FILTER”

FIELD OF THE INVENTION

[0001] The present disclosure relates to devices and techniques to introduce tunable band pass filter (BPF) in radio frequency (RF) and microwave application such as for example, in military, civilian and space applications using substrate integrated waveguide (SIW) technology.

BACKGROUND OF THE INVENTION

[0002] The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.

[0003] Recent development of substrate integrated waveguide (SIW) technology has presented new opportunities for circuits and systems in the microwave and millimeter-wave frequency range. SIW is a promising technology that inherits almost all the characteristics of a rectangular waveguide and planar structure. SIW structures are based on a synthesized waveguide in a planar dielectric substrate with two rows of metallic vias, and exhibit a number of advantages, including easy fabrication, compact size, low loss, complete shielding, and easy integration with active devices and other planar circuits. Half-mode substrate integrated waveguide (HMSIW) as an improved structure of SIW, can reduce the width to only half of its equivalent SIW counterpart, but still retains identical cut off frequency and propagation characteristics. SIW filters are capable of achieving higher quality factor compared to classical planar filters in microstrip and coplanar-waveguide technology. [0004] Frequency-agile RF and microwave devices have gained much attention from growing demands for dynamic spectrum management in cognitive and software-define-radio designed platforms and phase-controlled systems for both military and civilian applications. Low loss tunable filters are essential components in multiband communication systems and wideband tracking receivers.

[0005] Different types of tunable filters have been implemented in the past using four typical tuning techniques viz. magnetic materials such as yttrium- iron-garnet (YIG), semiconductor varactor, ferroelectric (e.g., BST), and microelectromechanical systems (MEMS). These tuning techniques often exhibit limited degree of freedom such as limited tuning range and do not provide any optimal design regarding other key parameters over whole tuning range which are interlinked with each other in the design.

[0006] SIW filters are conceptually similar to rectangular waveguide filter, which are conventionally tuned using metallic screws into resonant cavity and coupling aperture. Similar mechanical tuning approach is difficult in SIW technology because of its compact physical structure, variations in the dielectric permittivity and thickness of the substrate which can introduce additional perturbation in the electromagnetic response. Different tunable SIW filters have been already reported in the past.

[0007] Discrete electrical tuning such as PIN diode based tunable SIW filter exhibits 25% tuning in center frequency over 1.8GHz. Discrete mechanical tuning is proposed by opening or short circuiting a capacitive circular slot, with a tuning range of 5%. MEMS devices based tunable SIW filter achieves a tuning range of 7% around 2GHz. SIW tunable BPF with only electric tuning using varactor diodes accomplishes 1.3% of total tuning range around center frequency of 12GHz, while for simultaneous electric and magnetic tuning (using ferrite material), it is extended to 7.9% with an unloaded factor of better than 130. Mechanically tunable SIW filters are designed using mechanical flaps and slots at certain locations of the filter, demonstrating excellent trimming, 10% tuning of the center frequency around 10GHz, and 100% tuning of the bandwidth, respectively.

[0008] On the other hand, Dielectric Resonators (DR) with high permittivity can confine electric field inside dielectric resonators which results in mass size reduction. Furthermore, DRs have some other advantages like high Q factor, superior temperature stability and low manufacturing cost. The dielectric resonators based BPFs often have good selectivity and low insertion loss. More recently, BPFs using SIW cavity loaded with dielectric resonators have been explored by many researchers which are mainly focused on miniaturization.

OBJECTIVE OF THE INVENTION

[0009] Dielectric materials of different dielectric permittivity in the form of cylindrical rods may be integrated with BPF to achieve tunability in its center frequency. SIW BPF loaded with dielectric rods shows good performance such as good tunability range, ultra-wide out-of-band rejection, low insertion loss and easy to integrate with other planar circuits.

