| 摘要: | 本論文是在天線內負載可調元件及開關來達成頻率可調與切換的效果。我們利用可調元件來改變天線的電氣長度以提升操作頻率範圍。論文中包含兩個天線，分別為：使用鐵電可變電容實現之頻率可調環形槽孔天線與2.45-GHz及5.8-GHz ISM頻帶切換微帶天線。
我們設計並且實作量測出一個使用可調匹配網路的頻率可調環形槽孔天線。此頻率可調天線是由負載鐵電可變電容在環形槽孔上設計而成。饋入方式使用共平面波導以保持單平面的優點。然而，使用共平面波導饋入難以在較大的頻寬上有良好的匹配，因此我們添加了可調匹配網路。可調匹配網路是使用串連一個鐵電可變電容來實現，此方法並不會增加天線的面積。量測結果顯示:當天線中鐵電可變電容偏壓由0 V調至15 V，天線操作頻率從6.71 GHz改變至9.14 GHz，其頻寬為30.6%。當偏壓15 V時，天線增益為−3.1 dBi。在整個操作頻帶內返回損耗皆大於20 dB，可表示可調匹配網路的效果良好。
論文中還設計了能切換於2.45-GHz及5.8-GHz ISM頻帶的微帶天線。在兩片patch中間以等距5個PIN二極體串聯。在開關為關閉的狀態時，只一片patch接通訊號；使天線共振頻率為5.8 GHz。反之，在開關為開啟的狀態下，兩片patch由開關接通，使電氣長度變長；其天線共振頻率改變為2.45 GHz。饋入方式為同軸探針的方法，並設計於適當的饋入位置可達到阻抗匹配的效果。量測結果顯示：當偏壓為−10 V時，開關為關閉的狀態時，天線共振頻率為5.75 GHz，天線增益為6 dBi；而當偏流為250 mA時，開關為開啟的狀態時，天線共振頻率為2.53 GHz，天線增益為−0.8 dBi。在兩個頻帶的返回損耗皆大於15 dB。
本論文成功設計並實現了使用鐵電可變電容實現之頻率可調環形槽孔天線與2.45-GHz及5.8-GHz ISM頻帶切換微帶天線。其中頻率可調環形槽孔天線的頻寬在現有使用鐵電可調電容之文獻中最寬的。
;In this thesis, by loading the antennas with either tuning elements or switches, the operating frequency is made reconfigurable. Two antennas are presented: a frequency-reconfigurable slot-loop antenna with ferroelectric varactors and a switchable patch antenna for 2.45-GHz and 5.8-GHz ISM bands.
First, a frequency-reconfigurable slot-loop antenna with a tunable matching network is designed, fabricated, and measured. The frequency-reconfigurable antenna is implemented by loading ferroelectric varactors along a slot loop. CPW (coplanar waveguide) feed is used to preserve the advantage of being uniplanar. However, it is usually difficult to provide a good matching over wide frequency by a direct CPW feed. To solve this problem, a tunable matching network is added. The tunable matching network is implemented using a varactor in series, which does not increase the area of the antenna. Measurement results show that, when the bias voltage of the ferroelectric varactors is increased from 0 V to 15 V, the operating frequency of the antenna can be tuned from 6.71 GHz to 9.14 GHz, equivalent to a 30.6% bandwidth. When biased at 15 V, the antenna gain is −3.1 dBi. Over the entire frequency tuning range, the return loss is greater than 20 dB, validating the effectiveness of the tunable matching network.
Second, a patch antenna that can be switched between 2.45-GHz ad 5.8-GHz ISM bands is designed, fabricated, and measured. The antenna is designed by connecting two patches with five equally spaced PIN diodes, which act as switches. When the switches are off, only one patch is connected to the feed and the operating frequency is designed to be 5.8 GHz. On the other hand, when the switches are turned on, the two patches are electrically connected, resulting in an increase in electrical length and lowering the operating frequency to 2.45 GHz. The switchable patch antenna is fed using a coaxial probe feed. The position of the feed is adjusted so that good matching is observed for both frequencies. Measurement results show that, when the bias voltage of the PIN diodes is −10 V, i.e., when operated in the off state, the resonant frequency of the patch antenna is 5.75 GHz and its gain is 6 dBi. On the other hand, when the overall bias current is 250 mA, when operated in the on state, the resonant frequency of the patch antenna is 2.53 GHz with a gain of −0.8 dBi. At both frequency bands, the return loss is greater than 15 dB.
In this thesis, two frequency-reconfigurable antennas using either ferroelectric varactors or PIN diodes are successfully designed and implemented. The tunable slot-loop antenna achieves the widest effective bandwidth when compared with other ferroelectric-based tunable antennas in the literature. |
