Slot-fed patch antenna for GNSS applications

Abstract

The broadband GNSS antenna includes a top-surface slot-fed broadband patch radiator and a single-grooved vertical choke ring structure surrounding the patch radiator. The patch radiator includes a radiator ground plane, a slot-fed radiating patch, a broadband feed network, and a set of elements with vertical currents. The vertical choke ring structure includes a conductive top surface with a set of slots, a conductive bottom surface, and an adjacent vertical conductive cylinder.

Description

[Technical Field]

[0001] The present invention relates generally to antennas, and more particularly to wideband circularly polarized antennas with improved multipath rejection for receiving signals from Global Navigation Satellite Systems (GNSS). [Background technology]

[0002] One of the factors affecting the quality of positioning information determined based on data from a Global Navigation Satellite System (GNSS) is the performance of the receiving antenna. One source of positioning error is multipath signals. Multipath signals are signals from GNSS satellites received by an antenna via paths other than the direct path from the GNSS satellite to the antenna. Such signals can occur when signals from GNSS satellites are reflected by objects near the antenna. For example, an object located below the antenna can cause a reflected signal. Multipath signals are classified into far-field and near-field multipath signals. Far-field multipath signals are reflected signals from objects located several wavelengths (e.g., five wavelengths) or more away. The Earth's surface below the antenna can be considered an object located several wavelengths away. Near-field multipath signals arise from objects located within a few wavelengths of the antenna. Such objects are mainly antenna accessories, such as Tribrach antennas. GNSS base station antennas require an effective level of multipath signal suppression.

[0003] Qualitative parameters for the suppression of far-field multipath signals include the radiation pattern (RP) and, in particular, the level of the back lobe or the front-to-back ratio. Qualitative parameters for the suppression of near-field multipath signals can be expressed by the magnitude of the near field, in particular the distribution of the horizontal component of the near-field electric field vector that occurs below the antenna along the antenna's axis of symmetry.

[0004] Signals broadcast from GNSS satellites typically have right-hand circular polarization (RHCP). The full GNSS frequency band is divided into two smaller frequency bands: low frequency (LF) (approximately 1165-1300 MHz) and high frequency (HF) (approximately 1525-1605 MHz).

[0005] A GNSS antenna should have a stable phase center and azimuth RP symmetry within the required bandwidth. This can be achieved by using four feed points. Microstrip patch antennas excited by probes or slots can be used for this purpose. Slot excitation allows the use of a compact feed network.

[0006] Positioning information generated using signals from GNSS satellites can be achieved using an antenna that receives RHCP signals arriving from above-horizon directions and suppresses multipath signals arriving from below-horizon directions. Such an antenna should have a feeding network with four feed points that operates across the entire GNSS frequency band.

[0007] A conventional patch antenna with a flat ground plane does not sufficiently suppress multipath signals for GNSS antenna applications. When the size of the ground plane is equal to the size of the radiating patch, the backlobe signal level is the same as the mainlobe signal level. To reduce the backlobe level, the patch antenna can be placed on a special ground plane. For example, the patch antenna can be placed on a choke ring. Summary of the Invention [Problem to be solved by the invention]

[0008] Figure 1 shows a prior art antenna described in U.S. Patent No. 6,940,457 configured to receive GNSS signals. A multi-frequency slot-fed antenna 101 is rear-mounted with an edge diffraction reflector 102. A dielectric and magnetic material 103 encases the opposing sides and rear of the antenna 101 to reduce multipath signals. The edge diffraction reflector 102 includes a set of stacked grooves 104, 105, 106, and 107 formed by adjacent plates and a central cylinder. This type of edge diffraction reflector design is often referred to as a vertical choke ring. The multi-frequency antenna is a stacked patch antenna consisting of a pair of patch radiators 108 and 109 stacked on top of each other. The lower patch radiator has a pair of excitation slots excited by a microstrip line. Graphs in U.S. Patent No. 6,940,457 demonstrate that an edge diffraction reflector design with at least two stacked grooves is required to achieve front-to-back levels on the order of 20 dB or greater. In the LF band, a pair of laminated grooves 104, 105 of a particular depth are used. In the HF band, a pair of laminated grooves 106, 107 of a depth different from the particular depth of the laminated grooves 104, 105 are used. To obtain the required level of front-to-back ratio in both the LF and HF bands, at least four laminated grooves 104, 105, 106, 107 of different depths are used. The availability of a set of laminated patch radiators 108, 109 as well as the laminated grooves 104, 105, 106, 107 makes the antenna complex and difficult to manufacture.

[0009] The prior art antenna shown and described in U.S. Patent No. 10,197,679 relates to an antenna design that provides good suppression of both far-field and near-field multipath signals. The antenna's ground plane is a printed circuit board ("PCB") that has inductance and resistance and includes slots. There is an additional vertical mushroom-shaped element to suppress near-field multipath signals. These features make the antenna complex and difficult to manufacture.

