eLORAN Receiver with Tuned Antenna and Related Methods - Patent application

Abstract

To provide an increment long distance navigation (eLORAN) receiver.SOLUTION: An eLORAN receiver contains: an antenna 116; and an eLORAN receiver circuit connected to the antenna 116. The antenna 116 contains a ferromagnetic core 120 and magnetic field signal windings 121a to 121d connected to the ferromagnetic core 120. The eLORAN receiver includes tuned windings 123a and 123b surrounding the ferromagnetic core 120 and a tuned antenna device containing a tuned antenna circuit connected to the tuned windings 123a and 123b.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to the field of communication systems, and more particularly, to radio frequency antennas and related methods. [Background technology]

[0002] For example, for radio frequency (RF) communications in the very low frequency (VLF), low frequency (LF), and mid frequency (MF) ranges, relatively large ground antenna towers are used to transmit such signals. Such antenna configurations may include a tower several hundred feet tall that is connected to the ground at its pedestal, with numerous guy lines connecting the tower to the ground for stability.

[0003] Another example where large tower-based antennas are used is as low-frequency transmitting stations for navigation systems, such as the Long Range Navigation (LORAN) system. LORAN was developed in the United States and the United Kingdom during World War II. Subsequent implementations, including LORAN-C, and later Enhanced LOng-RAnge Navigation (eLORAN) implementations, provided increased accuracy and availability. More specifically, eLORAN is a low-frequency radio navigation system that operates in the 90-110 kHz frequency band allocation. Low-frequency eLORAN transmissions may be propagated by ground waves, a type of surface wave that travels along the Earth's surface. Ionospheric reflections, or sky waves, are another important mechanism for eLORAN wave propagation. In a typical low-frequency antenna, the tower itself is used as a monopole antenna. Due to the tower height, which can be 600 feet or more as a result of the operating wavelength, a number of top wires are connected to the top of the tower to form a resonant capacitor. These wires are known as top-loading elements (TLEs) and may approximate a solid cone. A typical tower in use in the United States was 625 feet tall, had 24 top-loading elements, and a natural resonance near 110 kHz. A base-loading coil was used to force resonance at 100 kHz.

[0004] eLORAN operates at low frequencies, such as 100 kHz, which may allow for large physical sizes of transmitting antennas. However, in eLORAN, the electrical size of the antenna is small compared to the wavelength. Physical properties may limit the fixed tuning bandwidth of electrically small antennas. One theory is the Chu Limit, as described in the reference "Physical limitations of omnidirectional antennas," Chu, LJ (December 1948), Journal of Applied Physics 19:1163-1175, which is incorporated herein by reference. Chu's bandwidth limit formula is Q=1 / kr 3 where Q is a dimensionless number for bandwidth, k is the wave number=2π / λ, and r is the radius in meters of the spherical analytical volume surrounding the antenna. The 3 dB antenna bandwidth is equal to 200 / Q. Antenna radiation bandwidth is a matter of considerable importance for eLORAN because it allows for sharp eLORAN pulses with fast rise times to be transmitted and received. Sharper pulses allow for more transmitting stations, and faster rise times better distinguish ground waves from sky waves. Also, a 60% rise time of, for example, 50 microseconds or less is preferred for eLORAN pulses to distinguish received ground waves from received sky waves.

[0005] While transmitting antennas require high radiation efficiency, eLORAN receiving antennas do not require high antenna efficiency because naturally occurring "atmospheric noise" is abundant at the low frequencies used by eLORAN. Atmospheric noise is so important in spectrum allocation that it has been cataloged by the International Telecommunication Union in the report "Radio Noise", Recommendation ITU-R P.372-8, FIG.2 "Fa Versus Frequency". Curves B and A of this report show that at a frequency of 100 kHz, atmospheric noise exceeds antenna thermal noise by 77 dB in quiet natural conditions without artificial interference, and by 140 dB in high artificial noise conditions, i.e., significantly "static" so to speak. Assuming that the receiver noise figure (transistor thermal noise) contribution is about 10 dB, and knowing that the directivity of an electrically small antenna cannot exceed 1.8 dB, the receive antenna gain required to overcome the natural noise in quiet conditions is -77 + 10 + 1.8 = -65 dBi or decibels relative to isotropy. Therefore, at eLORAN frequencies, a small, inefficient antenna will suffice for reception.

