K波段單平衡混頻器的ADS設計和仿真
Design and Simulation of a K-Band Single-balanced Mixer by ADS

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摘 要
現(xiàn)如今，隨著微波技術的發(fā)展，混頻器作為微射頻電路中不可或缺的部件，已成為儀器科學的重要研究領域之一。無論是微波通信、雷達、遙控、遙感，還是偵查與電子對抗，以及微波測量系統(tǒng)，都必須把微波信號用頻器降到中低頻來進行處理。而集成式混頻器體積小，設計技術成熟，性能穩(wěn)定可靠，結構靈活多樣，可以適合各種特殊應用。就研制小型化、功率小、結構緊湊的測速雷達微波收發(fā)裝置，實現(xiàn)高速目標多普勒雷達測速信號的采集和前端信號處理而言，混頻器實現(xiàn)對輸入信號的頻移，把頻率較高的微波信號降到中低頻進行處理，是需要研究的主要內(nèi)容之一。
本論文主要研究K波段單平衡混頻器，即將頻率范圍為18-26GHz的波段信號通過混頻器后，獲得中頻信號輸出。本文設計的是一無源單平衡混頻器，射頻頻率為23.965-24.035GHz，本振輸入為24GHz，輸出中頻信號的頻率為35MHz。選用羅杰斯公司生產(chǎn)的Rogers RT/duriod5880基板，介電常數(shù)為2.5，基板厚度選用0.17mm,導體介質選用電導率為58000000的銅箔，厚度選用0.01mm。基于課題中提出的研究目的與當前國內(nèi)外的研究現(xiàn)狀，論文主要就項目中涉及到的單平衡混頻器的ADS設計研究，主要分以下幾個方面：
（1）設計一個耦合度為3 dB的定向耦合器，耦合器用于射頻與本振信號的混合。它的主要技術指標有駐波比、耦合度、插入損耗。定向耦合器采用同軸線、帶狀線、微帶線、金屬波導或介質波導等各種型式。它的工作原理是主線中傳輸?shù)墓β释ㄟ^多種途徑耦合到副線,并互相干涉而在副線中只沿一個方向傳輸。
（2）設計低通濾波器。濾波器是一個二端口網(wǎng)絡，在設計射頻系統(tǒng)時通常會加入濾波器以精確實現(xiàn)預定的頻率特性。當頻率不高時，濾波器可由集總元件的電感和電容構成，但當頻率高于500MHz時，由于電路寄生參數(shù)的影響不可忽略，濾波器通常由分布參數(shù)元件構成。
（3）研究定向耦合器和低通濾波器之間的匹配網(wǎng)絡。在射頻電路中，阻抗匹配是最重要的概念之一，它是電路設計時必須要考慮的重要問題。匹配包括多個方面，例如傳輸線與負載之間的匹配，以及信號源與負載之間的共軛匹配等。
關鍵詞：K波段；單平衡混頻器；射頻；本振；阻抗匹配
Abstract
In the past years, RF mixer circuit has become an important instrument in the field of scientific research as an integral part of the micro- parts. we have to decrease the frequency of the microwave signal by using the mixer to deal with information when it is applied in the field about microwave 、radar、remote control 、remote sense and investigation and electronic warfare.
The integrated mixer small size, design technology is mature, stable and reliable performance, flexible structure that can fit a variety of special applications. On the development of small, low power compact speed radar microwave transceiver means, the front-end signal processing to achieve high-speed acquisition and Doppler radar target speed signal. One of the main research need is the mixer input signal to achieve the frequency shift to higher frequencies down to the low-frequency microwave signal processing. In this thesis, K -band single balanced mixer. Coming in the frequency range 18-26.5GHz band signal through the mixer to obtain an intermediate frequency signal output is a passive single- balanced mixer, RF frequency of 24GHz, the LO input is 26GHz, the frequency of the output IF signal is 35MHz.
Optional Rogers produced Rogers RT/duriod5880 substrate, a dielectric constant of 2.5, substrate thickness selection 0.17mm, conductor medium chosen for the 58 million of copper conductivity, thickness optional 0.01mm. ADS design studies based on single- balanced mixer issues raised in the research purpose and research status at home and abroad, the paper mainly on projects related to the main points the following aspects.
First, for the design of a coupling 3 dB directional coupler, the coupler for mixing the RF signal with the local oscillator. Its main technical indicators VSWR, coupling degree of insertion loss. Directional coupler using various types of coaxial, stripline, microstrip lines, metal waveguide or dielectric waveguides. It works by mainline transmission power coupled to the secondary line through a variety of ways, and interfere with each other while in the sub- transmission line in one direction only.
Second, Design a low-pass filter. Filter is a two-port network, in the design of RF systems usually add filters to accurately achieve a predetermined frequency characteristics. When the frequency is not high, the filter can be lumped inductance and capacitance of the element, but higher than the frequency of 500MHz, the influence of the parasitic parameters of the circuit can not be ignored, the filter usually consists of distributed elements. This design requires a low-pass filter with a cutoff frequency of 35MHz.
Directional coupler and the matching network between the low - pass filter. In RF circuits, impedance matching is the most important concept, it is an important issue that must be considered when designing the circuit. Match comprising a plurality of areas, for example, matching between the transmission line and the load, and the conjugate match between the signal source and the load and the like.
Keywords : K - band; S..