DESC:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to radio frequency (RF) circuits, and more specifically, relates to passive RF power-dividing and power combining circuits for an array antenna.

BACKGROUND
[0002] RF feed networks, either divide power applied to a single input among N outputs and conversely, combine power applied to N inputs to a single output. It can be realized with active components or entirely passive RF feed networks. As per requirements of gain, beam width, side lob level of the antennas, different standard distributions such as TAYLOR, COSECANT SQURE and the like are need to be given to antenna array elements. Theses distributions are implemented in RF feed networks.
[0003] For array environment prime requirements for feed networks are high power carrying capability, low voltage standing wave ratio (VSWR) at input and output ports, high isolation between output ports, low insertion loss and compact in size. There are, in general, four feed techniques for the array antenna.
• Series Fed
Path length to different elements is different introducing a frequency dependent phase shift with the result that the beam direction will change with frequency
• Corporate
More complicated but equal path lengths to all elements, eliminates beam steering with frequency
• Butler Matrix
NxN inputs and output are combined and recombined to introduce phase shifts which provide
multiple simultaneous orthogonal beams
Iridium uses this technique
• Blass Matrix
NxM inputs and output are combined and recombined to introduce path length differences
which provide multiple simultaneous beams
[0004] Most popular technique for feeding array antenna is corporate feed technique and the same can be achieved through number of design techniques, for example Inline, Wilkinson, Rat race and the like. In Inline technique VSWR and isolation between ports are compromised and affects the gain and side lobes of the antenna. Wilkinson approach provides good results when division/distribution ration between ports is low and equal, however, for high division ration it is not preferable. For the requirements, where high division ration is to be achieve with low insertion loss, low VSWR, high RF power carrying capability and high isolation, corporate feed is used with rate race technique, however, this results in bulky size.
[0005] Therefore, there is a need in the art to provide a compact RF feed network that enables high RF power handling capacity, low insertion loss, low VSWR, high isolation with a high division ration.

OBJECTS OF THE PRESENT DISCLOSURE
[0006] An object of the present disclosure relates, in general, to radio frequency (RF) circuits, and more specifically, relates to passive RF power-dividing and power combining circuits for an array antenna.
[0007] Another object of the present disclosure provides integrated RF feed network for generating sum, control and delta patterns.
[0008] Another object of the present disclosure provides unequal power divider of modular design.
[0009] Another object of the present disclosure provides high isolation among the ports.
[0010] Another object of the present disclosure provides high power handling as there is no add-on component on RF printed circuit board (PCB).
[0011] Another object of the present disclosure provides low insertion loss, low VSWR, high isolation with high division ration.
[0012] Another object of the present disclosure provides a power divider that is compact in size as per array requirement, and entire feed network is designed for easy maintenance of antenna.
[0013] Another object of the present disclosure provides extendable feed network for odd element array.
[0014] Another object of the present disclosure provides ruggedized power dividers.
[0015] Yet another object of the present disclosure provides PCBs layout that is designed in such a way that same mechanical housing can be used for all the power dividers.

SUMMARY
[0016] The present disclosure relates, in general, to radio frequency (RF) circuits, and more specifically, relates to passive RF power-dividing and power combining circuits for an array antenna. The present disclosure relates to a 27-element passive phased array antenna for Identification, friend or foe (IFF) systems. The feed network has been realized through a cascaded approach to achieve electrical, mechanical and maintenance requirement. The main objective of the present disclosure seeks to overcome various limitations of the prior art by providing a compact RF feed network that enables high RF power handling capacity, low insertion loss, low VSWR, high isolation with a high division ration.
[0017] In an aspect, the present disclosure provides an apparatus for linear array IFF antenna, the apparatus includes a plurality of power dividers integrated on a substrate, each of the plurality of power dividers comprising an input port that accepts an input signal from a source; and one or more output ports that divide the received input signal into one or more output signals of unequal power, each of the one or more output ports are separated by termination ports, wherein the plurality of power dividers are arranged in a cascaded fashion to feed adjacent power dividers of the plurality of power dividers, and wherein each of the plurality of power dividers feed an array of antenna elements.
