Devices and methods for phase shifting a radio frequency (RF) signal for a base station antenna

Methods and devices for phase shifting an RF signal for a base station antenna are provided. The device includes a transmission line that has a stationary ground plane coupled to the top of a substrate and a signal line on the bottom of the substrate. The signal line has an input port and an output port. The input port receives the RF signal with a certain phase and travels across the bottom of the substrate to the output port. The RF signal has a different phase at the output port because defected ground structures etched on the stationary ground plane shift the phase of the RF signal. In addition, the device includes a movable ground plane that may cover a portion of the defected ground structures, the substrate, and the stationary ground plane such that the moveable ground plane further adjusts the phase of the RF signal.

BACKGROUND

Cellular networks have limited capacity for transmitting and receiving voice calls and electronic data (e.g., text messages, multimedia messages, email, web browsing, etc.) between base stations and cellular telephones due to the finite frequency bandwidth or spectrum available to the network. A voice call and/or electronic data can be delivered to a cellular telephone using a radio frequency (RF) signal at a certain operating frequency. Capacity in cellular networks may be increased by implementing a frequency reuse scheme. In such a scheme, RF signals with the same operating frequency may be used by different cellular telephone users in different cells. Typically, the different users are several cells apart to limit the interference between the RF signals of the different users. However, significant interference between the users may still exist which can decrease quality of the voice calls or corrupt the electronic data received by the different users.

An approach to reducing interference due to frequency reuse may include tilting antenna beams of base stations of cellular networks such that the transmitted RF signal is confined to the cell. Beam tilting may be performed in several different ways including mechanical, electrical, and optical methods. Electronic beam tilting can be used in cellular applications as well as satellite communication networks, smart weapons, radar applications, and other RF systems where RF signals may interfere with each other.

Decreases in a quality of service in such systems and applications can occur when two or more RF signals are in phase with each other resulting in the RF signals destructively interfering with each other. Beam tilting may be achieved by varying the phase of the transmitted RF signal. The phase variation can be performed in two ways, for example. First, the phase can be adjusted by changing the operating frequency of the signal. This may not be desirable in some applications, such as cellular applications, because the transmitted signal would not be properly decoded at the receiver. Secondly, electronic phase shifters can be used to vary the phase at a fixed operating frequency. However, traditional electronic phase shifters may be expensive as well as may have high power consumption requirements.

SUMMARY

Within embodiments described below, a device for phase shifting an RF signal for a base station antenna is disclosed. The device includes a transmission line that delivers an RF signal from an RF transmitter to the base station antenna as well as a substrate with a top planar surface and a bottom planar surface. The device also includes a stationary ground plane coupled to the top planar surface of the substrate and a signal line on the bottom planar surface of the substrate. The signal line has an input port and an output port and is made of conducting material. The input port receives the RF signal with a certain phase from the RF transmitter then the conducting material transmits the RF signal across the bottom planar surface of the substrate to the output port. The RF signal has a different phase at than at the output port. The device further includes one or more types of defected ground structures on the top planar surface of the substrate. The defected ground structure may be a short stem dumbbell structure or a long stem dumbbell structure. The defected ground structures may shift the phase of the RF signal from the phase at the input port to the different phase at the output port. The difference between the phase at the input port and the phase at the output port is a phase shift of the RF signal. In addition, the device includes a movable ground plane that may cover a portion of the defected ground structures, the top planar surface of the substrate, and the stationary ground plane to further adjust the phase shift of the RF signal.

Another embodiment of the present disclosure includes a method for phase shifting an RF signal for a base station antenna that comprises receiving an RF signal with a certain phase at an input port of a signal line and transmitting the RF signal across the signal line to an output port. The signal line is on a bottom planar surface of a substrate. The method also includes shifting a phase of the RF signal from a phase at the input port to a different phase at the output port using one or more types of defected ground structures. The top of a stationary ground plane attached to a top planar surface of the substrate may be etched with the defected ground structures. Types of defected ground structures may include a short stem dumbbell structure and a long stem dumbbell structure. Further, a difference between the phase of the RF signal at the input port and the different phase at the output port is a phase shift of the RF signal. Additionally, the method includes further adjusting the phase shift of the RF signal by covering a portion of the one or more defected ground structures, the stationary ground plane, and the top planar surface of the substrate with a moveable ground plane and providing the RF signal with the different phase at the output port.

