KR100895851B1 - Circuit for QHA feeder to measure the antenna impedance - Google Patents

Abstract

The present invention is to provide a QHA feeding structure for measuring antenna impedance, and an input port to which a signal is applied; An observation port where a signal is observed; A first output port for outputting a signal having a zero degree phase difference when a signal is applied to the input port; A second output port for outputting a signal having a 90 degree phase difference when a signal is applied to the input port; A first λ / 2 transmission line connected to the first output port; A third output port configured to output a signal having a 180 degree phase difference by the first λ / 2 transmission line when a signal is applied to the input port; A second λ / 2 transmission line connected to the second output port; And a fourth output port for outputting a signal having a phase difference of 270 degrees by the second λ / 2 transmission line when a signal is applied to the input port, by using a 90 degree hybrid and a λ / 2 transmission line. Therefore, it is possible to implement a QHA power supply circuit having a good performance in a relatively small area.

QHA, feed structure, orthogonal signal, 90-degree hybrid, matching circuit, transfer scattering coefficient

Description

Circuit for QHA feeder to measure the antenna impedance

1 is a structural diagram of a patch antenna for a conventional satellite communication.

2 is a structural diagram of a conventional helical antenna.

3 is a structural diagram of a conventional QHA antenna.

4 is a schematic diagram of a conventional QHA antenna.

5 is a perspective view showing the configuration of a conventional QHA antenna.

6 is a schematic diagram of a QHA feeding structure for antenna impedance measurement according to an embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating an input signal and an output signal at each port of the 90-degree hybrid circuit in FIG. 6.

FIG. 8 is a schematic diagram illustrating an example in which an antenna matching part is added between the 90 degree hybrid and the antenna connection part in FIG. 6.

FIG. 9 is a graph illustrating power distribution characteristics according to frequencies of the QHA power supply structure for antenna impedance measurement of FIG. 6.

FIG. 10 is a graph illustrating a phase change of a quadrature signal output in a QHA feeding structure for antenna impedance measurement of FIG. 6 according to frequency.

FIG. 11 is a schematic diagram of a structure in which the λ / 4 transmission line portion of the 90-degree hybrid in FIG. 6 is replaced with an equivalent circuit composed of a capacitor connected in parallel with a transmission line of an arbitrary length to reduce its size.

<Description of Symbols for Main Parts of Drawings>

1: input port 2: observation port

3: 1st output port (0 degree) 4: 2nd output port (-90 degree)

5: 3rd output port (-180 degree) 6: 4th output port (-270 degree)

7: 1 λ / 2 Transmission Line 8: 2 λ / 2 Transmission Line

9: matching part

[1] Kilgus, C.C, "Multielement Fractional Turn Helices", IEEE Trans. Antennas and Propagation, Vol. AP-16, No. 4, July PP. 400-501 (1968)

[2] Kilgus, C.C, "Resonant Quadrifilar Helix", IEEE Trans. Antennas and Propagation, Vol. AP-17, No. 3, May PP. 349-351 (1969)

[3] Bricker, R. W., "A Shaped Beam Antenna for Satellite Data Communication", IEEE AP-S Int. Symp. Digest, October pp. 121-126 (1976)

[4] Patton, W.T., "The Backfire Bifilar Helical Antenna", Antenna Laboratory Resort 61, AD 289084, Univ. of Illinois, Urbana, IL, September 1962

[5] Kilgus, C.C, "Resonant Quadrifilar Helix Design", Microwave Journal, Vol. 13, No. 12, December pp. 49-54 (1970)

[6] Adam, A.T, R.K. Greenough, R. F. Wallenberg, A. Mendlovics, and C. Lumjiak, "The Quadrifilar Helix Antenna", IEEE Trans. Antennas and Propagation, Vol. Ap-22, no. 2, March pp. 173-178 (1974)

[7] Korean Intellectual Property Office Application No. 20-2006-0003127 (filed February 02, 2006), "Antenna module for satellite communication in mobile wireless communication device"

