Design of Ku-band dual-feed high-frequency head

Jacktang

Design of Ku-band dual-feed high-frequency head [Copy link]

This paper introduces the design method of a Ku-band dual-feed high-frequency head developed. Main performance indicators required by the project 1. Performance indicator requirements (1) Input frequency: 11 7 12.75GHz (2) Noise figure: NF≤0.8dB (3) Gain: G=55±5dB (4) Image suppression: ≥30dB (5) Local oscillator nominal frequency: 10.75 GHz_1MHz (6) Local oscillator stability: f±2MHz (7) Carrier intermodulation ratio: >140 dB (8) Gain stability: ≤0.5 dB (@/36MHz) (9) Output frequency: 950~2000MHz (10) Local oscillator leakage level: ≤-50dBmW (11) Local oscillator phase noise: ≥60dB(@/1KHz) ≥85dB(@/10KHz) ≥100dB(@/100KHz) (12) Operating voltage range: 10--20V 2. Structural requirements: The sample cavity is made of aluminum die casting, and the cavity surface is treated with plastic spraying. 3. Environmental adaptability requirements (1) Temperature requirements The working temperature range of the high-frequency head is -40℃-+60℃ (2) Humidity requirements The high-frequency head should be able to work normally in an environment with a relative humidity of 5%-100%: (3) Atmospheric pressure requirements The high-frequency head should be able to work normally in an environment with the following atmospheric pressure conditions: 86-106KPa Basic working principle and system block diagram of Ku-band dual-feed high-frequency head 1. Basic working principle The Ku-band high-frequency head is also called Ku-band down-converter. It transmits the downlink signal transmitted by the satellite to the LNB feed waveguide input after amplification by the antenna, and then inputs it to the high-frequency amplifier through the coupling probe (or coupling microstrip transmission line). After amplification by the low-noise amplifier, the PF signal of the required frequency band is selected through the band-pass image frequency suppression filter. It is then mixed with the local oscillator signal to produce the intermediate frequency signal. The output signal is sent to the satellite receiver through a cable to complete QPSK demodulation and MPEG-2 decoding. It is provided to the TV in the form of A/V signal. The user can select the signal from any of the two satellites through the control signal. Design of the main unit circuit of Ku-band dual-feed high-frequency head 1. Field effect tube low noise amplifier (FET LNA) When designing an amplifier circuit, many characteristics need to be considered, but the most important ones are stability, power gain, noise figure, output power, input and output voltage standing wave ratio, dynamic range, power gain band flatness, etc. The low noise amplifier of this product adopts NEC's NE4210S01 field effect tube low noise amplifier. The function of the field effect tube low noise amplifier is to amplify the weak signal fed from the cavity feed source. (1) Design of the first-stage FET LNA This circuit is at the forefront of the high-frequency head active circuit, so the best noise matching is adopted. Generally, any noisy two-port network can be represented by a noise voltage source and a noise current source connected to the input end of the noiseless two-port network. If the circuit is dominated by voltage noise, then using a high source impedance will minimize the transmitted noise signal. If it is dominated by current noise, connecting a low source impedance will minimize the transmitted noise signal. When two noise sources exist at the same time, a specific source admittance (or source impedance) will be derived from the minimum noise factor of the circuit, which is called the optimal source admittance. The Li Jiao Smith chart can give the equal noise factor circle on the input admittance or impedance plane. We use the following relationship to describe how the noise factor increases as it deviates from the minimum value: F2Fmin+lKn/Gs】Ys-YoI In the formula, F=noise factor, Fmin=minimum noise factor, Rn=equivalent noise resistance, Yo=optimal source admittance that gives the minimum noise factor=Go+jBo, Ys=source admittance. The noise factor calculation formula of the multi-stage cascade amplifier is as follows: NF=NFl+(NF2-1), Gl+((NF3-1)/Gl G2+…. From the above formula, it can be seen that the noise factor of the first-stage amplifier will play a decisive role in the size of the noise factor of the entire high-frequency head product. The microwave circuit board we use is Rogers' high-performance circuit Rogers board, whose dielectric constant is 3.38-+0 05, thickness is 0.5mm, and loss tangent is 0.0027. We use advanced microwave circuit simulation software ADS for optimization simulation, and then through careful debugging, after several tests and debugging. Finally, our design requirements were met, and the overall noise of the high-frequency head was less than 0.8dB, as shown in the figure below: 2. Design of microstrip bandpass filter (1) The main technical indicators of the bandpass filter: ① Passband boundary frequency and passband attenuation and fluctuation ② Stopband boundary frequency and stopband attenuation (2) Design steps of microstrip bandpass filter We use ADS software to design the filter. The design steps include: ① Schematic drawing ② Circuit parameter optimization and simulation ③ Layout simulation, etc. Draw the circuit layout according to the results of software simulation design and process it into a circuit board. We debug the processed circuit, simulate it through software, debug it again, and after several repeated simulations and tests, it meets our design requirements. The main indicators of the bandpass filter we designed are as follows: ① Passband frequency: 11.7-12.75GHz ② Attenuation within the passband is less than 3dB ③ Fluctuation within the passband is less than ldB ④ Stopband attenuation is greater than 30dB 3. Design of dielectric frequency-stabilized oscillator The dielectric frequency-stabilized oscillator is an oscillator that uses a microwave dielectric resonator as a high-Q cavity to stabilize the frequency of a FET oscillator. In recent years, low-loss materials used as dielectric resonators have made great progress. The Q value of the dielectric resonator is close to that of the metal cavity resonator, and its temperature coefficient can be controlled by using different material formulas to achieve mutual compensation with the FET circuit, so that a very