US20100033393A1 - Techniques for Mounting a Millimeter Wave Antenna and a Radio Frequency Integrated Circuit Onto a PCB - Google Patents

Abstract

A printed circuit board (PCB) assembled to include at least one millimeter wave antenna and a radio frequency integrated circuit (RF IC). The PCB comprises a square-shaped cavity in the PCB, wherein one of the edges of the cavity is substantially parallel to connecting pins of the at least one millimeter wave antenna; a RF IC placed in the cavity, wherein one side of the RF IC including RF pads is substantially at the edge of the cavity that is substantially parallel to the connecting pins; and traces connecting the RF pads and the connecting pins, wherein the connection between the at least one millimeter wave antenna and the RF IC shortens the length of the traces.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims the benefit of U.S. provisional application No. 61/086,924 filed on Aug. 7, 2008, the contents of which are herein incorporated by reference.
TECHNICAL FIELD
• The present invention relates generally to radio frequency integrated circuits, and particularly to connecting radio frequency integrated circuits to millimeter wave antennas.
BACKGROUND OF THE INVENTION
• The 60 Giga Hertz (GHz) band is an unlicensed band which features a large amount of bandwidth allowing a very high volume of information to be transmitted wirelessly. As a result, multiple applications, that require transmission of a large amount of data, can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, a wireless high definition TV (HDTV), a wireless docking station, a wireless Gigabit Ethernet, and many others.
• In order to facilitate such applications there is a need to develop integrated circuits (ICs), such as amplifiers, mixers, and radio frequency (RF) analog circuits that operate in the 60 GHz frequency band. Such circuits should be fabricated as a chip that can be assembled on a printed circuit board (PCB). In addition, there is a need to develop low-cost and high-performance millimeter wave antennas to enable the integration of 60 GHz communication applications in consumer electronics products.
• One of the requirements of millimeter wave antennas is minimal energy loss, to achieve maximum power antenna gain. Most of the energy is lost due to the connection between an antenna and an integrated circuit (IC), or chip, processing the RF signals to be transmitted or received. With the aim to minimize energy loss, prior art approaches suggest mounting millimeter wave antennas directly on the surface of a PCB using, for example, a surface mount technology (SMT). A SMT is a method for constructing electronic circuits in which the components are mounted directly onto the surface of a PCB.
• One type of millimeter wave antenna suitable for the 60 GHz band is the on-chip dipole antenna. An exemplary diagram of on-chip dipole antenna100 is shown inFIG. 1. Theantenna100 includes two printeddipole strips110 and anelectrical transmission line120 that acts as an unbalanced-to-balanced transformer between a feedcoaxial line130 and the two printeddipole strips110. The length of the dipole strips is approximately a ¼ wavelength. Theelectrical line120 and thedipole strips110 are printed on the same plane. In addition, theantenna100 does not provide spectrum coverage of 360 degrees.
• The on-chip dipole antenna100 is not feasible for commercial uses due to its inefficiency. For example, experiments show that the simulated antenna radiation efficiency is approximately 16 percent. In addition, the maximum transmit power of the antenna at 60 GHz is approximately −20 dBi. This is due to the substrate and connection losses.
• Another technique for mounting an antenna onto a PCB is known as the low temperature co-fired ceramic (LTCC) process. The LTCC is a complex process that allows on-chip connection to an antenna. Particularly, a unit produced using this process is a compact multilayer three-dimensional design allowing other components to be combined within a miniature surface-mount package, and eliminating the need for many external components. However, the LTCC process is very costly, and therefore is not feasible for commercial uses.
• It would be therefore advantageous to provide an efficient and low-cost solution for connecting millimeter wave antennas and ICs onto PCBs.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the invention are particularly pointed out and distinctly claimed at the conclusion of the specification in the claims. The foregoing and other objects, features and advantages of exemplary embodiments of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.
• FIG. 1 is a diagram of an on-chip dipole antenna.
• FIG. 2 is a three-dimensional diagram illustrating the assembly of a millimeter antenna on a PCB in accordance with an embodiment of the present invention.
• FIG. 3 is a flowchart describing a method for mounting a RF IC and a millimeter wave antenna onto a PCB in accordance with an embodiment of the invention.
• FIGS. 4A and 4B are graphs showing radiation patterns of quasi-omni printed antennas.
• FIG. 5 is a cross-section diagram illustrating the structure of a quasi-omni printed antenna constructed in accordance with an embodiment of the invention.
• FIG. 6 is a schematic diagram of a PCB constructed to include a pair of quasi-omni printed antennas connected to a RF IC.
SUMMARY OF THE INVENTION
• Certain embodiments of the invention include a printed circuit board (PCB) assembled to include at least one millimeter wave antenna and a radio frequency integrated circuit (RF IC). The PCB comprises a square-shaped cavity in the PCB, wherein one of the edges of the cavity is substantially parallel to connecting pins of the at least one millimeter wave antenna; a RF IC placed in the cavity, wherein one side of the RF IC including RF pads is substantially at the edge of the cavity that is substantially parallel to the connecting pins; and traces connecting the RF pads and the connecting pins, wherein the connection between the at least one millimeter wave antenna and the RF IC shortens the length of the traces.
• Certain embodiments of the invention also include method for mounting a millimeter wave antenna and a radio frequency integrated circuit (RF IC) onto a printed circuit board (PCB). The method comprises forming a square-shaped cavity in the PCB wherein one of edges of the cavity is substantially parallel to connecting pins of the millimeter wave antenna, wherein the millimeter wave antenna is printed on a first substrate layer of the PCB; placing the RF IC in the cavity by positioning one side of the RF IC including RF pads substantially at the edge of the cavity that is substantially parallel to the connecting pins; and bonding the RF pads and the connecting pins.
