High frequency communication device on multilayered substrate

A communication device (110, 210) has an antenna (150, 152, 250, 252) positioned on a multilayer substrate/printed circuit board (154, 254, 254′). A first high frequency material (116, 216) is disposed over a first side of the substrate (154, 254) characterized for low frequency devices. A conductive layer (118, 218) is patterned over the first high frequency material (116, 216), defining first and second circuit traces (122, 124, 222, 224) and first and second antenna traces (132, 134, 232, 234). The first and second antenna traces (132, 134, 232, 234) define a first slot (116, 216) in the first conductive layer (122, 222), which is aligned with a cutout (162, 262) defined by the substrate (154, 254). One of a transmitter (112, 212) and a receiver (114, 214) are disposed over the high frequency material (116, 216) and coupled to the edge emitting antenna (150, 250) by the first and second circuit traces (122, 124, 222, 224). The other of the transmitter (112) and receiver (114) may be positioned on the same or opposed side (aligned or staggered) of the substrate (254) in a similar manner. One or more layers (262), which may be patterned to provide resonant features, are formed between the substrate (254, 254′) for isolation.

RELATED APPLICATIONS

This application relates to U.S. application Ser. No. 11/675,152, A High Frequency Coplanar Strip Transmission Line on a Lossy Substrate, filed Feb. 15, 2007.

FIELD

The present invention generally relates to transmission and reception of high frequency signals and more particularly to a communication device having an antenna and/or antennas for transmission and/or reception of high frequency signals on a multilayered substrate typically used for lower frequency devices.

BACKGROUND

Circuits used in many electronic devices, for example, cellular phones and radios, produce, receive, or function with high frequency signals as well as low frequency signals. Integration of high and low frequency circuits typically involve the use of hybrid substrates, with low frequency devices formed on FR4, for example, and high frequency devices formed on RT/Duroid®, for example. Both the low and high frequency signals may be transmitted across a substrate or printed circuit board by metal traces; however, while low frequency signals may be transmitted along a single metal trace, the high frequency signal is typically transmitted by multiple metal traces which form a waveguide structure, such as a microstrip or coplanar trace. The coplanar trace is one in which two or more metal traces are formed on the same surface, thereby guiding an electromagnetic signal between them. These metal traces typically transmit the high frequency signal between circuits such as amplifiers, oscillators, and mixers positioned on a printed circuit board.

Coplanar circuit structures conventionally include coplanar waveguide structures and slotline structures. A coplanar waveguide structure has one or more spaced longitudinal coplanar strip signal conductors positioned between and separated from two longitudinal coplanar ground conductors by respective gap widths, wherein the ground conductors are typically much wider than the gaps. A slotline structure has two spaced longitudinal coplanar conductors having a gap therebetween, wherein the gap is typically much smaller than the lateral width of the conductors.

The metal traces of a coplanar strip transmission line conventionally are formed on a dielectric material, such as a printed circuit board. The high frequency signal exists as an electromagnetic field in the gap between the metal traces. The gap includes the dielectric material as well as air between and above the metal traces. The existence of the electric field in the dielectric material results in undesirable losses in signal strength. This is exacerbated by the electric field naturally concentrating in the higher dielectric constant material over the lower dielectric air.

This loss in signal strength may be reduced by forming the circuitry (both low and high frequency) on a high frequency substrate. For circuit board applications, the loss is reduced by using high frequency substrates such as RT/Duroid® from the Rogers Corp., instead of traditional circuit board material, such as FR4. However, substrates and printed circuit boards typically used for high frequency signals are much more costly than substrates typically used for low frequency signals.

Another known approach to reduce this loss in signal strength is to form a substrate suitable for high frequency devices, e.g., RT/Duroid®, on or over a substrate suitable for low frequency devices, e.g., an FR4 material. High frequency circuitry would be formed on the substrate suitable for high frequency devices and the low frequency circuitry would be formed on the substrate suitable for low frequency devices. However, this approach is still a complicated and costly process.

Furthermore, transmitting and receiving antennas formed on such high frequency substrate materials typically lack sufficient isolation and can be poorly matched if there are any discontinuities.

Accordingly, it is desirable to provide a low cost substrate supporting high frequency circuitry including isolated and matched antennas. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.

