Combined mechanical package shield antenna

The present invention relates to antennas for radio signal frequencies, an electromagnetic shield and a mechanical package for electronic components. The antenna uses a three-dimensional conductive structure to enclose the components that are used for the transmission and reception of wireless devices. This conductive structure preferably encloses electronic components. The structure can be divided into two or more sections such that each section is enclosed providing shielding from external electromagnetic fields. Each conductive section is connected to the antenna port or ports of the device it contains. The conductive mechanical package is preferably sized to resonant at the desired frequency of operation. If the electromagnetic fields to be radiated are within and outside the package, the internal bulkheads can be used to control the desired resonant modes. Photonic band gap structures can be also used to connect the pole elements.

BACKGROUND

The present invention relates to antennas for radio signal frequencies, an electromagnetic shield, and a mechanical package for electronic components.

One of the fast growing segments of the computer industry today is wireless networks. Wireless networks avoid the cost of the wiring infrastructure, and permit computing mobility. Some of the more common wireless networks are based on the 802.11 standard, Bluetooth, cellular networks, i-mode, and WAP. Cell phones are in use nearly everywhere. Some standards such as 802.11, also known as wireless Ethernet or Wi-Fi, are also ubiquitous and can be found in many companies, offices, airports, and even coffee shops. With Wi-Fi you only need to be in range of a peer or a base station which connects the wireless network to a wired one. Thus, a person can carry Wi-Fi enabled personal digital assistant (PDA) or a notebook computer about without giving up his or her network connection. Bluetooth is another known wireless standard designed for interconnection of computing devices such as computer peripherals.

No matter what wireless standard is used, there is a fundamental need to increase antenna performance. Wireless devices emphasize compactness, however, which impacts performance. For example, if an embedded antenna is placed on a printed circuit board in close proximity to the ground plane or adjacent metal objects, the antenna performance will be degraded. The ground plane will reduce the antenna's radiation resistance, which lowers the antenna efficiency and adversely affects the antenna gain pattern. In addition, a completely shielded mechanical package will prevent the antenna from propagating the radio through the shield. Yet, the transceiver must be shielded from stray electromagnetic fields. The shield for the transceiver will also function as a ground plane in close proximity with the antenna. Again, this degrades the antenna performance. Further, the antenna performance generally increases with the length of the radiating elements of the antenna, but this means the printed circuit board will need to increase in size, which conflicts with the small size requirements of mobile devices.

FIG. 1Aillustrates how an embedded antenna14might be configured for a cell phone to try to address these problems. As shown, the printed circuit board20supports a set of electronic components such as the electronic component22. A mechanical package10encloses the printed circuit board20.FIG. 1Acuts away a portion of the mechanical package10to show the inside of the cell phone. The antenna14is adjacent to an area (indicated by dotted lines12) where the ground plane is removed in the printed circuit board20. This removal avoids a ground plane in close proximity to the antenna14, which would interfere with the antenna pattern. The mechanical package10must be also non-conductive to avoid shielding the antenna14. Because the mechanical package10is non-conductive, a radiation shield18must enclose the RF transceiver chips16,17, which are sensitive to stray electromagnetic radiation.FIG. 1Aalso cuts away the radiation shield18to show the RF transceiver chips16,17. The antenna14must not be too close to electronic components on the printed circuit board20or to the radiation shield18to avoid affects on the antenna pattern. As a result of these constraints, the manufacturer will need to increase the size of the printed circuit board20and the mechanical package10.

FIG. 1Billustrates how a protruding antenna15might be configured for a cell phone in another attempt to address these problems. The printed circuit board20again supports electronic components such as the electronic component22. A mechanical package24encloses the printed circuit board20, but is cut-away inFIG. 1Bto show the inner arrangement. The antenna15is placed outside the mechanical package24so there is no longer the need to remove the ground plane of the printed circuit board20as indicated by the absence of dotted lines. The mechanical package24also can be conductive because it will no longer shield the antenna15. Further, if the mechanical package24is non-conductive, a radiation shield18must enclose the RF transceiver chips16,17, which are sensitive to stray electromagnetic fields.FIG. 1Acuts away part of the radiation shield18to reveal the RF transceiver chips16,17. However, these advantages are dampened because the protruding antenna15must now be small enough to avoid user discomfort, and more rugged since it is outside the protection of the mechanical package24. This raises the cost of the antenna15and limits suitable size and shapes of the antenna.

