The present invention relates generally to antennas, and more specifically to a vehicle antenna system having a parasitic element.
Many vehicle components include an antenna for transmitting and receiving wireless signals related to the vehicle, e.g., tire pressure, door locking/unlocking, etc. Since transmission and reception can involve battery powered remote devices, battery life can be important to design criteria, so both signal strength and battery power are considered when designing the antenna.
One embodiment of the present invention includes an antenna system for a vehicle having a housing defining an interior space with a center. A component is provided for at least one of transmitting and receiving signals indicative of a vehicle condition. A loop antenna is provided in the interior space and electrically connected to the component. A parasitic element is provided for increasing a signal strength of the antenna system. The parasitic element extends from a first end to a second end spaced from the first end by a gap.
In another example, an antenna system for a vehicle includes a housing defining an interior space. A transmitter includes an output for transmitting signals indicative of a vehicle condition and operating at a predetermined frequency. A loop antenna provided in the interior space is electrically connected to the transmitter output. An open loop parasitic element positioned outside the loop antenna increases a signal strength of the loop antenna.
Other objects and advantages and a fuller understanding of the invention will be had from the following detailed description and the accompanying drawings.
The present invention relates generally to antennas, and more specifically to a vehicle antenna system having a parasitic element.
Generally speaking, the remote component, e.g., key fob 90 or TCM sensor 36, can communicate wirelessly vehicle based systems 26 in order to carry out their specific functions. In
For example, where the remote component is a key fob 90, the vehicle based system 26 with which the fob communicates wirelessly can be a centralized RKE control module that communicates with a central vehicle control module, such as a body control module (BCM) over a communication bus, such as a CAN bus. Alternatively, the BCM itself could include wireless communication capabilities and therefore could communicate directly with the fob 90.
As another example, where the remote component is a TCM sensor 36, the sensor could communicate wirelessly and at close range with a tire specific receiver mounted, for example, in the area of the wheel well of that specific tire 24. This tire specific receiver could be wired to a TCM control module which communicates with a BCM via the vehicle CAN bus, or could be wired directly to the BCM. Alternatively, the TCM sensor 36 could communicate wirelessly with a TCM control module which communicates with a BCM via the vehicle CAN bus, or could communicate wirelessly with the BCM directly.
As shown in
For purposes of reference in this description of the antenna system 20, the interior space 34 is referred to as having a geometric center indicated generally at A. It is from this center A that characteristics of the antenna system 20, such as dimensions, spacing, and relative positioning of components, can be described. It should be understood that selecting the center A for this purpose is a matter of convenience, as the dimensions, spacing, and relative positioning of components of the antenna system 20 could be described from another reference point. The housing 30 is rectangular and can be formed from any non-conductive material, e.g., plastic or polymer, that does not adversely affect the transmission of radio waves or signals therethrough. The housing 30 could have any alternative shape depending, for example, on its intended purpose (e.g., TCM vs. RKE) and/or its location within the vehicle 22.
The antenna system 20 includes a loop antenna 40 positioned within the interior space 34 of the housing 30 and connected to a printed circuit board (PCB) 45. The antenna 40 can have alternative configurations. For example, the loop antenna 40 can be a small, standup antenna (not shown) positioned in the interior space 34. As another example, although the loop antenna 40 is illustrated as including a single loop, it could alternatively have a multiple loop configuration (not shown). In any case, the loop antenna 40 has a closed configuration in that it has no discernible ends. The loop antenna 40 is formed from suitable antenna material, such as an electrically conductive, e.g., metal, rod, wire, or tubing.
The loop antenna 40 is spaced a distance D1 from the center A at its closest point. A component 50 constituting a transmitter, receiver, or transceiver is secured to the loop antenna 40 for transmitting and/or receiving radio signals. In the example configuration of
A parasitic element 60 is connected to the housing 30 at a second distance D2 from the center A greater than the first distance D1. The parasitic element 60 is therefore located outside the loop antenna 40 relative to the center A of the interior space 34. The parasitic element 60 is a resonating structure and therefore can be secured to the housing 30 or component(s) mounted in the housing in any manner suited to permit the parasitic element to resonate under predetermined conditions. Examples of manners in which the parasitic element 60 can be secured to the housing 30 include securing the parasitic element 60 to the housing 30 via adhesive, fastener, or a mechanical component, such as a clip. As another alternative, the parasitic element 60 could be printed or plated directly on the housing.
Referring further to
The parasitic element 60 has a rectangular configuration that is similar in shape to the loop antenna 40, but has corresponding dimension(s) that are larger than those of the loop antenna. The length and width dimensions of the parasitic element 60 are indicated at a and b, respectively. The parasitic element 60 and the loop antenna 40 are arranged within the housing 30 in a generally concentric manner, although other configurations can be contemplated. For example, in alternative configurations, the loop antenna 40 and the parasitic element 60 could have similar square, round, elliptical, or other geometric shape with the parasitic element configured to be the larger element. The parasitic element 60 can be concentric with the loop antenna 40 or non-concentric with the loop antenna 40.
