively. The central section of the RF transmission path denoted as Element 900A comprising first and second Filter TL Sections 910 and 920 and third Inductor 220 to ground. This portion being denoted in Figure 10 which depicts a Photograph 1000A of an assembled RF surge protector exploiting the circuit depicted in Figure 9.

[0042] The measured RF performance of RF Surge Protector 900 according to an embodiment of the invention being presented in Graph 1000B in Figure 10 where the insertion loss is below approximately 0.5 dB over the frequency range 1150 MHz - 1650 MHz, versus ~ 1.0 dB for the RF Surge Protector 600 without the modified transmission sections whilst the return loss performance over this band is similar although the return loss performance is improved within the frequency range 1425 MHz - 1525MHz.

[0043] The inventors modelled and evaluated alternate geometries of the first and second Filter TL Sections 910 and 920in terms of track geometry and track length. Figure 11 in Graph 1100 depicts the measured performance of a variant design of the RF surge protector depicted in Figure 9 wherein the central transmission line comprising first and second Filter TL Sections 910 and 920 have a track width of 3.8 mm and length 10.5 mm with a track capacitance of 1.4 pF versus a central transmission line comprising first and second Filter TL Sections 910 and 920 of width 5.4 mm and length 9.2 mm with a track capacitance of 1.8 pF employed in the circuit whose results are depicted in Graph 1000B in Figure 10. In both instances the In-Line Capacitor 130 and another In-Line Capacitor 210 are 68 nH inductors.

[0044] Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.

[0045] The foregoing disclosure of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.

[0046] Further, in describing representative embodiments of the present invention, the specification may have presented the method and / or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be constmed as limitations on the claims. Inaddition, the claims directed to the method and / or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.

Claims

CLAIMSWhat is claimed is:

1. A surge protector for an RF circuit comprising: an input port for receiving RF signals; a first circuit disposed between the input port and an output port wherein the first circuit comprises a filter circuit which blocks DC and low frequency signals; and a second circuit disposed between the input port and the output port wherein the second circuit comprises one or more surge protection elements; wherein an end of the second circuit is coupled to an end of the first circuit via an inductor; a distal end of the second circuit is coupled to a distal end of the first circuit via another inductor.

2. The surge protector according to claim 1, wherein each surge protection element of the one or more surge protection elements triggers with a defined surge voltage and a defined response time.

3. The surge protector according to claim 1, wherein the one of more surge protection elements comprise a gas discharge tube coupled to ground and a Zener diode coupled to ground; and the second circuit comprises an inductance between the gas discharge tube and the Zener diode.

4. The surge protector according to claim 1, wherein the filter circuit comprises: a first capacitor coupled to the input port via a first transmission line; a second capacitor coupled to the output port via a second transmission line; and an inductor having an end coupled to a third transmission line between the first capacitor and second capacitor and a distal end coupled to ground; wherein the third transmission line has a different design to the first transmission line and the second transmission line.

5. A method comprising: providing a surge protector for an RF circuit comprising a filter circuit disposed in parallel to a surge protection circuit; wherein the filter circuit comprises a transmission line segment to which an inductor is coupled at one end and ground at its distal end; and the transmission line segment within the filter circuit has a different design to those other transmission line segments which couple the filter circuit to an input port of the surge protector and an output port of the surge protector.

6. The method according to claim 5, wherein the filter circuit comprises: a first capacitor coupled to the input port via a first transmission line segment; a second capacitor couped to the output port via a second transmission line segment; and the inductor.

7. The method according to claim 5, wherein the surge protection circuit comprises one or more surge protection elements where each surge protection element of the one or more surge protection elements triggers with a defined surge voltage and a defined response time.

8. The method according to claim 5, wherein the surge protection circuit comprises a gas discharge tube coupled to ground and a Zener diode coupled to ground; and the surge protection circuit comprises an inductance between the gas discharge tube and the Zener diode.

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