[0006] Antennas that receive eLORAN transmissions are classified into electric field and magnetic field types. Electric field antennas can be whip or patch shaped, whereas magnetic field types can be loop, circular, or wound. Electric field types are based on the divergence of current and are associated with dipoles and monopoles. Magnetic field types are based on the swirling of current and are therefore associated with loops and half loops. Both electric field and magnetic field antenna types respond to far-field radio waves and provide useful reception. Additionally, both electric field and magnetic field antenna types respond to both the electric and magnetic fields present in far-field radio waves.

[0007] There are many trades between the two receiving antenna types. There is a key difference between the near-field response of electric field and magnetic field antenna types. The electric field type has a strong radial electric field reactive near-field response. The magnetic field type, by contrast, has a strong radial magnetic field reactive near-field response. The electric field antenna may pick up more man-made electromagnetic interference (EMI) than the magnetic field antenna type. Human accessories such as high voltage power lines result in significant charge separation and strong electric field EMI that the electric field type receiving antenna will respond to. However, the electric field antenna type is useful for small size and sensitivity, and a 24 inch long whip may be sensitive enough to receive against atmospheric noise levels. The magnetic field receiving antenna may have improved rejection of localized EMI, rejection of P static or noise due to charge buildup, and direction of arrival information. Disadvantages of the magnetic field antenna may include increased cost because ferrite rods may be used.

[0008] With the rise of satellite-based navigation systems such as the Global Positioning System (GPS), there has until recently been little development or investment in ground-based navigation systems such as eLORAN. There has been renewed interest in such systems as a backup for satellite navigation systems, especially since the low frequency eLORAN signals are less susceptible to jamming and spoofing compared to the relatively high frequency GPS signals. In free space, radio waves are spread in both azimuth and elevation with a propagation delay of 1 / r 2 where r is in the range of meters. Thus, free space waves become up to four times weaker with doubling of distance. Ground wave propagation of eLORAN signals occurs with very little elevation plane wave spreading, only azimuth spreading. Thus, eLORAN ground waves can weaken with a decay rate of approximately 1 / r. This fact, together with the practical high powers at ground transmitting stations, means that the received eLORAN signal can be very strong relative to GPS signals. Summary of the Invention

[0009] In general, an eLORAN receiver includes an antenna and eLORAN receiver circuitry coupled to the antenna. The antenna includes a ferromagnetic core and a magnetic field signal winding coupled to the ferromagnetic core. The eLORAN receiver also includes an antenna tuning device. The antenna tuning device includes at least one tuning winding surrounding the ferromagnetic core and a tuning circuit coupled to the at least one tuning winding.

[0010] In some embodiments, the at least one tuning winding comprises a plurality of tuning windings. The tuning circuit may include a resistor and a capacitor coupled in series with the resistor. The antenna may include a pair of electrostatic patch elements on opposite sides of a ferromagnetic core.

[0011] More specifically, the ferromagnetic core may include a ferromagnetic intermediate portion and a plurality of ferromagnetic arms extending outwardly from the ferromagnetic intermediate portion. The plurality of ferromagnetic arms may be arranged in aligned pairs. The plurality of ferromagnetic arms may define a cross shape. The antenna may include a correction winding surrounding the ferromagnetic core and configured to receive a calibration signal from the eLORAN receiver circuitry. For example, the ferromagnetic core may include at least one of ferrite, powdered iron, electric steel, and nanocrystalline iron.

[0012] Another aspect relates to an antenna coupled to an eLORAN receiver circuit, the antenna including a ferromagnetic core, a magnetic field signal winding coupled to the ferromagnetic core, and an antenna tuning device including at least one tuning winding surrounding the ferromagnetic core and a tuning circuit coupled to the at least one tuning winding.