[0010] What is needed is a patch antenna for GNSS applications that has a minimal number of elements and is easy to manufacture, suppressing far-field and near-field multipath. [Means for solving the problem]

[0011] In one embodiment, the antenna has a vertical axis and includes a patch radiator, a ground plane, a dielectric, multiple vertical conductors, and a choke ring structure. The patch radiator includes a printed circuit board ("PCB") including a feed network and a slot-fed radiating patch including a set of four excitation slots perpendicular to the vertical axis and connected to the feed network through microstrip lines. The dielectric and / or multiple vertical conductors are disposed between the ground plane and the slot-fed radiating patch and are configured to carry one or both of a conduction current and / or a polarization current flowing in the direction of the vertical axis. The feed network is configured to ensure reception or transmission of right-hand circularly polarized ("RHCP") waves. The choke ring structure includes a conductive top surface, a conductive bottom surface, and a conductive cylinder. The conductive top surface includes a set of extension slots, each having a termination located around the periphery of the conductive top surface. The conductive cylinder includes a top end and a bottom end, the top end connected to the conductive top surface and the bottom end connected to the conductive bottom surface, and the ground plane is connected to the conductive cylinder along the periphery of the ground plane.

[0012] In one embodiment, the antenna also includes four capacitive circuits disposed on the PCB outside the perimeter of the slot-fed radiating patch, each circuit having a first end, a second end, and at least three capacitors connected in series. In one embodiment, the first end of each of the four capacitive circuits is connected to a respective first point disposed on the perimeter of the slot-fed radiating patch, the second end of each of the capacitive circuits is connected to a respective second point disposed on the perimeter of the slot-fed radiating patch, each first point and each second point is disposed opposite a corresponding one of the set of four excitation slots, and a first capacitor of the at least three capacitors is disposed near the first point, a second capacitor of the at least three capacitors is disposed near the second point, and a third capacitor of the at least three capacitors is disposed opposite the corresponding excitation slot.

[0013] In one embodiment, the three capacitors are formed using lumped elements. In one embodiment, a third of the at least three capacitors is formed as a distributed element including three conductors disposed on a first surface of the PCB and a set of compensation conductors disposed on a second surface of the PCB, wherein a first conductor of the three conductors has a first end connected to the first capacitive element and an isolated second end, a second conductor of the three conductors has a first end connected to the second capacitive element and an isolated second end, a third conductor is disposed opposite the excitation slot and both ends of the third conductor are insulated, and a set of compensation conductors is disposed between the third conductor and the first conductor and between the third conductor and the second conductor, wherein the first end of the third conductor overlaps the second end of the first conductor and the second end of the third conductor overlaps the second end of the second conductor.

[0014] In one embodiment, the dielectric includes a dielectric cylinder having a top surface and a bottom surface, the top surface adjacent to the PCB and the bottom surface adjacent to the ground plane. Each of the plurality of conductors disposed between the ground plane and the slot-fed radiating patch may include a pin connected to the ground plane and located inside the periphery of the PCB. Each of the excitation slots may be substantially straight and have a termination located on the periphery of the slot-fed radiating patch, or may be T-shaped and have a termination located on the periphery of the slot-fed radiating patch. A set of conductive ribs may be connected to the ground plane or located outside the periphery of the PCB. In one embodiment, each slot in the set of expansion slots in the conductive top surface is rotated by an angle. In one embodiment, the conductive bottom surface includes a set of expansion slots, each having a termination located on the periphery of the conductive bottom surface. In one embodiment, the conductive bottom surface, the conductive cylinder, the ground plane, and the set of conductive ribs are integrally formed.

[0015] In one embodiment, the antenna has a vertical axis and includes a single grooved vertical choke ring structure having a conductive notched upper surface, an integral element attached to the conductive notched upper surface, and a patch radiator connected to the integral element. [Brief explanation of the drawings]

[0016] In the drawings, like numbers refer to like elements in different figures. Like numbers with different letter suffixes represent different instances of like elements and / or signals.

[0017] [Figure 1] 1 shows a prior art antenna.

[0018] [Figure 2A] 1 illustrates a side view of an antenna according to one embodiment.

[0019] [Figure 2B] 2B shows an isometric view of the antenna shown in FIG. 2A.

[0020] [Figure 2C] 2C shows an isometric view of an antenna according to an embodiment that is a variation of the antenna shown in FIG. 2B.

[0021] [Figure 3] 1 illustrates a top-side slot-fed patch radiator according to one embodiment.

[0022] [Figure 4] 1 illustrates the placement of radiator ground planes and vertical pins according to one embodiment.