The parasitic element 60 is formed from an electrically conducive material, such as a metal or polymer material, and has a rectangular cross-section with a width w and thickness t. The width w and thickness t can vary. In one example configuration, the width w and thickness t can be about 1 mm to about 4 mm. The width w and thickness t can be the same, i.e., the parasitic element 60 can be square in cross-section. The width w and thickness t can be different, i.e., the parasitic element 60 can be rectangular in cross-section. Alternatively, the parasitic element 60 could have a different cross-sectional shape, such as a polygonal cross-section or a circular cross-section (not shown).
Regardless of its specific shape and cross-section, the parasitic element 60 is configured as a resonating structure that resonates at a frequency approximating the operating frequency of the transmitter 50. The parasitic element 60, having a loop size and area that is larger than that of the loop antenna 40, exhibits better radiation performance than the loop antenna. When the transmitter 50 is operated to excite the loop antenna 40 at the desired operating frequency to transmit a signal, the transmitted signal will act upon the parasitic element 60 and cause it to resonate at that same operating frequency. As a result, the resonating parasitic element 60 will boost the transmitting power of the loop antenna 40.
The signal boost afforded by the parasitic element 60 allows the antenna system 20 to meet range requirements for the vehicle systems in which it is implemented by improving the transmission efficiency of the antenna system. The additional transmitting power afforded by the inclusion of the parasitic element 60 also allows the antenna system 20 to be operated with reduced battery power. Furthermore, utilizing a parasitic element 60 instead of a larger loop antenna 40 reduces both the size and weight of the antenna system 20, which is advantageous due to spatial restrictions in the vehicle 22.
The parasitic element 60 can be modeled as an inductor “L” and the ends defining the air gap 66 can be modeled as a capacitor “C”. The capacitance of the air gap 66 can be governed by the following equation (1):
where C is the capacitance (in microfarads μF), ε is the absolute dielectric permittivity (˜1 for air), S is the surface area of the parasitic element cross-section (w×t in mm2), and d is the air gap length (in mm). When present, the capacitance C of the capacitor 70 is used instead.
The parasitic element 60 can be considered a single turn wire coil and its inductance L can therefore be governed by the following equation (2):
where μ0 is the permeability of free space or magnetic constant (1.2566370614 . . . ×10−6 H/m), N is the number of turns in the coil (i.e., 1 in the case of the parasitic element 60), A is the cross-sectional area of the parasitic element (w×t), and l is the length of the coil.
The frequency of the parasitic element can be governed by the following equation (3):
where f is the frequency (in Hz), C is the capacitance from equation (1) and L is the inductance (in henrys H) from equation (2).
It is clear from equation (2) that the configuration of the parasitic element 60 can be adjusted to produce a desired resonating frequency. In order to boost the signal of the transmitter 50 and loop antenna 40, the parasitic element 60 can be configured to resonate at a frequency that matches the operating frequency of the transmitter. More specifically, the gap length d, width w, thickness t, and/or lengths a, b of the parasitic element 60 can be tailored to provide the desired resonating frequency. It will be appreciated that where multiple gaps 66 are present, each gap can be modeled as a separate capacitor C1, C2, . . . Cn using the same modeled inductor L. When multiple gaps 66 exist, the total equivalent capacitance (C1/C2// . . . //Cn) is used as the capacitance C in equation (3) to evaluate the antenna system 20.
As noted previously, the antenna system 20 can be implemented in vehicle components such as TCM sensors 36 and RKE key fobs 90. In both cases, the inductance of the open parasitic element 60 can be controlled to provide a resonating frequency approximating the intended operating frequency of the loop antenna 40, thereby boosting the output power of the antenna system 20 due to the larger size of the parasitic element compared to the loop antenna. In this manner, the antenna system 20 can provide increased power while helping to conserve battery life.
The PCB 45 and loop antenna 40 are vertically oriented and positioned adjacent the right side wall 32 of the housing 30. In the configuration of
In the example configurations of
In operation, air within the tire 24 (see
In both cases, the buttons 92 are electrically connected to the transmitter 50. In operation, the user actuates one of the buttons 92, which transmit the respective operating signal to the PCB 45 and transmitter 50. The transmitter 50 excites the loop antenna 40, causing it to transmit a signal at a predetermined frequency. The transmitted signal acts on the parasitic element 60 causing it to resonate at the same frequency. The transmitter 50 signal, boosted by the parasitic element 60, transmits the operating signal to the vehicle based system 26, such as a RKE controller module.
By providing the loop antenna 40 with the larger parasitic element 60, the antenna systems 20 in the example configurations of
In this example (see
The dipole receiving antenna had an operating frequency of about 434 Hz. In
The parasitic transmitting path loss S21 was −39.5 dB. The loop antenna by itself had a transmitting path loss S31 of −48.7 dB. The parasitic ring/loop antenna combination therefore had a path loss 9.2 dB less than the loop antenna alone. In other words, with the same input power the parasitic ring can provide 9.2 dB more output power compared to the loop antenna alone.
What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. For example, while the example configurations of the antenna systems described herein are those of remote, battery powered devices where battery conservation can be desirable, it should be appreciated that the antenna systems described herein are not limited to remote, battery powered implementations. Indeed, the antenna systems described herein can be applied to any wireless signal transmitting application where a signal boost is desired. The loop antenna is a primary antenna used in this application. The coupling principle and its application can be applied to other antenna types to improve the power, miniaturize the module size and reduce the power consumption. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.