[8] Korean Intellectual Property Office Application No. 10-2004-0014926 (Application Date: March 05, 2004), "Antenna for Portable Wireless Communication Device"

[9] Korean Intellectual Property Office Application No. 10-2000-7008943 (Application Date: August 16, 2000), "Adaptive Multi-Pillar Antenna"

[10] Korean Intellectual Property Office Application No. 10-2002-7003119 (Application Date: March 08, 2002), "Adaptive Multi-Pillar Antenna"

[11] Korean Intellectual Property Office Application No. 10-2005-0067681 (filed July 26, 2005), "Handset Quadreplier Spiral Antenna Mechanical Structures"

[12] Korean Intellectual Property Office Application No. 10-2005-0022253 (filed March 17, 2005), "Antenna with four spiral radiator structures"

The present invention relates to a QHA (Quadrifilar Helix Antenna), and is particularly suitable for implementing a QHA power supply circuit having good performance in a relatively small area by using a 90 degree hybrid and a λ / 2 transmission line. A QHA feeding structure for measuring antenna impedance.

In general, the satellite, broadcasting, telecommunications, and internet industries are exploding, and are becoming the core medium of the information society in the 21st century. The satellite broadcasting receiving equipment industry has already been developed, including satellite antennas, and this is especially noticeable in the recent fields of global positioning system (GPS) and satellite digital multimedia broadcasting (DMB). . In addition, with the development of semiconductors and the development of communication technologies, as the size of the device becomes smaller and lighter, its application range becomes wider, and its use such as GPS and DMB reception functions in vehicles as well as personal portable devices is becoming more common.

1 is a structural diagram of a patch antenna for a conventional satellite communication.

Thus, as a representative example of an antenna for receiving a conventional satellite signal, a patch antenna refers to an antenna having a planar shape, as shown in FIG.

This conventional method is advantageous in that it is small, light, inexpensive, and easy to integrate, but due to the characteristics of the directional antenna, the front of the antenna should always be installed upward to receive satellite signals. There was a disadvantage that there are many installation restrictions, such as to be mounted. This installation limitation has a limitation in design application, and when carrying, there is a problem that the reception level may drop due to friction, accessories, and mounting positions.

What has emerged as an antenna to compensate for this problem is a QHA (Quadrifilar Helix Antenna) using a conventional helix antenna.

2 is a structural diagram of a conventional helical antenna.

As shown, the helical antenna refers to an antenna which is wound around a coil 21 having a spring shape electrically having a length of λ / 4, and connects a spiral conductor to the center conductor of the coaxial feeder and connects the coaxial cable 23 The outer conductor is an antenna connected to the ground plane 25. Helical antenna has the advantage that can be implemented in a much smaller size than the dipole antenna and monopole antenna at the same frequency.

3 is a structural diagram of a conventional QHA antenna.

QHA type antennas are a type of antenna used for satellite communication in mobile wireless communication devices such as mobile terminals or GPS receivers. The antenna provides circularly polarized radiation and can be designed to have a quarter-wave or half-wavelength structure with shorted ends. Referring to the drawings, the QHA forms the ground section 35 to form the feed section 31 and the short circuit section 37 and to electrically connect therebetween. Comprising four radiating elements 33 electrically connected to one side of the feed section and the short circuit section, the feed section is arranged to feed the four radiating elements with a phase difference of 90 degrees to provide a circularly polarized radiation pattern .

1 to 3 are contents described in the prior art document information [7] (hereinafter, only the document number is described).

The quadrupole antenna is an electrical microantenna for providing circular polarization in the broad angular region. The antenna generally consists of four Helices, each Helix placed equally on the circumferential surface of the dielectric cylinder or any dielectric disk support, with four equally applied signals of four phases each Is fed. The quadruple can also be described as two orthogonal bifilars fed in four phases, where the bifilar is a two-element helical antenna.

