JP5700418B2 - Feed matrix circuit and phased array antenna using the same - Google Patents

Description

  The present invention relates to a feed matrix circuit in which a beam direction is determined by a position of a feed port and a phased array antenna including the feed matrix circuit.

  Conventionally, it has an array of a plurality of antenna elements for microwaves and millimeter waves, and each antenna element itself is controlled by electrically controlling the phase of a received signal from each antenna element and a feeding signal to each antenna element. A phased array antenna device that can change the beam direction as a whole without moving is known. Since this phased array antenna is very expensive and large in size, it is mainly used in military and professional applications.

A phased array antenna using a matrix circuit in which the beam direction is determined by the position of the feeding port changes the beam direction in accordance with the position of the port (feeding point) of the matrix circuit that feeds power, so the feeding point switching scanning type Also called the phased array antenna.
As a small and inexpensive matrix circuit for switching beams, a Butler matrix feed circuit that uses four hybrid circuits to switch the beam direction to four directions is well known. Signals input to the power supply circuit are distributed in the matrix circuit and output with different phase differences for each port. Since the phase gradient generated on the output side differs depending on the port position where the signal is input, the beam direction changes depending on the port position of the power feeding circuit.

  However, since the Butler matrix circuit uses four hybrid circuits, it cannot be said that the size is still small enough to be used in consumer products. Butler matrix circuits are rarely used in consumer products. It is. Further, the Butler matrix circuit has a drawback that the beam cannot be directed in the boresight direction. However, in a system using an antenna, the beam in the boresight direction is often important, which is a problem.

  In view of this, the inventor has proposed a power feeding circuit called HTBM (Hybrid Three Direction Beam Matrix) for switching the antenna beam in three directions including boresight (Non-patent Document 1). The HTBM is a power supply circuit consisting of a transmission line of λ / 4, two hybrid couplers, and three switches. With one input and four outputs, the phase difference between the antennas is switched between ± 90 ° and 0 °. It is something that can be done.

  Further, the inventor has proposed a power feeding circuit called QTBM (Quarter Wavelength Three Direction Beam Matrix) as a smaller power feeding matrix circuit. This is a power supply circuit that includes only a transmission line of λ / 4 and has performance equivalent to that of HTBM (Patent Document 1, Non-Patent Document 2). However, QTBM needed to use five switches.

JP 2009-44495 A

Masatoshi Tsuji, 4 others, “3-beam direction control small array antenna including bore sight using hybrid matrix”, IEICE Transactions B, Vol. J90-B, No. 3, Mar. 2007 Masatoshi Tsuji, “Three Beam Direction Control Small Feed Matrix Circuit with Boresight Using λ / 4 Line”, IEEJ Transactions C, Vol.128, No.6, Jun. 2008

  As an application of the small phased array antenna, for example, a security system can be cited. That is, when a microwave is transmitted to a detection area and a human body (intruder) exists in the detection area, a reflected wave from the human body (a microwave modulated by the Doppler effect) is received to It is used in a security system that detects anomalies with a security sensor that detects it, shoots the scene with a camera, and sends it to a monitoring center.

  However, it is known that the security sensor has a problem of false alarm. For example, since the security sensor reacts due to insects, rain, or other misinformation factors, it takes a long time to check whether the detection signal is from an intruder. Another problem is that when a wide area is monitored with a camera, the face of a distant intruder becomes small, and even if the intruder is photographed, it is difficult to identify a person. Therefore, there is a need to identify the position of the intruder with the microwave sensor and take an enlarged image with the camera facing the intruder.

  One method to solve these problems is to detect the target position by combining a beam switching antenna that moves the beam from the antenna of the microwave sensor to the left and right and a microwave sensor that can measure the distance (two-frequency CW method). There is a technique. This is a technique for obtaining the two-dimensional position information of the target by detecting the position of the target in the horizontal direction by swinging the beam left and right and the distance from the sensor by the two-frequency CW method. Further, by shaking the beam, it is possible to determine from the detection level whether the object is a nearby insect, a distant person, or rain.

  However, if the conventional beam switching method is used, the structure of the sensor is complicated, the size is large, and the cost is high, so that it has been difficult to use it for consumer devices. In particular, switches used for microwaves and millimeter waves are expensive, and phased array antenna devices that require a large number of switches have become expensive products. Moreover, since many switch circuits are required, the size has been increased.

  Accordingly, an object of the present invention is to provide a feed matrix circuit that can reduce the manufacturing cost with a simple structure and can be reduced in size, and a phased array antenna including the same.