DETAILED DESCRIPTION

As used hereinafter, “substrate” shall refer to either a substrate and/or a printed circuit board; “low frequency substrate” shall refer to a substrate of a material having characteristics favorable for low frequency circuitry (loss characteristics of circuit devices favorable at low frequency), generally referred to as a “lossy” material (at a high frequency), e.g., epoxy resin or FR-4 (flame resistant 4) which is a composite of resin epoxy reinforced with a woven fiberglass mat; and “high frequency material” shall refer to a material having characteristics favorable for high frequency circuitry (loss characteristics of circuit devices favorable at high frequency), e.g., liquid crystal polymer (LCP) and a high frequency foam such as FoamCladR/F™ manufactured by Arlon.

High frequency devices, for example, transmitter and receiver modules, are fabricated using existing low cost methods for fabricating lower frequency applications on low cost, low frequency substrates. Standard circuit board manufacturing techniques with minimal post-processing steps enhance performance at a lower cost. Slots, which may also be called gaps, are defined between conductive, e.g., metal, traces carrying a high frequency signal in the range of 2 to 100 gigahertz (GHz). Edge emitting antennas, having slots in the metal antenna traces and cutouts in the substrate, are coupled to the high frequency devices. In one exemplary embodiment, the high frequency devices may be deposed on opposed sides of the substrate, thereby providing isolation, compactness, and lower unit cost. Generally, a thicker high frequency substrate is preferred, because of the detuning/losses from the adjacent FR4 (low frequency substrate), as well as, in some embodiments, providing an increase in distance between antennas resulting in an increased isolation.

The low cost, low frequency substrate, for example FR-4, provides mechanical support for the high frequency circuitry. A high frequency material, for example liquid crystal polymer (LCP), is easily attached to the substrate and contains the high frequency circuitry for easy integration with the low frequency circuitry on the substrate. Selective ground plane placement on or within the substrate allows for end-fire antennas, thereby allowing electromagnetic radiation to emit from the edge of the substrate rather than perpendicular to it. These antennas may be placed on one or both sides of the substrate to provide electromagnetic radiation in a single direction.

Referring toFIG. 1, a partial cross section and block diagram of an exemplary embodiment includes a communication device110having a transmitter112and a receiver114disposed on a layer116of material characterized for high frequency devices, for example, liquid crystal polymer (LCP). The transmitter112and receiver114, collectively referred to as a transceiver, typically include for example baseband circuits, a filter, a detector, a mixer, a local oscillator, an amplifier, and a low noise amplifier (none shown) as is known in the industry. A patterned conductive layer118includes circuit traces122,124,126,128and antenna traces132,134,136,138. The term “trace” is well known in the industry and is meant to be a conductive line. These circuit traces122,124,126,128and antenna traces132,134,136,138may be formed on a first surface (or side) of the layer116by selectively introducing or removing various materials. The patterns that define such traces may be created by lithographic processes. For example, a layer of photoresist material is applied onto a layer overlying the substrate. A photomask (containing clear and opaque areas) is used to selectively expose this photoresist material by a form of radiation, such as ultraviolet light, electrons, or x-rays. Either the photoresist material exposed to the radiation, or that not exposed to the radiation, is removed by the application of a developer. An etch may then be applied to the layer not protected by the remaining resist, and when the resist is removed, the layer overlying the substrate is patterned. Alternatively, an additive process could also be used, e.g., building a structure using the photoresist as a template. Yet another method of forming the circuit traces122,124,126,128and antenna traces132,134,136,138may be by ink jet printing. The traces are spatially positioned on the layer116wherein the width, or distance between adjacent circuit traces122,124,126,128, preferably is in the range of 25 to 500 microns.

Circuit traces122and124define a slot142therebetween, and circuit traces126and128define a slot144therebetween. Antenna traces132and134define a slot146therebetween as an antenna150, and antenna traces136and138define a slot148therebetween as an antenna152. Circuit trace122is connected to antenna trace132and circuit trace124is connected to antenna trace134so that slots142and146are aligned for transmission of an RF signal from the transmitter112to the edge of the device110. Likewise, circuit trace126is connected to antenna trace136and circuit trace128is connected to antenna trace138so that slots144and148are aligned for transmission of an RF signal to the receiver114from the antenna152at the edge of the device110. An exemplary embodiment may include only one of the transmitter112and receiver114and one of the antennas150and152respectively coupled thereto.

