1. Hanyang University 1/17 Antennas & RF Devices Lab. MODERN ANTENNA HANDBOOK by CONSTANTINE A.BALANIS ch. 4.4 – 4.5.2 Jeong Gu Ho

2. Hanyang University 2/17 Contents 4.4 FEED/EXCITATION METHODS 4.4.1 Coax probe feed 4.4.2 Coax probe with capacitive feed 4.4.3 Microstrip-line feed 4.4.4 Proximity-coupled microstrip line feed 4.4.5 Aperture-coupled feed 4.4.6 Coax probe with a U-slot feed 4.5 DUAL-POLARIZATION AND CIRCULAR-POLARIZATION TECHNIQUES 4.5.1 Dual polarization 4.5.2 Circular polarization

3. Hanyang University 3/17 4.4 FEED/EXCITATION METHODS 4.4.1 Coax probe feed This feed method easy to fabricate. But its major disadvantage is that is provides narrow bandwidth. The center conductor pin penetrates through the substrate and the patch and is then soldered to the top of the patch. The location of the probe should be at a 50-ohm point of the patch to achieve impedance matching. substrate thickness -> capacitor (store energy) -> Q(quality factor) ->BW(bandwidth)

4. Hanyang University 4/17 4.4.2 Coax probe with capacitive feed For wider bandwidth, thicker substrate is generally used. If a regular coax probe were used, a larger inductance would be introduced, which results in impedance mismatch. To use a capacitive disk introduces complexity and additional loss to the feed circuit. To reduce this complexity, use a “tear-drop” or a cylindrical shaped probe. Method(2) Method(1) coupling

5. Hanyang University 5/17 It describes energy absorbed by one antenna’s receiver when another nearby antenna is operating. That is, mutual coupling is typically undesirable because energy that should be radiated away is absorbed by a nearby antenna.

6. Hanyang University 6/17 4.4.3 Microstrip-line feed It can be connected directly to microstrip transmission line. It has the advantage of the feed can be etched on the same substrate to provide a planar structure. The purpose of the inset cut in the patch is to match the impedance of the feed line to the patch without the need for any additional matching element. To avoid impedance mismatch, sections of quarter-wavelength long impedance transformers can be used to transform a large input impedance to a 50-ohm line. 50ohm

7. Hanyang University 7/17 [60] R. Q. Lee, K. F. Lee, and J. Bobinchak, Characteristics of a two-layer electromagnetically coupled rectangular patch antenna, Electron. Lett., Vol. 23, pp. 1070–1072, 1987.

8. Hanyang University 8/17 4.4.4 Proximity-coupled microstrip line feed –This can be used to feed a patch radiator through proximity coupling. –The main advantage of this feed provides very high bandwidth. –The major disadvantage of this feed scheme is that it is difficult to fabricate.

9. Hanyang University 9/17 4.4.5 Aperture-Coupled feed –In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane. Coupling between the patch and the feed line is made through a slot or an aperture in the ground plane. Bandwidth Optimization of Aperture-Coupled Stacked Patch Antenna Marek Bugaj 1 and Marian Wnuk 1

10. Hanyang University 10/17 4.4.6 Coax probe with a U-slot feed –U-shaped slot on the patch has been developed to achieve very wide bandwidth. 3.72Ghz 5.16Ghz

11. Hanyang University 11/17 directly Negatively effect of microstrip line Low effect of microstrip line To solve thickness (coax connector)

12. Hanyang University 12/17 4.5 DUAL-POLARIZATION AND CIRCULAR - POLARIZATION TECHNIQUES 4.5.1 Dual polarization For either a square patch or a circular patch with thickness and fundamental mode, the two orthogonal points on the patch are generally isolated from each other. The field at the orthogonal region of the feed is always zero. So two orthogonal locations can achieve dual polarization. For thick substrate, instead of two, four feed probes are needed. Because of the presence of stronger higher order modes in a thick substrate, using only two orthogonal feeds will result in a large amount of mutual coupling.

13. Hanyang University 13/17 The cross-polarizations will be canceled in both the E-and H-planes, while the co-polarization fields reinforce each other. Two pairs

14. Hanyang University 14/17 V-port (vertical polarization) and the H-port (horizontal polarization) feed locations are offset from the centers of the feed transmission lines to achieve the required 180° phase differential. This 180° phase differential of each port is not only for the purpose of suppressing the cross-polarization as explained. And it is this cancellation that provides the high isolation between the two input ports.

15. Hanyang University 15/17 4.5.2 circular-polarization CP(circular-polarization)from a micro strip antenna can generally be achieved by either a square or a circular patch with two orthogonal feeds having equal amplitudes and 90° phase differential. When it is asymmetry CP be created x y

16. Hanyang University 16/17 Each element is a CP(Circular Polarization) – figure 4.30, 4.31 Each element is a linearly polarized patch –figure 4.32

17. Hanyang University 17/17 Antennas & RF Devices Lab. Thank you for your attention Antennas & RF Devices Lab.

18. Hanyang University 18/17 Patch cavity can be approximately modeled as a resonant RLC circuit.

19. Hanyang University 19/17 >>Result graph

20. Hanyang University 20/17

21. Hanyang University 21/17 Patch antenna design

22. Hanyang University 22/17 coaxial antenna design Simple Approximate Formulas for Input Resistance, Bandwidth, and Efficiency of a Resonant Rectangular Patch - David R. Jackson and Nicolaos G. Alexopoulo

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