In yet another embodiment, another a method for phase shifting an RF signal for a base station antenna is disclosed using a transmission line that includes transmission line components such as signal line, a substrate, a stationary ground plane, defected ground structures, and a moveable ground plane. The method includes receiving a target beam tilt value at the user interface of the computer. The method also includes calculating a target phase shift based on the target beam tilt value and the dimensions of the transmission line and the transmission line components. Further, the method includes determining a target distance to slide the moveable ground plane to cover portions of the transmission line and the transmission line components to achieve the target phase shift. Additionally, the method includes sending instructions to a microcontroller to rotate a stepper motor a certain amount that translates to the target distance for sliding the moveable ground plane.

DETAILED DESCRIPTION

A cellular network may have limited bandwidth or frequency spectrum available to transmit voice calls or electronic data (e.g. text messaging, multimedia messaging, web browsing, email, etc.) to network users with cellular telephones, smartphones, laptops, personal digital assistants (PDAs) or other user terminals. A cellular service provider may utilize different transmission schemes to maximize capacity to in the cellular network. Example transmission schemes may include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). Further, a transmission scheme utilizes a RF signal at a particular operating frequency in the frequency spectrum to deliver a voice call or electronic data to a particular user terminal. Further, to maximize capacity in the cellular network, the service provider may implement a frequency reuse scheme. A frequency reuse scheme allows different user terminals, separated by several cells, to use the same frequency to receive voice calls and electronic data. However, the RF signal to each different user terminal may interfere with each other to reduce the quality of voice calls or corrupt the electronic data.

FIG. 1is an example cellular network100illustrating signal interference using a frequency reuse scheme. The cellular network100includes four cells, Cell1(105), Cell2(110), Cell3(115), and Cell4(120). In Cell1(105), a base station125transmits a RF signal A (132) to a User1Terminal (134). The RF signal A (132) may carry a voice call or electronic data and may be of the form A=M1sin({acute over (ω)}xt+ψ1) where M1is the amplitude, {acute over (ω)}xis the frequency, and ψ1is the phase of RF signal A. Alternatively, in Cell4(120) a base station130transmits a RF signal B (140) to a User Terminal2(145). The RF signal B (14) may also carry a voice call or electronic data to the User2Terminal (145) and may be of the form B=M2sin({acute over (ω)}xt+ψ2) where M2is the amplitude, {acute over (ω)}xis the frequency, and ψ2is the phase of RF signal B.

The cellular service provider may implement a frequency reuse scheme such that RF signals A and B have the same operating frequency {acute over (ω)}x. Consequently, User Terminal2(145) may receive RF signal A (135) from Cell1(105) such that RF signal A (135) may interfere with RF signal B (140) to distort the voice call or corrupt electronic data destined for User Terminal2(145). For example, if θ1is out of phase from θ2, then RF signal A (135) and RF signal B (140) destructively interfere with each other resulting in a decrease in quality of service to User Terminal2(145).

Interference between RF signals in cellular networks may occur when two or more RF signals are out of phase with each other resulting in the RF signals destructively interfering with each other. A cellular service provider may implement several mechanisms to control a phase of an RF signal that may include using a microstrip transmission line.FIG. 2is an example functional block diagram of a base station200for Cell1and a base station217for Cell4, each base station using a microstrip transmission line to control a phase shift of the RF signal. The base station200for Cell1may have an RF transmitter205that generates an RF signal A=M1sin({acute over (ω)}xt) where M1is the amplitude and {acute over (ω)}xis the frequency. The RF signal may then be transmitted over a microstrip transmission line210. The microstrip transmission line210may shift or control a phase of the RF signal A. The microstrip transmission line210may provide an output RF signal A with a phase shift such as A=M1sin({acute over (ω)}xt+θ1) to a base station antenna215where θ1is the phase shift. Further, the base station217for Cell4may also have an RF transmitter220that generates an RF signal B=M2sin({acute over (ω)}xt) where M2is the amplitude and {acute over (ω)}xis the frequency. The RF signal B may then be transmitted over a microstrip transmission line225to shift or control a phase of RF signal B. The microstrip transmission225line may provide an output RF signal B with a phase shift such as B=M2sin({acute over (ω)}xt+θ2) where θ2is the phase shift. However, the service provider may construct the microstrip transmission lines (210,225) to control θ1and θ2such that the two RF signals do not interfere with each other when transmitted to different user terminals in a cellular network.