SUMMARY OF THE INVENTION

[0010] The present disclosure overcomes one or more shortcomings of the prior art and provides additional advantages discussed throughout the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. [0011] The present disclosure provides for a low cost tunable SIW band pass filter that achieves good tunability range, low insertion loss and good out-of- band rejection within a compact size for radio frequency signal in X-band of the radio frequency spectrum. The tunable BPF utilizes dielectric rods of different dielectric materials placed in resonant cavities and coupling apertures of an iris window type third order Chebyshev BPF formed in SIW technology.

[0012] One aspect of the present disclosure provides for a BPF. The band pass filter circuits include an input port for receiving an incoming radio frequency signal, an output port for transmitting an outgoing radio frequency signal, an input taper transmission line section to transform input RF signal from microstrip line to substrate integrated waveguide, an output taper transmission line to transform input RF signal from substrate integrated waveguide section to microstrip line and an SIW/HMSIW filter section in between these two taper sections.

[0013] Basic SIW/HMSIW BPF structure consists of three resonant cavities which are cascaded through coupling apertures to form iris window type third order Chebyshev BPF. Dielectric rods may be placed in this filter section at different locations depending on tunability requirement.

[0014] In some examples, dielectric rods may be placed at centre of cavities only or apertures only or both and their permittivity may be varied simultaneously for all of them to achieve frequency tunability. In some other examples, dimension of rods may be varied to achieve some tunability. In yet further examples, their location may be varied.

[0015] In some of the above examples, for SIW BPF it may occupy an area of about 90mm by about 18mm. in some other examples, for HMSIW tunable BPF it may occupy an area of about 90mm by about 11mm.

[0016] Alternatively, this tuning technique may be implemented in cross coupled SIW filter as well in which, circuits include an input port (in inset feed position) for receiving an incoming radio frequency signal, an output port (in inset feed position) for transmitting an outgoing radio frequency signal and a main SIW section which has three resonant cavities which are connected through four apertures and two through sections. In this structure, tuning dielectric rods may be placed only at the center of resonant cavities and their dimension and permittivity may be varied simultaneously. In such an example, the BPF may require an area of about 31mm by about 35mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed embodiments. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

[0018] FIG. 1 is a plan view diagram illustrating the reference SIW band pass filter in accordance with the present disclosure. [0019] FIG. 2 is graphical representation of return loss and insertion loss for the reference filter of FIG. 1.

[0020] FIG. 3 is a plan view diagram showing an example tunable SIW band pass filter in accordance with the present disclosure.

[0021] FIG. 4 is graphical representation of return loss and insertion loss for the tunable filter with variation in relative permittivity of dielectric rods embedded as shown in FIG. 3. [0022] FIG. 5 is a plan view diagram showing another example tunable SIW band pass filter in accordance with the present disclosure. [0023] FIG. 6 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 5.

[0024] FIG. 7 is a plan view diagram showing an example tunable SIW band pass filter in accordance with the present disclosure.

[0025] FIG. 8 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 7.

[0026] FIG. 9 is a plan view diagram showing an example tunable SIW band pass filter in accordance with the present disclosure.

[0027] FIG. 10 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 9.

[0028] FIG. 11 is a plan view diagram showing reference HMSIW band pass filter in accordance with the present disclosure.

[0029] FIG. 12 is graphical representation of return loss and insertion loss for the reference filter of FIG. 11.

[0030] FIG. 13 is a plan view diagram illustrating an example tunable HMSIW band pass filter in accordance with the present disclosure.

[0031] FIG. 14 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 13.

[0032] FIG. 15 is a plan view diagram illustrating an example tunable HMSIW band pass filter in accordance with the present disclosure.

[0033] FIG. 16 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 15. [0034] FIG. 17 is a plan view diagram showing reference SIW cross coupled band pass filter in accordance with the present disclosure.

[0035] FIG. 18 is graphical representation of loss performance for the cross coupled filter with variation in permittivity of dielectric rods of FIG. 17.

[0036] FIG. 19 is a plan view diagram illustrating an example tunable SIW cross coupled band pass filter in accordance with the present disclosure.