high frequency stability can be obtained. Moreover, it is small in size and light in weight, and is easy to integrate with microstrip circuit components. The circuit form of the dielectric frequency-stabilized oscillator we designed is a feedback circuit, using a microwave gallium arsenide field effect tube as an oscillator tube, and a dielectric oscillator as a high-Q frequency-stabilizing cavity. The main advantages of this design are that the main oscillation power is generated once, there is no subharmonic interference below the main oscillation frequency, and it is small in size, simple in structure, low in power consumption, small in number of components, and high in reliability. The basic principle of dielectric oscillator is that when dielectric resonator is not added, FET circuit is in the working state of microwave amplifier, and there is no oscillation at this time. In order to obtain self-excited oscillation, dielectric resonator is placed between output microstrip line and input microstrip line, and part of output power is fed back to gate through magnetic field coupling. When feedback phase and feedback power are appropriate, oscillation will occur. Dielectric resonator is equivalent to narrowband bandpass filter. At the center frequency of dielectric resonator, feedback is strongest and phase is appropriate. Changing the angle between gate and drain microstrip line and the position of dielectric will change feedback phase and power at the same time, and repeated trials are required to obtain the best structural position. The design of oscillator includes output matching circuit and input matching circuit, coupling of dielectric resonator and microstrip line, and distance L to FET, etc. We simulated and tested the ADS software, repeatedly simulated and tested, and finally achieved the following main design indicators of the dielectric stabilized frequency oscillator: ① Nominal frequency of the local pulse oscillator: 10.75GHz±1MHz ② Local oscillator stability: 10.75GHz±2MHz (-40℃—+60℃) ③ Local oscillator phase noise: ≥60dB(@/1KHz) ≥85dB(@/10KHz) ≥lOOdB(@/100KHz) ④ Local oscillator leakage level: ≤-50dBmw 4 Feed design According to the requirements of the Ku-band integrated high-frequency head, the feed of the reflector antenna needs to be designed as one with the downconverter. After the downlink signal is received by the antenna feed, it is directly sent to the downconverter through the waveguide coaxial conversion to complete the frequency conversion. In the design, the antenna feed uses a conical corrugated horn, and adopts broadband technology with variable slot depth and slot width, so that it has good VSWR and radiation characteristics within the signal bandwidth of 1.05GHz. The results of HIS simulation design are shown in Figures 1, 2, and 3. Since the satellite high-frequency head works outdoors, its operating temperature range should reach -40°C to 60°C, the relative humidity should meet 10%--100%, and the feed port should be water-tight. Product innovation and advancement 1.Dual-feed design of the cavity According to the customer's requirements, they need to receive signals from two satellites at the same time. In response to the special requirements of the customer, we adopted a dual-feed design in the design of the product solution to achieve the simultaneous reception of signals from two stars, and used the reflector antenna deflection feeding technology to achieve two beams with a certain angle. (Use a feed source to receive the signal from a satellite respectively). In the design process, it is necessary to focus on solving problems such as the mutual interference of the signal beams of the two satellites. 2. Low noise Using Microwave office and ADS for simulation and optimization, the total noise coefficient NF of the designed Ku-band high-frequency head is ≤0.8dB. 3. Low power consumption One of the future development trends of high-frequency heads is low power consumption. When the input voltage is l3/18V, the Ku dual-feed high-frequency head we developed uses a high-integration, low-current tube, so that the power supply current Imax of the whole machine is <120mA. 4. Novelty This product is independently developed by SiChuang. From the design of the cavity and feed port, solution selection, circuit design, component selection, PCB board production and product appearance design, there is no similar product in the domestic and foreign markets. Its novel and unique appearance will surely be recognized by customers. 5. High profit In the design, we use a large number of domestic and Taiwanese components and strictly control the cost of the product. The material cost of the product is less than 5 US dollars, while the price of this product in the foreign market is about 10 US dollars. The profit margin is large. 6. Good reliability Since the satellite high-frequency head is an outdoor product with a harsh working environment, it has high requirements for the reliability index of the product. To ensure the stability of the product, we completed the following tests during the design confirmation process: (1) 24-hour immersion test - no leakage was found: (2) Continuous copying at -40 ℃ and 60 ℃ for 12 hours - the local oscillator is stable within f0±1.5MHz. There is no self-excitation phenomenon: (2) Continuous operation outdoors for 30 working days with power on - the performance index is normal. No abnormal phenomenon occurs. The above experiments have verified the reliability of the product in the client's use. In summary, through our more than ten years of accumulation in technology, production, market and other aspects of the high-frequency head industry, we have formed a deep understanding of high-frequency head products. Based on the actual use of customers as the objective condition, we have successfully developed a Ku-band dual-feed satellite high-frequency head and achieved the design indicators. Compared with similar products on the international market, the dual-feed Ku high-frequency head we developed has obvious performance indicator advantages in major performance indicators such as noise coefficient, local oscillator stability, and gain flatness. It is an excellent and cost-effective Ku-band downconverter. The product is currently in a leading position in domestic technology and is also a very competitive product internationally.

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Good summary.