The design, fabrication, and measurement of a 16 × 16 dual-polarized planar ultrawideband modular antenna (PUMA) array operating over 7-21 GHz (3:1 bandwidth) are presented. The array is comprised of tightly coupled dipoles printed on a grounded dielectric substrate and are excited by an unbalanced feeding scheme that eliminates external wideband baluns and feed organizers. The array can be assembled modularly, where each low-profile, fully planar, low-cost tile is fabricated using standard multilayer microwave PCB techniques. A unique solderless, modular interconnect mates the array to a dilation fixture that facilitates measurements using standard surface-mount assembly (SMA) connectors and terminations. After presenting the most critical design trends, simulation results of the final array in infinite, infinite × finite, and finite × finite models are compared with measurements. This prototype array exhibits a measured active VSWR <; 2.1 and close to ideal gain at broadside, and VSWR <; 2.8 with low cross-polarization out to θ = 45° in all planes, showing close agreement with simulations.

A 7–21 GHz Dual-Polarized Planar Ultrawideband Modular Antenna (PUMA) Array

Methods for controlling orthogonal frequency division multiple access (OFDMA) communications over satellite links. The methods include estimating a differential delay (x ms) in a satellite spotbeam between a mean propagation delay (250 ms) in the spotbeam and a propagation delay ((250-x)ms) between a user terminal in the spotbeam and a satellite, estimating an overlap (215) between an OFDMA uplink frame and an OFDMA downlink frame as a result of the differential delay, and providing a guard band (215) in the OFDMA uplink frame and/or the OFDMA. downlink frame to reduce an overlap between remaining portions of the OFDMA uplink frame and the OFDMA downlink frame other than the guard band. Corresponding systems and devices are also disclosed.

Systems and methods for orthogonal frequency division multiple access (ofdma) communications over satellite links

LOW-PROFILE, MODULAR, ULTRA-WIDEBAND PHASED ARRAYS

Low-profile, modular, ultra-wideband phased arrays

Soft-decision decoded performance of fast frequency-hopped (FH) M-ary FSK signals over partial band noise jammed binary channels is studied. The effects of metrics conversion, quantization, and the presence of regenerative nodes on the system's cutoff rate performance are investigated. It is found that the conversion from an M-ary metric to a binary one suffers only negligible degradations. For communication links without regenerative nodes, as expected, the infinite-bit soft-decision is the optimal metric, followed by finite-bit soft decision and then hard-decision. For those with regenerative nodes, however, the infinite-bit soft-decision is outperformed by the hard-decision, but the finite-bit soft-decision decoder still keeps its edge over the latter. The issue concerning the order of metric conversion and diversity combining is also analyzed. Numerical results indicate that the conclusion obtained by an earlier simulation report addressing a similar design alternative in fading channels is valid for jammed binary channels, as well. That is, the precombining metric conversion technique gives up only minor performance degradations when compared to the more sophisticated postcombining metric conversion technique. >

https://ir.nctu.edu.tw:443/bitstream/11536/2416/1/A1994NY45400012.pdf

Performance of fast FH/MFSK signals in jammed binary channels

Frequency-hopped M-ary frequency-shift-keyed (FH-MFSK) has the ability to handle with long multipath, large Doppler spreads, high ambient noise and rapid phase fluctuation, and is proved to be a robust modulation scheme in mobile shallow underwater acoustic channels. Aiming at this topic, a convolutionally encoded FH-MFSK modulation scheme with a novel iterative multi-channel reception is proposed. To obtain the novel reception suitable for non-coherent M-ary frequency-shift-keyed, the ideas of iterative multi-channel demodulation and decoding are combined and extended. A modified multi-channel soft-input–soft-output demodulator based on maximum-a-posterior criterion is derived, and substantial gains of several decibels in power efficiency are achieved. Extra gain can be obtained by utilising time diversity with long multipath delay. Simulation shows that a non-coherent receiver equipped with five arrays obtains around 5.5 dB gain over the single non-iterative receiver. A shallow water field testing at Songhua Lake with 300 m distance confirms that the proposed receiver verifies its robustness and usability.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-com.2019.1045

Iterative multi-channel FH-MFSK reception in mobile shallow underwater acoustic channels

The initiative to reduce military platform signature has encouraged the consideration of phased arrays as viable alternatives to traditional reflector-based communication antennas. Phased arrays enhance a military platform's mission effectiveness not only by providing reduced radar cross section (RCS) relative to reflector-based implementations, but also by adding increased flexibility via simultaneous multi-beam operation, increased mean time between failure (MTBF), and increased operational availability resulting from graceful degradation. This paper discusses phased array antenna principles with respect to military communication system applications. Specifically, consideration of phased array antenna performance parameters as they relate to existing governing standards for satellite communications is explored. These standards implicitly assume a scan invariant reflector-based implementation. Examples of scan dependent phased array antenna performance parameters include antenna gain, sidelobes, cross-polarization isolation and instantaneous bandwidth. Performance versus implementation complexity with respect to these parameters is discussed

Phased array performance characteristics and compliance with SATCOM military standards

The authors consider MFSK (M-ary frequency shift keying) communications systems that achieve time diversity by using convolutional interleaving of L repeated chips per symbol. Two system processing options are investigated. The first is that of conventional deinterleaving followed by demodulator magnitude accumulation and soft decision bit recovery. The second is predeinterleaver soft decision, in which demodulator magnitudes are soft detected before recombination. The soft decision metric used in each case is the difference of maximums algorithm. The advantage of soft decision before deinterleaving is a significant deinterleaver memory reduction at the cost of a performance degradation. This degradation is quantified for an ideal Rayleigh fading channel by simulation for a range of chip repeats and bit energy to noise ratios. Preliminary results indicate an implementation loss of 1-4 dB or less for diversities up to 16 over the signal-to-noise ratios of interest. System implementation complexity reductions for several deinterleaver cases are also given. >

Predeinterleaving soft decision performance for MFSK detection on the Rayleigh fading channel

A synchronous spread-spectrum communications system utilizing the resources of a nonprocessing satellite transponder is considered. The systemwide time and frequency standard (which is assumed to be maintained by the system master terminal) is transferred to the satellite, and from there it is disseminated and used by all slave terminals in synchronizing their downlink and uplink operations. The downlink and uplink time and frequency tracking processes that must be performed by each system terminal in order to achieve and maintain synchronization are described, analyzed, and evaluated. The mechanism that establishes system time and frequency reference at the satellite is also described. The authors present computer simulation results illustrating the transient as well as the steady-state performance capabilities of the synchronization mechanisms in the presence of satellite and platform motion. >

T. McGree

Papers

Phased array performance characteristics and compliance with SATCOM military standards

Predeinterleaving soft decision performance for MFSK detection on the Rayleigh fading channel

Downlink and uplink synchronization concepts for spread spectrum communications via satellite