In example embodiments, electronic phase shifters may be incorporated in a microstrip transmission line that is coupled between an RF transmitter at a cellular base station in the base station antenna or antenna array. The microstrip transmission line may include a substrate with a stationary ground plane attached to one side and the signal line carrying the RF signal from the RF transmitter on an opposite side. Defected Ground Structures (DGS) may be etched into the stationary ground plane. DGS structures may change the capacitance and inductance of the microstrip transmission line and thus vary the phase of the RF signal. Further, the transmission line may include a moveable ground plane that covers portions of the DGS structures, altering the capacitance and inductance to further adjust the phase of the RF signal. An equivalent inductance-capacitance (LC) circuit may be used to model the effects of the DGS structures (may be fully or partially covered by moveable ground plane) on the RF signal carried by the transmission line. DGS structures may take many different forms or shapes. These may include triangular, elliptical, rectangular, and dumbbell forms. A different LC circuit may be used to model each different form or shape of a DGS structure. Values for the inductance and capacitance of the LC circuit model may be a function of the dimensions of the DGS structures. Therefore, the phase of the RF signal traveling along the transmission line can be shifted by varying the dimensions of the DGS structures.

In addition, a base station antenna system may have multiple antenna elements in an array and a separate phase shifter may be connected at the input of each antenna element. For example, an array of five antenna elements may require five different phase shifters. The phase shifters can be separate units or as a single phase shifter bank with five parallel signal lines and the corresponding DGS structures etched or printed on the bottom of the transmission line. In such an example, the movable ground plane may be a single unit that slides over the entire phase shifter bank.

FIG. 3is an example of a microstrip transmission line300used to phase shift an RF signal. The microstrip transmission line300may have an input port and an output port. The input port may be coupled to an RF transmitter that generates and modulates the RF signal. Further, the input port transmits the RF signal across the microstrip transmission line along a signal line320to the output port. In addition, the output port may be coupled to a base station antenna that may direct the RF signal to a user terminal. The microstrip transmission line300may also include a substrate310. The substrate310may comprise several different types of materials that may include a type of dielectric material, for example. On one side of the substrate310is the signal line320. The signal line320comprises conducting material that carries the RF signal from the input port to the output port. Coupled onto the opposite side of the substrate310is a stationary ground plane330. It will be shown when describingFIG. 4that Defected Ground Structures (DGS) may be etched into the stationary ground plane330to shift a phase of the RF signal as the RF signal travels across the microstrip transmission line300along the signal line320. In addition, a moveable ground plane340may be used to cover a portion or all of the stationary ground plane330including a portion or all of the DGS structures to further adjust the phase of the RF signal, for example.

FIG. 4illustrates a microstrip transmission line400used to phase shift an RF signal. A stationary ground plane430is coupled to a substrate (not shown). A signal line420is coupled to an opposite side of the substrate with respect to the stationary ground plane430. A series of Defected Ground Structures (DGS)490may be etched into the stationary ground plane430comprising one or more unit DGS structures (410). A DGS structure is generated by etching conducting material into certain patterns on the stationary ground plane430. The series of DGS structures may comprise a nested dumbbell pattern410, for example. That is, the unit DGS structure410may include two short stem dumbbells430nested within a long stem dumbbell pattern420. The series of DGS structures490may shift a phase of an RF signal traveling along the signal line420based on the transmission line components (e.g. substrate, signal line420, stationary ground plane430, and a moveable ground plane440). In addition, the moveable ground plane440may be manually or motor controlled to cover a portion of the stationary ground plane430including a portion of the series of DGS structures490to further adjust the phase of the RF signal.

