A double balanced mixer circuit comprising: a substrate; a first balun circuit (200; 300; 410) formed on the substrate; a second balun circuit (200; 300; 420) formed on the substrate; and a switch coupled to each of the first and second balun circuits (200; 300; 410, 420) and operative to mix the respective output frequencies of the first and second balun circuits (200; 300; 410; 420), wherein each of the first and second balun circuits (200; 300; 410; 420) includes a respective: first output stripline (220; 320; 414, 424) formed on a first surface of the substrate; second output stripline (230; 330; 416, 426) formed on the first surface of the substrate; input stripline (210; 310; 412, 422) formed on the first surface of the substrate; and slotline (240; 340) formed on a second surface of the substrate (201; 301; 401) opposite the first surface, the slotline (240; 340) having first and second ends, the first end overlapping the first output stripline (220; 320; 414, 424) and the second end overlapping the second output stripline (230; 330; 416; 426), and the input stripline (210; 310; 412, 422) overlapping the slotline (240; 340) midway between the first end and the second end, thereby forming a microstrip-to-slotline cross junction transition with each of the microstrip input and output lines, wherein the input stripline (210; 310; 412, 422) extends from a side of the substrate to its respective microstrip-to-slotline cross junction transition along a straight line, wherein the first output strip line and a second output strip line are, up to a pair of corresponding bends (415; 415') that are bent in the same direction, rotationally symmetrical with one another, and wherein each of the first output stripline (220; 320; 414, 424), the second output stripline (230; 330; 416, 426), the input stripline (210; 310; 412, 422), and each end of the slotline (240; 340) includes a radial stub (214, 224, 234, 244, 246; 314, 324, 334, 344, 346). a substrate; a first balun circuit (200; 300; 410) formed on the substrate; a second balun circuit (200; 300; 420) formed on the substrate; and a switch coupled to each of the first and second balun circuits (200; 300; 410, 420) and operative to mix the respective output frequencies of the first and second balun circuits (200; 300; 410; 420), wherein each of the first and second balun circuits (200; 300; 410; 420) includes a respective: first output stripline (220; 320; 414, 424) formed on a first surface of the substrate; second output stripline (230; 330; 416, 426) formed on the first surface of the substrate; input stripline (210; 310; 412, 422) formed on the first surface of the substrate; and slotline (240; 340) formed on a second surface of the substrate (201; 301; 401) opposite the first surface, the slotline (240; 340) having first and second ends, the first end overlapping the first output stripline (220; 320; 414, 424) and the second end overlapping the second output stripline (230; 330; 416; 426), and the input stripline (210; 310; 412, 422) overlapping the slotline (240; 340) midway between the first end and the second end, thereby forming a microstrip-to-slotline cross junction transition with each of the microstrip input and output lines, wherein the input stripline (210; 310; 412, 422) extends from a side of the substrate to its respective microstrip-to-slotline cross junction transition along a straight line, wherein the first output strip line and a second output strip line are, up to a pair of corresponding bends (415; 415') that are bent in the same direction, rotationally symmetrical with one another, and wherein each of the first output stripline (220; 320; 414, 424), the second output stripline (230; 330; 416, 426), the input stripline (210; 310; 412, 422), and each end of the slotline (240; 340) includes a radial stub (214, 224, 234, 244, 246; 314, 324, 334, 344, 346).