It would be desirable if an antenna could propagate electromagnetic radiation at frequencies of interest, shield against any stray electromagnetic radiation, save printed circuit space, reduce ground plane interference, and provide a rugged low cost mechanical package for the wireless device itself.

SUMMARY OF THE INVENTION

This invention uses a three-dimensional conductive structure to enclose the components that are used for the transmission and reception of wireless devices. This conductive structure preferably forms a mechanical package with the electronic components inside it. In one embodiment, the structure is divided into two or more sections by conductive bulkheads such that each section is completely enclosed providing shielding from external electromagnetic fields. Each conductive section is connected to the antenna port or ports of the device it contains. The conductive mechanical package is preferably sized to resonant at the desired frequency of operation The electromagnetic fields to be radiated can exist on the inside and outside, or just on the surface of the package. If the electromagnetic fields to be radiated are within and outside the package, internal bulkheads can be used to control the desired resonant modes. In another feature, photonic band gap ground plane printed circuit boards can be used to connect separated sections of the conductive structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description includes the best mode of carrying out the invention. The detailed description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the claims. Each part, even if structurally identical to other parts, is assigned its own part number to help distinguish where the part appears in the drawings.

FIG. 2shows an embodiment of an antenna25functioning as a mechanical package and an electromagnetic shield for the associated electronics. As shownFIG. 2, the antenna25is no longer mounted on a printed circuit board30or printed circuit board38as shown in FIG.1A. This expands available space on the printed circuit boards30,38for added circuitry and electronic components such as the electronic components28,34. The antenna25also no longer protrudes beyond the mechanical package, because the package is the antenna25. This reduces manufacturing costs by eliminating the cost of a separate conventional antenna and permits using conductive materials for the mechanical package shown here as combination of the pole element26, the pole element36, and the pole interconnect32without degrading the performance of antenna25by acting as a ground plane in close proximity. Because the antenna25is also the mechanical package, the invention permits an increase in the size of the radiating pole elements26,36, without extending the structure of the antenna25beyond the shape of the mechanical package. This has advantages for wireless applications such as cell phones. The antenna25also fully encloses the printed circuit boards30and38, which permits the antenna25to act as an electromagnetic shield against stray electromagnetic radiation which can cause interference.

It can be understood by review of the specification that the antennas25can be made from a variety of materials including metals such as copper, aluminum, steel, or brass. In addition, the antenna25might be made from a metallized plastic, a conductive plastic, a conductive ceramic, a conductive composite, or any other suitable conductive materials useful for antennas, packaging and electromagnetic shielding of electronic components.

If the antenna25is made of a metal, the sides of the pole elements26,36, can be sealed by metal fasteners, brazing, welding, soldering, etc. The material and techniques used will be guided by manufacturing requirements. For example, the thickness of the walls of the antenna25will be a function of the material, the characteristics of the antenna, the amount of electromagnetic shielding required, and the cost of the material. If the antenna material is a relative good conductor, for example, such as copper, the walls can be relatively thin. Conversely, if the material is a relatively poor conductor, such as steel, the walls will be necessarily thicker to achieve an adequate electromagnetic shield.

FIG. 2depicts the pole elements26and36as hollow cubes, but they could be other closed surface figures. For example, the pole elements26and36might be a rectangular prism, a square pyramid, a cylinder, a right circular cone or a sphere, etc. However, whatever shape is selected, it is preferred that the pole elements26and36of the antenna25enclose the printed circuit boards30and38to shield against stray electromagnetic radiation reaching the electronic components. Further, as shown inFIG. 2, the length of the antenna25is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna25.

FIG. 3Ais an elevation view of the antenna illustrated inFIG. 2showing an embodiment for wiring the components between the printed circuit boards. As shown, the interconnect32mechanically joins the pole element26to the pole element36. A solder joint50attaches one end of the interconnect32to the pole element36, while an insulator46spaces and holds the other end of the interconnect32in the hole in the pole element26. As an alternative, seeFIG. 2where the end of interconnect32is substantially flush with the pole element26. The pole element26encloses the printed circuit board30, while the pole element36encloses a printed circuit board38. The interconnect32also protects and shields a set of wires represented by a data line40and a power line42. One end of the data line40electrically connects, e.g., by soldering it, to a pad63on the printed circuit board30. The other end of the data line40electrically connects to a pad55on the printed circuit board38. One end of the power line42electrically connects to a pad62on the printed circuit board30. The other end of the power line42electrically connects to a pad57on the printed circuit board38. The antenna25includes a low-side pole wire65, which is soldered to the interconnect32and to a low-side pad61. The antenna also includes a high-side pole wire60, which is soldered to the pole element26and to the high-side pad59. Upon review of the specification, it would be understood that different wiring configurations are possible. For example, there can be a different number of wires running inside the interconnect32, and the polarities could be reversed, and/or different techniques can be used to connect the wiring.