[0013] Yet another aspect relates to a method of making an antenna coupled to an eLORAN receiver circuit, the method including coupling a magnetic field signal winding to a ferromagnetic core, the method further including coupling an antenna tuning device to the ferromagnetic core, the antenna tuning device including at least one tuning winding surrounding the ferromagnetic core and a tuning circuit coupled to the at least one tuning winding. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of an eLORAN communication system according to the present disclosure. [Diagram 2] FIG. 2 is an eLORAN receiver of the eLORAN communications system. [Diagram 3] FIG. 1 is a schematic diagram of an eLORAN receiver in accordance with the present disclosure. [Figure 4] FIG. 4 is a schematic perspective view of an exemplary embodiment of an antenna for the eLORAN receiver of FIG. 3 , without windings and circuitry. [Diagram 5] FIG. 5 is a schematic diagram of the tuning circuit and antenna of FIG. 4. [Figure 6] FIG. 5 is a top view of an exemplary embodiment of the antenna of FIG. 4. [Figure 7] FIG. 4 is a circuit diagram of the amplifier of the eLORAN receiver of FIG. [Figure 8] 5 is a schematic diagram of the frequency response of the antenna of FIG. 4; [Figure 9] FIG. 4 is a schematic diagram of a balun for the amplifier output of the eLORAN receiver of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present disclosure will now be described more fully below with reference to the accompanying drawings, in which several embodiments of the present disclosure are shown. However, the present disclosure can be embodied in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Throughout, the same numerals refer to the same elements, and 100-series reference numerals are used to indicate similar elements in alternative embodiments.

[0016] Therefore, further development of eLORAN antenna systems may be desirable in certain applications. As noted above, given the operating frequencies of eLORAN systems and the typical placement of land vehicles and ships, there may be unique design challenges in the design of eLORAN antennas. In particular, given mobile applications of eLORAN antennas, it may be desirable for the antenna to be small sized, durable, and have sufficient bandwidth. It is important that eLORAN receiving antennas function in complex human environments and provide accurate navigation and time.

[0017] 1-2, an eLORAN communications system 10 according to the present disclosure will now be described. The eLORAN communications system 10 illustratively includes an eLORAN broadcast station 11 configured to transmit an eLORAN broadcast signal.

[0018] A number of GPS satellites 13a-13c are shown, although they are not part of the eLORAN communications system 10. It should be appreciated that due to the low power and high frequency nature of the GPS signals from the multiple GPS satellites 13a-13c, each GPS signal is subject to natural and man-made interference (e.g., ionospheric, spoofing, jamming) and may be unusable in mountainous areas. For this reason, it is useful to provide the eLORAN communications system 10, as detailed herein. Many systems will use both GPS satnav information and eLORAN terrestrial nab information in a coordinated fashion.

[0019] The eLORAN communications system 10 illustratively includes a plurality of vehicles 14a-14c. In the illustrated embodiment, the plurality of vehicles 14a-14c illustratively includes a marine vehicle 14a, a land vehicle 14b, and an air vehicle 14c. Each of the plurality of vehicles 14a-14c illustratively includes an eLORAN receiver 15a-15c configured to receive and process eLORAN broadcast signals.

[0020] Each eLORAN receiver 15a-15c illustratively includes an antenna 16 and an eLORAN receiver circuit 17 coupled to the antenna. The eLORAN receivers 15a-15c illustratively include a processor 18 coupled to the eLORAN receiver circuit 17 and configured to determine position / location data based on the eLORAN broadcast signals. As will be appreciated, the eLORAN receivers 15a-15c may include multiple internal receivers to receive and process the RF outputs of multiple receive antennas.

[0021] As will be appreciated by those skilled in the art, antenna 16 is a dual magnetic and electric field antenna system. Antenna 16 provides three antenna channels designated as the E channel, the Hx channel, and the Hy channel. Electric field antennas have a strong response to nearby electric fields, and magnetic field antennas have a strong response to nearby magnetic fields. Also, a typical magnetic field antenna is a closed electrical circuit loop, while an electric field antenna is an open circuit whip.

