First, airborne high power RF coaxial relay design
1, technical indicators
The main technical indicators of the airborne high power RF coaxial relay are shown in Table 1. The product is characterized by small drive current, low power consumption, high vibration, high power.
Table 1 Technical indicators
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2, product structure and working principle
The airborne high power RF coaxial relay is mainly composed of circuit control, electromagnetic system, push system, radio frequency switching, radio frequency interface, auxiliary contact switch, and D-type low frequency interface. The product structure is shown in Figure 1. The working principle is shown in Figure 2.
Figure 1 Map of airborne high power RF coaxial relay
The overall structure of the product is a long square. The outer interface of the upper end is a standard 9-core D-type connector low-frequency interface. It is directly welded to the printed circuit board, the circuit board, and the electromagnetic system are fixed in the microwave channel through four screws. Cavity cover. The promotion system includes two plastic push rods in the inside of the core, two pushers connected to the microwave channel and the microwave spring, and the armature that can be freely rotated, and the armature can achieve auxiliary reed and microwave transmission. The connection of the reed. The radio frequency switch consists of a rectangular coaxial transmission line, and the microwave transfer reed is in the intermediate position of the transmission line, and the spring in the microwave channel can realize the automatic reset of the microwave transmission. The external interface at the lower end is a standard N-type radio connector.
The outer cover, microwave cavity, and cavity cover are used aluminum alloy materials, which can greatly reduce self-weight, and the surface of the outer cover is effectively prevented from being etched by oxidation. Circuit control, electromagnetic system and radio frequency portion are placed up and down to prevent electromagnetic interference between each other. The D-type connector is equipped with a sealing pad with the outer cover contact, and the microwave cavity is contained with the outer cover, the circuit control, the electromagnetic system, the radio frequency switching portion is wrapped in a relatively closed space. Inside, the entry of dust, water vapor, etc.
The working principle of the airborne high power RF coaxial relay is: the D-type connector low-frequency interface is powered up, and the rated operating voltage applied to the electromagnetic system through the circuit control section. The effect of the electromagnetic system is to convert the electrical energy into mechanical energy, and complete the radio frequency and The auxiliary contact synchronous switching, the RF signal is input or output by the RF interface, and the auxiliary signal is input or output by the D-type interface.
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Figure 2 Mageptu function block diagram of airborne high power RF coaxial relay
3, program design
(1) Control circuit design
From energy saving and reduced wire fever angles, circuit control uses self-maintenance and RC self-turning structure. In order to facilitate automatic control, auxiliary contacts and TTL control methods are designed. The 9-core D-type connector, electronic component, and auxiliary contact welding of the control circuit portion are shown in Figure 3.
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Figure 3 Control circuit schematic
The D-type connector 1, 2 terminal applies 28VD.c. The excitation voltage, when the terminal 4 is high, the excitation voltage is applied to the coil L1, and there is current to pass on the coil L1, and produce electromagnetic force to operate, RF switch S1 Closed, S2 is disconnected, due to the RC-powered circuit, as the charge is continuous, the voltage of the capacitor C is constantly rising, and when completely closed, the current is zero. Since this product is self-holding type, even if the coil L1 is changed to zero, the mechanism does not flip, it is still maintained as shown in the state, and when the flip is needed, only the D-connector terminal 5 applies high electricity. Flat, the principle is the same.
The actual operation time of the product is not more than 15ms, in order to ensure the reliable action of the product, the duration of the current in the coil should be greater than 25 ms, which is determined by the capacitance charging time, and its theoretical calculation formula is as follows:
05 (temporary)
In the formula (1): c is a charging capacitor, R is a charging circuit resistor, V is a capacitance end voltage, and V0 is a capacitor initial voltage, and Vt is a T hour capacitor voltage.
(2) Electromagnetic system design
In RF coaxial relay products, electromagnetic drive is a general method, and the type used in general electromagnetic systems is mainly "balance rotary" and "spiral tube". The "balance rotary" electromagnetic system has its advantage that the armature portion of the rotating shaft is relatively balanced, and the total torque of the rotating shaft is "zero", which can high impact and vibration to ensure the reliability in harsh environments. "Spiral" electromagnetic system has the advantage of that the utilization rate of magnetic is high, and the magnetic circuit system is small, the iron core is large.
According to the application of the product, the electromagnetic system uses the "balance rotary" structure, see Figure 4, and the magnetic circuit principle is shown in Figure 5.
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Figure 4 Balance rotary type
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Figure 5 Magnetic circuit schematic
HL-magnetic steel magnetic; (IW) - magnetic potential generated by the coil is powered by the coil; R steel - magnetic steel magnetic resistance; R core - core magnetic resistance; R yoke - yoke magnetoresistance; R tango - armrests; Air gap magnetoresistance between RΔx-magnetic steel and armature; RΔ1-armature in the left loop; RΔ2-armature in the right loop.
