диафрагмированные волноводные фильтры / 27b67dd4-9814-4238-a2b2-e177b1bc01c6

Abstract—A linearly polarized omnidirectional planar filtenna at Ku-band is presented in this letter. It is a seamless and incorporate design of an inductive window bandpass filter and a planar coaxial collinear (COCO) radiation element. The radiation element has a linearly polarized omnidirectional radiation characteristic. The substrate integrated waveguide filter is used for RF channel selection as well as a balun. The proposed filtenna has merits of light weight, compact size, low cost, and easy integration with other planar circuits. Simulation and measurement results show that the radiation characteristics of the filtenna keep nearly no change within the working band, while unwanted signals at out-band can be effectively filtered.

Index Terms—Filtenna, linearly polarized, omnidirectional, planar, substrate integrated waveguide (SIW).

I. INTRODUCTION

H IGHER frequency than 10 GHz is now considered to be a promising candidate for the future wireless communications due to its availability of unused wide bandwidth. Wire-

less communication systems at Ku-band have attracted more and more attention for their advantages of better tradeoff on capacity, rain attenuation, and circuit size, compared to systems at other bands like C-band and Ka-band.

The linearly polarized antenna working at vertically polarized mode has the merit of less generating polarized current, which makes it avoid significant attenuation of energy and ensure effective propagation of signals. Furthermore, omnidirectional antennas are required for wireless terminals for their uniform power radiation in all directions in one plane.

The accuracy of circuit fabrication is an important issue for the small wavelength at Ku-band. The coaxial collinear (COCO) antenna [1] has been used successfully in a number of wireless communication systems for many years. The planar COCO antenna [2] is a good choice for its easy manufacture using the standard printed circuit board (PCB) process and easy integration with other planar microwave circuits.

Substrate integrated waveguide (SIW) with merits of low insertion loss, high power capability, low cost, easy integration, and easy fabrication has been widely investigated in recent

Manuscript received December 18, 2011; revised February 19, 2012; accepted March 13, 2012. Date of publication March 19, 2012; date of current version April 02, 2012. This work was supported in part by the Natural Science Foundation of China under Grants60921063 and 61132003 and the Natural Science Foundation of Jiangsu Province of China under Grant BK2011019.

The authors are with the State Key Laboratory of Millimeter Waves, School of Information Science and Engineering, Southeast University, Nanjing 210096, China (e-mail: chenyu@emfield.org).

Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/LAWP.2012.2191259

years [3]–[5]. SIW filters have also been reported in several works [6]–[8].

A filtenna is a co-design of a radio frequency (RF) filter and a radiation element. The filtenna can be used for reducing the loss introduced by the transmission between the RF filter and the radiation element and suppressing unwanted signals out of the band. Previous work on the filtenna includes, but is not limited to, [9]–[13]. A new design of microwave structure for integrating filter and antenna functions on a single device was presented in [9]. The integration antenna-filter applied to the horn was investigated in [10]. A design concept of filtenna integrated with SIW cavity frequency selective surface and horn antenna was proposed in [11]. A co-designed antenna-filter consisting of a microstrip patch antenna and a hairpin filter was presented in [12]. A novel prototype of multilayer PCB circular SIW filter and circular microstrip antenna was reported in [13].

In this letter, a linearly polarized omnidirectional planar filtenna working at Ku-band is designed, simulated, and measured. Integrating the planar COCO radiation element with the SIW bandpass filter (RF filter) in one substrate without cable connection reduces the insertion loss between the antenna and the RF filter. The conventional planar COCO radiation element requires the balanced feeding line. While in the proposed filtenna, the planar COCO radiation element and the SIW filter are directly connected by the tapered broadside coupled dual-line for the impedance matching, and here the SIW also acts as the balun.

The presented filtenna has merits of light weight, compact size, low cost, accurate fabrication with PCB process, and easy integration with other planar circuits. The simulated and measured results are in good agreement. They verify that the presented filtenna is able to suppress unwanted signals out of the band effectively because only signals passing the bandpass filter excite the radiation element and keep the linearly polarized omnidirectional radiation characteristics similar to the planar COCO radiation element because the SIW does not introduce any radiation components due to its close structure.

II. FILTENNA DESIGN

As shown in Fig. 1, the conventional planar COCO antenna consists of serially fed microstrip metallic patches that are alternately printed on the top and bottom surfaces of the substrate. The central distance of adjacent microstrip patches is about half the transmission-line wavelength at the working frequency. The length of microstrip patches is determined by the working frequency. The width of microstrip patches and the width of feeding lines are adjusted for obtaining the best omnidirectional radiation pattern of the planar COCO antenna. The gap of adjacent patches is adjusted for the impedance match of

Fig. 3. Photograph of the presented filtenna compared with the planar COCO antenna.

TABLE I

PARAMETERS OF THE PRESENTED ANTENNA AND FILTENNA

The radiation patterns are measured in an anechoic chamber. Fig. 5 shows the simulated and measured E-plane (-plane) radiation patterns of the presented antenna and filtenna at 14.4 GHz. Fig. 6 shows the simulated and measured H-plane

Fig. 5. Simulated and measured E-plane radiation pattern of the planar COCO antenna and the presented filtenna.

Fig. 6. Simulated and measured H-plane radiation patterns of the planar COCO antenna and the presented filtenna.

(-plane) radiation patterns of the presented antenna and filtenna at 14.4 GHz. Simulated and measured results are in

YU et al.: Ku-BAND LINEARLY POLARIZED OMNIDIRECTIONAL PLANAR FILTENNA

TABLE II

COMPARISON OF GAINS OF THE PRESENTED FILTENNA AND THE COCO

ANTENNA

good agreement. The measured H-plane (-plane) fluctuation of the presented antenna and filtenna is less than 0.7 and 0.8 dB, respectively. Furthermore, the presented filtenna keeps the linearly polarized omnidirectional radiation characteristics of the planar COCO radiation element.

Table II lists measured gains of the presented antenna and filtenna. The measured gain of the presented antenna is 8.8, 8.9, and 9.0 dBi at 14.3, 14.4, and 14.5 GHz. The measured gain of the presented filtenna is 7.7, 7.8, and 7.9 dBi at 14.3, 14.4, and 14.5 GHz. It is seen that the loss introduced by the integrated filter is only about 1.1 dB within the working bandwidth.

IV. CONCLUSION

The Ku-band linearly polarized omnidirectional planar filtenna has been designed, simulated, fabricated, and measured. The reflection coefficient of the presented filtenna is mainly affected by the filter of the filtenna. Simulated and measured results have shown that the presented filtenna effectively suppresses unwanted signals out of the band while keeping radiation characteristics nearly no change within the working bandwidth. The insertion loss is reduced due to the direct connection between the radiation element and the RF bandpass filter.

ACKNOWLEDGMENT

The authors are grateful to their colleagues in the State Key Laboratory of Millimeter Waves, Southeast University, Nanjing, China, for their valuable discussions and support in measurement.

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