1. Technical Field
The present invention relates to frequency band splitting in general, and, in particular, to a method for performing passive frequency band splitting.
2. Description of Related Art
High-speed signaling systems typically employ multiple single carrier frequency channels to transfer data present within a frequency band from a transmitter (or driver) to a receiver on a printed circuit board. Those single carrier frequency channels are physical channels that are required to maintain wiring rules, such as spacing and density requirements, in order to be able to transmit signals with integrity within a high-speed signaling system.
Instead of using separate physical channels for each carrier frequency signal, a single guiding structure can be utilized to transfer multiple carrier frequency signals. This would require combining and splitting individual carrier frequency signals at the inset and outset of the wave-guiding structure. This approach can be achieved by using frequency division multiplexing methods. To separate signals at the receiving end a power divider and band pass filters arc utilized. Power divided signals are sent to band pass filters, each designed for a specific carrier frequency and associated with a certain receiver. Due to the power division, signals sent to band-pass filters have less amplitude. This approach makes the data signals at each individual receiver more prone to noise. To alleviate the lower signal amplitude characteristic, various amplifiers may be employed; however, this would result in increased costs and resource utilization.
Consequently it would be desirable to provide an improved method to perform frequency band splitting in high-speed signaling systems.
In accordance with a preferred embodiment of the present invention, a frequency band splitter includes a first, a second, and a third waveguides. A first narrow rectangular waveguide is utilized to connect the first waveguide to second waveguide. The first narrow rectangular waveguide has a first width to allow signals of a frequency band centered around a first frequency to be transmitted from the first waveguide to the second waveguide. A second narrow rectangular waveguide is utilized to connect the first waveguide to the third waveguide. The second narrow rectangular waveguide has a second width, which is different from the first width, to allow signals of a frequency band centered around a second frequency to be transmitted from the first waveguide to the third waveguide.
All features and advantages of the present invention will become apparent in the following detailed written description.
The invention itself, as well as a preferred mode of use, further objects, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
Referring now to the drawings and in particular to
Wave-guiding structure 10 can be represented as a transmission line equivalent circuit as shown in
Consider dominant mode (TE01) wave propagation in waveguides 11 and 12, propagation constant β1 can be described as
where k1 represents the wave number within waveguides 11, 12 and is described as k1=2π/λ1, where λ1 is the wavelength of the dielectric material filling waveguides 11, 12, which can he expressed as
when c is the speed of light in free space, f is frequency, and ε1, is the dielectric constant of the material filling waveguides 11, 12. Similarly, the propagation constant β2 can be described as
where k2 re-presents the wave number within the waveguide and is described as k2=2π/λ2, where λ2 is the wavelength of the dielectric material filling narrow rectangular waveguide 15, which can be expressed as
where c is the speed of light in free space, f is frequency, and ε2, the dielectric constant of the material filling narrow rectangular waveguide 15.
The characteristic impedances of waveguides 11, 12 and narrow rectangular waveguide 15 can he described as
Assuming h2<<h1, w2<w1, and ε1, =ε2r, it can be thought, at a first glance, that the impedance mismatch between waveguides 11. 12 and narrow rectangular waveguide 15 will lead to almost complete reflection at the interface, resulting in very minute transmission between waveguides 11 and 12. However, the reality is different and may be understood upon examining the global reflection coefficient R due to narrow rectangular waveguide 15.
The global reflection coefficient R can be described as
where e−j·2·β2·d2 represents the phase shift factor due to wave propagation twice the length of narrow rectangular waveguide 15 in which d2 represents the length of narrow rectangular waveguide 15 along the propagation direction, and Y is the interfacial reflection coefficient between waveguides 11,12 and narrow rectangular waveguide 15, which is a function of Z1, Z2 and jB.
The main idea behind super tunneling is that a wave can be transmitted (or tunneled) within a narrow frequency band between two transmission lines that are mismatched to a large extent. This may be reached when R=0 by making
1−ej−·2·β2·d2=0 (6)
Equation (6) can be achieved when β2 tends to 0. This property takes place at the dominant mode cut-off frequency within narrow rectangular waveguide 15, which is when
The super tunneling effect resulting from satisfying equation (7) is not dependent on the length of narrow rectangular waveguide 15 or its intermediary shape as long as the width and narrow height relative to the large waveguides are preserved. However, there might exist within a certain frequency hand higher frequency tunneling effects due to the Fabry Perot resonance. Unlike the super tunneling effect resulting from satisfying equation (7), such tunneling will depend on, inter alia, the length of narrow rectangular waveguide 15.
Based on the theoretical description in the previous section, a frequency band splitter can be built by connecting a large rectangular waveguide section characterized by a wide frequency band to similar large rectangular waveguide sections using narrow rectangular waveguides each having a different width w. In this case, each narrow rectangular waveguide passes only a narrow frequency band centered around the cutoff frequency f, which results in a β tending to 0. Due to reciprocity, this same frequency bund splitter can also be utilized as a frequency band combiner (coupler).
Referring now to
As has been described, the present invention provides an improved method for performing passive frequency band splitting in high-speed signaling systems.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.