[0023] [Figure 5] 1 illustrates a slot-fed radiating patch according to one embodiment.

[0024] [Figure 6A] 1 illustrates a printed circuit board ("PCB") having a slot-fed radiating patch according to one embodiment. [Figure 6B] 1 illustrates a printed circuit board ("PCB") having a slot-fed radiating patch according to one embodiment.

[0025] [Figure 6C] 1 illustrates a capacitive circuit according to one embodiment.

[0026] [Figure 6D] 1 illustrates a PCB cross section with compensation conductors and equivalent capacitors of a capacitive circuit according to one embodiment.

[0027] [Figure 7] 10A-10C show schematic diagrams of example limitations on the dimensions of a patch radiator according to one embodiment.

[0028] [Figure 8] 1 shows a graph of the normalized radiation pattern.

[0029] [Figure 9] 1 shows a signal propagation diagram illustrating the operation of an antenna according to one embodiment.

[0030] [Figure 10] 1 shows a graph of an experimental plot of front-to-back ratio in decibels (dB) versus frequency.

[0031] [Figure 11] 10 shows a graph of the horizontal component of the electric field in the rear near-field region.

[0032] [Figure 12] 10 shows a graph of experimental plots of radiation patterns at different slot angles.

[0033] [Figure 13] 1 shows a graph of the frequency dependence of voltage standing wave ratio ("VSWR") versus frequency in MHz.

[0034] [Figure 14] 1 illustrates an antenna according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0035] A wideband right-hand circularly polarized (RHCP) antenna for Global Navigation Satellite System (GNSS) applications is described herein, having a radiating patch and a single groove in the vertical choke ring structure. In one embodiment, the antenna has only one radiating patch and a single groove in the vertical choke ring structure. This antenna design suppresses multipath signals and provides a front-to-back ratio of 20 dB or greater for all frequencies in the GNSS frequency range.

[0036] Figure 2A shows a side view of antenna 200 according to one embodiment. Figure 2B shows an isometric view of antenna 200. Figure 2C shows an antenna that is a variation of the antenna shown in Figures 2A and 2B. Antenna 200 has four-fold rotational symmetry about axis of symmetry 201 (i.e., each quarter of the antenna is symmetric about axis of symmetry 201). The direction of axis of symmetry 201 coincides with the zenith direction. The direction along axis of symmetry 201 is referred to as the vertical direction, and the plane perpendicular to axis of symmetry 201 is referred to as the horizontal direction. Antenna 200 includes a top-side slot-fed patch radiator 21 and a single-grooved vertical choke ring structure 22.

[0037] The top-side slot-fed patch radiator 21 includes a radiator ground plane 211, a slot-fed radiating patch 212, a feed network 214, and elements carrying vertical currents (i.e., vertically flowing conduction currents and / or polarization currents) which may include vertical pin conductors 213 and / or dielectrics 220. Compared to conventional patch radiators, a notable feature of the top-side slot-fed patch radiator 21 is that the top-side slot-fed patch radiator 21 can suppress signals arriving from the lower hemisphere even with a small ground plane.

[0038] The slot-fed radiating patch 212 is positioned above the radiator ground plane 211. The slot-fed radiating patch 212 can be secured in place using, for example, a plastic spacer (not shown in FIGS. 2A and 2B). The slot-fed radiating patch 212 is a conductive surface with a set of excitation slots 215. In one embodiment, the input end of the feed network 214 is connected to the excitation slots 215.

[0039] The vertical current carrying structure provides the required level of antenna gain and axial ratio throughout the upper hemisphere, especially for elevation angles close to the horizon. The antenna should have an antenna gain of -8 dBic (i.e., dB of an isotropic circular antenna) or greater at the horizon for high-quality reception of signals from low-flying satellites. In one embodiment, vertical current carrying conductors and dielectrics are disposed in the space between the slot-fed radiating patch 212 and the radiator ground plane 211. For example, FIG. 2A shows a pair of vertical pin conductors 213 connected to the radiator ground plane 211 as well as a dielectric 220, shown as a dielectric cylinder, according to one embodiment. In one embodiment, the feed network 214 is a power divider configured to ensure optimal reception of RHCP waves.

