Monopulse Waveguide Patch Array Antenna in 37 GHz Band

Manuel Sierra Pérez, Pedro Rodríguez Fernández, José Luis Masa Campos, José Luis Fernández Jambrina

Department: Señales y sistemas de Radiocomunicación. E.T.S.I. de Telecomunicación (Universidad Politécnica de Madrid).

Madrid (Spain). m.sierra.perez@gr.ssr.upm.es

Abstract— This paper presents a circularly polarized patch array in 37 GHz frequency, integrated in a narrow band application (BW < 1%) for signal detection. The designed array has to fulfill some specific requirements related to its radiation pattern (monopulse in the horizontal pattern and cosecant shape in the vertical one); other significant requirements are: circular polarization (RHCP with axial ratio under 3 dB), low side lobes (-20 dB below the main lobe) in the sum pattern of the monopulse, and high gain (greater than 32.5 dB).

I. INTRODUCTION

Due to the high operation frequency and gain, a lossless scheme is required. A waveguide feeding provides it in a satisfactory way. The power coupling mechanism from the waveguides to the radiating elements is done through a new concept, which is based on microstrip lines located inside the waveguides.

The radiating element is a modified circular patch easily manufactured on printed circuit. Circular polarization has been forced by a proper design of the dimensions of the perturbation elements inserted in the standard circular patch.

Three different modules have been projected (Fig. 1), namely: (1) the radiating circuit (patches and microstrip coupling lines), (2) the waveguide feeding network and (3) the monopulse network in charge of obtaining the right phase configuration in each subarray to get a sum pattern or a difference pattern for a monopulse working in the horizontal plane; if the outputs of the network present the same phase a sum pattern is obtained, however, if there is a phase difference of 180º between the two outputs in the left part of the circuit and the two outputs in the right part, the difference radiation pattern is achieved.

II. ANTENNA STRUCTURE

Figure 1. : Antenna structure.

The first module of the antenna (1) consists of four sub-arrays fed, named “horizontal/radiating waveguides” (Fig. 1) (module 2). Inside these radiating waveguide rectangular microstrip coupling lines have been placed. They carry the power to each radiating element (Fig. 2) through a metallic via hole.

Figure 2. : Detailed horizontal waveguide and coupling microstrip lines.

0

180 0

180

0 0

0

0

0

Red Rediferenc

Waveguide connection to the monopulse beam

forming network -

Vertical feeding waveguides

Patch

ANTEN

0

Phases in sum Phases in difference

Mono-pulse beam forming

0

180 0

180

0 0

0

0

0

Sum Difference

Coupling slots between radiating and feeding waveguidesAntenna

00

Radiating waveguide

Cosecant feeding network

IEEE MELECON 2006, May 16-19, Benalmádena (Málaga), Spain

1-4244-0088-0/06/$20.00 ©2006 IEEE 324

The width and length of those microstrip lines control the coupled power amplitude to the patches. Likewise, each subarray is fed by means of a “vertical/feeding waveguide” (Fig. 3).

Figure 3. Detailed vertical waveguide with its slots to feed one subarray

The field from those vertical waveguides is coupled to the horizontal ones by slots placed in every junction wall between them. The monopulse network (3), placed in the bottom side of the structure, presents two different inputs related to the obtaining of the sum or difference pattern, as well as four outputs corresponding to each subarray. Connection between the monopulse network and the feeding network (vertical waveguides) is carried out by a hybrid based waveguide circuit. Over the radiating circuit a foam layer will be placed to fasten it. Covering the antenna it’s placed a radome taken into account in the design process to minimize the reflection coefficient at the working frequency (Fig. 4).

Figure 4. : Picture of the antenna.

III. RADIATING ELEMENT

The radiating elements are printed patches on a thin dielectric plate with a 2.17 dielectric constant. The resultant circuit is placed over the top walls of every single horizontal waveguide (Fig. 1). The main characteristic of the patches used in this design is the circular polarization of the radiated field. To get this sort of polarization a modified circular patch has been used (Fig. 4).

S/22.65 mm

0.25 mm

0.25 mm

S/2S/22.65 mm

0.25 mm

0.25 mm

Figure 5. :Detailed modified circular patch (radiating element).

The perturbations generate two orthogonal modes and, as the dimensions of the additional elements are adjusted to the optimum value both modes are excited in equal amplitude and 90º out of phase at the centre frequency, getting the rotation of the field. With the dimensions shown in Fig. 4 the following axial ratio is obtained (Fig. 5).