Dimensions of the ground plane as well the as dimensions of the DGS structures may effect the phase shift of the RF signal traveling along the signal line. The dimensions that vary a phase of the RF signal may include the length (L) and width (W) of the stationary ground plane430. Further dimensions that effect the phase may include length L1and width W1of a unit410in the series of DGS structures. In addition, the width Wsof the signal line420may vary the phase. Example dimensions may include L=113 mm, W=70 mm, L1=8 mm, W1=40 mm, and Ws=3 mm.

FIG. 5is an example circuit model550of an example defected ground structures500in a microstrip transmission line that phase shifts an RF signal. As discussed inFIG. 4, the dimensions of transmission components as well as DGS structures may contribute to the phase shift of the RF signal. The DGS structure may be a nested dumbbell structure500such that two short stem dumbbell DGS structures530are nested within a long stem dumbbell DGS structure532. The short stem dumbbell DGS structure530comprises two rectangular or square defects (505and512) connected by a narrow slot510. A length of the rectangular defects (505and512) is “a” and a width of the rectangular defects (505and512) is “b”. The width of the narrow slot510is gs. Alternatively, the long stem dumbbell DGS structure532comprises two narrow rectangular defects (515and525) with length “y” and width “z” connected by a narrow slot520with width gL.

DGS structures can shift the phase of the signal because the DGS structures change inductance and capacitance of the transmission line based on DGS structure dimensions. An etched defect in the ground plane may disturb current distribution in a stationary ground plane. Such disturbances can change characteristics of a transmission line such as line capacitance and inductance. Etched areas of a DGS structure may give rise to increasing the effective capacitance and inductance of a transmission line. Thus, an example equivalent LC circuit550can represent a DGS structure500, as shown inFIG. 5. Values for the effective capacitance and effective inductance in the equivalent parallel LC circuit model may be based on the dimensions of the DGS structures.

The dumbbell structure includes a narrow stem cell connected to two wide etched (e.g. rectangular) regions which contribute to a net effective capacitance and inductance of the transmission line, respectively. The stem width gs510and gL520are inversely proportional to the amount of effective capacitance. That is, a decrease in width of either stem gs510and gL520increases the effective capacitance of the transmission line. The wide etched rectangular areas of dimension “a”505and “b”512and “y”515and “z”525, respectively, are directly proportional to the effective inductance of the transmission line. That is, an increase in the area of rectangular regions (505,515,530) increases the inductance of the transmission line.

The parallel LC circuit model inFIG. 5may show that the DGS structures behave like a low pass or bandgap filter. Accordingly, a resonance occurs at a certain frequency due to the parallel LC circuit. The resonance frequency is a frequency at which a parallel LC circuit has infinite impedance. The rectangular defects of the short stem dumbbell DGS structure530increase route length of a current and the effective inductance of the transmission line. The narrow slot of the short stem dumbbell DGS structure510may accumulate charge and increases the effective capacitance of the transmission line. Alternatively, when the etched gap distance decreases, the effective capacitance decreases such that the attenuation pole location (resonance frequency) moves up to a higher frequency. Further, as the etched area of the unit DGS structure increases, the effective inductance increases giving rise to a lower cutoff frequency or the 3 dB point of the low pass or bandgap filter, for example.

Further, analyzing the parallel LC circuit model inFIG. 5shows an example in which the DGS structure shifts the phase of an RF signal traveling along a signal line of a transmission line. The inductance and capacitance in the parallel LC circuit gives rise to reactance in the circuit. Alternatively, the circuit may contain impedances that have resistive components as well as the reactive components. When an RF signal is applied to the input port of a parallel LC circuit having both resistive and reactive components, the RF signal may be shifted in phase at the output port of the circuit. The phase of the signal at the output port could be given by
θ=βl  (1)
where β is the propagation constant and l is the physical length of the transmission line. Further
β=ω(LC)1/2(2)
where ω is the frequency of operation, L and C are the equivalent inductance and capacitance, of the transmission line respectively. Thus from the above equations (1) and (2), the change in the line inductance and capacitance attributed by the DGS structures can, in turn, change the phase of the output RF signal.