[0022] Due to the small size of the eLORAN antennas employed in the illustrated mobile applications, there is a design challenge to increase the instantaneous gain bandwidth or reception bandwidth of these eLORAN antennas. Also, in a typical mobile application, there may be tuning drift due to changes in the eLORAN antenna environment, such as mounting the eLORAN antenna on a metallic or non-metallic surface. Proximity to a metallic surface may shield the radial magnetic near-field of a magnetic field type antenna, thereby reducing the inductance of the antenna loop and thus raising the antenna resonant frequency. On a metallic surface, an electric field type antenna may be a monopole rather than a dipole. The low frequencies used by eLORAN mean that all eLORAN antennas reach into the reactive near-field that extends quite far.

[0023] 3-5, an eLORAN receiver 115 according to the present disclosure is described hereinafter. This eLORAN receiver 115 may provide an approach to the above problems and may also be used in the eLORAN receivers 15a-15c of FIGS. 1-2. Three separate antenna channels E, Hx, and Hy may enable the receiver 115 to pick out the signal within the interference, make angle of arrival determinations, determine propagation delays from wave impedances, and mitigate re-radiation effects from nearby structures.

[0024] The eLORAN receiver 115 includes an antenna 116 and an eLORAN receiver circuit 117 coupled to the antenna by transmission line cabling, printed wiring patterns, or the like. The antenna 116 includes a ferromagnetic core 120 and a number of magnetic field signal windings 121a-b coupled to the ferromagnetic core. In some embodiments (FIG. 4), the ferromagnetic core 120 may include orthogonal ferromagnetic cores. In particular, the number of magnetic field signal windings 121a-b are each wound around the ferromagnetic core 120 and illustratively include a H x Magnetic field signal and H y For example, the ferromagnetic core 120 may include at least one of ferrite, powdered iron, electrolytic steel, and nanocrystalline iron.

[0025] The eLORAN receiver 115 also includes a plurality of antenna tuning devices 122a-b coupled to the antenna 116. Each of the plurality of antenna tuning devices 122a-b includes a tuning winding 123a-b that surrounds (i.e., is wound around) the ferromagnetic core 120, and a tuning circuit 124a-b that is respectively coupled to the tuning winding. Each tuning circuit 124a-b includes a resistor 125a-b and a capacitor 126a-b that is coupled in series with the resistor. As will be appreciated, the resistor 125a-b and the capacitor 126a-b resonate with a respective one of the plurality of tuning windings 123a-b to increase the bandwidth of the system. In some embodiments, resistors 125a-125b and capacitors 126a-126b have adjustable resistance and capacitance, respectively, to allow tuning adjustment in real time.

[0026] Each of the plurality of tuning windings 123a-123b may have a number of turns greater than the number of turns of the plurality of magnetic field signal windings 121a-121b. For example, the plurality of magnetic field signal windings 121a-121b may have 9 turns, and each of the plurality of tuning windings 123a-123b may have the same number of turns, 80 turns.

[0027] For clarity of illustration, only two antenna tuning devices 122a-122b are shown, but it should be understood that some embodiments may include three or more antenna tuning devices, and in other embodiments, only a single antenna tuning device may be used.

[0028] As perhaps best seen in FIG. 4, the antenna 116 includes a pair of electrostatic patch elements 127a-127b on opposite sides of the ferromagnetic core 120 and configured to provide an electric field signal. In addition to this electric field signal function, the pair of electrostatic patch elements 127a-127b act as an electrostatic shield for the multiple magnetic field signal windings 121a-121b. Additionally, the electrostatic patch elements 127a-127b shield the magnetic near-fields of the Hx and Hy antennas to stabilize the tuning of the Hx and Hy antennas in different operating environments and reduce near-field EMI coupling that may otherwise be caused by the dipole moments of the Hx and Hy antennas. For example, if the antenna 116 is installed on the metal roof of an automobile, the metal roof will never change the tuning of the Hx and Hy antennas because the electrostatic patch elements 127a-127b provide a metallic, shielded or "shielded" operating environment for the magnetic field signal windings 121a-121b. Without the electrostatic patch elements 127a-127b, the roof of the vehicle would change the inductance and tuning of the magnetic field signal windings 121a-121b. The Hx and Hy antennas are pre-tuned for the presence of the electrostatic patch elements 127a-127b. The electrostatic patch elements 127a-127b do not include a closed electrical circuit to the Hx and Hy antennas and do not inhibit signal reception by the Hx and Hy antennas.

