FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules  2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“COMPACT MICRO STRIP DIRECTIONAL COUPLER WITH HIGH DIRECTIVITY FOR BROADBAND APPLICATIONS”

APPLICANTS:

Name : HCL Technologies Limited

Nationality : Indian

Address : HCL Technologies Ltd.  50-53 Greams Road 
Chennai – 600006  Tamil Nadu  India

The following Specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:
FIELD OF INVENTION
[001] This invention relates to wideband directional coupler and more particularly to a compact directional coupler with high directivity and capable of operating on ultra-high bandwidth.

BACKGROUND OF INVENTION
[002] Directional couplers are passive radio frequency components used in radio frequency and microwave signal routing for isolating  separating or combining signals. With advances in telecommunications and wireless technologies  directional couplers are required to support wide bandwidth  have high directivity  better coupling and provide better isolation. – Microstrip based directional couplers have proven to be compact with ease to integrate and hence popular.
[003] However  inmost directional couplers  there is a trade-off between bandwidth  directivity and compactness. This trade off works satisfactorily in case of narrow band or for extremely high frequencies and provides high directivity along with compactness.

OBJECT OF INVENTION
[004] The principal object of this invention is to provide a compact microstrip directional coupler providing high directivity over a wide bandwidth.
[005] Another object of the invention is to ensure that the microstrip directional coupler is suited for broadband systems supporting the frequency range of 400MHz to 6000MHz.
[006] Another object of the invention is compact enough to be incorporated as a monolithic microwave integrated circuit (MMIC).