Quadrupole antennas have been developed by many researchers, and Kilgus has proposed a halt-turn current distribution, and the half-wavelength quadrifilar is shown to be similar to the current distribution of a loop dipole antenna ([1], [2]. From this interpretation, Kilgus derives an equation describing the normalized radiant field and presents circular polarizations that exist outside of the sphere ([2]).

In the QHA, dielectric support pieces are important. Cylindrical foam, hollow dielectric tubes, or periodic dielectric spacers are used to support helical devices. These dielectric materials must have low loss tangent and low permittivity to meet the phase velocity required for radiation ([3]).

Quadruple helix feeds at 1) top and 2) bottom. In case 1) the helix element is fed at the top and these elements are shorted at the bottom above the ground plane. Electromagnetic radiation radiates towards the feed point and this arrangement is called backfire quadrifilar helix. Patton showed that as the backfire bifilar creates a conical beam and the size of the antenna increases, the beam is scanned from the backfire to the broadside and the front-to-back ratio drops to unity when the number of turns decreases to 1 (4). Kilgus provided a design technique for a short backfire quadrifilar helice. [5] When powered from the bottom, the quadruple helical antenna feeds toward the ground plane, radiates in the forward direction and forwards it. Called fire quadrifilar helix. Adam provided design data for this ([6]).

Referring to the technology filed for such a QHA antenna as follows.

FIG. 3 shows the structure of the quadruple helix antenna proposed in the [8] antenna for a portable radio communication device.

Thus comprising four radiating elements 33 for forming a quarter-wave quadruple helix structure, each of the radiating elements 33 being arranged for electrical connection to a wireless circuit of a portable radio communication device. At one end, each of the radiating elements 33 is at a second end facing the first end electrically connected to a corresponding second end of the other three radiating elements, thereby providing four radiating elements 33 An antenna unit for a portable radio communication device which forms a short circuit 37 for an electric field, wherein the quadruple helix structure is arranged between the ground and the short circuit 37 for electrical connection to the portable radio communication device. It characterized in that it comprises a grounding portion 35 is arranged coaxially along the inside of.

4 is a schematic diagram of a conventional QHA antenna, which is described in "Adaptive Multi-Pillar Antenna" of [9] and "Adaptive Multi-Pillar Antenna" of [10].

The QHA thus comprises four helical filaments (10-40) and eight radial filaments (50-120). (Other embodiments may use spiral filaments spacing six angles, and may also use spiral filaments spacing even angles.) The spiral filaments are intertwined as shown in FIG. And are positioned around the longitudinal axis of the antenna at 90 degrees to each other. Four radial filaments 50-80 are disposed at the top and 90-120 are disposed at the bottom of the spiral to connect with the helical filaments and form two bifilar loops. The antenna is fed to a set of radial filaments 90, 110 with a 90 degree phase difference between the two feeds. The radial filaments 50-80 at the top of the antenna for the feed may be a circuit that is partially shorted or open depending on the resonant length of the helical filament and the required response.

Fig. 5 is a perspective view showing the structure of a conventional QHA antenna, which is described in "Handset Quadreplier Spiral Antenna Mechanical Structures" in [11] and "Antenna with Four Spiral Radiator Structures" in [12].

Thus, it includes filler windings 12, 14, 16, and 18 that extend from the lower portion 20 to the upper portion 22 of the QHA 10 having a cylindrical shape. FIG. 5 shows that the fillers 12, 16 arranged in opposite positions are electrically connected by the conductive bridge 23 and the pillars 14, 18 are electrically connected by the conductive bridge 24. QHA is indicated. The signal propagating through the filler 12/16 has a quadrature phase relationship with the signal propagating through the filler 14/18 to produce the desired circular signal polarization. Each of the pillars 12, 14, 16, 18 comprises a conductive element such as a conductor having a circular or rectangular cross section or a wire having conductive lines or lines on the dielectric.