[0029] In particular, the antenna 116 includes an intermediate circuit wiring board 128a that holds the ferromagnetic core 120, a first outer circuit wiring board 128b that holds respective electrostatic patch elements 127a on an outer surface (i.e., a surface that faces away from the intermediate circuit wiring board), and a second outer circuit wiring board 128c that holds respective electrostatic patch elements 127b on an outer surface (i.e., a surface that faces away from the intermediate circuit wiring board). The antenna 116 also includes a plurality of vertical supports 129a-129c coupled between the intermediate circuit wiring board 128a and the first and second outer circuit wiring boards 128b-128c. Each of the plurality of vertical supports 129a-129c may include a dielectric material.

[0030] The intermediate circuit wiring board 128a and the first and second outer circuit wiring boards 128b-128c are each planar circuit wiring boards. Also, as illustrated, the intermediate circuit wiring board 128a and the first and second outer circuit wiring boards 128b-128c are arranged in a stacked configuration. The intermediate circuit wiring board 128a includes a dielectric base layer and associated circuitry carried on the dielectric base layer. The first and second outer circuit wiring boards 128b-128c also each include a dielectric base layer (e.g., fiberglass) and a conductive patch layer (e.g., copper, aluminum) on the dielectric base layer.

[0031] More specifically, and perhaps best seen in FIG. 6, the ferromagnetic core 120 includes a ferromagnetic middle portion 130 and a plurality of ferromagnetic arms 131a-131d extending outwardly from the ferromagnetic middle portion. The plurality of ferromagnetic arms 131a-131d are illustratively arranged in aligned pairs to define a cross or X-shape (i.e., non-orthogonal pairs). This avoids a closed magnetic circuit effect that would occur if the ferromagnetic arms were arranged in a square rather than an X-shape. In some embodiments, the ferromagnetic core 120 includes an integrated single piece, while in other embodiments, the ferromagnetic core may include ferromagnetic segments, as illustrated in FIG. 6. The illustrated embodiment may provide 360° azimuth coverage and angle of arrival information.

[0032] In some embodiments (not shown), the ferromagnetic core 120 may comprise the shape of a single rectangular bar. In this embodiment, the pair of electrostatic patch elements 127a-b may be replaced by a thin sheet of conductive material (e.g., copper, aluminum) wrapped around the opposing distal ends of the rectangular bar.

[0033] The antenna 116 illustratively includes a correction winding 132 surrounding the ferromagnetic core 120 and configured to receive a calibration signal from the eLORAN receiver circuitry 117. The antenna 116 illustratively includes first and second resistors 134a-134b coupled to the correction winding 132 for adjusting a coupling level, which may be a "loose coupling" or low coupling level, since the calibration injection signal may be sent from the receiver at a large amplitude. The first and second resistors 134a-134b are level adjustment resistors (i.e., provide a desired voltage drop). The correction winding 132 is configured to inject the calibration signal. The eLORAN receiver circuitry 117 is configured to generate a calibration signal, including an amplitude and phase calibration signal, based on the output from the multiple magnetic field signal windings 121a-121b. In particular, the calibration signal is generated from a sweep signal applied to the multiple magnetic field signal windings 121a-121b.

[0034] The eLORAN receiver 115 illustratively includes a number of amplifiers 133a-133c, which are coupled between the pair of electrostatic patch elements 127a-127b, the magnetic field signal windings 121a-121b, and the eLORAN receiver circuitry 117, respectively. Although not shown in FIG. 4, the antenna 116 also includes a number of feed lines coupled between the pair of electrostatic patch elements 127a-127b and the amplifier 133a, respectively. The antenna 116 also includes a number of feed lines coupled between the plurality of tuning windings 123a-123b and the amplifiers 133b-133c, respectively. In some embodiments, the amplifiers 133a-133c are carried by an intermediate circuit wiring board 128a, which provides a compact package useful for mobile applications.