The present invention is a feeding matrix circuit for a phased array antenna with one input and four outputs, wherein the signal input terminal (IN), the four antenna terminals (ANT1 to ANT4), and the signal phase difference between the antenna terminals is set to 0 °. A first feeding point to be changed, a second feeding point to change the signal phase difference between the antenna terminals to −90 °, and a third feeding point to change the signal phase difference between the antenna terminals to + 90 ° And a first rat race circuit (HB1) disposed on the front side of the substrate and connected to two of the four antenna terminals, and disposed on the back side of the substrate, A second rat race circuit (HB2) connected to two of the four antenna terminals and an electrical length of a quarter wavelength of the input signal, the first rat race circuit (HB1) And a first line (Ta) that connects the second rat race circuit (HB2) and an input A second line (Tb) having an electrical length of a quarter wavelength of the signal and connected to the signal input terminal (Port1), the second line (Tb), and the first to third A three-way selector switch (SW) that selectively switches the connection with the feeding point, and by switching the feeding to the first to third feeding points with the three-way selector switch (SW) The main point is that the feed matrix circuit is capable of switching the beam direction of the four-element array antenna to three directions including the boresight direction, and preferably the first line (Ta) is arranged on the front side of the substrate. A front line having an electrical length of 1/8 wavelength of the input signal, a back line having an electrical length of 1/8 wavelength of the input signal disposed on the back side of the substrate, the front line and the back line And vias that connect to each other.
Moreover, this invention makes a summary the phased array antenna provided with the said electric power feeding matrix circuit.

  According to the present invention, it is possible to provide a low-cost power feeding matrix circuit that can obtain the same characteristics as those of the prior art with a simple structure and can be reduced in size, and a phased array antenna including the same.

Circuit diagram of the surface side of the feeder circuit according to the embodiment Circuit diagram of the back side of the feeder circuit according to the embodiment S-parameters of the power supply circuit according to the example plotted on the polar chart

  The present invention relates to a small feed matrix circuit of a 1-input 4-output phased array antenna called RTBM (Rat-race Tree Beam Matrix). This feeding circuit can switch the phase difference between the antennas to + 90 °, -90 °, and 0 ° by setting the switch. Therefore, the beam direction of the 4-element array antenna is changed to three directions including the boresight direction. Switching is possible. The power level of each antenna is uniformly 1/4 of the input signal. The main components used in this circuit are two rat race circuits and one three-way selector switch, and the structure is simple. When a three-layer substrate having a dielectric constant of 3.3 is used, the size of this circuit is, for example, 46 × 55 mm as shown in the embodiment, and can be made smaller than the conventional power supply circuit.

  The characteristic of this power feeding matrix circuit is that the phase differences between the antennas can be made uniform at 0 °, −90 °, and + 90 ° by setting the switches. The power supply circuit of the present invention is calculated by an RF circuit simulator, and the result almost matches the theoretical value, and it can be confirmed that it operates correctly. The power feeding circuit of the present invention contributes to miniaturization of a phased array antenna having a plurality of element antennas arranged at equal intervals.

  Hereinafter, details of the present invention will be described with reference to examples, but the present invention is not limited to the examples.

"Constitution"
FIG. 1 is a circuit diagram on the front surface side of the power feeding circuit according to the embodiment, and FIG. 2 is a circuit diagram on the back surface side. The substrate is composed of three layers, and circuits using microstrip lines are arranged on the front and back surfaces. The middle layer is the ground plane. In each figure, the pattern on the opposite side is written in light gray. Black spots are vias that connect the front and back surfaces. HB1 and HB2 arranged on the front and back are 1.5λ type 3dB rat race circuits, which are designed with a characteristic impedance of 70.7Ω. The four lines connected from the rat race circuit to the antenna terminals ANT1 to 4 have the characteristic impedance of 50Ω and the line lengths are all the same. The line lengths of the lines Ta, Tb, and Tc are λ / 8, λ / 4, and “not specified”, respectively, and the characteristic impedances are 50Ω, 35.3Ω, and 25Ω. Ta is used to obtain the electrical length of λ / 4 by combining the front and back lines. Tb is used for impedance conversion from 25Ω to 50Ω. SW is a three-way selector switch, placed right next to the ports A1 and A2 of the rat race circuit, and the length of the line connecting the switch and the rat race circuit is negligible.

  The input / output impedance of the antenna and signal source is 50Ω. When the switch setting is 1 (SW1), the signal input from the IN terminal is converted to 25Ω by λ / 4 impedance conversion, and then half of the power is left to port C1 of the rat race circuit HB1 on the surface. Half is led to port C2 of the rat race circuit HB2 on the back side. The signal is output from ports B1 and D1 on the front side and from ports B2 and D2 on the back side. Each port B1, B2, D1, and D2 is supplied with power to four antennas ANT1, ANT2, ANT3, and ANT4, respectively. Due to the characteristics of the rat race circuit, it is known that signals are not output from ports A1 and A2 (Fumiaki Okada, “Basics and Applications of Microwave Engineering”, published by Sankaido). Therefore, the line Ta connected here can be ignored. Here, when ignoring the length of the line Tc and the length of the line between the rat race circuit and the antenna, the phases and power levels of the four antenna ports all match, and the phase is − based on the input signal IN. The output is 180 ° and the power level is -6dB.