FIG. 2is a cross sectional view taken along line2-2ofFIG. 1. The layer116is positioned on a substrate154. The substrate154preferably comprises a printed circuit board made of FR4 (flame resistant 4) material, but may comprise any material, such as epoxy resin, that comprises a lossy material. FR4 material is a composite of resin epoxy reinforced with a woven fiberglass mat and is more economical, absorbs less moisture, has great strength and stiffness and is highly flame resistant. For these reasons, FR4 material is widely used for printed circuit boards for low frequency devices. FR4 material previously has been thought to have an upper frequency limit of around 10.0 GHz. A ground plane156is formed on a first portion158of the substrate154. A second portion160of the substrate154, minus the ground plane156, underlies the antennas150and152.

FIG. 3is a view of the substrate154including the cutouts162,164as taken along the line3-3ofFIG. 2. Cutouts162and164are formed in the substrate154in line with the slots146and148, respectively. The cutouts162and164may be created by mechanical drilling, laser burning, or any method of forming a slot in the substrate154known in the industry. Alternatively, the cutouts162,164may be formed prior to the patterned conductive layer118being formed. The cutouts162,164may vary in shape and dimension from the slots146,148.

FIG. 4further shows how low frequency circuitry166, including DC circuitry, may be disposed on a side of the substrate154opposed to the high frequency circuitry (transmitter112and receiver114), providing isolation therebetween. The low frequency circuitry166may be coupled to the high frequency circuitry172, for example by vias168formed within the substrate154. The high frequency circuitry172may be coupled to the patterned conductive layer118by, for example, a wire bond174.

FIG. 5is a cross section of another embodiment of a communication device510having a transmitter212and a receiver214positioned on opposed sides of a substrate254.FIGS. 6 and 7are top and bottom views, respectively, ofFIG. 5when the transmitter212and receiver214are aligned. The communication device210has the transmitter212disposed on a layer216of high frequency material, for example, liquid crystal polymer (LCP). A patterned conductive layer218includes circuit traces222,224and antenna traces232,234.

Circuit traces222and224define a slot242therebetween. Antenna traces232and234define a slot246therebetween as an antenna250. Circuit trace222is connected to antenna trace232and circuit trace224is connected to antenna trace234so that slots242and246are aligned for transmission of an RF signal from the transmitter212to the edge of the device210. A ground plane256is formed on a first portion258of the substrate254. A second portion260of the substrate254, minus the ground plane256, underlies the antennas250.

In a similar manner, a receiver214is disposed on a layer216′ of high frequency material, for example, liquid crystal polymer (LCP). A patterned conductive layer218′ includes circuit traces226,228and antenna traces236,238. Circuit traces226and228define a slot244therebetween. Antenna traces236and238define a slot248therebetween as an antenna252. Circuit trace226is connected to antenna trace236and circuit trace228is connected to antenna trace238so that slots244and248are aligned for transmission of an RF signal to the receiver214from the edge of the device210. A ground plane256′ is formed on a first portion258′ of the substrate254′. A second portion260′ of the substrate254′, minus the ground plane256′, underlies the antennas250′.

Additional isolation optionally may be provided by forming a layer262between the substrates254and254′. It should be noted that substrates254and254′ may comprise a unitary substrate, having the layer262formed within. The layer262may comprise a plurality of layers, optionally coupled by vias. Furthermore, the layer262may be patterned to provide resonant features to provide resonant features which may help to increase loss in layers254,254′, thereby increasing isolation between the antennas.

FIGS. 8 and 9are top and bottom views, respectively, ofFIG. 5when the transmitter212and receiver214are staggered. As in the previous exemplary embodiment, antenna traces232and234define a slot246therebetween as an antenna250and antenna traces236and238define a slot248therebetween as an antenna252. This exemplary embodiment shows the layer216removed from the cutouts in the substrate adjacent the slots246and248. For horizontal isolation, vertical vias (not shown) may be coupled between layer262and the ground planes256,256′, or may be coupled between layer262and the patterned conductive layers218,218′.