[0035] 7, an embodiment of an exemplary amplifier 133 of the multiple amplifiers 133b-133c (magnetic fields) is shown. The amplifier 133 illustratively includes a first resistor 141, a first capacitor 142 coupled in parallel to the first resistor, a second capacitor 143 coupled in parallel to the first resistor, and a third capacitor 144 coupled in parallel to the first resistor. The amplifier 133 also includes a fourth capacitor 145 coupled in series to the third capacitor 144, a second resistor 146 coupled downstream from the fourth capacitor, a third resistor 147 coupled to the second resistor, and a fourth resistor 150 coupled between the second resistor and the third resistor.

[0036] The amplifier 133 illustratively includes an amplifier circuit 154 having an inverting input, a non-inverting input coupled to a fourth resistor 150, and an output. The amplifier 133 includes a fifth resistor 151 and a fifth capacitor 152 coupled between the inverting input of the amplifier circuit 154 and a reference voltage (e.g., ground potential). The amplifier 133 includes a sixth resistor 153 coupled between the output and the inverting input of the amplifier circuit 154. The sixth resistor 153 and the fifth resistor 151 cooperate to adjust the gain level of the amplifier circuit 154. Gain in decibels=10LOG(1+R 153 / R 151 ), where R 153 is the resistor in ohms of the feedback providing the sixth resistor 153, and R 151 is a resistor in ohms to ground providing a sixth resistor 153. In the prototype, gain values ​​of 10-20 dB suffice. The amplifier 133 most importantly performs an impedance matching function, when the energy received from the antenna is moderate so that the energy required for amplification is rather low.

[0037] The amplifier 133 illustratively includes a sixth capacitor 155 and a seventh capacitor 156 coupled in series to the output of the amplifier circuit 154. The amplifier 133 includes an output transformer / balun 157 coupled to the seventh capacitor 156, and an eighth capacitor 160 coupled to the output transformer / balun 157.

[0038] The amplifier 133a, which functions as an electric field antenna, may be implemented as a differential amplifier having two active amplifier elements. As can be seen, a differential amplifier rejects common mode signals and noise such as those riding on ground.

[0039] With additional reference now to FIG. 8, a diagram 900 illustrates a measured voltage standing wave ratio (VSWR) versus frequency response of an antenna 116 having two illustrated antenna tuning arrangements 122a-122b (i.e., a dual-tuned magnetic field antenna circuit). The antenna 116 can also be operated in a parallel resonant mode. Advantageously, the antenna 116 provides a wideband Chebyshev frequency response with a passband ripple peak 902. The bandwidth of the antenna 116 can be traded for the level of passband ripple 902 in FIG. 8, for example, in this case providing a 3 dB gain bandwidth of 80 percent. In the diagram 900 of FIG. 8, the 6 to 1 VSWR frequency corresponds to a 3 dB down frequency in the antenna gain response, as shown by the dashed line 904. Other passband shapes can be provided by the antenna 116, for example, a Butterworth passband shape by adjusting the winding position and coupling. By way of background, in a typical approach, an antenna may provide a second order frequency response with a single VSWR dip and a single gain peak.

[0040] Each separately resonant tuning winding 123a-123b adds another frequency band, providing a single receive band of extended bandwidth with controlled amplitude ripple. As illustrated, the frequency response includes two dips in the passband, as opposed to a typical approach that has one dip and a narrower bandwidth.