Analyzing the parallel LC circuit inFIG. 5, an overall impedance (Z) can be determined based on the values of R, L, and C. The overall impedance of the LC circuit may be of the form Z=R+jX where R represents the resistive and X represents the reactive components of the overall impedance Z, respectively. Hence, when an RF signal is applied to an input port of the parallel LC circuit, then the RF signal at an output port may have a shifted phase. The shifted phase may be equal to the arctan(X/R).

In one example, the DGS structures and covering of the structures by a moveable ground plane may give rise to inductance and capacitance values to the transmission line of about 3.6 nH and about 0.1 pF, respectively, for example. Further, the resistive component of the overall impedance of the transmission line may be equal to about 50Ω. The overall impedance of the parallel LC circuit model for the transmission line for an RF signal operating at a frequency of about 8 GHz may be found by the following:

Thus, for the values for R, L, C and {acute over (ω)} (2πf where f=8 GHz), the overall impedance is given by Z=50−22.5j. Further, the phase shift of the RF signal is given by the arctan(−22.5/50)=24 degrees. Therefore, the RF signal at the output port of the transmission line has a phase shift equal to about 24 degrees.

In addition, the phase shift of the RF signal may be adjusted by varying the reactive components (inductance or capacitance) of the parallel LC circuit. Hence, the phase of an RF signal may be varied using a transmission line by varying the dimensions of the DGS structures which give rise to the values of the reactive components (inductance and capacitance) components of the transmission line. Values for the inductance and capacitance vary depending on the shape and dimensions of the DGS structures. The equivalent circuit of a DGS structure is derived by simulating a single DGS structure along with a microstrip line using simulation and test equipment such as a 3D EM simulator. For example, for a nested dumbbell structure, simulation results may show a one pole low pass filter response with a 3 dB cut off frequency and an attenuation pole frequency. Values of equivalent L and C can be calculated by the following formulae:
C=ω0/Z0g1(ω02−ωc2)  (4)
L=¼π2f02C(5)
where ω0is the angular frequency at the location of the attenuation point, ωcis the angular frequency at the 3 dB cutoff point, Zois the characteristic impedance of the transmission line, g1is a prototype value of a Butterworth low pass filter of first order=2, f0is the frequency at the 3 db cutoff point.

In addition, a moveable ground plane covering the etched DGS structures on the stationary ground plane may also vary the inductance and capacitance of the transmission line resulting in adjusting the phase of the RF signal traveling along the signal line. The movable ground plane that slides above the DGS structures can be made to fully open or fully close or partially close the DGS structures. When the DGS structures are fully closed there is no reactive loading in the line and the signal line directly transmits the signal in the input port to the output port with a phase proportional to the physical length of the line, also called the reference phase.

When the movable ground plane is kept at fully open position, the maximum reactive loading occurs and thus, the signal at the output port has a shifted phase when compared to the reference phase. The effective phase shift between the fully closed and fully open state is given by
Effective maximum phase shift=Phase at fully open state−Reference phase  (6)

However, when the movable ground plane is at intermediate positions resulting in partially opened defected ground structures, the transmission line may have reactive loading less than the maximum loading due to the fully open stage. Thus, intermediate phase values which are less than that obtained in the fully open stage and greater than that obtained in the fully closed stage are achieved. For example if a line of length X has a reference output phase of 20 degrees in fully closed stage and 200 degrees in fully open stage, then the movement of the movable ground plane would result in phase values in between 20 and 200 degrees.

The phase shift of the RF signal can range from about 0 degrees when the moveable ground plane is fully open (covers no portion of the stationary ground plane and/or any portion of the DGS structures) up to about 190 degrees when fully closed (covers almost every portion of the stationary ground plane and/or almost every portion of the DGS structures), for example.

FIG. 6is an example functional block diagram of a phase shift system600using a microstrip transmission line610and stepper motor620to control phase shift in an RF signal. The microstrip transmission line610receives a signal from an RF transmitter605, and subsequently passes a phase shift signal to an antenna615.