[0037] FIG. 20 is graphical representation of loss performance for the tunable filter with variation in permittivity of dielectric rods of FIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

[0038] In the present document, the word“exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or implementation of the present subject-matter described herein as“exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0039] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0040] The terms “comprises”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, system or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or system or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

[0041] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense. [0042] The present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. [0043] FIG. 1 is a schematic representation of reference SIW BPF 100. The overall size of the BPF is about 90mm by about 18 mm as shown in FIG. 1.

The BPF circuit 100 includes an input port 110 which is a microstrip line at which an RF input is provided and 112 which is a linearly tapered transmission line section to match field of microstrip line to SIW section 114. Then a similar taper section 116 is included to send filtered microwave signal to output port 118 which is again a microstrip line. Width of the SIW section, diameter of the plated through holes and their pitch are decided according to RF solution frequency which is 10GHz. Width of the 50W microstrip line section 110 and 118 is also determined according to the RF solution frequency and substrate height and permittivity. Length and width of taper sections 112 and 116 are optimized for good impedance matching. SIW section 114 comprises of three resonant cavities 120,122 and 124 and four coupling apertures 130, 132, 134 and 136. Length of resonant cavities and width of coupling apertures determine resonant frequency of the filter.

[0044] FIG. 2 shows graphical representation of simulated and measured return loss and insertion loss (Sn and S21 respectively measured in dB) of reference SIW BPF shown in FIG. 1 across a range of frequencies (measured in GHz). As shown in FIG. 2, measured in-band insertion loss of the filter is around 1 dB and measured in band return loss is greater than lOdB over a frequency band of about 440MHz around 11.08GHz center frequency. From frequency response of FIG. 2, it can be observed that simulated and measured S-parameters of the SIW BPF operating in X-band match well.

[0045] FIG. 3 shows tunable SIW BPF 300 with dielectric rods placed along the central line of the SIW section 310 at the center of resonant cavities and coupling apertures. When permittivity of all the dielectric rods is fixed, then diameter 320 of these dielectric rods decides the center frequency of the tunable filter. Once diameter gets optimized, permittivity of those rods are changed to observe tunability of center frequency of the BPF. [0046] FIG. 4 shows loss performance (measured in dB) of the tunable BPF shown in FIG. 3 across a range of frequencies (measured in GHz) when permittivity of all dielectric rods are changed simultaneously. Dielectric rods of permittivity erl, er2 and er3 (where erl, er2 and er3 are in increasing order of values) were fabricated in order to place them according to the hole positions as depicted in FIG. 3. Initially the filter was measured with all air holes (denoted by erO ), then dielectric rods of permittivity erl (which is same as that of the substrate) were pressed into those air holes to take next measurement of S-parameters. In a similar way, dielectric rods of permittivity er2 and er3 are placed into those holes respectively to take next 2 sets of measurements. In the S-parameter response of FIG. 4, it can be observed that the frequency response of the tunable SIW BPF shifts to lower frequency of X-band as relative permittivity of dielectric rods increases. Approximately 600MHz frequency tunability in center frequency was observed about 11.1 GHz with change in relative permittivity of dielectric rods in this arrangement.

[0047] FIG. 5 shows another tunable SIW BPF 500 where dielectric rods were placed only at the center of three resonant cavities. Diameter of these rods 510 was optimized to dia_c in order to achieve maximum possible tunability in center frequency.

[0048] FIG. 6 shows graphical representation of return loss and insertion loss (measured in dB) of the tunable BPF shown in FIG. 5 across a range of frequencies (measured in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to take four sets of measurements and their different S-parameter responses are marked with different colour code as shown in FIG. 6. In the S-parameter response of FIG.

6, it can be observed that here also the frequency response of the tunable SIW BPF shifts to lower frequency region in X-band, as relative permittivity of dielectric rods increases. With change in relative permittivity of dielectric rods, around 700MHz center frequency tunability about 11.15GHzwas achieved in measurement.