Conductive bridges are used with QHA having a filler length equal to an even multiple of one-quarter wavelength at the operating frequency, but are not generally used when the length of the filler includes an odd multiple of one-fourth wavelength. Each conductive bridge 23, 24 (also referred to as a crossbar) comprises a conductive tape strip.

As such, the conventional QHA has a spotlight in the fields of satellite radio or satellite mobile phone system because it is physically small and light, so that it is easy to apply to a portable satellite communication device and the price is low.

QHA is particularly advantageous for satellite communication systems because it exhibits a radiation pattern with higher antenna gain when the satellite is between the ceiling and the horizon.

In order for QHA to emit excellent circular polarization, a relatively accurate orthogonal signal must be applied, and for this, a feeding network with excellent performance is required.

However, the feeding network required for the operation of the QHA, i.e., the feeder circuit, is commonly used in applications such as ring hybrids, 90 degree hybrids, Wilkinson power dividers, etc. to reduce insertion loss and return loss and improve isolation between each output port. However, since these circuits require a relatively large area, there is a problem that is difficult to apply to portable satellite communication devices, and the prior arts have limitations that do not solve these problems.

Therefore, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to implement a QHA power supply circuit having a good performance in a relatively small area by using a 90-degree hybrid and a λ / 2 transmission line. To provide a QHA feed structure for antenna impedance measurement.

In order to achieve the above object, a QHA feeding structure for measuring antenna impedance according to an embodiment of the present invention includes an input port to which a signal is applied; An observation port where a signal is observed; A first output port for outputting a signal having a zero degree phase difference when a signal is applied to the input port; A second output port for outputting a signal having a 90 degree phase difference when a signal is applied to the input port; A first λ / 2 transmission line connected to the first output port; A third output port configured to output a signal having a 180 degree phase difference by the first λ / 2 transmission line when a signal is applied to the input port; A second λ / 2 transmission line connected to the second output port; And a fourth output port for outputting a signal having a 270 degree phase difference by the second λ / 2 transmission line when a signal is applied to the input port.

Hereinafter, an embodiment according to the present invention as described above, the technical concept of the QHA power supply structure for antenna impedance measurement will be described with reference to the drawings.

FIG. 6 is a schematic diagram of a QHA feeding structure for antenna impedance measurement according to an embodiment of the present invention. FIG. 7 is a schematic diagram illustrating input signals and output signals at respective ports of a 90-degree hybrid circuit in FIG. 6, and FIG. 8. 6 is a schematic diagram illustrating an example in which an antenna matching unit is added between a 90 degree hybrid and an antenna connection unit in FIG. 6.

As shown therein, an input port 1 to which a signal is applied; An observation port 2 in which a signal is observed; A first output port (3) for outputting a signal having a zero degree phase difference when a signal is applied to the input port (1); A second output port (4) for outputting a signal having a phase difference of 90 degrees when a signal is applied to the input port (1); A first λ / 2 transmission line (7) connected to the first output port (3); A third output port (5) for outputting a signal having a phase difference of 180 degrees by the first λ / 2 transmission line (7) when a signal is applied to the input port (1); A second λ / 2 transmission line (8) connected to the second output port (4); And a fourth output port 4 outputting a signal having a 270 degree phase difference by the second λ / 2 transmission line 8 when a signal is applied to the input port 1.

The QHA feeding structure for measuring the antenna impedance is characterized in that the matching unit 9 is inserted between the output terminal of the 90 degree hybrid and the antenna connection unit.

The matching section 9 is characterized by consisting of a lumped element or a distributed element.

The QHA feeding structure for measuring the antenna impedance has the following antenna input impedance,

Where Z _ant is the input impedance of each port of the antenna, Z ₀ is the characteristic impedance of the circuit, and S ₄₁ is the propagation scattering coefficient.

The QHA feeding structure for measuring the antenna impedance is characterized in that it is applied to Left Hand Circular Polarization (LHCP) or Right Hand Circular Polarization (RHCP).

The QHA feeding structure for measuring the antenna impedance has a value of a capacitor connected in parallel with the characteristic impedance of each transmission line as follows.