[0018] In an embodiment, the plurality of power dividers can be a 1: 5 way unequal power divider.
[0019] In another embodiment, a 1:13 way feed network is realized through three 1:5 way unequal power dividers.
[0020] In another embodiment, the mounting arrangement is same for the plurality of power dividers.
[0021] In another embodiment, the three 1:5 way unequal power dividers are arranged in cascaded fashion, where the three 1:5 way unequal power dividers are first power divider, second power divider and third power divider configured on left side and right side respectively.
[0022] In another embodiment, the one or more output ports of the first power divider feeds first antenna elements of the array of antenna elements, at least one output port of the one or more output ports coupled to the input port of the second power divider to feed the second power divider.
[0023] In another embodiment, the one or more output ports of the second power divider feeds second antenna elements of the array of antenna elements, the one or more output ports of the second power divider coupled to the input port of the third power divider to feed the third power divider.
[0024] In another embodiment, each of the 1:5 way unequal power dividers is realized through cascading of four numbers of unequal 2 way power dividers.
[0025] In another embodiment, the array of antenna elements is 27-element passive phased array antenna, wherein the array is symmetric from center such that the first power divider, the second power divider and the third power divider of the 1:5 way unequal power dividers are assembled in mirror configuration.
[0026] In another embodiment, the Rat Race configuration is integrated in the 1:5 way unequal power dividers.
[0027] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0029] FIG. 1 illustrates a schematic view of the corporate feed network.
[0030] FIG. 2A illustrates an exemplary view of power divider, in accordance with an embodiment of the present disclosure.
[0031] FIG. 2B illustrates an exemplary view of the cascaded 1:5 way unequal power dividers, in accordance with an embodiment of the present disclosure.
[0032] FIG. 2C illustrates an exemplary view of unequal 2 way power divider, in accordance with an embodiment of the present disclosure.
[0033] FIG. 2D illustrates an exemplary view of RF-feed network for 27 element array antenna, in accordance with an embodiment of the present disclosure.
[0034] FIGs. 3A-3B illustrate exemplary view of mounting arrangement of power dividers inside antenna housing, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0035] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0036] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0037] FIG. 1 illustrates a schematic view of the corporate feed network.
[0038] Referring to FIG. 1, the most popular technique for feeding array antenna is corporate feed technique 100 as illustrated in FIG. 1 and the same can be achieved through a number of design techniques, for example, Inline, Wilkinson, Rat race and the like. For the requirements, where high division ration is to be achieved with low insertion loss, low VSWR, high RF power carrying capability and high isolation, corporate feed is used with rat race technique, that can include one input port 102 and one or more output ports (104-1 to 104-n), however, this results in bulky size as shown in FIG. 1.
[0039] The present disclosure relates, in general, to radio frequency (RF) circuits, and more specifically, relates to passive RF power-dividing and power combining circuits for an array antenna. The present disclosure relates to a 27-element passive phased array antenna for Identification, friend or foe (IFF) systems. The feed network has been realized through a cascaded approach to achieve electrical, mechanical and maintenance requirement. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0040] FIG. 2A illustrates an exemplary view of power divider, in accordance with an embodiment of the present disclosure.
[0041] Referring to FIG. 2A, RF non-binary feed network 200 (also referred to as an apparatus 200, herein) can include M-way radio frequency (RF) unequal power divider 202 that can divide an input signal into one or more output signals of unequal power. The power is distributed to the radiating elements also interchangeably referred to as an array of antenna elements through the M-way power divider 202 and is useful for microwave device for phased-array antennas. The feed network 200 is a RF power-dividing and/or power combining circuits and has been realized through a cascaded approach to achieve electrical, mechanical and maintenance requirement. The present disclosure relates to a compact RF feed network 200 using modular cascaded unequal power dividers 202 for linear array Identification, friend or foe (IFF) antenna.