• Certain embodiments of the invention further include a quasi-omni printed dipole antenna. The antenna comprises two dipole strips printed on a first substrate layer of a printed circuit board (PCB); a transmission line printed on the first substrate layer and between the two dipole strips; and a cavity directly under the two dipole strips, wherein a perimeter of the cavity is substantially the same as the perimeter of the two dipole strips and a depth of the cavity is a number of substrate layers of the PCB under the first substrate layer.
DETAILED DESCRIPTION OF THE INVENTION
• The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.
• Certain embodiments of the invention include a method for mounting a millimeter wave antenna and a RF IC onto a PCB. Certain embodiments of the method reduce the energy lost on the connection between these two circuits. Other embodiments of the invention include a quasi-omnidirectional (omni) millimeter wave antenna, and a method of manufacture. Certain embodiments of the invention enable a mass production of low-cost and high performance RF devices that can be utilized in millimeter wave bands including, but not limited to, 60 GHz and 77 GHz.
• FIG. 2 shows a three-dimensional diagram illustrating the assembly of aRF IC210 and amillimeter wave antenna220 on aPCB230. The RF IC210 may be either a receiver or transmitter and theantenna220 may be either a receive-antenna or a transmit-antenna. In certain implementation, atypical PCB230 may include at least two RF ICs acting as a receiver and transmitter as well as receive and transmit antennas. Without departing from the scope of the invention, a connection of a single RF IC210 to asingle antenna220 will be described herein.
• In accordance with certain principles of the invention the length of the traces240 (or wires) connecting the RF IC210 to theantenna220 is minimized, thereby minimizing the energy lost on this connection. With this aim, the RF IC210 is placed in a cavity trimmed down in thePCB230. The depth of the cavity is substantially the same as the height of theRF IC210, thus the upper surface of theRF IC210 is at the same level as the surface of thePCB230. Specifically, as thePCB230 is multilayer, the depth of the cavity is one or more substrate layers being cut out thePCB230. In addition, in order to ensure the possibleshortest traces240, the RF IC210 is placed in the cavity in such way that the IC's210 side havingRF pads250 is located at an edge of the cavity. In accordance with an embodiment of the invention the RF IC210 is in a form of a die (i.e., unpackaged IC).
• FIG. 3 shows anon-limiting flowchart300 describing the method for mounting a millimeter wave antenna and a RF IC onto a PCB implemented in accordance with an embodiment of the invention. The method allows shortening the lengths of wires connecting the RF IC to a millimeter wave antenna. Certain specific embodiments of this method minimize the energy loss and increase the antenna gain. At S310, a square-shaped cavity is cut into the substrate layers of the PCB in a way that one of the edges of the cavity is substantially parallel to the connecting pins (e.g., pins240) leading to the antenna. The depth of the cavity is substantially the same as the height of RF IC and its perimeter is approximately the same as of the RF IC. At S320 the RF IC is placed in the cavity in a way that the side including the RF pads (e.g., pads250) is located at the edge of the cavity. At S330, the RF pads on the RF IC and the pins leading to the antenna are bonded, thereby forming a connection between the RF IC and antenna.
• Another embodiment of the invention includes a quasi-omni printed antenna that provides180 degrees beamwidth (on the A-z plane). An exemplary radiation pattern on the A-z plane of the disclosed quasi-omni printed antenna is shown inFIG. 4A. Simulations show that the antenna gain of the quasi-omni printed antenna is5dBi. The quasi-omni printed antenna is constructed by printing a dipole pointing to a certain direction on a first substrate layer of the PCB and forming a cavity under the printed dipole.
• FIG. 5 shows a cross-section diagram of a quasi-omni printedantenna500 constructed in accordance with an embodiment of the invention. Twodipole strips501 and anelectrical transmission line502 of theantenna500 are printed on a first substrate layer of aPCB510. The length of the dipole strips501 is approximately a ¼ wavelength. Acavity520 is created by cutting out all substrate layers of thePCB510 under theantenna500. In the diagram shown inFIG. 5, thePCB510 includes 5 layers, 4 of which are cut out. The size of thecavity520 is substantially the same as the size of theantenna500. It should be noted that thecavity520 is not the cavity mentioned above with reference the embodiment of mounting a RF IC onto a PCB. Theantenna500 operates in millimeter wave bands including, but not limiting to, 60 GHz and 77 GHz.
• In accordance with another embodiment of the invention two quasi-omni printedantennas500 are used to achieve spectrum coverage of 360 degrees in transmission or reception of radio signals. As illustrated inFIG. 6, on a PCB600 aRF IC610 is mounted. TheRF IC610 is connected to two quasi-omni printed antennas500-A and500-B, pointing to different directions. TheRF IC610 is connected to the antennas500-A and500-B as described in detail above. TheRF IC610 includes a switch (not shown) adapted to switch between the antenna500-A or500-B according to desirable transmission/reception direction, thereby providing coverage of 360 degrees. An exemplary radiation pattern on the A-z plane achieved using two quasi-omni printed antennas is shown inFIG. 4B.
• While the present invention has been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in view of the prior art and, therefore, to effectively encompass the intended scope of the invention. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto. The word “substantially” is used based on the nature of the invention, in order to accommodate the minor variations that may be appropriate as understood by one of ordinary skill in the art to describe the invention with precision appropriate to the technology.