[0040] In one embodiment, the single-grooved vertical choke ring structure 22 includes a conductive notched top surface 217 (also referred to as the conductive top surface), a conductive bottom surface 218, and a groove 216 of a specific depth formed by a vertical conductive cylinder 219 adjacent to the conductive notched top surface 217 and the conductive bottom surface 218. The vertical conductive cylinder 219 is connected to the outer periphery of the radiator ground plane 211. In one embodiment, the radiator ground plane 211 and the conductive notched top surface 217 may be disposed in the same plane. In other embodiments, the radiator ground plane 211 and the conductive notched top surface 217 may be disposed in different planes. The conductive notched top surface 217 includes a pair of elongated (i.e., elongated) slots 221. Each slot 221 has a terminal end disposed at the outer periphery of the conductive notched top surface 217. The slots 221 may be disposed radially (as shown in FIG. 2B ) and at an angle α relative to the radial direction 224 (as shown in FIG. 2C ). Varying the angle α of the slots 221 can change the level of antenna gain. If the angle α is positive, the antenna gain in the horizontal direction decreases. If the angle α is negative, the antenna gain in the horizontal direction increases. Figure 2C shows an embodiment with a positive angle α. Note that the conductive bottom surface 218 may also include a set of slots 222 as shown in Figure 2B. These slots allow for near-field multipath reduction.

[0041] High-quality matching is necessary to maximize power transfer to the antenna. VSWR (Voltage Standing Wave Ratio) level is an index used to evaluate the degree of matching of an antenna. Antenna matching is primarily determined by the design of the patch radiator 21. Varying the height of the vertical pin conductor 213 affects both the radiation pattern and the matching. To adjust the radiation pattern without affecting the matching in the embodiment shown in Figures 2A and 2B, a set of conductive ribs 223 is placed on the surface of the radiator ground plane 211. Because the conductive ribs 223 are placed outside the periphery of the slot-fed radiating patch 212, the set of ribs 223 has only a small effect on the matching of the patch radiator 21 (compared to the vertical pin conductor 213), but can improve the radiation pattern (RP) level in the direction perpendicular to the axis 201. Additionally, changing the height of one rib in the set of ribs 223 can adjust the horizontal phase center of the antenna.

[0042] FIG. 3 shows one embodiment of a top-side slot-fed patch radiator 21. In this embodiment, the patch radiator 21 includes a PCB 301 and a metal portion 302. These portions are stacked together, for example, using a plastic spacer (not shown in FIG. 3). In this embodiment, the slot-fed radiating patch 212 (shown in FIG. 2A) and the feed network 214 are made in the form of a metallization layer of the PCB 301. In this embodiment, a low-noise amplifier ("LNA") may be located on the PCB 301, which is covered by a shield 303. The LNA output is connected to an output cable 304 arranged vertically at the center of the antenna.

[0043] 4 shows radiator ground plane 211 and vertical pin conductors 213 (shown as a set of vertical pins 213 in FIG. 2A) formed as metal portions 302 according to one embodiment. In this embodiment, vertical pin conductors 213 are arranged along the periphery of horizontal plane 401 and carry conduction and / or polarization currents. In this embodiment, horizontal plane 401 is part of radiator ground plane 211 (shown in FIG. 2A). Metal portions 302 may be formed by stamping and then bending any sheet material to form vertical pin conductors 213.

[0044] FIG. 5 illustrates a slot-fed radiating patch 212 (shown in FIG. 2A) configured in the form of a metallization layer according to one embodiment. In this embodiment, the metallization layer is PCB 301, and the antenna design has four-fold rotational symmetry. In this embodiment, slot-fed radiating patch 212 includes a conductive disk 501 having four substantially linear excitation slots 215. Each excitation slot 215 has a termination 502 located on the outer periphery of disk 501. Four capacitive circuits 505 are connected to conductive disk 501 and located outside the outer periphery of conductive disk 501. In one embodiment, each of capacitance circuits 505 is located the same distance from the outer periphery of conductive disk 501. Each of capacitance circuits 505 includes a series of conductors and capacitors. Each capacitor may be fabricated as a lumped element or a distributed element. In one embodiment, capacitance circuits 505 are configured as arcs terminating in radial segments 511, 512. Each capacitance circuit 505 surrounds a respective excitation slot 215. Each capacitance circuit has a first end 503 and a second end 504 connected to the conductive disk 501. The ends 503, 504 are located on opposite sides of the corresponding excitation slot 215. Each capacitance circuit 505 includes at least three capacitors 506, 507, and 508 connected in series and located opposite each excitation slot 215. The capacitors 506, 507 are connected to the capacitance circuit 505 near the point where the capacitance circuit 505 joins with the disk 501. The capacitor 508 is located in the capacitance circuit 505 opposite the excitation slot 215.

[0045] Antenna 200 (shown in FIGS. 2A and 2B) has two resonances: low frequency ("LF") and high frequency ("HF"). The LF resonant frequency is determined by the size of radiating patch 212, the height of vertical pin conductor 213, and the capacitance values ​​of capacitors 506 and 507 (shown in FIG. 5). Referring again to FIG. 5, the high frequency resonance is implemented using capacitive circuit 505. The HF resonant frequency is primarily determined by the capacitance of capacitor 508. Thus, dual-band antenna operation is achieved with good matching across the required frequency band, even though the antenna design includes only a single PCB 301.