Where θ represents the electrical length of the transmission line, and Z ₀ has a 90-degree hybrid structure with reduced magnitude, which is a characteristic impedance in an equivalent λ / 4 transmission line.

A preferred embodiment of the QHA feeding structure for antenna impedance measurement according to the present invention configured as described above will be described in detail with reference to the accompanying drawings. In the following description of the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to intention or precedent of a user or an operator, and thus, the meaning of each term should be interpreted based on the contents throughout the present specification. will be.

First, the present invention is to implement a QHA power supply circuit having a good performance in a relatively small area by using a 90-degree hybrid and λ / 2 transmission line.

In addition, since the matching circuit for antenna matching can be applied by applying the power feeding structure according to the present invention, it is advantageous in the case of a small antenna.

In addition, the input impedance of the antenna can be obtained simply by measuring the propagation scattering coefficient, which is advantageous when designing a matching circuit.

In addition, due to the symmetry of the entire circuit, it is a feed structure that can be applied to all cases of Left Hand Circular Polarization (LHCP) and Right Hand Circular Polarization (RHCP) antenna systems.

Thus, the feeding structure of the present invention primarily uses a 90 degree hybrid circuit to make two orthogonal signals, and each λ / 2 transmission line to obtain more signals having a phase difference of 180 degrees for the two output terminals of the 90 degree hybrid. This is an additional form of.

6 is a schematic diagram of a QHA feeding structure for antenna impedance measurement according to an embodiment of the present invention.

Thus, when a signal is applied to the input port 1, an orthogonal signal having a phase difference of 90 degrees appears at each of the two output terminals of the 90 degree hybrid circuit, and a phase difference of 180 degrees and 270 degrees is further provided through the first λ / 2 transmission line 7. A signal having

That is, four input ports of QHA are connected to the first output port 3, the second output port 4, the third output port 5, and the fourth output port 6 of FIG. 6, respectively.

When the random impedance is viewed through the λ / 2 transmission line, the impedance is seen as the same impedance. Therefore, at the output terminal of the 90 degree hybrid, the impedances of the two input ports of the antenna appear in parallel with each other.

Assuming the four input port impedances of the QHA are the same, the impedance seen toward the antenna from the output of the 90-degree hybrid will actually appear as half of each QHA port input impedance.

When each port impedance of the antenna is 100 Ohm, the output of the 90-degree hybrid appears to be half that 50 Ohm, so it is in a matched state.

Scattered Coefficient of a general 90 degree hybrid is represented by Equation 1 below.

Where 1 is a real number 1, j is an imaginary number 1, a ₁ to a ₄ represent an input signal at each port of a 90 degree hybrid circuit as shown in FIG. 7, and b ₁ to b ₄ represent an output signal, respectively. .

FIG. 7 is a schematic diagram illustrating an input signal and an output signal at each port of the 90-degree hybrid circuit in FIG. 6.

Thus, if the output of the 90-degree hybrid is not matched, reflection occurs as shown in FIG. 7, and the relationship of Equation 2 is established if the reflection coefficient at this time is Γ.

By substituting Equation 2 into Equation 1, it can be seen that the scattering coefficient is reduced to a 2 * 2 matrix as shown in Equation 3 below.

When the input impedance of each port of the antenna is Z _ant , the reflection coefficient Γ can be expressed by Equation 4 below.

Z ₀ is the characteristic impedance of the QHA power supply circuit according to the present invention.

Substituting the reflection coefficient of Equation 4 into the transfer scattering coefficient S ₄₁ obtained in Equation 3 is expressed as Equation 5 below.

That is, when the input impedance of the antenna is mismatched, observing S ₄₁ of the 90-degree hybrid enables the input impedance of the antenna to be calculated using the relationship of Equation 5, and Equation 5 is summarized with respect to Z _ant . It can be calculated using the following equation (6).

FIG. 8 is a schematic diagram illustrating an example in which an antenna matching part is added between the 90 degree hybrid and the antenna connection part in FIG. 6.

