TMm0 Mode Rectangular Patch Antennas with Improved Radiation Characteristics
High gain, low-cost planar antennas are desired in many point to point wireless communication applications. The fundamental TM10 mode of rectangular patch antenna has a drawback of low gain in broadside direction. Higher-order TMm0 (m = 3, 5, ) modes can provide large broadside gain but suers from high E-plane sidelobe levels (SLL) and non-optimum gain. In this thesis, two techniques namely slot-loading and partial notch-loading techniques for improving the radiation characteristics of higher-order TMm0 (m = 3, 5, ) modes in rectangular patch antennas are presented. Dierent single-layer high gain TMm0 mode patch antennas having high gain (12-16 dBi) and reduced SLLs (< -12 dB) suitable for broadside medium-range applications are demonstrated.
In 1st part of the thesis, a slot-loading technique inspired by slotted waveguide antennas is proposed. In this technique, a pair of resonant slots is placed in the center out-of-phase region of TM30 mode rectangular patch antenna, which acts as a new radiating edge. Superposition of radiated elds of TM30 mode patch and fundamental mode of slots results in high directivity with reduced SLL. The placement of resonant slots also has a slight adverse eect on the in-phase current distribution resulting in an asymmetric radiation pattern. It is shown that a dierential feeding scheme can be employed to achieve symmetric radiation pattern and gain enhancement by keeping the desired in-phase current distribution intact. The proposed antenna shows a measured gain of 12.8 dBi and SLL of -12 dB, and it can be used as a substitute for 22 array of patch antennas operating in fundamental mode. Furthermore, since some applications require single-fed patch antennas; therefore, a method for designing single-fed high gain TM30 mode patch with symmetric radiation pattern using a planar 22 slot array etched at the center of the patch is also presented.
In the 2nd part, a novel notch-loading technique for gain enhancement and E-plane SLL reduction in TMm0 (m = 3, 5, ) mode patch antennas is presented. In this method, undesired out-of-phase surface current distribution regions of higher-order mode TMm0 (m = 3, 5, ) patch are partially removed (notch-loaded) to create additional radiating edges. It is demonstrated using an analytical model that the superposition of radiated elds due to these new radiating edges and unperturbed TMm0 (m = 3, 5, ) mode results in gain enhancement and E-plane SLL reduction. Moreover, the proposed antennas are easy to fabricate due to their single-layer conguration. To verify the design, two notch-loaded higher mode patch antennas operating in TM30 and TM70 mode are fabricated and tested. Notch-loaded TM30 mode patch shows a measured E-plane SLL of -10.5 dB and gain of 12.9 dBi whereas, notch-loaded TM70 mode patch shows a measured E-plane SLL of -12.8 dB and gain of 16 dBi which is the highest reported antenna gain for single-layer TM70 mode rectangular patch antenna so far. In some applications, further reduction in SLL is desired. A method for designing low SLL TM30 mode patch with improved return loss using a combined notch and fractal slot loading is also presented. The new antenna shows a 5 dB reduction in SLL and 7 dB improvement in return loss compared to notch loaded TM30 mode patch.
Finally, in the 3rd part of the thesis, high gain frequency recongurable dual-band patch antennas are investigated. A new technique based on metamaterial loaded patch antennas is developed. In this technique, a composite right/left-handed transmission line (CRLH TL) unit cell is gap-coupled with the radiating edge of a rectangular patch antenna. The dual-band behavior is achieved due to the coupling of zeroth-order resonance mode of CRLH TL and TM10 mode of the patch antenna. It is shown that the frequency ratio can be changed by varying the gap between the patch and CRLH TL unit cell. The proposed conguration enables frequency recongurability by changing the CRLH TL unit cell using a switch. A prototype of the antenna having frequency ratio f2=f1 = 1:08 is designed and fabricated. The proposed antenna shows measured S11 10 dB bandwidth of 100 MHz and 50 MHz at resonance frequencies of f1 = 4.84 GHz and f2 = 5.22 GHz, respectively. A 22 dual-band CRLH TL coupled patch array is also presented, showing more than 12.7 dBi gain at both resonant frequencies.