[0046] The excitation slots 215 include excitation probes 509, shown as arrows in FIG. 5. The excitation probes 509 are connected to a feed network 214. The feed network 214 is designed so that pairs of opposing excitation slots 215 are excited in phase. In-phase excitation of opposing slots 215 is conditionally indicated by arrows pointing in the same direction, while pairs of excitation slots 215 positioned at 90 degrees to each other are excited 90 degrees out of phase. This ensures the excitation of RHCP waves. This excitation is achieved by the feed network 214.

[0047] In one embodiment, the excitation slots 215 may be shaped in different shapes, such as a T-shape, etc. In one embodiment, the radius on which the set of vertical pin conductors 213 are arranged does not exceed the radius of the capacitive circuit 505.

[0048] 6A-6D illustrate one variation of a printed circuit board ("PCB") 301 configured to accommodate distributed element placement of capacitors 508. FIG. 6A illustrates the top metallization layer of PCB 301, and FIG. 6B illustrates the bottom metallization layer of PCB 301. In this embodiment, as described in connection with both FIGS. 6A and 6B, slot-fed radiating patch 212 (shown in FIG. 2A) is a conductive disk 601 disposed on the top metallization layer of PCB 301. The excitation slots 215 disposed on disk 601 are T-shaped in this embodiment. Correspondingly, each slot 215 has a radial portion 602 and an arc portion 603. One end of radial portion 602 of slot 215 contacts the outer periphery of conductive disk 601, and the other end contacts arc portion 603.

[0049] The probe 509 is disposed on the lower metallization layer. The probe 509 is configured so that the electromagnetic field of the incident wave from the satellite, guided by the excitation slot 215, enters the feed network 214 (shown in FIG. 2A). The probe 509 is a continuous microstrip line passing above the excitation slot 215. The technique of exciting the slot 215 using this type of probe 509 is well known. The probe 509 is connected to the feed network 214 (shown in FIG. 2A) via the microstrip line. The feed network 214, in one embodiment, is a set of power dividers designed to excite RHCP waves. The feed network 214 may be disposed on the PCB 301.

[0050] Capacitive circuit 505 is formed on the lower metallization layer of PCB 301. Figure 6C shows one of four capacitive circuits located on the lower metallization layer of PCB 301. Each capacitive circuit 505 includes capacitors 506 and 507 and conductors 606, 607, and 608. Capacitors 506 and 507 are implemented as lumped elements. Conductors 606, 607, and 608 are located outside the perimeter of disk 601 (shown in Figure 6A). One end of capacitors 506 and 507 is connected to conductive disk 601 through metallized holes 604 and 605. The other ends of capacitors 506 and 507 are connected to conductors 606 and 607, respectively. Conductor 608 is located opposite conductors 606 and 607. There is a gap between conductors 608 and 606. Similarly, there is a gap between conductors 608 and 607. Therefore, conductors 608 and 607 are capacitively coupled, and similarly, conductors 608 and 606 are capacitively coupled. Therefore, equivalent capacitor 508 is implemented as a distributed constant circuit including conductors 606, 607, and 608.

[0051] In one embodiment, a set of compensation conductors 609 are disposed on the top metallization layer of PCB 301. These conductors are disposed in the gaps between conductors 608 and 606 and between conductors 608 and 607.

[0052] 6D shows a cross section of PCB 301 in the region where conductors 607, 608, and 609 are located. Capacitor 610 is formed by conductors 607 and 608. Compensation capacitor 611 is formed by conductors 607 and 609. Compensation capacitor 612 is formed by conductors 608 and 609. As the height "h" of dielectric substrate 613 increases, the capacitance of capacitor 610 increases and the capacitance of capacitors 611 and 612 decreases. Therefore, the total capacitance of all three capacitors changes only slightly. In this configuration, compensating conductor 609 reduces the effect that variations in the value of thickness "h" of dielectric substrate 613 of PCB 301 have on the capacitance formed by conductors 606, 608, 607, and 608.

[0053] By changing the lengths of the conductors 606 and 607, it is possible to adjust the antenna in the LF band, and by changing the length of the conductor 608, it is possible to adjust the antenna in the HF band.

[0054] The top-side slot-fed patch radiator 21 has an advantage over conventional patch radiators. The advantage is that the use of this radiator simplifies the design of the vertical choke ring structure. To demonstrate this advantage, the characteristics of the patch radiator 21 itself (i.e., without the vertical choke ring structure) are described below. Figure 7 shows the characteristics of the patch radiator 21 (with length L RP The size of the slot-fed radiating patch 212 (denoted by L GP 7 is a schematic diagram of a patch radiator 21 without a vertical choke ring structure in the limiting case where the size of the radiating ground plane 211 is equal to the size of the radiating ground plane 211 (denoted by ). This limiting case is indicative because in this case the ground plane 211 does not affect the level of the back lobe. As shown in FIG. 7, the angle θ is the elevation angle from a particular direction to the horizon.