9 is a graph showing the power distribution characteristics according to the frequency of the QHA feeding structure for measuring the antenna impedance of FIG. 6, and shows a magnitude error of 1 dB or less within the + -300 MHz band around the center frequency 2.33875 GHz.

FIG. 10 is a graph illustrating a phase change of an orthogonal signal output from the QHA feeding structure for antenna impedance measurement of FIG. 6 according to a frequency, and an accurate orthogonal signal is generated near a center frequency.

When the input impedance of the QHA is mismatched, a reflection wave is generated and an insertion loss occurs. As shown in FIG. 8, between the output terminal of the 90 degree hybrid and the antenna connection part in the QHA feeding structure for antenna impedance measurement according to the present invention. Application is possible so that the insertion loss characteristic of the feeding structure is improved by inserting the matching portion 9.

As shown in FIG. 11, four λ / 4 transmission line parts forming a 90-degree hybrid can be replaced with a capacitor connected in parallel with a transmission line of an arbitrary length, thereby reducing its size. In this case, the length of each transmission line, the characteristic impedance, and the value of the capacitors connected in parallel may have a relationship as shown in Equation 7, Equation 8 below from the equivalent ABCD parameter equation.

.

.

Where Z is the characteristic impedance in the λ / 4 transmission line, and Z ', θ, and C are capacitors connected in parallel to both the characteristic impedance and the electrical length in the transmission line of arbitrary length, respectively, and the transmission line in parallel. Where f is the center frequency of the circuit. In FIG. 11, C ₁ , C ₂ , C ₃ , and C ₄ are values formed by adding two capacitors in parallel at each end of four equivalent transmission lines. Here, each capacitor can be implemented as a lumped element, but it can be advantageous to implement it as a distributed element for a more continuous value.

In addition, as shown in FIG. 6, since the overall circuit structure is symmetrical, when the input signal is applied to the input port 1, the power supply structure for the LHCP QHA operates, but the observation port 2 and the input port 1 If the signal is applied to the observation port 2 and the input port 1 is observed in the opposite direction, the signal can be operated as a power supply structure for the RHCP QHA.

As such, the present invention implements a QHA power supply circuit having good performance in a relatively small area by using a 90 degree hybrid and a λ / 2 transmission line.

As described above, the QHA feeding structure for antenna impedance measurement according to the present invention is effective to implement a QHA feeding circuit having good performance in a relatively small area by using a 90 degree hybrid and a λ / 2 transmission line. .

Although the above has been described as being limited to the preferred embodiment of the present invention, the present invention is not limited thereto and various changes, modifications, and equivalents may be used. Therefore, the present invention can be applied by appropriately modifying the above embodiments, and it will be obvious that such an application also belongs to the scope of the present invention based on the technical idea described in the following claims.

Claims (6)

An input port to which a signal is applied; An observation port where a signal is observed; A first output port connected to the input port and the observation port and outputting a signal having a zero degree phase difference when a signal is applied to the input port; A second output port connected to the input port and the observation port and outputting a signal having a phase difference of 90 degrees when a signal is applied to the input port; A first λ / 2 transmission line connected to the first output port; A third output port configured to output a signal having a 180 degree phase difference by the first λ / 2 transmission line when a signal is applied to the input port; A second λ / 2 transmission line connected to the second output port; And A fourth output port configured to output a signal having a 270 degree phase difference by the second λ / 2 transmission line when a signal is applied to the input port; QHA feed circuit for antenna impedance measurement. delete delete The method according to claim 1, The QHA feed circuit for measuring the antenna impedance, Has the following antenna input impedance,

Where Z _ant is the input impedance of each port of the antenna connected to the first to fourth output ports, Z ₀ is the characteristic impedance of the QHA feed circuit, and S ₄₁ is the transfer scattering coefficient of the QHA feed circuit. QHA feed circuit for antenna impedance measurement. delete delete

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