[0041] The three different receiving channels provided by the antenna 116, namely, electric field antenna, Hx magnetic field antenna, and Hy magnetic field antenna, have several advantages. The two magnetic field antenna types are decoupled from each other, their orientations are orthogonal, and they create separate sinusoidal and cosine-like radiation patterns in azimuth. The amplitude and phase information from each radiation pattern indicates the angle of arrival of the eLORAN signal, which may be useful to detect and remove re-radiation effects from any nearby structures. Also, by knowing the direction of arrival, the eLORAN signal path correction signal may be processed to modify the required propagation delay in azimuth. The amplitude and phase difference between the electric field antenna and the magnetic field antenna may, for example, synthesize one cosθ pattern and one sinθ pattern, thus eliminating ambiguity in the angle of arrival. On an aircraft platform, the magnetic field antenna may be operational when the electric field type antenna is inoperable due to precipitation straits, aircraft charging, and proximity to thunderstorms. Thus, the antenna 116, which is composed of several antennas, provides numerous system advantages.

[0042] Yet another aspect relates to a method of coupling an antenna 116 to an eLORAN receiver circuit 117. The method includes coupling a magnetic field signal winding 121a-121b to a ferromagnetic core 120 and coupling an antenna tuning device 122a-122b to the ferromagnetic core. The antenna tuning device 122a-122b includes at least one tuning winding 123a-123b surrounding the ferromagnetic core 120 and a tuning circuit 124a-124b coupled to the at least one tuning winding.

[0043] 9, a balun 200 that may be associated with the antenna 116 is described below. The balun 200 may prevent the transfer of conducted common mode electromagnetic interference currents to the antenna 116 circuitry. Such interference currents may be on the RF cabling between the antenna 116 and the associated eLORAN receiver, for example, due to the vehicle alternator, digital electronics, or switching power supplies that share a ground with the eLORAN receiver. The balun 200 may function as the output transformer / balun 157 of FIG. 7.

[0044] The balun 200 illustratively includes a magnetic core 210, such as ferrite or powdered iron. In the illustrated example, the magnetic core 210 is toroidal and effectively provides a magnetic circuit for coupling the primary winding 220 to the secondary winding 230. The primary winding 220 provides terminals 222, 224 and a center tap terminal 226. The secondary winding 230 provides terminals 232, 234 and a center tap terminal 236. The balun 200 illustratively includes an I-shaped metal shield 240, such as an I-shaped sheet metal plate, between the primary winding 220 and the secondary winding 230. A ground connection 242 provides a conductive contact between the metal shield 240 and a local ground, such as a PWB ground layer in an antenna preamplifier. The metallic shield 240 reduces capacitive coupling between the primary winding 220 and the secondary winding 230, which in turn reduces the coupling of common mode noise currents that might otherwise be transmitted between the windings of the balun 200.

[0045] Other features related to the communication system are disclosed in the following co-pending applications: Docket No. 16 / 013,106, entitled "ELORAN RECEIVER WITH FERROMAGNETIC BODY AND RELATED ANTENNAS AND METHODS," Attorney Docket No. GCSD-2971(62529); Docket No. 15 / 980,857, entitled "TOWER BASED ANTENNA INCLUDING MULTIPLE SETS OF ELONGATE ANTENNA ELEMENTS AND RELATED METHODS," Attorney Docket No. GCSD-2979(62519); and Docket No. 16 / 419,568, entitled "ELORAN RECEIVER AND ANTENNA WITH FERROMAGNETIC BODY AND WINDINGS AND RELATED METHODS," Attorney Docket No. GCSD-3017(62539), each of which is incorporated herein by reference in its entirety.

[0046] Numerous modifications and other embodiments of the present disclosure may come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings, and it is understood that the disclosure should not be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.

Claims

1. 1. An enhanced long range navigation (eLORAN) receiver, comprising: an antenna and an eLORAN receiver circuit coupled to the antenna, an antenna and an eLORAN receiver circuit coupled to the antenna, the antenna comprising a ferromagnetic core and a magnetic field signal winding coupled to the ferromagnetic core; 1. An antenna tuning device, comprising: at least one tuning winding surrounding the ferromagnetic core; and a tuning circuit coupled to the at least one tuning winding; an antenna tuning device comprising: An eLORAN receiver comprising:

2. 10. The eLORAN receiver of claim 1, wherein the at least one tuning winding comprises a plurality of tuning windings.

3. 2. The eLORAN receiver of claim 1, wherein the tuning circuit comprises a resistor and a capacitor coupled in series with the resistor.