When the coil is in the excitation state, the static suction force of the drive mechanism is:
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ΦM2, φm1 is magnetic flux of magnetic steel, and is obtained from formula (3):
In the formula (3): The magnetic field strength in the HM magnet body is obtained by the demagnetism curve of magnet, and the LM is the length of the magnetic steel, and K1 is the correction coefficient, and the Rδ is the air gap resistance, and the μ0 is a vacuum magnetic guidance coefficient. S is the area of the boots.
Φn is the magnetic flux of the coil, and is obtained from the formula (4):
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In the formula (4): n is the number of turns of the coil, i is a coil current, and Rm is a magnetic circuit magnetic resistance.
The electromagnetic suction calculation of the electromagnetic system is more cumbersome, usually using the ANSOFT MAXWELL software to simulate, in order to improve the product reliability, ensure normal operation in the full temperature range (-55 ° C ~ + 85 ° C), the actual action voltage is carried out at + 85 ° C design. Due to the rated operating voltage range 24V ~ 32V, in order to ensure the reliable driving current, the electrical resistance of the electromagnetic coil lacquer line copper material must be considered with the ambient temperature change, determined by the formula (5):
11 (temporary)
In the formula (5): R20 is a resistance value of 20 ° C; RT is the resistance value measured at the T temperature range; T is the measured ambient temperature; α is a resistance temperature coefficient, unit 1 / ° C.
(3) RF switching and radio frequency interface design
RF switch is completed in a rectangular coaxial transmission line, a rectangular coaxial transmission line cross section is shown in FIG. 6, in the rectangular transmission line, the interruption switching structure of the intermediate reed, its structural feature is the symmetry of the middle reed on the upper and lower floors. superior.
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Figure 6 Rectangular coaxial transmission line cross-sectional view
The transmission power of the rectangular coaxial transmission line is determined by the following formula:
13 (temporary)
In the formula (6): PMAX is the breakdown power (kW) of the maximum peak; ρ is a voltage stationary wave ratio; P is air atmospheric pressure (ATM); B is the upper plate height (cm); T is the thickness of the middle reed; Z0 is characteristic impedance, 50Ω.
It can be seen from the formula (6). To increase the transmission power of the rectangular coaxial transmission line, the middle reed thickness T can be increased, the distance B between the ground plate, reduce the voltage station wave ratio, and the voltage station wave ratio ρ is coaxial The characteristic impedance Z0 is related, and the important parameters affect the rectangular coaxial characteristic impedance Z0 are the middle reed thickness T, width W and the ground plate height B, width W '. In the case of the correlation of the rectangular coaxial characteristics, see Table 1.
Table 1 Rectangular coaxial characteristics
The RF input output port is an N-type coaxial connector, which is a circular coaxial transmission line. The cross section is shown in Figure 7, which is mainly related to the equipotaxial transmission line theory related formula (7), (8), (9) (10) Determine the size of the internal and external conductor.
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Figure 7 Circular coaxial transmission line cross-sectional view
Characteristic impedance Zc of the same axis is:
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In the formula (7): Z0 is characteristic impedance, 50Ω; εr is a relative dielectric constant of the internal and external conductor medium material; μγ is the relative magnetic coefficient of the medium, and B is the outer conductor radius, mm; A is the inner conductor outer radius, MM.
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Equation (8), (9), (10), medium: the highest frequency transmitted by the coaxial wire; the maximum transmission power of the same axis; the VM is the same axial line wave peak voltage; C is a light speed 3 × 108 m / Second,; z0 is the characteristic impedance; EBR is strong in the media breakdown.
By the formula (7), when the characteristic impedance Z0 is constant, B / A is the value, and when the formula (8), A, B increases, the cutoff frequency is lowered, from (9), (10), A, and B, The maximum transmission power also increases. Since the radio frequency coaxial relay decreases with the operating frequency, its transmission power is rising, so the cutoff frequency should not be designed too high, and it should be higher than its maximum operating frequency, which is an important method of ensuring the large power of the product, ie When you meet the maximum operating frequency of the product, in order to increase the power, you should increase the size of B and A.
After initially determining the correlation size, modeling, see Figure 8, using HFSS software to perform electric field simulation verification, RF input port input power signal, and the electric field distribution map is shown in Figure 9.
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Figure 8 RF transmission line model
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Figure 9 RF transmission line electric field simulation model
The middle reed and the upper floor is 1.5mm, and the air strike is about 4.5 × 106V / m. The maximum number of radio frequency transmission lines obtained by simulation is 4.6672 × 105V / m, fully meet the design requirements, and the product It has passed multiple power test validation.
Second, conclusions
According to the special requirements of airborne products, the product is resistant to environmental adaptability and electromagnetic interference performance by enhanced structures and anti-electromagnetic interference properties. TTL self-turning circuit design, self-holding structure design reduces product drive current and power consumption, "balance rotary" electromagnetic system design, improve impact, vibration performance, and use radiofrequency high-power design technology to improve product RF power transmission capacity. At present, the product has passed the identification test, and the performance indicators fully reached the airborne requirements, and performance is stable and has been widely used.
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Reprinted from -Wiku Electronic Market Network
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