STATEMENT OF INVENTION
[007] Accordingly the invention provides a compact microstrip directional coupler providing high directivity and capable of operating over an ultra-high bandwidth comprising of a first stage and second stage coupler. The first stage coupler operates over a frequency range of 0.4GHz to 1 GHz and the second stage. The second stage coupler operates over a frequency range of 1 to 6GHz. A radio frequency switch is used to select between the first stage and second coupler based on the input frequency.
[008] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood  however  that the following descriptions  while indicating preferred embodiments and numerous specific details thereof  are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof  and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES
[009] This invention is illustrated in the accompanying drawings  throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings  in which:
[0010] FIG. 1 illustrates a block diagram of the microstrip directional coupler  according to the embodiments as disclosed herein;
[0011] FIG. 2 shows the first stage directional coupler  according to embodiments disclosed herein;
[0012] FIG. 3 shows the second stage directional coupler  according to embodiments disclosed herein;
[0013] FIG. 4 shows the s- parameters of first stage coupler operating over 1 to 6GHz simulated over 0.4 to 6 GHz  according to embodiments disclosed herein;
[0014] FIG. 5 shows the s- parameters of second stage coupler operating over .4 to 1 GHz simulated over 0.4 to 6 GHz  according to embodiments disclosed herein; and
[0015] FIG. 6 shows the simulated s- parameters of integrated coupler (first stage+ second stage) operating over 0.4 to 6 GHz  according to embodiments disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0016] The embodiments herein  the various features  and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly  the examples should not be construed as limiting the scope of the embodiments herein.
[0017] Referring now to the drawings  and more particularly to FIGS. 1 through 6  where similar reference characters denote corresponding features consistently throughout the figures  there are shown preferred embodiments.
[0018] FIG. 1 illustrates a block diagram of an integrated microstrip directional coupler  according to the embodiments as disclosed herein. The integrated directional coupler comprises of multiple stages of directional couplers. The first stage directional coupler 101 operates over a frequency range of 0.4 to 1 GHz and the second stage directional coupler operates over a frequency range of 1 to 6 GHz. The coupled port of the integrated directional coupler connects to an RF switch 103. The figure shows an example application of a power detector 104 connected to an as per the system. Appropriate 50 Ohms termination to the isolation ports is also shown in the figure. As per the system need say for power detection  if the coupled signal from 0.4 GHz to 1 GHz is required the coupled signal from the first stage of the coupler can be routed to the Power detector 104 using the RF Switch 103. Similarly  if the signal from 1GHz to 6GHz is required  the couple signal from the second stage of the coupler will be routed to the power detector 104 using the RF switch 103. Thus  the coupler could satisfactorily work for the broadband of 0.4GHz to 6 GHz. The RF switch can be controlled using an external control. The directional coupler supports ultra high bandwidth of 5600 MHz (from 400 MHz till 6 GHz) in compact structure and also provide high directivity of >15dB. The directional coupler is compact enough and is suitable to be incorporated as a Monolithic Microwave Integrated Circuit (MMIC). The compactness in size is achieved using unique approach of combining the two stages. The realizable physical size is approximately 27mm * 51mm *1.6mm.
[0019] FIG. 2 shows the first stage directional coupler  according to embodiments disclosed herein. The first stage directional coupler 101 comprises of a single section -20dB coupled line coupler and is designed with meandered structure over the frequency range of 0.4 to 1GHZ. This frequency range has been found to be a suitable option for achieving the design target. The dimensions of the microstrip-coupled lines are W1  L1 and S1. The values of W1  L1 and S1 are chosen based on results required. The upper arm receives the wideband input and acts as a through arm  while the lower produces the coupled output.
[0020] FIG. 3 shows the second stage directional coupler  according to embodiments disclosed herein. For the second stage coupler 102 operating over 1 to 6GHZ  a three section -20dB maximally flat couplers design based on quadrupled inductive compensated micro strip coupled lines is used for directivity improvement. The required optimum Inductor for the inner and outer coupled-Line section are LIn and Lout. The dimensions of the microstrip coupled lines for the first and the third sections are found to be W3  S3 and L3. The dimension of the mictrostrip couple lines for the second section is W2  S2 and L2.
[0021] As two separate stages supporting 400MHz to 1000MHz and 1000 MHz to 6000 MHz are combined  the required coupled port can be chosen using switch. A high directivity of 15dB is achieved using the integrated approach for ultrawide bandwidth of 5600 MHz. The compact  ultra high-bandwidth and high directivity microstrip directional coupler is majorly applicable in broadband transceivers / broadband transmitters / broadband receivers. In these systems  the invention can be used as the major component in signal / power detection circuitry.
[0022] FIG. 4 shows the s- parameters of first stage coupler operating over 0.4 to 1GHz simulated over 0.4 to 6 GHz  according to embodiments disclosed herein.
[0023] FIG. 5 shows the s- parameters of second stage coupler operating over 1 to 6GHz simulated over 0.4 to 6 GHz  according to embodiments disclosed herein.
[0024] FIG. 6 shows the simulated s- parameters of integrated coupler (first stage+ second stage) operating over 0.4 to 6 GHz  according to embodiments disclosed herein.
[0025] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can  by applying current knowledge  readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept  and  therefore  such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore  while the embodiments herein have been described in terms of preferred embodiments  those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

STATEMENT OF CLAIMS
We Claim:
1. A compact microstrip directional coupler providing high directivity and capable of operating over an ultra-high bandwidth comprising of:
a first stage coupler operating at 0.4 to 1GHz;
a second stage coupler operating at 1 to 6 GHz; and
a radio frequency switch to select between said first stage and said second stage.
2. The compact microstrip directional coupler of claim 1  wherein said first stage and second stage couplers coupler are connected through a through arm.
3. The compact microstrip directional coupler of claim 1  wherein said radio frequency switch selects between the first stage coupler and second stage coupler based on the frequency of the input signal.

Dated: 19th Day of June 2012 Signature:

Dr Kalyan Chakravarthy
(Patent Agent)

ABSTRACT
A Micro-strip directional coupler with high directivity for broadband application. The directional coupler supports ultra high bandwidth of 5600MHz (from 400 MHz to 6GHz) in compact structure and also provides high directivity of (>15dB). The coupler uses a two stage micro-strip directional coupler for a frequency range of 400MHz to 6GHz  where the first stage supports a frequency of operation from 0.4 to 1 GHZ and the second stage supports a frequency of operation from 1GHz to 6GHz and the required coupled port can be chosen using a radio frequency switch as required by the application used in.
FIG. 2