A moveable ground plane (not shown) of a microstrip transmission line may further adjust the phase shift of an RF signal by covering a portion of a stationary ground plane and portions of a series of DGS structures. The moveable ground plane may be controlled manually or by the stepper motor620. A stepper motor (or step motor) may be a brushless, synchronous electric motor that can divide a full rotation of a motor into a large number of steps. A position of the stepper motor620can be controlled precisely, without any feedback mechanism, for example.

A stepper motor may have multiple toothed electromagnets arranged around a central gear-shaped piece. The electromagnets are energized by an external control circuit, such as a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are thus aligned to the first electromagnet, the teeth are slightly offset from the next electromagnet. Hence, when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next electromagnet, and from there the process is repeated. Each slight rotation may be called a “step,” with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle.

The stepper motor620may be controlled by a motor microcontroller630such that the phase of the RF signal can be controlled in a precise manner to reduce interference with other RF signals on the same frequency destined to other user terminals. The motor microcontroller630may be programmed in advance or in real-time by computer625to adjust the phase of an RF signal based on the dimensions of the transmission line, substrate, signal line, stationary and moveable ground planes as well as the DGS structures and other transmission line components.

The computer625may include one or more user interfaces and/or electronic input/output ports to receive the dimensions of the transmission line components as well as a target beam tilt value and a target phase shift for the RF signal. The method in which the phase is adjusted based on the target beam tilt value and the dimensions and the target phase shift is discussed when describingFIG. 9.

FIG. 7is a block diagram illustrating an example computing device700that is used to control a stepper motor as part of an example phase shift system. In a very basic configuration701, computing device700typically includes one or more processors710and system memory720. A memory bus730can be used for communicating between the processor710and the system memory720. Depending on the desired configuration, processor710can be of any type including but not limited to a microprocessor (μP), a microcontroller (μC), a digital signal processor (DSP), or any combination thereof. Processor710can include one more levels of caching, such as a level one cache711and a level two cache712, a processor core713, and registers714. The processor core713can include an arithmetic logic unit (ALU), a floating point unit (FPU), a digital signal processing core (DSP Core), or any combination thereof. A memory controller715can also be used with the processor710, or in some implementations the memory controller715can be an internal part of the processor710.

Depending on the desired configuration, the system memory720can be of any type including but not limited to volatile memory (such as RAM), non-volatile memory (such as ROM, flash memory, etc.) or any combination thereof. System memory720typically includes an operating system721, one or more applications722, and program data724. Application722includes control input processing algorithm723that is arranged to provide inputs to the electronic circuits, in accordance with the present disclosure. Program Data724includes control input data725that is useful for minimizing power consumption of the circuits, as will be further described below. In some example embodiments, application722can be arranged to operate with program data724on an operating system721such that power consumption by an electronic circuit is minimized. This described basic configuration is illustrated inFIG. 7by those components within dashed line701.

Computing device700can have additional features or functionality, and additional interfaces to facilitate communications between the basic configuration701and any required devices and interfaces. For example, a bus/interface controller740can be used to facilitate communications between the basic configuration701and one or more data storage devices750via a storage interface bus741. The data storage devices750can be removable storage devices751, non-removable storage devices752, or a combination thereof. Examples of removable storage and non-removable storage devices include magnetic disk devices such as flexible disk drives and hard-disk drives (HDD), optical disk drives such as compact disk (CD) drives or digital versatile disk (DVD) drives, solid state drives (SSD), and tape drives to name a few. Exemplary computer storage media can include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data.

System memory720, removable storage751and non-removable storage752are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by computing device700. Any such computer storage media can be part of device700.

Computing device700can also include an interface bus742for facilitating communication from various interface devices (e.g., output interfaces, peripheral interfaces, and communication interfaces) to the basic configuration701via the bus/interface controller740. Exemplary output interfaces760include a graphics processing unit761and an audio processing unit762, which can be configured to communicate to various external devices such as a display or speakers via one or more A/V ports763. Exemplary peripheral interfaces760include a serial interface controller771or a parallel interface controller772, which can be configured to communicate with external devices such as input devices (e.g., keyboard, mouse, pen, voice input device, touch input device, etc.) or other peripheral devices (e.g., printer, scanner, etc.) via one or more I/O ports773. An exemplary communication interface780includes a network controller781, which can be arranged to facilitate communications with one or more other computing devices790over a network communication via one or more communication ports782. The Communication connection is one example of a communication media. Communication media may typically be embodied by computer readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and includes any information delivery media. A “modulated data signal” can be a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media can include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency (RF), infrared (IR) and other wireless media. The term computer readable media as used herein can include both storage media and communication media.