Figure 6. : Axial ratio

IV. FEEDING NETWORK

As it was mentioned previously, the antenna feeding network was implemented by using waveguide technology, due to losses requirements. The main advantage of this technology is lossless design; however it has some drawbacks compared to PCB design as bigger cost and size. Fig. 6 shows a transverse view of the feeding network:

325

F o a m

7 m m

63 m m

0 .5m m> 6 m m

R a d o m eF ib e r g la ss

6 m m

5

R a d ia tin gW a ve g u id e s

F e e d in gW a ve g u id e

F o a m

7 m m

63 m m

0 .5m m> 6 m m

R a d o m eF ib e r g la ss

6 m m

5

R a d ia tin gW a ve g u id e s

F e e d in gW a ve g u id e

Figure 7. : Waveguides dimensions.

The dimensions of the horizontal waveguides are selected to work with only one propagating mode. We must realize that with this configuration the horizontal waveguides are not totally closed because of the thickness of the substrate of the coupling microstrip lines; therefore each horizontal waveguide is fed with opposite phase respect to the contiguous one, in order to generate a virtual short-circuit that electromagnetically closes the waveguide; this can be done in a simple way by choosing a vertical waveguide whose half wavelength was equal to the distance between two consecutive horizontal waveguides ( gv/2 = 7 mm. ). Fig. 8 shows a picture of the manufactured feeding network where we can see the horizontal waveguides that distribute the power among the radiating elements through the microstrip coupling lines. The slots to couple power from every single vertical waveguide to the corresponding horizontal one are also shown.

Figure 8. :Feeding network

V. RADIATION PATTERNS

The design requires a monopulse radiation pattern in the horizontal plane (Fig. 9), with secondary lobes level under

-20 dB from the main lobe level in the sum pattern. The difference radiation pattern must be over the sum pattern except in the pointing angular zone (6º).

Figure 9. Monopulse radiation pattern.

In the vertical plane a cosecant shape is needed for the radiation pattern (Fig. 10).

0

-5

-10

-15

-20

-25

-30

-35

-40-90 -60 -30 0 30 60 90

0

-5

-10

-15

-20

-25

-30

-35

-40-90 -60 -30 0 30 60 90

Figure 10. Cosecant radiation pattern.

The radiating patches must be fed in order to achieve the radiation pattern in the two main planes. The feeding amplitude will be controlled by the dimensions of the microstrip coupling lines in the horizontal plane (Fig. 11) and by the length of every slot and its distance to the centre of the vertical waveguide in the vertical plane (Fig. 12).

Figure 11. Microstrip coupling lines.

326

Figure 12. Slots in printed circuit.

In the case of the cosecant radiation pattern (vertical array) the feeding phase must also be controlled. It hast to be different between consecutive horizontal waveguides. It is carried out by turning the patches around its feeding point an appropriate angle (in vertical direction). Furthermore, patches separation in a same horizontal waveguide has been selected to be 3 grad/4 to minimize both reflections between microstrip lines and grating lobes appearance; however, the same feeding phase in the radiating elements of the horizontal array is needed, so an additional patch rotation must be done (in horizontal direction). Fig. 13 shows the complete array where the visual effect of the patch rotation is observed.

Figure 13. Patch array.

VI. MONOPULSE NETWORK

In order to get the monopulse functioning in the horizontal plane, a waveguide network has been designed (Fig. 14).

Figure 14. Waveguide monopulse networkt.

Figure 15. Measured output phases-(a)sum input, (b) diff. input..

The structure presents four outputs each for the corresponding subarray. The hybrid circuit together with the control of the waveguides length obtain the desired phase difference at the outputs depending on the excited input (Fig. 15). Using one of the inputs the same feed phase is obtained for both horizontal semi-arrays, which leads to a sum pattern. If the other input is excited, a phase difference of 180º will be obtained, resulting in a difference radiation pattern.

REFERENCES

[1] Manuel Sierra Castañer, Manuel Sierra Pérez, María Vera Isasa, José Luis Fernández Jambrina, “Low-Cost Monopulse Radial Line Slot Antenna,” IEEE Trans. on Antennas and Propagat., vol. 51, no2, pp.

256-263, Feb. 2003 [2] J. R. James, P.S. Hall, “Handbook of Microstrip Antennas,” IEE

ELECROMAGNETIC WAVES SERIES 28, Peter Peregrinus Ltd.,

1989[3] J.L. Masa, M. Sierra Pérez, “A New Feeding Structure For Radial

Line Planar Match Antenna,” Proceedings of Symposium on APS, pp.