[0055] FIG. 8 shows graphs of normalized radiation patterns calculated based on elevation angle θ for a configuration in which the slot-fed radiating patch 212 and radiating ground plane 211 (shown in FIG. 2A) have a nominal length of 0.42λ. In these configurations, λ is the signal wavelength in vacuum. In this configuration, a dielectric with a dielectric constant of 4 was used for the dielectric substrate 220 through which the vertically polarized current flows. Curve 801 corresponds to the top-side slot-fed patch radiator configuration. Curve 802 corresponds to the conventional patch radiator configuration. In one embodiment, a probe feed was used when calculating curve 802. For curve 802, which represents the conventional patch radiator, the backlobe level is equal to the mainlobe level. For curve 801, which represents the top-side slot-fed patch radiator, the backlobe level is 13 dB lower than the mainlobe level. This is because the top-side slot-fed patch radiator radiates from the excitation slot 215 and the side slots 701 and 702. The side slots 701, 702 are opposite legs of a cylindrical peripheral slot formed by the slot-fed radiating patch 212 and the edges of the radiator ground plane 211. The electric fields formed by the side slots 701, 702 and the drive slot 215 in the θ=90° direction are additive, and the electric field in the θ=-90° direction is subtractive. Figure 8 shows that the front-to-back ratio is about 13 dB. In the case of the conventional patch radiator, only the side slots radiate. L RP =L GP , the side slots at θ=90 degrees and θ=-90 degrees radiate similarly, i.e. the front-to-back ratio is 0 dB.

[0056] The top-surface slot-fed patch radiator 21 does not have a deep beam dip in the horizontal direction when the size of the radiating patch 212 is about 0.5λ. The radiation pattern of a conventional patch antenna usually has a deep dip in the horizontal direction. This is because RP= 0.5λ (i.e., the distance between side slots 701 and 702 is 0.5λ). In the case of a conventional patch antenna without excitation slot 215, the electromagnetic fields formed by side slots 701 and 702 in the horizontal direction are in opposite phase and cancel each other out. The top-side slot-excited patch radiator 21 also has radiation formed by excitation slot 215. Since the electromagnetic fields are not subtracted, there is no deep dip in the horizontal direction in this scenario.

[0057] As shown in Figure 8, at θ = 0 degrees, curve 802 has a deep dip, and the level of curve 801 is approximately -10 dB. This level is acceptable for receiving signals from satellites located near the horizon. Therefore, the top-surface slot-fed patch radiator 21 can have a diameter of up to 0.5λ, which allows for an extended operating frequency band and allows for the placement of a feed network 214, an LNA, and a set of filters, which may occupy a significantly larger area, in the slot-fed radiating patch 212. The diameter of the radiating patch of a conventional patch antenna typically does not exceed 0.3λ.

[0058] As mentioned above, the top-surface slot-excited patch radiator 21 itself has the function of suppressing multipath signals. Therefore, to obtain the required front-to-back ratio of about 20 dB or more, it is sufficient to install the patch radiator 21 in a vertical choke ring structure 22 having only one groove 216.

[0059] FIG. 9 shows a signal propagation diagram illustrating the operation of antenna 200 according to one embodiment. While the GNSS antenna is a receive antenna configured to operate in receive mode, the transmit mode is shown in FIG. 9 for clarity. Note that reciprocity dictates that the parameters for both transmit and receive modes of operation are equal. The excitation slot 215 radiates an electromagnetic field that propagates toward the horizon along two paths 901 and 902. Path 901 passes above the slot-fed radiating patch 212, while path 902 passes between the slot-fed radiating patch 212 and the radiator ground plane 211. The presence of the vertical pin conductor 213 or the dielectric substrate 220 results in a change in the phase of the wave along path 902. The parameters of the vertical pin conductor 213 or the dielectric substrate 220 can be selected so that the waves traveling along paths 901 and 902 are in opposite phase and cancel each other out. As a result, a weakened wave 903 approaches the groove 216 of the vertical choke ring structure. Wave 903 passing along groove 216 is further attenuated by interference with wave 904 reflected from groove 216. As a result, wave 905 propagating in the rear hemisphere is significantly attenuated.