FIG. 8is a flowchart for an example method for phase shifting an RF signal. The method may comprise receiving an RF signal at an input port of a signal line of a microstrip transmission line, as shown at block810, from an RF transmitter or some other device within a base station. A further step may be transmitting the RF signal across the signal line to an output port, as shown at block820. The signal line may comprise of conducting material that is coupled to one side of a substrate of the transmission line. Additionally, one or more types of DGS structures may be used to phase shift the RF signal, as shown at block830. The DGS structures may be constructed by etching conducting material onto a stationary ground plane of the transmission line. Further, the stationary ground plane is coupled onto an opposite side of the substrate with respect to the signal line. Also, the phase shift of the RF signal may be adjusted by covering a portion of the one or more defected ground structures, the stationary ground plane, and the associated planar surface of the substrate with a moveable ground plane, as shown at block840. The method may include controlling the moveable ground plane to cover the DGS structures, stationary ground plane, and the substrate using a stepper motor and/or computer, as shown at block850. Another step in the method may be providing the phase shifted RF signal at an output port such that the RF signal can be transmitted to a base station antenna, as shown at block860.

FIG. 9is a flowchart900for an example method for controlling a moveable ground plane of a microstrip transmission line to adjust a phase of an RF signal. As discussed when describingFIG. 6, a stepper motor may control a moveable ground plane to cover portions of a microstrip transmission line as part of a phase shift system to further adjust the phase of an RF signal. A microcontroller and a computer together may control the stepper motor based on the dimensions of transmission line components. The example method may include the computer receiving a target beam tilt value of the antenna at a user interface and/or input/output port, as shown at block930. The beam tilt of an antenna in an antenna array may correspond to a phase shift in a transmitted RF signal. The method may calculate a target phase shift be provided to the input of each antenna element in the base station antenna array using an automatic computer based program, as shown at block935. Thereafter, the computer may determine a target distance to slide the moveable ground plane and cover portions of the transmission line components to achieve the target phase shift, as shown at block940, based on the inductance, capacitance, and resistive effects arising from etched DGS structures on the stationary ground plane and covering provided by the moveable ground plane. The target distance may be obtained from a look-up table as shown in Table 1 linked to a computer program. The look-up table may be generated by phase measurements of an RF signal at an output port of a transmission line using a network analyzer while varying the movable ground plane

Another step in the method includes sending instructions to a microcontroller that controls the stepper motor, as shown at block950. An additional step may include the microcontroller adjusting the stepper motor which in turn slides the moveable ground plane, as shown at block960, to the target distance thereby adjusting the phase of the RF signal to the target phase shift. Additional steps in the method may include the computer receiving as input the dimensions of the transmission line components, at a user interface and/or input/output port. The dimensions may include the microstrip transmission line itself, a substrate, a signal line, a stationary and a moveable ground planes as well DGS structures etched into the stationary ground plane. Thereafter the computer may then model the transmission line components as an equivalent parallel LC circuit and calculate inductance, capacitance, and resistive values of the LC circuit.

Example values of distances to slide the moveable ground plane to cover a microstrip transmission line with a series DGS structures and associated phase shifts are shown in Table 1. The unit DGS structure of the series DGS structures comprises of two short stem dumbbell structures nested in a long stem dumbbell structure.

In general, it should be understood that the circuits described herein may be implemented in hardware using integrated circuit development technologies, or yet via some other methods, or the combination of hardware and software objects that could be ordered, parameterized, and connected in a software environment to implement different functions described herein. For example, the present application may be implemented using a general purpose or dedicated processor running a software application through volatile or non-volatile memory. Also, the hardware objects could communicate using electrical signals, with states of the signals representing different data.