7/30/2019 1569526483

1/3

A Novel Non-Foster Broadband Patch Antenna

Stavros Koulouridis, Spyros Stefanopoulos

Microwave Communication Group,

Electrical and Computer Engineering DeptUniversity of Patras

Patras, Greece

koulouridis@ece.upatras.gr

Abstract We propose a novel antenna matched with non-Foster

circuit. A simple narrow resonant patch is transformed into a

extremely broadband antenna (with impedance bandwidth less

than -10dB) starting from an aperture size /30x/30 up to

/13x/13. Patch is supported by a Rogers 6010 dielectric

substrate. non-Foster circuits are added at a two-step procedure.

First, an additional port is introduced inside the antenna and a

series negative network is applied at that port. The topology and

values of the elements are obtained from simple graphical

formulas. As a result the real part of input impedance is greatly

enhanced reaching values close to those of feeding network. At

the second step negative matching is added at the input of the

antenna to match the imaginary part of input impedance.

Keywords- Negative circuitry; minimization; broadband; novel

design technique

I. INTRODUCTIONNon-Foster matching has gained interest lately. It is true

that there are several efforts to design and realize non-Fosternetworks [1]-[17]. Since the research efforts are continuously

targeting antenna minimization it is natural that traditionaltechniques have reached their limits. Further transistortechnology has advanced and many transistors have been

proposed that present some stability at a relevant extendedbandwidth. Since negative impedance realization is based onactive elements transistor technology amelioration has givenattractiveness to negative circuits. Negative circuits can verysimply produce antennas that they are extremely broadbandwith low power consumption

In order to realize negative networks one has to overcome anumber of issues, the simpler of which being the activenetwork topology. Biasing is sometimes needed as commonground between matched device and matching network can

generate unwanted loop signals inside the systems and destroythe applied matching. Even if this is overcome, networkstability is big issue. In other words one cannot stop atobtaining the topology but he/she should study the circuit fromnoise and stability point of view.

While numerous non-Foster circuit realization have beenproposed very few have been actually tested. Further, it isequally important to implement design techniques that willallow improvements in active elements characteristics [7]. Useof FET cascading to decrease the unwanted paracitics of theactive elements [11] or transistor biasing [9] to decrease noise

and increase stability are some options. We can also design andimplement lossless matching networks for the tuning of thetransistors [12] or we may need to alter the internal design ofused amplifiers [13].

In this paper we propose a novel non-Foster design that hasbeen produced from a technique that can tune a large numberof different antenna types [14], [15] A port is appropriately

added inside the antenna. Then negative circuits areappropriately introduced (negative capacitance and inductance)that, as shown, can greatly alter input impedance. Appliednegative circuits permit to increase the very low radiationresistance values and significantly decrease the large antennareactance that demonstrate at the low frequency regions (i.e. we

put our focus on small antennas) Proposed approach can makenon-Foster implementation straightforward for severalantennas. Using the above technique we transform a simplenarrow resonant patch into a very broadband antenna (withimpedance bandwidth less than -10dB) starting from anaperture size /30x/30 up to /13x/13. Patch is supported bya Rogers 6010 dielectric substrate.

II. REALIZED ANTENNAA common patch antenna (see Fig. 1 and [14]) is employed.

It has 3.25x3.25cm2

aperture and is printed on Rogers 6010(r=10.2) substrate. Its thickness is 5mm. Antenna calculatedinput impedance is given at Fig 2. As can be seen antenna has anarrow resonance at f=1.59GHz with 30 MHz -10dBimpedance bandwidth. This is commonly expected. Naturallyoptimizing feeding positions, bandwidth could be somewhatenhanced, nevertheless this would not lead to significantchanges to the general antenna performance. Further, if wetried to apply matching (either passive or negative) at the inputwe would not achieve much since radiation resistance is nearly

zero away from the resonance.We can now select a second port inside the antenna to

apply our technique. Position of second port can be seen in Fig.1. As seen, port is placed at a symmetric point to the feeding inrelation with the antenna center. According to discussedmethod [14], [15] we can calculate a load ZL that, when appliedat the second port, could alter input impedance at will. In

practice needed load is not realizable at a wide frequency band[14], [15]. However, restricting the frequency region ofinterest, for example below 1GHz, certain characteristics ofideal load can be reproduced to our benefit. Then a second

7/30/2019 1569526483

2/3

negative network can be introduced at the input to finallymatch the antenna.

