X/K 頻帶昇頻混波器與線天線屏蔽效應之改善

Abstract

本論文分為兩部份: 第一部份是X頻帶單端電阻性混波器及K頻帶次諧波 昇頻混波器之設計,製造及量測. 在第二部份中,我們針對行動電話天線提 出一種有效的屏蔽方法來降低人腦曝露在電磁輻射中的潛在危險. X頻帶 昇頻混波器採用單端電阻性混波器,它具有低失真,低交戶調變的特性.昇 頻混波器IF頻段為0.9~1.4GHz, LO頻段為10GHz,RF信號為10.9~11.4GHz. 當LO功率為9dBm,外加偏壓為-0.8V時,變頻損耗在IF頻段小於9.6dB,最低 的變頻損耗為7.33dB. LO to RF和LO to IF 的隔絕度皆大於20dB. 為了 降低LO振盪源製作之困難度及取得不易,K頻帶昇頻器採用次諧波電阻性混 頻器. 這麼一來所需之LO頻率只要原來的一半,大大降低LO源取得之困難. 此二次諧波昇頻混波器的IF頻段為1~1.2GHz, LO頻率為9.8GHz. 當LO功率 為14.5dBm,外加偏壓為-0.8V時,變頻損耗在IF頻段小於16dB, 最低變頻損 耗為13dB. LO to RF和2LO to RF的隔絕度皆大於15dB. 在第二部份中, 我們研究了一種簡單的方法來防範日常使用的行動電話所產生之電磁輻射 對人腦的潛在傷害. 行動電話天線的輻射場形及其它特性因接近人腦而明 顯的被改變,這樣的交互作用使得部份的電磁能被人腦所吸收而造成潛在 的傷害. 我們藉由在行動電話線天線使用者端貼上金屬線或金屬貼片來達 成高效率的屏蔽作用以保護人腦. 此方法與未經屏蔽的天線電磁場形作比 較,發現在使用者端超過3dB以上電磁輻射功率被衰減掉. 如此一來,便大 大降低了電磁輻射對人腦的影響. There are two parts in this master project. The first part contains the design, fabrication, andmeasurement of an X-band single-ended resistive upconverter mixer and a K-band subharmonic resistiveupconverter mixer. In the second part, a novel shielding method of the dipole antenna for cellulartelephone is presented. It is for reducing the danger of human exposure to EM radiation. We selected the single-ended resistive mixer for X-band upconverter mixer, because it has thecharacteristic of low distortion and low intermodulation. In this upconverter mixer, the IF frequencyis 0.9~1.4GHz, LO frequency is 10GHz, and RF frequency is 10.9~11.4GHz. Conversion loss is lower than9.6dB and the minimum conversion loss is 7.33dB which LO power is 9dBm and dc bias is -0.8V. The LO toRF isolation and LO to IF isolation are larger than 20dB. We selected the subharmonic resistive mixer for K-band upconverter mixer, because the relative complexity and cost of mm-wave osillators. Due to subharmonic mixer is pumped by a half of the LO frequency, it greatly reduced the complexity and cost of the LO source. In this subharmonic upconvertermixer, IF frequency is 1~1.2GHz, LO frequency is 9.8GHz. Conversion loss is lower than 16dB and the minimum conversion loss is 13dB which LO power is 14.5dBm and dc bias is -0.8V. The LO to RF isolationand 2LO to RF isolation are larger than 15dB. In the second part, we study a simple method which may protect the human head from the potential danger of electromagnetic (EM) radiation in daily use of cellular telephone, especially in microwaveregion (such as ISM band 2.4GHz). The antenna radiation pattern and other characteristics are significantly altered by the presence of the human head, and this interaction as well as the resultantdeposition of microwave power in the head(specific absorption rate-SAR) are of particular interest forcellular telephones. It is possible to achieve high levels of shielding effectiveness by simply pastinga metal wire or metal tape on the user's side of dipole antenna of the cellular telephones. As comparingto the case without shielding, this method can effectively reduced EM radiation power by 3dB or more,thus produces lower SAR in the head.