FIG. 3Bis an end view showing the insulator46spacing the interconnect32from touching the pole element26of the antenna shown in FIG.3A.

FIG. 4Ais an embodiment of an antenna with a photonic band gap structure66. The photonic band gap structure66rejects unwanted frequencies by acting as an electromagnetic shield as will be explained. The antenna is made as described in connection withFIGS. 2 and 3A, but removes the opposite adjacent sides of the pole elements there to form the pole elements70and72. The pole elements70and72and the photonic band gap66enclose a single printed circuit board71, which in turn supports electronic components such as the electronic components67and69. In an alternative embodiment, the photonic band gap66can be replaced with an insulator, and the pole elements closed, that is, have six sides not five, and the interconnect32reintroduced as shown in FIGS.2and3A-3B. As discussed earlier, the length of the antenna is again preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna.

FIG. 4Benlarges part (dotted lines74) of the photonic band gap structure shown in FIG.4A. The photonic band gap66includes a periodic lattice structure of photonic band gap cells76and photonic band gap cell interconnects78. To the unwanted frequencies, the photonic band gap66conducts so that the pole element70, the pole element72, and the photonic band gap66together act as an electromagnetic shield. To the frequencies of electromagnetic wave that are to be transmitted and received by the antenna, the photonic band gap66functions as an insulator so that the antenna has functionally speaking no conducting structure between the pole elements70and72.

Sievenpiper et al., “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band” (IEEE Trans. on Microwave Theory and Techniques, Vol. 47, No. 11, Nov. 1999) describe suitable photonic band gap structures that could be used, which article is incorporated herein by reference. This embodiment is particularly useful when a given application requires that the circuitry reside on a single printed circuit board71rather than on a set of physically separate printed circuit boards30and38as shown in FIG.2.

FIG. 5is an embodiment of a dumbbell shaped antenna with hollow radiating cylindrical pole elements connected by an interconnect structure, which encloses a printed circuit board. The first pole element83includes a top face82, a side wall80, and a bottom face96. The second pole element89includes a top face88, a side wall90, and a bottom face92. The interconnect94mechanically joins the pole element83to the pole element89. The interconnect94also encloses a printed circuit board84, which supports electronic components such as an electronic component86. The antenna ofFIG. 5is constructed similar to the antenna described inFIG. 2, but places the printed circuit board84in the interconnect94, which eliminates the need for the interconnect wiring shown in FIG.3A. Instead, the wiring preferably resides on or in the printed circuit board84. At the same time, this antenna still needs connection to the high-side and low-side transceiver outputs as discussed in connection with FIG.3A. The materials, the geometric shapes of the pole elements, and the manufacturing techniques would be as described in the specification accompanying FIG.2. Further, as shown inFIG. 5, the length of the antenna is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna.

FIG. 6illustrates an embodiment of a dumbbell shaped antenna with thin radiating disks connected by an interconnect structure, which encloses a printed circuit board. The antenna ofFIG. 6is constructed similar to the antenna described inFIG. 5, but employs thin radiating disks for the pole elements, which can reduce the horizontal footprint of the antenna in certain applications. The antenna includes a radiating disk shaped pole element100and a radiating disk shaped pole element106. The interconnect structure104connects radiating disk shaped pole elements100,106, and encloses printed circuit board102supporting components such as electronic component108. Again, the length of the antenna is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna.

FIG. 7illustrates the antenna return loss expected from an embodiment of the antenna as shown in FIG.4A. The dimensions of the antenna should be about 5 cm by 5 cm by 8 mm. In this antenna embodiment, an insulator replaces the photonic bandgap structure66shown in FIG.4B. Antenna return loss is the ratio of the signal power provided to the antenna to the signal power reflected by the antenna. The best possible return loss ratio is 1:1 which means no signal power is reflected by the antenna. The data shown should be obtainable using a Hewlett Packard 8753D Network Analyzer. The antenna should be at least three feet away from all objects that could affect the return loss, when the measurements are taken. The return loss curve as shown inFIG. 7is that expected of a typical resonant antenna, in this case the lowest return loss should be in the order of −41 dB (the return loss ratio in decibels expected as indicated by the HP 8753D analyzer).