In Fig. 3 the designed non-Foster network topology isgiven. As seen, at the antenna second port (on the right) weintroduce a grounded series RLC circuit. Resistor R has a lowvalue of R=1 so losses should be low, still it is very importantfor the antenna matching network. At a second design phasewe add the non-Foster LC network at the antenna input (left ofantenna in Fig. 3). In Fig. 4 the input impedance (Z1, see Fig.3) before applying the second matching network is shown.Input resistance has been greatly ameliorated slightly varyingaround 50Ohm at a frequency from 100MHz up to 1GHz. Inputreactance can be now negated by applying a series non-FosterLC at the antenna input. Indeed as seen in Fig. 5 ideal finalmatched input impedance is demonstrating a wide 50 Ohm

bandwidth from around 300MHz up to 1GHz.

III. REALIZED NETWORKS AND STABILITYDesigning an ideal non-Foster network is certainly not

trivial. Still it can provide us with impressive results. Difficultyhowever emerges from non-Foster network realization. Acollection of non-Foster topologies can be found in [16].

Negative networks are realized with transistors and they aremainly divided into grounded and floating topologies.

Any of the topologies in [16] can be theoretically used andimplemented. However, their implementation can lead toinstabilities that need to be addressed. Therefore, the difficultyof negative networks implementation lies in the design andfabrication of a stable active network. While there are multipletheorems to define stability criteria (that sometimes can becontradictory [17]) it is not easy to define a common route fordesigning stable non-Foster networks. Usually one willimplement non-Foster active topology and then obtained circuitwill be validated against stability theorems.

For our case we will follow the open loop gain stabilityNyquist criterion [17], [18]. According to Nyquist criterion aclosed loop system with negative feedback will be stable if the

Nyquist plot of the open loop gain does not encircle the 1-j0point (see Fig. 6). Open loop gain is formed based on theanalysis in [18]. Outcome of the stability tests defines the typeand topology of negative inverters implemented.

In Fig. 7 we present the final input impedance afterapplying the actual network topology that passed the stabilitytest. As seen, there is a deviation from the ideally expectedresults. Input resistance have slight differences. Reactancethough is increasing after 700MHz and considerably deviates.

Therefore impedance bandwidth is now restricted to 300MHzto 700MHz. Still, results are impressive.

IV. CONCLUSIONIn present work, a broadband patch antenna is introduced withthe utilization of non-Foster matching. The antenna, beinginitially narrow resonant, is loaded with non-Foster matching atan imaginary port inside its structure. In that way we controlinput impedance and match the antenna at frequency ofinterest. Apart from applying ideal lumped negative elementsthough, of equal importance is the realization of non-Foster

topology. While a number of Negative Impedance Converters(NIC) based on transistors have been proposed, stability of thefinal network is not assured. To that end, we test severaltopologies that are evaluated against Nyquist stability criterion.Final antenna presents an impressive impedance bandwidth foran aperture of/30 x /30 up to /13 x /13.

Figure 1. A second port is introduced at a 3.25x3.25cm2 patch antenna with

r= 10.2. This will allow us to match the antenna with negative elements and

increase its bandwidth relatively easily.

200 400 600 800 1000 1200 1400 1600 1800 2000-100

-50

0

50

100

Figure 2. Initial input impedance of the antenna (see also [14])

Figure 3. Non-Foster network with a series RLC (R=1, C=-17pF, L= -4nH

connected at the new port (see Fig. 1) and a series LC (L=-8nH, C=-2.5pF) at

the input.

0.3 0.5 0.7 0.90.1 1.0

-500

-400

-300

-200

-100

0

-600

100

Figure 4. Input Impedance Z1 (see Fig. 3) after adding the RLC (see Fig 4)

combination at the antenna additional port and before introducing the LC

combination at the antenna input.

Feeding

Substrate:r=10.2

Introduced Port

7/30/2019 1569526483

3/3

0.3 0.5 0.7 0.90.1 1.0

0

20

40

-20

60

Figure 5. Final expected input impedance Zin (see Fig. 3) after introducing

the additional LC circuit at the antenna input.

Figure 6. Stability criterion for Nyquist diagram of open loop gain for

transistor network of the Negative Impedance Converters

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1 1.0

0

50

-50

100

Figure 7. Final input impedance (simulated) after implementing the actual

active network topology.

