Design of FSS for Wideband and Wide-Angle

Coverage—Challenges and Possible Solutions

Raj Mittra1,2

and Nathawut Homsup1

1EMC Lab, University of Central Florida, Orlando, FL, USA

2EE Department, KAU, Saudi Arabia

rajmittra@ieee.org

Abstract – This paper examines the challenges

encountered in the process of designing Frequency

Selective Surfaces (FSSs) for applications that call for

simultaneous coverage over very wide frequency band

as well as wide angle. The paper begins with a review of

existing literature and concludes that none of them can

provide, even with the suggested modifications, a design

that meets our needs of 3:1 bandwidth over an angular

range of 60deg or higher. Next, we propose some new

designs and examine how well we can meet the stated

goals Index Terms — Frequency selective surfaces; Wideband

FSS; FSS with wide-angle coverage.

1. Introduction

Even though there are literally hundreds of publications,

both journal papers and books which provide the theory of

operation of Frequency Selective Surfaces (FSSs),

designing them remains a challenging task when the

specifications call for coverage over a wide band of

frequencies, say 3:1, and over a wide range of angles going

up to 700, as is sometimes desired. What makes the design

problem even more challenging is that while many

publications describe FSS designs over a relatively wide

band, say 2:1, which cover angles up to 30 0r 40 degrees (at

most), they do not provide a clue as to how to extend these

limits of their designs. In this work we describe the results

of parametric studies that we have carried out of a number

of existing wide-band and wide-angle FSS designs in an

attempt to cover the following specifications:

a. Passband: Frequency range f1 to f2 (ratio of f2/f1

equal to 3:1)

b. Coverage up to 60 deg., or higher TE and TM

polarizations

c. Low ripple in the passband

d. Better than 10 dB in the stopbands, at both low

and high ends, past the shoulder regions.

It is interesting to note that the strategies followed in

these works, whose designs we have investigated, are quite

different from each other and, hence, the proposed physical

structures are also somewhat unique to these designs,

despite the fact that their stated goals for meeting the

wideband and wide-angle coverage are the same. We did

find several papers which proposed a universal approach

(see [1], for instance), based on filter theory, which has

been well developed for microwave circuits, and has been

extensively used for waveguide filters for satellite

communication. However, we found that it is not possible,

in general, to transition from lumped circuits to distributed

circuits representing FSSs, especially in designs where the

higher-order Floquet modes are considered, as they must be

in the FSS designs we have studied. Thus, while the filter

theory was somewhat helpful in leading us to the right

direction, we found that it was quite inadequate for our

designs; hence it was necessary to develop new design

strategies, which we will describe in the presentation, and

which enabled us to extend the boundaries of the existing

designs to help our stated goals.

Fig. 1. Third Order Frequency Selective Surface (FSS).

(a)

(c)

(b)

Fig. 2. A unit cell of Frequency Selective Surface (FSS) (a)

Top view, (b) Bottom View, and (c) Isometric view.

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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Fig. 3. Transmission (TE) with incidence angle is at 30

degrees

Fig. 4. Transmission (TM) with incidence angle is at 30

degrees

The paper will present the details of the design strategy,

together with a summary of the results that will show how

well we are able to meet our goals. We will also describe

some of the future directions that we consider worthwhile

to explore in order to systematically design FSSs for both

wide-angle and wide frequency coverage. Additional

references to related works [2-16] are also included in the

paper.

References

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2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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