3409-3412, Monterey, California, USA, June 2004 [4] K. Sakakibara, Y. Kimura, J. Hirokawa, M. Ando, N. Goto, “A Two-

Beam Slotted Leaky Waveguide Array for Mobile Reception of Dual-

Polarization DBS,” IEEE Trans. on Vehicular Technology., vol. 48, no1, pp. 1-7, Jan. 1999

[5] C.G Montgomery, R. H. Dicke, E.M. Purcell, “Principles of

Microwave Circuits vol. 8,” M.I.T. Radiation Laboratory Series, Boston Technical Publishers, Inc., pp. 306-308, Ed.1964

[6] Y. Kimura, T. Hirano, J. Hirokawa, M. Ando, “Alternating-Phase Fed Single-Layer Slotted Waveguide Arrays with Chokes Dispensing With Narrow Wall Contacts,” IEE. Proc. Microw. Antennas Propag., vol. 148, no.5, Oct. 2001.

327

专注于微波、射频、天线设计人才的培养 易迪拓培训 网址：http://www.edatop.com

如 何 学 习 天 线 设 计

天线设计理论晦涩高深，让许多工程师望而却步，然而实际工程或实际工作中在设计天线时却很

少用到这些高深晦涩的理论。实际上，我们只需要懂得最基本的天线和射频基础知识，借助于 HFSS、

CST 软件或者测试仪器就可以设计出工作性能良好的各类天线。

易迪拓培训(www.edatop.com)专注于微波射频和天线设计人才的培养，推出了一系列天线设计培

训视频课程。我们的视频培训课程，化繁为简，直观易学，可以帮助您快速学习掌握天线设计的真谛，

让天线设计不再难…

HFSS 天线设计培训课程套装

套装包含 6 门视频课程和 1 本图书，课程从基础讲起，内容由浅入深，

理论介绍和实际操作讲解相结合，全面系统的讲解了 HFSS 天线设计的

全过程。是国内最全面、最专业的 HFSS 天线设计课程，可以帮助你快

速学习掌握如何使用 HFSS 软件进行天线设计，让天线设计不再难…

课程网址：http://www.edatop.com/peixun/hfss/122.html

CST 天线设计视频培训课程套装

套装包含 5 门视频培训课程，由经验丰富的专家授课，旨在帮助您从

零开始，全面系统地学习掌握 CST 微波工作室的功能应用和使用 CST

微波工作室进行天线设计实际过程和具体操作。视频课程，边操作边

讲解，直观易学；购买套装同时赠送 3 个月在线答疑，帮您解答学习

中遇到的问题，让您学习无忧。

详情浏览：http://www.edatop.com/peixun/cst/127.html

13.56MHz NFC/RFID 线圈天线设计培训课程套装

套装包含 4 门视频培训课程，培训将 13.56MHz 线圈天线设计原理和仿

真设计实践相结合，全面系统地讲解了 13.56MHz 线圈天线的工作原

理、设计方法、设计考量以及使用 HFSS 和 CST 仿真分析线圈天线的

具体操作，同时还介绍了 13.56MHz 线圈天线匹配电路的设计和调试。

通过该套课程的学习，可以帮助您快速学习掌握 13.56MHz 线圈天线及

其匹配电路的原理、设计和调试…

详情浏览：http://www.edatop.com/peixun/antenna/116.html

`

专注于微波、射频、天线设计人才的培养 易迪拓培训 网址：http://www.edatop.com

关于易迪拓培训：

易迪拓培训(www.edatop.com)由数名来自于研发第一线的资深工程师发起成立，一直致力和专注

于微波、射频、天线设计研发人才的培养；后于 2006 年整合合并微波 EDA 网(www.mweda.com)，

现已发展成为国内最大的微波射频和天线设计人才培养基地，成功推出多套微波射频以及天线设计经

典培训课程和 ADS、HFSS 等专业软件使用培训课程，广受客户好评；并先后与人民邮电出版社、电

子工业出版社合作出版了多本专业图书，帮助数万名工程师提升了专业技术能力。客户遍布中兴通讯、

研通高频、埃威航电、国人通信等多家国内知名公司，以及台湾工业技术研究院、永业科技、全一电

子等多家台湾地区企业。

我们的课程优势：

※ 成立于 2004 年，10 多年丰富的行业经验

※ 一直专注于微波射频和天线设计工程师的培养，更了解该行业对人才的要求

※ 视频课程、既能达到了现场培训的效果，又能免除您舟车劳顿的辛苦，学习工作两不误

※ 经验丰富的一线资深工程师主讲，结合实际工程案例，直观、实用、易学

联系我们：

※ 易迪拓培训官网：http://www.edatop.com

※ 微波 EDA 网：http://www.mweda.com

※ 官方淘宝店：http://shop36920890.taobao.com