[0060] FIG. 10 shows a graph of an experimental plot of the front-to-back ratio in decibels (dB) versus frequency. The antenna design used to generate the plot shown in FIG. 10 has the following dimensions (see dimension labels in FIG. 9): D=250 mm, h2=22 mm, h1=22 mm, and d2=47 mm. Curve 1001 corresponds to an antenna design according to one embodiment in which a top-side slot-fed patch radiator 21 is mounted on a single-grooved vertical choke ring structure 22. As shown in FIG. 10, in this scenario, the front-to-back ratio is no lower than 25 dB across the entire operating frequency band of the GNSS range. Curve 1002 is measured with a conventional stacked patch antenna mounted on the same single-grooved vertical choke ring structure 22. As shown in FIG. 10, in this scenario, the front-to-back ratio is significantly lower, approximately 17 dB, in the high-frequency GNSS range.

[0061] The presence of slots 221 located on the top surface 217 of the conductive cutout (shown in FIGS. 2A and 2B) reduces the near-field multipath signal strength. The magnitude of the unwanted near-field in the rear hemisphere can be estimated from the magnitude of the electric field on the axis of symmetry of the antenna.

[0062] Figure 11 shows a graph of the horizontal component of the electric field in the rear near-field region, plotting voltage in millimeters per meter versus distance from the antenna in the nadir direction. The distance is measured from the radiator ground plane in the direction opposite axis 201 (shown in Figure 2A), i.e., in the nadir direction. Curve 1101 corresponds to the case with slot 221 (shown in Figure 2B), and curve 1102 corresponds to the case without slot 221. As shown in Figure 11, the availability of slot 221 located on top surface 217 of the conductive cutout leads to a reduction in the undesired near-field by approximately a factor of two.

[0063] As mentioned above, the antenna gain in the zenith and horizontal directions can be changed by changing the rotation angle α of the slot 221 located in the conductive cutout top surface 217. The direction of the angle α is shown in Figure 2C.

[0064] Figure 12 shows a graph of experimental plots of radiation patterns for different slot angles α, plotting dBic (i.e., dB of an isotropic circular antenna) in degrees versus elevation angle θ. It can be seen that by varying the angle α from -10° to +20°, the antenna gain can be changed by 3 dB towards the horizon (θ=0°).

[0065] FIG. 13 shows a graph of the frequency dependence of voltage standing wave ratio ("VSWR"), plotting VSWR versus frequency in MHz. Curve 1301 shows the case where the capacitive circuit 505 (shown in FIGS. 5, 6B, and 6C) is connected to the radiating patch, while curve 1302 shows the case where the capacitive circuit 505 is not present. In one embodiment, the diameter of the PCB 301 with the slot-fed radiating patch 212 and capacitive circuit 505 is 80 mm, and the distance between the radiating patch PCB 301 and the radiating ground plane is 22 mm. It can be seen that an antenna according to one embodiment has a VSWR level of less than 2 over the entire GNSS range with the capacitive circuit 505 present.

[0066] FIG. 14 shows one embodiment of an antenna formed using three main elements. As shown in FIG. 14, conductive bottom surface 218, vertical conductive cylinder 219, radiator ground plane 211, and a set of conductive ribs 223 are formed as a unitary element 1401, which may be made of metallized plastic. Conductive notched top surface 217 is screwed to element 1401 with screws 1402. In one embodiment, conductive notched top surface 217 can be manufactured from sheet material, for example, by laser cutting. Thus, in one embodiment, single-groove vertical choke ring structure 22 includes only two sections. Top-surface slot-fed patch radiator 21 is mounted on radiator ground plane 211. In this embodiment, horizontal surface 401 of portion 302 is in contact with radiator ground plane 211. Vertical conductive cylinder 219 may have a vertical section 1403 and a conical section 1404.

[0067] It is to be understood that the foregoing detailed description is in all respects illustrative and exemplary and not restrictive, and the scope of the inventive concepts disclosed herein is to be construed in accordance with the full scope permitted by patent law. It will be understood that the embodiments shown and described herein are merely illustrative of the principles of the inventive concepts, and that various modifications may be made by those skilled in the art without departing from the scope and spirit of the inventive concepts. Various other feature combinations may be implemented by those skilled in the art without departing from the scope and spirit of the inventive concepts.

Claims

1. An antenna having a vertical axis, said antenna comprising: a patch radiator, the patch radiator comprising: a printed circuit board ("PCB"), said PCB comprising: a feed network configured to receive or transmit right-hand circularly polarized ("RHCP") waves; a slot-fed radiating patch orthogonal to the vertical axis, the slot-fed radiating patch comprising: a set of four excitation slots connected to the feed network via microstrip lines; a ground plane; a dielectric disposed between the ground plane and the slot-fed radiating patch; a plurality of vertical conductors disposed between the ground plane and the slot-fed radiating patch; and a vertical choke ring structure, wherein the dielectric and the plurality of vertical conductors are configured to carry one or both of a conduction current and a polarization current in the direction of the vertical axis, and the vertical choke ring structure comprises: a conductive top surface including a set of expansion slots, each slot including a termination located on the periphery of the conductive top surface; a conductive bottom surface; a conductive cylinder including a top end and a bottom end, the top end connected to the top conductive surface, the bottom end connected to the bottom conductive surface, and the ground plane connected to the conductive cylinder along an outer edge of the ground plane; Including, an antenna.