[0049] FIG. 7 shows another tunable SIW BPF 700 where dielectric rods were placed only at the center of four coupling apertures. Diameter of these rods 702 was optimized to dia_a in order to achieve maximum possible tunability in center frequency in this case as well.

[0050] FIG. 8 shows graphical representation of return loss and insertion loss (measured in dB) of the tunable BPF shown in FIG. 7 across a range of frequencies (measured in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to take four sets of measurements and their different S-parameter responses are marked with different colour code as shown in FIG. 8. As depicted in the S-parameter response, it is observed that with change in relative permittivity of dielectric rods, around 200MHz tunability of center frequency about 11 GHz was achieved in measurement. [0051] FIG. 9 shows another example of tunable SIW BPF 900. To change tuning range of center frequency, diameters of dielectric rods were varied in decreasing order from center to the taper section marked as 960, 962, 963, 964,

966, 968 and 970 as shown in FIG. 9. and these dimensions were optimized to achieve maximum tunability.

[0052] FIG. 10 shows graphical representation of return loss and insertion loss (measured in dB) of the tunable BPF shown in FIG. 9 across a range of frequencies (measured in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to take four sets of measurements and their different S-parameter responses are marked with different colour code as shown in FIG. 10. In the S-parameter response, it is observed that center frequency of the tunable SIW BPF shifts towards lower frequency of X-band with increase in relative permittivity of dielectric rods. Around 150MHz tunability of center frequency about 11.2 GHz was achieved in measurement.

[0053] FIG. 11 is a schematic representation of reference HMSIW BPF 1100.

The overall size of the BPF is about 90mm by about 11 mm as shown in FIG. 11. The BPF circuit 1100 includes an input port 1110 which is a microstrip line at which an RF input is provided and 1112 which is a linearly tapered transmission line section to match field of microstrip line to HMSIW section 1114. Then a similar taper section 1116 is included to send filtered microwave signal to output port 1118 which is again a microstrip line. Width of the SIW section, diameter of the plated through holes and their pitch are decided according to RF solution frequency which is 10GHz. Width of the 50W microstrip line section 1110 and 1118 is also determined according to the RF solution frequency and substrate height and permittivity. Length and width of taper sections 1112 and 1116 are optimized for good impedance matching. HMSIW section 1114 comprises of three resonant cavities 1120,1122 and 1124 and four coupling apertures 1130, 1132, 1134 and 1136. Length of resonant cavities and width of coupling apertures determine resonant frequency of the filter.

[0054] FIG. 12 shows graphical representation of simulated and measured return loss and insertion loss (measured in dB) of reference HMSIW BPF shown in FIG. 11 across a range of frequencies (measured in GHz). As shown in FIG. 12, measured in-band insertion loss of the filter is around 1 dB and measured in band return loss is greater than lOdB (approximately) over a frequency band of about lGHz around 10GHz center frequency. From frequency response of FIG. 12, it can be observed that simulated and measured S-parameters of the HMSIW BPF operating in X-band match well with a little shift in frequency response because of fabrication error.

[0055] FIG. 13 shows tunable HMSIW BPF 1300 with dielectric rods placed along the central line of the SIW section 1310 at the center of resonant cavities and coupling apertures. Diameter 1320 of these dielectric rods decides the center frequency of the tunable filter. Once diameter gets optimized, permittivity of those rods are changed to observe tunability of center frequency of the BPF.

[0056] FIG. 14 shows graphical representation of return loss and insertion loss (in dB) of the tunable BPF shown in FIG. 13 across a range of frequencies (in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to perform four sets of simulations and their different S -parameter responses are marked with different colour code as shown in FIG. 14. From the S-parameter response, it can be observed that here also the frequency response of the tunable HMSIW BPF shifts to lower frequency region in X-band, as relative permittivity of dielectric rods increases. With change in relative permittivity of dielectric rods, approximately 1.2GHz tunability of center frequency about 10 GHz, was achieved in simulation.