[0042] In an exemplary embodiment, the M-way unequal power divider 202 as presented in the example may be 1:5 way unequal power dividers. As can be appreciated, the present disclosure may not be limited to the above provided configuration and may be applied to other configurations. The M-way power dividers 202 also interchangeably referred to as one or more power dividers 202 that are arranged in the cascaded fashion to feed adjacent power dividers of the M-way power dividers, where each of the M-way power dividers feed the array of antenna elements.
[0043] The M-way power divider 202 is designed in micro strip line technology. Rat Race configuration with compact topology is used at each division due to its advantages of low loss distribution and better return loss at all its ports. The basic theory of Rat Race is used taking its length equal to 1.5?. There are number of Rat Race couplers connected in the cascade fashion to restrict its dimension in the y-direction. Lay outing freeze in such a way that width of micro strip line is required to be changed as per the required distribution for IFF band.
[0044] The 1:5 way power divider 202 as illustrated in FIG. 2A can be integrated on a substrate of printed circuit board (PCB), the 1:5 way power divider can include an RF input port 204 and one or more RF output ports (206-1 to 206-5 (which are collectively referred to as RF output ports 206, hereinafter)). In an exemplary embodiment, the one or more RF output ports 206 can be five RF output ports. The RF input port 204 configured to accept one RF input signal and the five RF output ports configured to divide the received input signal into one or more output signals of unequal power. The one or more output ports 206 are separated from each other by termination ports (208-1 to 208-4 (which are collectively referred to as termination ports 208, hereinafter). For example, in the three 1:5 way power divider shown in FIG. 2D and described in detail below, each of the 1:5 way power divider can include input port J0, output ports J1, J2, J3, J4, J5 and terminated ports L1, L2, L3, L4. RF power can be distributed by cascading the 1:5 way unequal power dividers, where the power is distributed to the array of antenna elements through the 1:5 way power divider.
[0045] FIG. 2B illustrates an exemplary view of the cascaded 1:5 way unequal power dividers, in accordance with an embodiment of the present disclosure.
[0046] The present disclosure may utilize cascaded variants of the embodiments illustrated herein. The three 1:5 way power dividers (202-1 to 202-3) are arranged in the cascaded fashion. In an exemplary embodiment, a 1:13 way feed network can be realised through utilising the modular design of three 1:5 way unequal power dividers (202-1 to 202-3), where the three 1:5 way unequal power dividers are first power divider 202-1, the second power divider 202-2 and the third power divider 202-3 configured on left side and right side respectively. The three numbers of 1:5 way power dividers are designed to achieve required distribution across 13 elements at each side from center element. RF power can be distributed by cascading the 1:5 way unequal power dividers, where the power is distributed to the array of antenna elements through the 1:5 way unequal power dividers (202-1 to 202-3).
[0047] In an embodiment, Rat Race configuration is integrated in the 1:5 way unequal power dividers (202-1 to 202-3), where the Rat-Race configuration is manufactured using microstrips. Each port placed at a specific distance away from the other. The cut size and location of the RF connectors is the same for all three types of RF PCBs and hence same mechanical housing can be used for all three 1:5 way unequal power dividers (202-1 to 202-3). The PCB layout can be designed in such a way that the same mechanical housing can be used for all three power dividers (202-1 to 202-3) i.e., power divider-1, power divider-2 and power divider-3.
[0048] In an exemplary embodiment, the one or more output ports i.e., four output ports (J1 to J4) shown in FIG. 2D of the first power divider 202-1 feeds first antenna elements of the array of antenna elements on the left side and right side, and at least one output port J5 of the first power divider 202-1 coupled to the input port J0 of the second power divider 202-2 to feed the second power divider 202-2. Similarly, the one or more output ports i.e., four output ports (J1 to J4) of the second power divider 202-2 feeds second antenna elements of the array of antenna elements on the left side and right side, and at least one output port J5 of the second power divider 202-2 coupled to the input port J0 of the third power divider 202-3 to feed the third power divider 202-3, where the five output ports (J1 to J5) of the third power divider 202-3 feed third antenna elements of the array of antenna elements on the left side and right side.
[0049] For example, power divider-1: In array configuration, two numbers are used to feed first four left elements (R10,R11,R12,R13) and four right elements(R15,R16,R17,R18) from center and to feed power divider-2.
