Dimitrios K. Papantonis

Dual-Polarized Tightly Coupled Array With Substrate Loading

A dual-polarized, tightly coupled dipole array (TCDA), delivering 13.1:1 bandwidth, is presented. The array incorporates a resistive sheet (R-Card) in the substrate to suppress resonances within the operational band and employs a dielectric layer as a superstrate to maintain high efficiency. The simulated infinite array demonstrates broadside VSWR <; 2.5 across a 13.5:1 bandwidth, and VSWR 13.1:1 bandwidth while scanning up to 45° , with cross-polarization levels <; -20 dB, in all planes. The array height, including the superstrate, is 0.08 wavelengths above the ground plane at the lowest operational frequency, and 1.1 wavelengths at the highest frequency. The infinite array overall efficiency, including mismatch reflections and aperture/resistive losses,> -2.2 is dB across all frequencies and scanning angles. An 8×8 prototype was fabricated and tested to validate the design. Measured array gain and mid-band and high-frequency patterns for the two principal scanning planes are presented, demonstrating good agreement with the respective simulations.

Reconfigurable ultra-wideband array with tunable band rejection across a 7∶1 Bandwidth

A reconfigurable tightly-coupled array (TCA) for tunable band rejection is presented. This is achieved, for the first time, by a capacitively-reconfigured balun feed, integrated with an ultra-wideband phased array. The carefully-introduced capacitance creates a resonance that can be tuned within the total arrays bandwidth covering 0.6 to 4 GHz (7:1). The achieved gain rejection is of at least 15dB at the resonance without any efficiency reduction at other frequencies. The design is carried out using equivalent-circuit simulations of the arrays unit cell and verified via respective full-wave simulations. Preliminary measurements of the balun are performed by introducing fixed capacitors on the integrated Marchand balun. Three different capacitance values are tested corresponding to different rejection frequencies across the entire band. Future work entails a fully reconfigurable, 8×8 array prototype with variable capacitors to be presented at the symposium. It should be noted that the proposed system is the first reported reconfigurable array that enables interference rejection critical for ultra-wideband antennas.

Experimental Validation of On-Site Coding Digital Beamformer With Ultra-Wideband Antenna Arrays

Digital beamformers combined with ultra-wideband (UWB) antennas are essential for realizing cognitive and software defined radios. Concurrently, advances in digital technology and signal processing have drastically reduced digital beamforming complexity. Recently, a novel on-site coding receiver (OSCR) architecture was proposed to significantly reduce hardware requirement for digital beamforming. Using OSCR, the signal from each antenna element is encoded, then several of these signals are grouped and digitized using a single analog-to-digital converter. Doing so, hardware requirements are drastically reduced. At the digital back-end, field programmable gate arrays are used to decorrelate and recover the signals associated with each array element for beamforming. In this paper, we demonstrate the effectiveness of the OSCR concept by building and testing a multichannel receiver using commercial-off-the-shelf components. Various test bench measurements are performed in an anechoic chamber using an UWB antenna array operating from 200 MHz–2.5 GHz, and data were collected at multiple frequencies. Results show an accurate estimate of the angle of arrival for incidence angles of

Ultra-wideband conformal apertures with digital beamforming for UHF to millimeter-wave applications

\theta _{s} = 0^{\circ }

Bandwidth reconfigurable ultra-wideband arrays

, 15°, 30°, and 45° away from broadside. It is verified that on-site coding has minimal or no degradation in signal-to-noise ratio.

Tightly-coupled array with tunable BW using reconfigurable FFS/superstrate

This paper presents a reconfigurable low profile ultra-wideband (UWB) phased array, having as much as 14.1:1 instantaneous bandwidth suitable for UHF to millimeter wave applications, with unprecedented integrated digital beam-forming capability across the entire bandwidth. To realize spectrum efficiency, aperture reconfiguration is also proposed. That is, the system is tuned at the feed network rather than the aperture of the antenna by introducing switches and LC loads. Further, the proposed UWB phased array significantly reduces cost due to its novel on-site encoding for tracking individual array element signals to eliminate hardware phased shifters, a primary cost component of the phased arrays.

Tunable band rejection in a tightly-coupled array using varactor diodes

Past efforts on reconfiguration focused on modifying the antenna bandwidth by shifting the apertures frequency response using switches or piezoelectric materials. By contrast, this paper proposes bandwidth reconfiguration by starting with a wideband aperture and limiting its original bandwidth by modifying the array feed. The initial un-configured design provides 9.25:1 bandwidth for a VSWR 3:1 or better at broadside. With 5 switched components, 5 distinct bandwidth configurations are realized, namely: low-pass, high-pass, band-pass, band-stop, and the un-configured response.

Tunable band rejection of wideband arrays using digital variable capacitors

A novel way to reconfigure the bandwidth (BW) of a tightly-coupled array (TCA) is presented. This is done using a reconfigurable frequency selective surface (FSS) on top of the array. The reconfigurable FSS demonstrates a tunable narrow passband, emulating an L-C bandpass filter. The bandwidth tunability is achieved by varying the capacitance C of the FSS/“filter”. For this purpose, varactor diodes or any available commercial variable capacitor can be used. The resulting FSS-enhanced TCA is shown to achieve a tunable center-frequency range from 1GHz to 3GHz, with less than 3dB additional loss due to the FSS presence. Higher-order FSS responses, scanning performance and practical implementation issues will be discussed at the symposium.

Dual-polarization TCDA-IB with substrate loading

A mechanism for tunable band rejection in the reconfigurable balun of an ultra-wideband (UWB) tightly-coupled array (TCA) is presented. A variable capacitor increases and controls the effective length of the baluns short stub, shorting out the dipoles of the array at a specific frequency. The practical implementation of the rejection scheme using varactor diodes is discussed. A number of different varactor diodes has been measured using a custom-made evaluation board to model their actual behavior. Simulation results, including the characterized components and their DC biasing network, verify the design. A fabricated prototype of the reconfigurable array will be presented at the conference.

UWB arrays with tunable band rejection

We present one of the very first reconfigurable, ultra-wideband (UWB) tightly-coupled array (TCA) with tunable band-rejection capabilities. The array is dual-polarized, achieving a 4:1 bandwidth (1-4GHz) while scanning down to 60° in all planes with a VSWR<;3. The dipoles are fed via a novel folded Marchand balun, customarily used for differential excitation, matching and impedance transformation. As an additional attribute, a variable capacitor, placed, in shunt, in the short stub of the balun, elongates the stubs electrical length and shorts out the dipoles. The latter mismatches the array and creates a rejection notch at a desired frequency, which is directly tuned by the variable capacitor. Besides the notch frequency, the notch BW can be controlled and the scheme operates for scanning without trade-offs. The rejection mechanism does not add to the total array volume or loss, as opposed to typical tunable notch filters. The concept has been verified by equivalent-circuit simulations, full-wave simulations and preliminary measurement results. A reconfigurable finite array with dynamic rejection of >20dB is under fabrication, using digitally-biased tunable capacitors.