Effect of feeding symmetry on resonances in patch and capacitor structures

Abstract

An L-band 360°broad-bandwidth analog phase shifter is designed using varactor. New design equations for expanding bandwidth and improving linear phase-shift are derived and applied to performances optimization in one circuit. The analog phase shifter is fabricated using MIC and SMT technologies. At 1.2 ϳ 2.0 GHz (L-band), total phase-shift of 360°and linear deviation of less than INTRODUCTIONAnalog phase shifters find uses in a number of applications that require continuous linear phase control of RF/microwave carrier signals. Examples of such applications include phased-array radar, heavy ion accelerators, microwave communications, and so on. The L-band 360°phase shifter described here can be applied in microwave phase-shift scanning of an electronic-optic sampling system [1].Previously reported analog phase shifters operate mostly in the 3-GHz to 18-GHz frequency range [2][3][4]. There have been few reports on 360°analog phase shifters operating at the L band (1 ϳ 2 GHz). An analog phase shifter for adaptive antennas at 1 GHz has been reported, but it has only 90°phase shift [5].The ideal electrical control phase shifter should have the following properties: (i) 360°phase shift, (ii) broad bandwidth, (iii) linear phase shift, and (iv) constant insertion loss. Many efforts have been made to solve above problems, but no effort has been made to solve all properties in one circuit. Conventional analog phase shifter generally uses reflection-type structure [4], which minimizes the number of diodes, as only one diode per 180°phase shift network is required. The reflection-type phase shifter produces the phase shift by reflecting the incident wave with a varactor whose capacitance varies according to the bias voltage. In this paper, an optimal design of the reflection-type phase shifter structure is presented and bandwidth design equations are deduced. The three performances: 360°phase shift, broad bandwidth, and linear phase shift were studied in one circuit. We found that the selection of a varactor diode directly affects performances of the phase shifter, and circuit optimization design also decreases the phase shifter's insertion loss. Figure 1 shows that the reflection termination composed of two varactors connected in parallel with g /4 transmission line length can achieve 360°phase shift [4]. Broad-band application of an analog phase shifter is to make phase shifter maintaining 360°p hase shift, high linearity (linear voltage-phase relationship), and constant insertion loss at the broadest frequency range. In this work, the bandwidth design equations against phase-shift error, varactor gamma value, and relative bandwidth will be derived. BROAD-BANDWIDTH DESIGNThe phase shifter's termination reactance curve A o Ϫ B o V n r must closely match the tangent curve Ϫtan(kV n ϩ o ) when working at centre frequency o , the linear phase shift can be obtained. This relationship is written as [6]:andwhere A o and B o are the design parameters at o . V n , ␥, and o are the normalized biased voltage of varactor, va...

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