[0057] FIG. 15 shows another HMSIW BPF where dielectric rods were placed only at the center of three resonant cavities. Diameter of these rods 1510 was optimized to dia in order to achieve maximum possible tunability in center frequency.

[0058] FIG. 16 shows graphical representation of return loss and insertion loss (in dB) of the tunable BPF shown in FIG. 15 across a range of frequencies (in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to perform four sets of simulations and their different S -parameter responses are marked with different colour code as shown in FIG. 16. From the S-parameter response, it can be observed that here also the frequency response of the tunable HMSIW BPF shifts to lower frequency region in X-band, as relative permittivity of dielectric rods increases. With change in relative permittivity of dielectric rods, approximately 800MHz tunability of center frequency was achieved in simulation about 10GHz.

[0059] FIG. 17 is a schematic representation of reference cross coupled SIW BPF 1700. The overall size of the BPF is about 35mm by about 31 mm as shown in FIG. 17. The BPF circuit 1700 includes an input port 1710 which is a microstrip line at which an RF input is provided. The line is in inset feed configuration to match field of microstrip line to SIW through section 1712.

Then a similar SIW section 1714 is included to send filtered microwave signal to output port 1716 which is again a microstrip line in inset feed configuration. Width of the SIW section, diameter of metallic vias and their pitch are decided according to RF solution frequency which is 14.83GHz. Width of the 50W microstrip line section 1710 and 1716 is also determined according to the RF solution frequency and substrate height and permittivity. Length and width of inset feed sections are optimized for good impedance matching. SIW section comprises of three resonant cavities 1720,1722 and 1724 and four coupling apertures 1730, 1732, 1734 and 1736. Length of resonant cavities and width of coupling apertures determine resonant frequency of the filter.

[0060] FIG. 18 shows graphical representation of simulated return loss and insertion loss (in dB) of reference SIW cross coupled filter shown in FIG. 17 across a range of frequencies (in GHz). As shown in FIG. 18, in-band insertion loss (S21) of the filter is around 1 dB and in band return loss (Sn) is greater than lOdB over a frequency band of about 300MHz around 14.8GHz center frequency which is clear from the S-parameter response of FIG. 18.

[0061] FIG. 19 shows another tunable SIW BPF 1900 where dielectric rods were placed only at the center of three resonant cavities. Diameter of these rods 1910 was varied from dia_xl to dia_x3 in increasing order of values in order to achieve maximum possible tunability in center frequency. When permittivity of all the dielectric rods is fixed, then diameter 1910 of these dielectric rods decides the center frequency of the tunable filter. Once diameter gets optimized, permittivity of those rods are changed to observe tunability of center frequency of the BPF. [0062] FIG. 20 shows graphical representation of return loss and insertion loss

(in dB) of the tunable BPF shown in FIG. 19 across a range of frequencies (in GHz) when permittivity of all dielectric rods are changed simultaneously. Here also dielectric rods of different dielectric materials were placed simultaneously one by one to perform three sets of simulations and their different S-parameter responses are marked with different colour code as shown in FIG. 20. From the S-parameter response, it can be observed that in this type of filter also, the frequency response of the tunable cross coupled SIW BPF shifts to lower frequency region in X-band, as relative permittivity of dielectric rods increases.

With change in relative permittivity of dielectric rods, approximately lGHz tunability of center frequency around 16.5GHz was achieved in simulation. [0063] Example applications for the tunable bandpass filters described herein may include construction of multiband wireless communication system, wideband tracking receivers and multichannel front end modules (FEM). [0064] Additionally, the example tunable circuits of the present disclosures include SIW, HMSIW and SIW cross coupled filter topology. However, in other examples, other types of tunable circuits may be utilized. For example, tunable phase shifters and tunable power dividers may be implemented using the same technique which may yield good phase tunability and good tunability in isolation and other parameters of power divider circuit respectively.

[0065] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from scope of the present invention.