REFERENCES

[1] S. Koulouridis and J. L. Volakis, Non-Foster circuits for smallbroadband antennas, in Proceedings IEEE Antennas PropagationSociety Inter. Sym., Charleston, SC, 2009

[2] S. Koulouridis, Impedance matching for small antennas using passiveand active circuits, in Small Antennas: Miniaturization Techniques &Applications, John Volakis, Chi-Chih Chen, Kyohei Fujimoto, Eds. NewYork: McGraw Hill, 2010, pp. 361-388,

[3] S. Koulouridis, Negative networks design for antennas, URSI NorthAmerican Radio Science Meeting Digest, Toronto, Canada, July 11-16,2010.

[4] K. Karlsson, J. Carlsson, "Non-Foster networks for improvement ofradiation efficiency and effective diversity gain of a multi-port antenna,"in Proceedings European Conference on Antennas and Propagation(EuCAP), pp.1-4, 12-16 April 2010.

[5] Keum-Su Song, R.G. Rojas, "Non-Foster impedance matching ofelectrically small antennas," in Proceedings Antennas and PropagationSociety International Symposium (APSURSI), pp.1-4, 11-17 July 2010.

[6] Keum-Su Song, R.G. Rojas, "Electrically small wire monopole antennawith non-Foster impedance element," in Proceedings EuropeanConference on Antennas and Propagation (EuCAP), pp.1-4, 12-16 April2010.

[7] S.E. Sussman-Fort, "Non-Foster vs. active matching of an electrically-small receive antenna in Proceedings Antennas and Propagation Society

International Symposium (APSURSI), pp.1-4, 11-17 July 2010.[8] Peng Jin, R.W. Ziolkowski, "Broadband, Efficient, Electrically Small

Metamaterial-Inspired Antennas Facilitated by Active Near-FieldResonant Parasitic Elements," IEEE Transactions on Antennas andPropagation, vol.58, no.2, pp.318-327, Feb. 2010.

[9] S. E. Sussman-Fort, R. M. Rudish, Non-Foster Impedance Matching ofElectrically-Small Antennas, IEEE Trans. Antennas and Propagation,pp.2230-2241, vol 57, Aug 2009.

[10] . T. Aberle, Two-port representation of an antenna with application tonon-Foster matching networks, IEEE Trans. on Antennas and Propag.,vol. 56, pp. 12181222, May 2008.

[11] I. J. Bahl, Fundamendals of RF and Microwave Transistor Amplifiers,John Wiley and Sons, 2009.

[12] S E. Sussman-Fort, An NIC-based negative resistance circuit formicrowave active filters, Inter. Journal of Microwave Millimeter-Wave

Computer Aided Design, pp. 130-139, vol. 4, 1994.[13] A. Kaya, Wide-Band Compact Microwave Transistor Amplifier

methodology and the analysis of its input matching mechanism usingnegative impedance converter, Microw Opt. Tech. Let., vol. 50, pp.192-197, Jan. 2008.

[14] S. Koulouridis, Non-Foster design for Antennas, in Proceedings ofInternational conference on Antennas and Propagation, Spokane, WA,USA, 2011.

[15] S. Koulouridis, Non Foster Cicrcuitry Design for AntennasEuropean Conference on Antennas and Propagation, EUCAP 2011,Rome, Italy, 2011

[16] S. E. Sussman-Fort, Gyrator-based biquad filters and negativeimpedance converters for microwaves, Int. J. RF Microw. Comput.-Aided Engi., (Special Issue on Netw. Synthesis Method. Microw. De.),vol. 8, no. 3, pp. 86---101, Mar. 1998.

[17]

D. Segovia-Vargas, V. Gonzalez-Posadas, J.L. Jimenez, E. Ugarte-Munoz, J. Herraiz-Martinez and L.E. Garcia-Munoz, "Negativeimpedance converters (NICs) in the design of small and multifrequencyantennas",Antennas and Propagation (EUCAP), Proceedings of the 5thEuropean Conference on, 2011, p. 2724-272.

[18] M. Randall and T. Hock, "General oscillator characterization usinglinear open-loop S-parameters", Microwave Theory and Techniques,IEEE Transactions on, 49, no. 6, p. 1094-1100, 2001.