2. and four capacitance circuits disposed on the PCB outside the periphery of the slot-fed radiating patch, each of the four capacitance circuits comprising: a first end; and a second end; and at least three capacitors connected in series with each other; 2. The antenna of claim 1, wherein the first ends of the four capacitive circuits are connected to respective first points located on the periphery of the slot-fed radiating patch, the second ends of the four capacitive circuits are connected to respective second points located on the periphery of the slot-fed radiating patch, each of the first points and each of the second points is located opposite a corresponding one of a set of four excitation slots, a first capacitor of the at least three capacitors is located near the first point, a second capacitor of the at least three capacitors is located near the second point, and a third capacitor of the at least three capacitors is located opposite a corresponding excitation slot.

3. 3. The antenna of claim 2, wherein the at least three capacitors are formed using lumped elements.

4. A third capacitor of the at least three capacitors is formed as a distributed element, the distributed element comprising: three conductors disposed on a first surface of the PCB; a set of compensation conductors disposed on a second surface of the PCB; a first conductor of the three conductors includes a first end connected to a first capacitive element and a second end that is isolated; a second conductor of the three conductors includes a first end connected to a second capacitive element and a second end that is isolated; a third conductor is disposed opposite the excitation slot, and both ends of the third conductor are insulated; the set of compensation conductors is disposed between the third conductor and the first conductor, and between the third conductor and the second conductor; 3. The antenna of claim 2, wherein the first end of the third conductor overlaps the second end of the first conductor and the second end of the third conductor overlaps the second end of the second conductor.

5. 2. The antenna of claim 1, wherein the dielectric comprises a dielectric cylinder having an upper surface and a lower surface, the upper surface adjacent the PCB and the lower surface adjacent the ground plane.

6. 2. The antenna of claim 1, wherein each of the plurality of conductors disposed between the ground plane and the slot-fed radiating patch includes a pin connected to the ground plane and disposed inside the periphery of the PCB.

7. 2. The antenna of claim 1, wherein each of said excitation slots is substantially straight and has terminations located at the periphery of said slot-fed radiating patch.

8. 2. The antenna of claim 1, wherein each of said excitation slots is T-shaped and has terminations located at the periphery of said slot-fed radiating patch.

9. 10. The antenna of claim 1, further comprising a set of conductive ribs connected to the ground plane and disposed outside the periphery of the PCB.

10. 2. The antenna of claim 1, wherein each slot in the set of expansion slots in the conductive top surface is rotated by an angle.

11. 2. The antenna of claim 1, wherein said conductive bottom surface includes a pair of expansion slots each having a termination located on the periphery of said conductive bottom surface.

12. 10. The antenna of claim 9, wherein the conductive base, the conductive cylinder, the ground plane, and the set of conductive ribs are integrally formed.

13. An antenna having a vertical axis, said antenna comprising: a single grooved vertical choke ring structure, the single grooved vertical choke ring structure comprising: a conductive notch top surface; and an integral element attached to the conductive cutout top surface, the integral element comprising: a conductive bottom surface; a vertical conductive cylinder connected to the conductive bottom surface; a radiator ground plane connected to the vertical conducting cylinder; a set of conductive ribs connected to the radiator ground plane; a patch radiator connected to said integral element; Including, an antenna.

14. The patch radiator is a printed circuit board ("PCB"), said PCB comprising: A power supply network; a slot-fed radiating patch orthogonal to the vertical axis, the slot-fed radiating patch comprising:

14. The antenna of claim 13, comprising a set of four excitation slots connected to the feed network via microstrip lines, each of the excitation slots having terminations located at the periphery of the slot-fed radiating patch.

15. The conductive cutout upper surface is 15. The antenna of claim 14, including a set of expansion slots, each slot including a termination located on the periphery of the conductive cutout top surface.

16. 15. The antenna of claim 14, wherein the antenna has four-fold symmetry about the vertical axis and a front-to-back ratio level of at least 20 dB in the operating frequency band.

17. 15. The antenna of claim 14, wherein each slot in the set of four excitation slots is substantially straight.

18. 15. The antenna of claim 14, wherein each slot in the set of four excitation slots is T-shaped.

19. 16. The antenna of claim 15, wherein each slot in the set of expansion slots in the conductive top surface is rotated by an angle.

20. 15. The antenna of claim 14, wherein the conductive bottom surface includes a pair of expansion slots each having a termination located on the periphery of the conductive bottom surface.

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