[0050] Power divider-2: In array configuration, two numbers are used to feed next four left elements (R6,R7,R8,R9) and right elements (R19,R20,R21,R22) from center and to feed power divider-3.
[0051] Power divider-3: In array configuration, two numbers are used to fed first five left elements (R1,R2,R3,R4,R5) and last five elements (R23,R24,R25,R26,R27).
[0052] FIG. 2C illustrates an exemplary view of unequal 2-way power divider, in accordance with an embodiment of the present disclosure. As shown in FIG. 2C, each of the 1:5 way power dividers (202-1 to 202-3) can be also realized through cascading of four numbers of unequal 2-way power dividers. The 2 way power divider can divide the received input signal into one or more output signals of unequal power.
[0053] FIG. 2D illustrates an exemplary view of RF-feed network for 27-element array antenna, in accordance with an embodiment of the present disclosure. The RF-feed network for 27 element array antenna for IFF system as illustrated in FIG. 2D. The array is symmetric from center so the other side of all the three power dividers (202-1 to 202-3) is assembled in mirror configuration as shown in FIG. 2D.
[0054] For example, in the 1:5 way power dividers (202-1 to 202-3), each of the 1:5 way power divider (202-1 to 202-3) can include input port J0, output ports J1, J2, J3, J4, J5. The cascaded arrangement of the 1:5 way power divider can include first power divider 202-1, second power divider 202-2 and third power divider 202-3. The input port J0 of the first power divider 202-1 receives the input signal that may be divided into five routes respectively corresponding to five output ports, the output ports J1, J2, J3, J4 feed first antenna elements of the array of antenna elements and the output port J5 can be coupled to the input port J0 of the second power divider 202-2 to feed the second power divider 202-2. The output ports J1, J2, J3, J4 of the second power divider 202-2 can feed second antenna elements of the array of antenna elements and the output port J5 of the second power divider 202-2 can be coupled to the input port J0 of the third power divider 202-3 to feed the third power divider 202-3. The output ports J1, J2, J3, J4, J5 of the third power divider 202-3 can feed third antenna elements of the array of antenna elements.
[0055] The embodiments of the present disclosure described above provide several advantages. The one or more of the embodiments provides integrated RF feed network for generating sum, control and delta patterns. The present disclosure achieves unequal power divider of modular design, high isolation among the ports, high power handling as there is no add-on component on RF PCB, low insertion loss, low VSWR, high isolation with high division ration. The present disclosure provides power divider that is compact in size as per array requirement, and entire feed network is designed for easy maintenance of antenna. The PCBs layout is designed in such a way that same mechanical housing can be used for all the power dividers. The power dividers are ruggedized and further provides extendable feed network for odd element array.
[0056] FIGs. 3A-3B illustrate exemplary view of mounting arrangement of power dividers inside antenna housing, in accordance with an embodiment of the present disclosure. As shown in FIG. 3A, the mounting arrangement 300 of power dividers 202 can be designed in such a way that the same housing 302 can be used for all the 1:5 way power divider. As illustrated in FIG. 3B, the power dividers 202 for the right side of the array are mounted facing the housing side while the left side of the array are mounted from the cover side of the housing.
[0057] The measured result of the power divider 202 can be illustrated in Table-1 and Table-2 shown below, where Table-1 lists return loss and isolation measurements for input port (J0) and output ports (J1-J5) for all the three power dividers and Table-2 lists insertion loss measurements at output port (J1-J5) at 1030MHz and 1090MHz for all the three power dividers.