  When the switch setting is 2 (SW2), half of the input signal enters port A1 of the front-side rat race circuit, and half of the signal passes through the front-side and back-side lines Ta, and the phase is 90 ° behind the phase. Enter port A2 of the race circuit. Due to the characteristics of the rat race circuit, the phases output to ANT1, ANT2, ANT3, and ANT4 are 180 °, 90 °, 0 °, and -90 °, respectively, with respect to the input signal. -90 ° with respect to. And each antenna output level is -6dB. At this time, since no signal is output from the ports C1 and C2, the line Tc can be ignored.

  When the switch setting is 3 (SW3), the input signal enters the rat race circuit HB2 from the port A2 on the back surface, and half of the signal passes through the line Ta and enters the rat race circuit HB1 on the front surface with a phase delay of 90 °. The phases output to the antennas ANT1, ANT2, ANT3, and ANT4 are 90 °, 180 °, -90 °, and 0 °, and the phase difference between the antennas is + 90 ° with respect to ANT1. And each antenna level is -6dB.

《Design and simulation》
In the simulation, the circuits shown in FIGS. 1 and 2 are analyzed by an RF circuit simulator SNAP (modified nodal analysis method, MEL). In the analysis, transfer characteristics S21 to S51 are obtained with input port IN as port 1 (P1) and antenna ports ANT1 to ANT4 as ports 1 to 5 (P2 to P5).
In addition, the analysis is performed by ignoring the “electric length of the line from the rat race circuit to the antenna, the length of the line Tc, the via, the switch, and the loss of the line”.

  The characteristics of the substrate shall be a dielectric constant of 3.3 and a plate thickness of 0.8 mm to match the values reported by HTBM. The width (W) and length (L) of each line are calculated by SNAP. Line width W = 1.0mm (Z0 = 70Ω) W = 1.8mm (Z0 = 50Ω) W = 3.1mm (Z0 / 2 = 35.3 Ω) W = 4.9mm (Z0 = 25Ω), λ / 4 line length L = 19.1mm. The analysis frequency is 2.4 to 2.5 GHz.

"Measurement result"
In FIG. 3, RTBM S21, S31, S41, and S51 calculated by the simulator are plotted on the polar chart. The circled markers in the data are points at 2.45 GHz, and Table 1 summarizes the angles and amplitude values.

[Table 1]

  In SW1, the four data are almost the same, the phase is 180 °, and the level is -6dB. In SW2, the phases of S21, S31, S41, and S51 are -179 °, 89 °, 0 °, and -90 °, and the phase between the antennas is delayed by about 90 ° with ANT1 as a reference. All four levels are about the same -6dB. In SW3, the phases of S21, S31, S41, and S51 are 89 °, -179 °, -90 °, and 0 °, and the phase between the antennas advances by about 90 ° with ANT1 as a reference. All four levels are about the same -6dB.

  As described above, the simulation results almost coincided with the theoretical values, and it was confirmed that the power supply circuit according to the example operates correctly. The size of the power supply circuit according to the embodiment is estimated to be 46 × 55 mm when the switch circuit is 20 × 20 mm. This is 80% of the size of HTBM in Non-Patent Document 1, and can be expected to be smaller than HTBM.

  The present invention is suitable for use as a consumer product such as a microwave sensor for a crime prevention system because it has a small and simple structure and can reduce the manufacturing cost.

Claims (3)

A feed matrix circuit for a phased array antenna with 1 input and 4 outputs,
A signal input terminal (IN), four antenna terminals (ANT1 to ANT4), a first feeding point that changes the signal phase difference between the antenna terminals to 0 °, and a signal phase difference between the antenna terminals of −90 ° A substrate provided with a second feeding point to be changed to, and a third feeding point to change the signal phase difference between the antenna terminals to + 90 °,
A first rat race circuit (HB1) disposed on the front side of the substrate and connected to two of the four antenna terminals;
A second rat race circuit (HB2) disposed on the back side of the substrate and connected to two of the four antenna terminals;
A first line (Ta) having an electrical length of a quarter wavelength of an input signal, and connecting the first rat race circuit (HB1) and the second rat race circuit (HB2);
A second line (Tb) having an electrical length of a quarter wavelength of the input signal and connected to the signal input terminal (Port1);
A three-way selector switch (SW) that selectively switches the connection between the second line (Tb) and the first to third feeding points;
Have
Feeding that can switch the beam direction of the four-element array antenna to three directions including the boresight direction by switching feeding to the first to third feeding points with the three-way selector switch (SW). Matrix circuit. The first line (Ta) has an electrical length of one-eighth wavelength of the input signal arranged on the front side of the substrate, and one-eighth of the input signal arranged on the back side of the substrate 2. The feed matrix circuit according to claim 1 , comprising a back line having an electrical length of a wavelength, and vias connecting the front line and the back line .   A phased array antenna comprising the feeding matrix circuit according to claim 1 or 2.