Claims (15)

1. A method for mounting a millimeter wave antenna and a radio frequency integrated circuit (RF IC) onto a printed circuit board (PCB), comprising:

forming a square-shaped cavity in the PCB wherein one of edges of the cavity is substantially parallel to connecting pins of the millimeter wave antenna, wherein the millimeter wave antenna is printed on a first substrate layer of the PCB;

placing the RF IC in the cavity by positioning one side of the RF IC including RF pads substantially at the edge of the cavity that is substantially parallel to the connecting pins; and

bonding the RF pads and the connecting pins.

2. The method ofclaim 1, wherein a depth of the cavity is substantially the same as a height of the RF IC.

3. The method ofclaim 1, wherein the RF pads include inputs and outputs of RF signals to the RF IC.

4. The method ofclaim 1, wherein the RF IC is in a form of a silicon die.

5. The method ofclaim 1, wherein the millimeter wave antenna operates in millimeter wave bands including at least one of: 60 GHz and 77 GHz.

6. The method ofclaim 1, wherein the millimeter wave antenna is at least a quasi-omni printed dipole antenna.

7. A printed circuit board (PCB) assembled to include at least one millimeter wave antenna and a radio frequency integrated circuit (RF IC), comprising:

a square-shaped cavity in the PCB, wherein one edge of the cavity is substantially parallel to connecting pins of the at least one millimeter wave antenna;

a RF IC placed in the cavity, wherein one side of the RF IC including RF pads is substantially at the edge of the cavity that is substantially parallel to the connecting pins, wherein the millimeter wave antenna is printed on a first substrate layer of the PCB; and

traces connecting the RF pads and the connecting pins, wherein the connection between the at least one millimeter wave antenna and the RF IC shortens the length of the traces.

8. The PCB ofclaim 7, wherein a depth of the cavity is substantially the same as a height of the RF IC.

9. The PCB ofclaim 7, wherein the RF pads include inputs and outputs of RF signals to the RF IC.

10. The PCB ofclaim 7, wherein the RF IC is in a form of a silicon die.

11. The PCB ofclaim 7, wherein the millimeter wave antenna operates in millimeter wave bands including at least one of: 60 GHz and 77 GHz.

12. The PCB ofclaim 7, wherein the millimeter wave antenna is at least a qusi-omni printed dipole antenna.

13. The PCB ofclaim 12, wherein the millimeter wave antenna comprises a pair of quasi-omni printed dipole antennas printed in opposite directions with reference to the RF IC, wherein the pair of quasi-omni printed dipole antennas together provide spectrum coverage of 360 degrees.

14. A quasi-omni printed dipole antenna comprising:

two dipole strips printed on a first substrate layer of a printed circuit board (PCB);

a transmission line printed on the first substrate layer and between the two dipole strips; and

a cavity directly under the two dipole strips, wherein a perimeter of the cavity is substantially the same as the perimeter of the two dipole strips and a depth of the cavity is a number of substrate layers of the PCB under the first substrate layer.

15. The antenna ofclaim 14, wherein spectrum coverage of the quasi-omni printed dipole antenna is 180 degrees.

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