Parameter PD-1 PD-2 PD-3
RL(dB) at J0 -16 to -27 -20 to -26 -20 to -36
RL(dB) at J1 to J5 -16 to -28 -18 to -43 -22 to -31
Isolation(dB) -21 to 55 -21 to -46 -22 to -41
Table-1: Measured range of return loss at the I/P and O/P ports and isolation between O/P ports for all three power dividers
Power Divider 1
Ports J1 J2 J3 J4 J5
Freq./Specs -8.2±0.3dB -8.4±0.4dB -8.8±0.4dB -9.3±0.5dB 3.8±0.3dB
1030MHz -8.34 -8.5 -8.87 -9.45 -3.88
1090MHz -8.35 -8.77 -9.09 -8.91 -4.13
Power Divider 2
Freq./Specs -6.2±0.3 -7.1±0.4 -8.1±0.4 -9.4±0.5 -6±0.5
1030MHz -6.38 -7.1 -8.21 -9.56 -6.07
1090MHz -6.39 -7.31 -8.38 -9.71 -6.27
Power Divider 3
Freq./Specs -4.7±0.3 -6.2±0.4 -7.8±0.4 -9.1±0.5 -9.9±0.5
1030MHz -4.8 -6.33 -7.84 -9.19 -9.99
1090MHz -4.81 -6.49 -7.99 -9.32 -10.23
Table-2: Measured insertion loss at O/P ports for all three power dividers
[0058] However, these are just exemplary values, and that the actual values can be a wide range, and the values included here are just for illustrative purposes other values and integer multiples are possible as well.
[0059] It will be apparent to those skilled in the art that the apparatus 200 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0060] The present disclosure provides integrated RF feed network for generating sum, control and delta patterns.
[0061] The present disclosure provides unequal power divider of modular design.
[0062] The present disclosure provides high isolation among the ports.
[0063] The present disclosure provides high power handling as there is no add-on component on RF printed circuit board (PCB).
[0064] The present disclosure provides low insertion loss, low VSWR, high isolation with high division ration.
[0065] The present disclosure provides a power divider that is compact in size as per array requirement, and entire feed network is designed for easy maintenance of antenna.
[0066] The present disclosure provides extendable feed network for odd element array.
[0067] The present disclosure provides PCBs layout that is designed in such a way that same mechanical housing can be used for all the power dividers.
[0068] The present disclosure provides ruggedized power dividers.
,CLAIMS:1. An apparatus (200) for linear array identification, friend or foe (IFF) antenna, the apparatus comprising:
a plurality of power dividers (202) integrated on a substrate, each of the plurality of power dividers comprising:
an input port (204) that accepts an input signal from a source; and
one or more output ports (206) that divide the received input signal into one or more output signals of unequal power, each of the one or more output ports are separated by termination ports (208),
wherein the plurality of power dividers is arranged in a cascaded fashion to feed adjacent power dividers of the plurality of power dividers, and wherein each of the plurality of power dividers feed an array of antenna elements.
2. The apparatus as claimed in claim 1, wherein the plurality of power dividers (202) is a 1: 5 way unequal power divider.
3. The apparatus as claimed in claim 2, wherein a 1:13 way feed network is realized through three 1:5 way unequal power dividers.
4. The apparatus as claimed in claim 1, wherein mounting arrangement (302) is same for the plurality of power dividers.
5. The apparatus as claimed in claim 3, wherein the three 1:5 way unequal power dividers are arranged in cascaded fashion, where the three 1:5 way unequal power dividers are first power divider (202-1), second power divider (202-2) and third power divider (202-3) configured on left side and right side respectively.
6. The apparatus as claimed in claim 5, wherein the one or more output ports of the first power divider (202-1) feeds first antenna elements of the array of antenna elements, and at least one output port of the one or more output ports coupled to the input port of the second power divider (202-2) to feed the second power divider.
7. The apparatus as claimed in claim 6, wherein the one or more output ports of the second power divider (202-2) feeds second antenna elements of the array of antenna elements, at least one output port of the one or more output ports coupled to the input port of the third power divider (202-3) to feed the third power divider.
8. The apparatus as claimed in claim 2, wherein each of the 1:5 way unequal power dividers is realized through cascading of four numbers of unequal 2 way power dividers.
9. The apparatus as claimed in claim 1, wherein the array of antenna elements is 27-element passive phased array antenna, wherein the array is symmetric from center such that the first power divider, the second power divider and the third power divider of the 1:5 way unequal power dividers are assembled in mirror configuration.
10. The apparatus as claimed in claim 1, wherein Rat Race configuration is integrated in the 1:5 way unequal power dividers.