4. The ferromagnetic core includes a first ferromagnetic core and a second ferromagnetic core that cross each other on a surface, 2. The eLORAN receiver of claim 1, wherein the antenna comprises a pair of electrostatic patch elements on opposite sides of the ferromagnetic core, the opposite sides being in a transverse direction to the surface.

5. 10. The eLORAN receiver of claim 1, wherein the ferromagnetic core comprises a ferromagnetic middle portion and a plurality of ferromagnetic arms extending outwardly from the ferromagnetic middle portion.

6. The eLORAN receiver of claim 5 , wherein the plurality of ferromagnetic arms are arranged in aligned pairs.

7. The eLORAN receiver of claim 5 , wherein the plurality of ferromagnetic arms define a cross.

8. 2. The eLORAN receiver of claim 1, wherein the antenna comprises a correction winding surrounding the ferromagnetic core and configured to receive a calibration signal from the eLORAN receiver circuitry.

9. 10. The eLORAN receiver of claim 1, wherein the ferromagnetic core comprises at least one of ferrite, powdered iron, electric steel, and nanocrystalline iron.

10. 1. An antenna coupled to an enhanced Long Range Navigation (eLORAN) receiver circuit, comprising: A ferromagnetic core; a magnetic field signal winding coupled to the ferromagnetic core; 1. An antenna tuning device, comprising: at least one tuning winding surrounding the ferromagnetic core; and a tuning circuit coupled to the at least one tuning winding; an antenna tuning device comprising: An antenna comprising:

11. The antenna of claim 10 , wherein the at least one tuning winding comprises a plurality of tuning windings.

12. 11. The antenna of claim 10, wherein the tuning circuit comprises a resistor and a capacitor coupled in series with the resistor.

13. The ferromagnetic core includes a first ferromagnetic core and a second ferromagnetic core that cross each other on a surface, 11. The antenna of claim 10, further comprising a pair of electrostatic patch elements on opposite sides of said ferromagnetic core, said opposite sides being in a transverse direction to said surface.

14. The antenna of claim 10 , wherein the ferromagnetic core comprises a ferromagnetic intermediate portion and a plurality of ferromagnetic arms extending outwardly from the ferromagnetic intermediate portion.

15. The antenna of claim 14 , wherein the plurality of ferromagnetic arms are arranged in aligned pairs.

16. The antenna of claim 14 , wherein the plurality of ferromagnetic arms define a cross.

17. 11. The antenna of claim 10, further comprising a correction winding surrounding the ferromagnetic core and configured to receive a calibration signal from the eLORAN receiver circuitry.

18. 1. A method of making an antenna coupled to an enhanced Long Range Navigation (eLORAN) receiver circuit, comprising: coupling a magnetic field signal winding to a ferromagnetic core; and coupling an antenna tuning device to the ferromagnetic core; The antenna tuning device comprises: at least one tuning winding surrounding the ferromagnetic core; and a tuning circuit coupled to the at least one tuning winding; A method comprising:

19. The method of claim 18 , wherein the at least one tuning winding comprises a plurality of tuning windings.

20. 20. The method of claim 18, wherein the tuning circuit comprises a resistor and a capacitor coupled in series with the resistor.

21. The ferromagnetic core includes a first ferromagnetic core and a second ferromagnetic core that cross each other on a surface, The method of claim 18 , further comprising disposing a pair of electrostatic patch elements on opposite sides of the ferromagnetic core, the opposite sides being in a transverse direction to the surface.

22. The method of claim 18 , wherein the ferromagnetic core comprises a ferromagnetic intermediate portion and a plurality of ferromagnetic arms extending outwardly from the ferromagnetic intermediate portion.

23. The method of claim 22 , wherein the plurality of ferromagnetic arms are arranged in aligned pairs.

24. The method of claim 22 , wherein the plurality of ferromagnetic arms defines a cross.

25. 20. The method of claim 18, further comprising coupling a correction winding, the correction winding surrounding the ferromagnetic core and configured to receive a calibration signal from the eLORAN receiver circuitry.

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